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The generation of IPDP micropulsations, with special attention to frequency shift mechanisms Koleszar, Thomas W. 1988

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THE GENERATION OF IPDF MICROPULSATIONS, WITH SPECIAL ATTENTION TO FREQUENCY SHIFT MECHANISMS by THOMAS W. ROLESZAR M . S c , The U n i v e r s i t y of B r i t i s h Columbia, 1980 B.Sc. (Honours), The U n i v e r s i t y of B r i t i s h C o lumbia, 1978 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES Geo p h y s i c s and Astronomy We ac c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA December 1988 © THOMAS W. KOLESZAR, 1988 In p resen t i ng this thesis in partial fu l f i lment of the requ i remen ts for an a d v a n c e d d e g r e e at the Un ivers i ty of Brit ish C o l u m b i a , I agree that t he Library shal l m a k e it f reely avai lable fo r re fe rence and s tudy. I fur ther agree that p e r m i s s i o n fo r ex tens ive c o p y i n g of this thes is fo r scho lar ly p u r p o s e s may b e g ran ted by the h e a d of m y d e p a r t m e n t o r by his o r her representa t ives . It is u n d e r s t o o d that c o p y i n g o r pub l i ca t i on of this thesis for f inancia l gain shal l no t b e a l l o w e d w i t hou t m y wr i t ten p e r m i s s i o n . D e p a r t m e n t of Q €• 0 A +~ A f~T/£ T h e Un ivers i ty of Brit ish C o l u m b i a V a n c o u v e r , C a n a d a Da te Q e c If J <P<? D E - 6 (2/88) ABSTRACT S h o r t p e r i o d geomagnetic m i c r o p u l s a t i o n s termed IPDPs ( I n t e r v a l s of P u l s a t i o n s of D i m i n i s h i n g P e r i o d ) a r e i n v e s t i g a t e d u s i n g ground s t a t i o n d a t a , geosynchronous s a t e l l i t e magnetograms, and the Kp and Dst geomagnetic i n d i c e s . A model f o r the g e n e r a t i o n of IPDPs i s d e s c r i b e d , and c o n s i d e r a t i o n i s g i v e n t o t h r e e mechanisms which c o u l d be r e s p o n s i b l e f o r the IPDP f r e q u e n c y r i s e : the inward m o t i o n , a z i m u t h a l d r i f t , and i n c r e a s i n g background magnetic f i e l d mechanisms. A s i m p l i f i e d IPDP g e n e r a t i o n model c o n t a i n i n g the f i r s t two of t h e s e mechanisms i s t e s t e d by computer s i m u l a t i o n . R e s u l t s from t h i s s i m u l a t i o n i n d i c a t e the p o s s i b i l i t y of s i g n i f i c a n t source r e g i o n inward motion w i t h o u t a c t u a l plasmapause d i s p l a c e m e n t , and the p o s s i b i l i t y of e astward d e v e l o p i n g IPDPs. U s i n g a m p l i t u d e v a r i a t i o n s a l o n g a n o r t h - s o u t h l i n e of ground s t a t i o n s , two methods, each a p p l i c a b l e under d i f f e r e n t i o n o s p h e r i c p r o p a g a t i o n c o n d i t i o n s , a r e d e v e l o p e d f o r q u a n t i t a t i v e l y d e t e r m i n i n g the inward motion of the IPDP sou r c e r e g i o n . A system f o r q u a l i t a t i v e l y d e t e r m i n i n g the p o t e n t i a l i n f l u e n c e of the i n c r e a s i n g background f i e l d mechanism on an IPDP u s i n g the Dst index and geosynchronous s a t e l l i t e magnetograms i s a l s o f o r m u l a t e d . L a s t l y , a t e c h n i q u e f o r the assessment of the e f f e c t s of the a z i m u t h a l d r i f t mechanism, i n c o n j u n c t i o n w i t h the inward motion mechanism, i s d e v e l o p e d . T h i s i i t e c h n i q u e assumes t h a t o n l y these two mechanisms a r e o p e r a t i n g . In a d d i t i o n t o a d d r e s s i n g the f r e q u e n c y s h i f t mechanisms, i t p r o v i d e s e s t i m a t e s of the i n j e c t i o n boundary p o s i t i o n and the magnitude of any ( r i n g c u r r e n t c r e a t e d ) magnetic f i e l d d e p r e s s i o n i n the IPDP source r e g i o n . The f r e q u e n c y r i s e s of two IPDPs a r e a n a l y z e d i n d e t a i l u s i n g these methods. In both c a s e s , the inward motion e f f e c t i s the dominant f a c t o r i n p r o d u c i n g the f r e q u e n c y r i s e , w i t h the i n c r e a s i n g background f i e l d mechanism h a v i n g no s i g n i f i c a n t e f f e c t . The a z i m u t h a l d r i f t mechanism i s a secondary f a c t o r i n c r e a t i n g one e v e n t ' s f r e q u e n c y r i s e , and a c t u a l l y s u p p r e s s e s the f r e q u e n c y r i s e of the o t h e r e v e n t . The computer s i m u l a t i o n c a l c u l a t i o n s a l s o g e n e r a l l y show the inward motion mechanism t o be the dominant e f f e c t i n p r o d u c i n g IPDP f r e q u e n c y r i s e s . L o n g i t u d i n a l v a r i a t i o n s w i t h i n an IPDP event a r e a l s o examined. The r e s u l t s of t h i s e x a m i n a t i o n a r e c o n s i s t e n t w i t h the IPDP g e n e r a t i o n model used h e r e , which i n c l u d e s showing s i g n i f i c a n t v a r i a t i o n s between s t a t i o n s spaced c o m p a r a t i v e l y c l o s e l y i n l o n g i t u d e . TABLE OF CONTENTS ABSTRACT i i ACKNOWLEDGEMENTS x Chapter 1. INTRODUCTION 1 Chapter 2. DATA SOURCES AND'ANALYSIS 8 2.1. Data Sources 8 2.2. Data P r o c e s s i n g 14 Chapter 3. PROPERTIES OF IPDPS 20 3.1. P h y s i c a l C h a r a c t e r i s t i c s 20 3.2. O c c u rrenc e of IPDPs 25 3.3. Network O b s e r v a t i o n s 31 3.4. S a t e l l i t e O b s e r v a t i o n s 34 3.5. R e l a t i o n t o Geomagnetic Phenomena .... 37 Chapter 4. MAGNETOSPHERIC MODEL OF IPDP GENERATION ...... 40 4.1. IPDP - Substorm Model 40 4.2. IPDP Frequency S h i f t Mechanisms 55 4.2.1. Inward M o t i o n 56 4.2.2. I n c r e a s i n g Background F i e l d . 58 4.2.3. A z i m u t h a l D r i f t 59 4.3. D i s c u s s i o n of IPDP Frequency S h i f t Mechanisms 61 4.4. IPDP Frequency B e h a v i o u r S i m u l a t i o n .. 65 4.4.1. C o m p u t a t i o n a l P r o c e d u r e 66 4.4.2. Model IPDPs v e r s u s Observed IPDPs 7 3 4.4.3. Other Model R e s u l t s and P r e d i c t i o n s 82 4.4.4. Model V e r s u s R e a l GMLTs 88 4.4.5. D i s c u s s i o n of IPDP S i m u l a t i o n Model 92 Chapter 5. EXPERIMENTAL RESULTS 95 5.1. Inward M o t i o n of IPDP Source Region .. 95 5.1.1. Feb. 14 Event 96 5.1.2. Feb. 15 Event 111 5.2. Magnetic F i e l d Changes i n IPDP Source Region 122 5.2.1. R i n g C u r r e n t V e r s u s IPDPs .. 125 5.2.2. I n d i v i d u a l IPDP Event Assessments 134 5.2.3. R i n g C u r r e n t and Inward M o t i o n Mechanism 148 5.2.4. D i s c u s s i o n of R i n g C u r r e n t E f f e c t s on IPDPs 152 i v 5.3. A z i m u t h a l D r i f t E f f e c t s on IPDP Frequency E v o l u t i o n 155 5.3. 1 . Feb. 14 Event 164 5.3.2. Feb. 15 Event 176 5.4. L o n g i t u d i n a l IPDP Development 182 5.4. 1 . Feb. 14 Event 184 5.4.2. Feb. 15 Event 186 5.4.3. Feb. 24c Event 190 5.4.4. D i s c u s s i o n 193 5.5. D i s c u s s i o n of E x p e r i m e n t a l R e s u l t s .. 196 Chapter 6. CONCLUSION 202 REFERENCES 206 Appendix A. THE ION-CYCLOTRON INSTABILITY AND IPDP FREQUENCY 214 Appendix B. THE IONOSPHERIC WAVEGUIDE 217 Appendix C. GEOMAGNETIC INDICES 227 v Li s t ofTables T a b l e I : Geomagnetic V a r i a t i o n s 2 T a b l e I I : M i c r o p u l s a t i o n C l a s s i f i c a t i o n 3 T a b l e I I I : ULF S t a t i o n C o o r d i n a t e s 9 T a b l e IV: IPDP Events 13 T a b l e V: M a g n e t i c O b s e r v a t o r y C o o r d i n a t e s 15 T a b l e V I : IPDP P h y s i c a l C h a r a c t e r i s t i c s 22 T a b l e V I I : IPDP Occurrence C h a r a c t e r i s t i c s 26 Ta b l e V I I I : Model IPDP C h a r a c t e r i s t i c s 75 v i Li st of Fi gures F i g u r e 1 : Pc 1 Range Dynamic S p e c t r a 5 F i g u r e 2: Feb. 15 IPDP Event 6 F i g u r e 3: ULF S t a t i o n L o c a t i o n Map 10 F i g u r e 4: Dynamic S p e c t r a : Feb. 14 IPDP 21 F i g u r e 5: C h a r t Record: Feb. 14 IPDP 24 F i g u r e 6: D i u r n a l D i s t r i b u t i o n of IPDP O c c u r r e n c e 27 F i g u r e 7: IPDP Occurrence v e r s u s Kp Index 28 F i g u r e 8: C o - L o n g i t u d i n a l S i t e Comparison: Feb. 14 IPDP ..33 F i g u r e 9: C o - L a t i t u d i n a l S i t e Comparison: Feb. 24c IPDP-..35 F i g u r e 10: IPDP O b s e r v a t i o n s : S a t e l l i t e v e r s u s Ground ....36 F i g u r e 11: D o u b l e - s p i r a l I n j e c t i o n Boundary 42 F i g u r e 12: I n j e c t i o n Boundary P o s i t i o n v e r s u s Kp 43 F i g u r e 13: P r o t o n I n j e c t i o n and D r i f t T r a j e c t o r i e s 48 F i g u r e 14: Substorm C u r r e n t Systems 50 F i g u r e 15: Three Average Plasmapause P r o f i l e s 54 F i g u r e 16: The Inward M o t i o n Af Mechanism 63 F i g u r e 17: Computer S i m u l a t i o n Flow Chart 69 F i g u r e 18: Frequency and Slo p e vs GM L a t . ( s i m u l a t i o n ) ...77 F i g u r e 19: IPDP Occurrence v e r s u s A c t v i t y ( s i m u l a t i o n ) ...78 F i g u r e 20: Frequency and S l o p e v e r s u s GMLT ( s i m u l a t i o n ) ..80 F i g u r e 21: Onset D r i f t v e r s u s A c t i v i t y ( s i m u l a t i o n ) 81 F i g u r e 22: Inward M o t i o n E f f e c t s on IPDPs ( s i m u l a t i o n ) ...83 F i g u r e 23: Westward and Eastward D e v e l o p i n g IPDP Models ..87 F i g u r e 24: West and Eastward IPDP r e s u l t s ( s i m u l a t i o n ) ...89 v i i F i g u r e 25: M o d e l l e d v e r s u s Observed IPDP GMLTs 91 F i g u r e 26: P o l a r i z a t i o n Spectrogram; 0840UT, Feb. 14 98 F i g u r e 27: P o l . Spectrograms; PS: 0900, 0940 UT, Feb. 14 100 F i g u r e 28: P o l . Spectrograms; LL: 0900, 0940 UT, Feb. 14 101 F i g u r e 29: X and Y Component Power V a r i a t i o n s , Feb. 14 ..103 F i g u r e 30: Power R a t i o s v e r s u s P o s i t i o n , Feb. 14 IPDP ...106 F i g u r e 31: Source Inward M o t i o n , Feb. 14 IPDP 110 F i g u r e 32: Inward M o t i o n Frequency R i s e , Feb. 14 IPDP ...112 F i g u r e 33: P o l a r i z a t i o n Spectrogram; 2157UT, Feb. 15 ....114 F i g u r e 34: PS and LL P o l . Spectrograms; 2201UT, Feb. 15 .115 F i g u r e 35: Source - S t a t i o n Geometry: 2149UT, Feb. 15 ...117 F i g u r e 36: Source P o s i t i o n E s t i m a t i o n : 2149UT, Feb. 15 ..119 F i g u r e 37: Power R a t i o s v e r s u s P o s i t i o n , Feb. 15 IPDP ...121 F i g u r e 38: Source Inward M o t i o n , Feb. 15 IPDP 123 F i g u r e 39: Inward M o t i o n Frequency R i s e , Feb. 15 IPDP ...124 F i g u r e 40: Ri n g C u r r e n t Development: AB P r o f i l e s 129 F i g u r e 41: Magnetic F i e l d B e h a v i o u r : IPDP Source Region .133 F i g u r e 42: IPDP Occurrence v e r s u s Dst Index 135 F i g u r e 43: IPDPs v e r s u s Dst Index: Case I - IV Samples ..136 F i g u r e 44: IPDP v e r s u s Dst and GOES 2; Feb. 14 138 F i g u r e 45: IPDP v e r s u s Dst and GOES 2; Feb. 15 140 F i g u r e 46: Great Whale R i v e r Magnetogram, Feb. 15 141 F i g u r e 47: IPDP v e r s u s Dst and GOES 3; J a n . 29 ....143 F i g u r e 48: IPDP v e r s u s Dst and GOES 3; Feb. 24c 145 F i g u r e 49: Inward M o t i o n + AB A f : Feb. 15 153 v i i i F i g u r e 50: I n j e c t i o n Boundary E s t i m a t i o n Flow Chart 165 F i g u r e 51: X-component Magnetogram: GWR, Feb. 14 167 F i g u r e 52: Model P l o t f o r the Feb. 14 IPDP 169 F i g u r e 53: Frequency S h i f t R e s u l t s : Feb. 14 IPDP 170 F i g u r e 54: Combined Frequency R i s e R e s u l t s : Feb. 14 IPDP 173 F i g u r e 55: Poor I n j e c t i o n Boundary R e s u l t s : Feb. 14 IPDP 175 F i g u r e 56: Great Whale R i v e r Magnetogram: Feb. 15 IPDP ..177 F i g u r e 57: Model P l o t f o r the Feb. 15 IPDP 179 F i g u r e 58: Frequency S h i f t R e s u l t s : Feb. 15 IPDP 181 F i g u r e 59: Combined Frequency R i s e R e s u l t s : Feb. 14 IPDP 183 F i g u r e 60: F r e q . P r o f i l e s from GM and PS: Feb. 14 IPDP ..185 F i g u r e 61: Power S p e c t r a from GM and PS: 0910UT, Feb. 14 187 F i g u r e 62: F r e q . P r o f i l e s from GM and PS: Feb. 15 IPDP ..188 F i g u r e 63: C r o s s - C o r r e l a t i o n s : LL-PS and GM-PS, Feb. 15 .191 F i g u r e 64: F r e q . P r o f i l e s : GM, PS, and PG; Feb. 24c IPDP 192 F i g u r e 65: I o n o s p h e r i c E l e c t r o n D e n s i t y P r o f i l e s 218 F i g u r e 66: I o n o s p h e r i c Duct Pat h s and R e f l e c t i o n C o e f f i c i e n t s ,. 221 i x ACKNOWLEDGEMENTS I e x p r e s s my deepest thanks t o my s u p e r v i s o r , Dr. T. Watanabe, f o r h i s i n v a l u a b l e a d v i c e and c o n s t a n t encouragement. I a l s o o f f e r my thanks t o Dr s . G. C l a r k e , R. E l l i s , G. Fahlmann, and B. S h i z g a l f o r t h e i r p a r t i c i p a t i o n as committee members. My s p e c i a l thanks go t o Sonya D e h l e r , who h e l p e d keep me sane t h r o u g h the t r i a l s of t h e s i s p r e p a r a t i o n , t o my mother, Mrs. S. K o l e s z a r , f o r her p a t i e n t e d i t i n g of t h i s t h e s i s , and t o w i f e , U l r i k e , f o r her unending encouragement and sup p o r t d u r i n g my time a t UBC. I e x p r e s s my a p p r e c i a t i o n t o Drs. T. O g u t i , S. Kokubun and K. H a y a s h i , U n i v e r s i t y of Tokyo, D r s . T.Kitamura and 0. Saka, Kyushu U n i v e r s i t y , and Dr. R.E. H o r i t a , U n i v e r s i t y of V i c t o r i a , f o r t h e i r e f f o r t s i n a c q u i r i n g the IPDP d a t a s e t • ( P u l s a t i n g A u r o r a Campaign). The GOES 2 and 3 magnetic d a t a were s u p p l i e d from the World Data C e n t e r , B o u l d e r , C o l o r a d o , and were p r o c e s s e d by Drs. S. Kokubun and G. I s h i d a of the U n i v e r s i t y of Tokyo. The a u r o r a l - z o n e s t a t i o n magnetograms and the Kp index d a t a were a l s o o b t a i n e d the World Data C e n t r e , B o u l d e r , C o l o r a d o , and the Dst index d a t a from the World Data C e n t r e , G r e e n b e l t , M a r y l a n d . T h i s t h e s i s r e s e a r c h was s u p p o r t e d by the N a t u r a l S c i e n c e s and E n g i n e e r i n g Research C o u n c i l of Canada through Grant A - 3564. The P u l s a t i n g A u r o r a Campaign was su p p o r t e d by the same agency t h r o u g h Grant A - 3397. x CHAPTER 1 . INTRODUCTION The E a r t h ' s magnetic f i e l d i s s u b j e c t t o many k i n d s of v a r i a t i o n s . These f l u c t u a t i o n s , which can be of e i t h e r i n t e r n a l or e x t e r n a l o r i g i n , range i n p e r i o d from 10 7 y e a r s down t o =0 second. T a b l e I p r e s e n t s a summary of such geomagnetic v a r i a t i o n s . The f a m i l y of f l u c t u a t i o n s of i n t e r e s t h e r e , the m i c r o p u l s a t i o n s , o c c u p i e s the s h o r t e r end of t h i s p e r i o d range. Geomagnetic m i c r o p u l s a t i o n s have p e r i o d s i n the range of 600 t o 0.2 seconds. They a re t r a n s i t o r y f l u c t u a t i o n s of s m a l l a m p l i t u d e , t y p i c a l l y l e s s than 1 p a r t i n 10" of the geomagnetic f i e l d s t r e n g t h a t the E a r t h ' s s u r f a c e , which l e a v e no permanent e f f e c t on E a r t h ' s main f i e l d . T h e i r o r i g i n i s e x t e r n a l , meaning t h a t they a r e g e n e r a t e d e i t h e r d i r e c t l y or i n d i r e c t l y as a r e s u l t of s o l a r wind magnetosphere i n t e r a c t i o n s . Though they were f i r s t r e p o r t e d more than a c e n t u r y ago ( S t e w a r t , 1861), the stu d y of m i c r o p u l s a t i o n s i s a r e l a t i v e l y young f i e l d w i t h most of the r e s e a r c h i n the area o c c u r r i n g w i t h i n the l a s t 25 y e a r s . Based on m o r p h o l o g i c a l d i f f e r e n c e s , m i c r o p u l s a t i o n s have been d i v i d e d i n t o two broad c l a s s e s ; c o n t i n u o u s p u l s a t i o n s , or Pc, and i r r e g u l a r or i m p u l s i v e p u l s a t i o n s , termed P i . These c l a s s e s have been f u r t h e r d i v i d e d i n t o s u b c l a s s e s as shown i n Tab l e I I . Each of thes e s u b c l a s s e s may a l s o c o n t a i n many m o r p h o l o g i c a l l y d i s t i n c t t y p e s of 1 2 Table I Geomagnetic Variations V a r i a t i o n D i p o l e R e v e r s a l s S e c u l a r M agnetic Storms D i u r n a l Substorms M i c r o p u l s a t i o n s O r i g i n I n t e r n a l I n t e r n a l E x t e r n a l E x t e r n a l E x t e r n a l E x t e r n a l P e r i o d (seconds) 1 0 1 5 10 s - 10 1° 10 6 10 5 10" - 10 5 10 2 - 10° ( A f t e r J a c o b s , 1970) 3 Table II  Micropulsation C l a s s i f i c a t i o n C o n t i n u o u s P u l s a t i o n s (Pc) Pc 1 Pc 2 Pc 3 Pc 4 Pc 5 Pc 6 P e r i o d Range (seconds) 0.2 - 5 5 - 1 0 10 - 45 45 - 150 150 - 600 600 -I r r e g u l a r P u l s a t i o n s ( P i ) P e r i o d Range (seconds) P i 1 1 - 4 0 P i 2 40 - 150 P i 3 150 -( A f t e r N i s h i d a , 1978) 4 m i c r o p u i s a t i o n . A summary p l o t ( f i g . 1) of Pc 1 range m i c r o p u l s a t i o n dynamic s p e c t r a shows those t y p e s f a l l i n g w i t h i n the Pc 1 f r e q u e n c y range, i n c l u d i n g IPDPs, the s u b j e c t of t h i s t h e s i s . The acronym IPDP comes from the name I n t e r v a l of P u l s a t i o n s of D i m i n i s h i n g P e r i o d . IPDPs were f i r s t named by T r o i t s k a y a and M e l n i k o v a (1959), and f i r s t d e s c r i b e d i n some d e t a i l by T r o i t s k a y a (1961). The name makes r e f e r e n c e t o the d i s t i n g u i s h i n g f e a t u r e of a l l IPDPs; the r i s i n g f r e q u e n c y t r e n d d i s p l a y e d throughout each 20 minute t o 2 hour l o n g e v e n t . In the p a s t , o t h e r names have a l s o been a p p l i e d t o IPDPs; t h e s e i n c l u d e S o l a r W h i s t l e s ( D u f f u s e t a l . , 1958), G u r g l e r s ( T e p l e y and Amundsen, 1964), and Sweepers (Heacock, 1967). More r e c e n t l y , the term ODP, meaning O s c i l l a t i o n s of D e c l i n i n g P e r i o d , has been used by Barkova and S o l o v ' e v (1984) and Dovbnya et a l . (1984). An example of an IPDP dynamic spectrum and waveform i s shown i n f i g u r e 2. I t has o f t e n been noted t h a t IPDPs c o u l d become a u s e f u l t o o l f o r magnetospheric r e s e a r c h ( T r o i t s k a y a , 1961; Bossen et a l . , 1976; Heacock et a l . , 1976; M a l t s e v a e t a l . , 1 9 8 1 ) . B e f o r e t h i s p o s s i b i l i t y can become a r e a l i t y however, we must d e v e l o p a good u n d e r s t a n d i n g of the IPDP g e n e r a t i o n mechanism, e s p e c i a l l y those e f f e c t s which c o n t r o l the f r e q u e n c y r i s e . In view of t h i s , t h r e e proposed f r e q u e n c y i n c r e a s e mechanisms have r e c e i v e d the most 5 1.5 5 i-o >-o z LU o m tr 0.5 P e r i o d i c HM Emission HM Emission Burst HM Whistler ,</',','.',"/<'''» . / ' / / ^ ,:tli:!,1 -Dotted •! f • l ' Morning *+V£f//////^ HM Chorus Pc 1-2 Band / / 6 12 18 M A G N E T I C L O C A L TIME (HOURS) 24 FIGURE 1 . Summary p l o t of dynamic s p e c t r a of Pc 1 range m i c r o p u l s a t i o n s v e r s u s geomagnetic l o c a l time ( a f t e r F u k u n i s h i et a l . , 1981). Note the IPDP s p e c t r a i n the lower p a r t of the Pc 1 fr e q u e n c y range near 1800 magnetic l o c a l t i m e . 6 , , — r ' — - — ' ; | « - 1 H i 21 24 UT 0 . 2 0 i , - 0 . 2 0 1 — 1 : — 1 : 1 1 — — — > 1 5 1 . 0 5 2 . 0 5 3 . 0 5 4 . 0 t ime (min . ) FIGURE 2 . Dynamic spectrum of the h o r i z o n t a l components ( t o p ) , and c h a r t r e c o r d (bottom) of the Y component f o r the Fe b r u a r y 15 IPDP event as obser v e d a t G i m l i , Manitoba ( c f . Tab l e I I I and f i g . 3 ) . The c h a r t r e c o r d c o v e r s o n l y 3 minutes (2151 - 2154 UT) near the b e g i n n i n g of the e v e n t . 7 a t t e n t i o n ; inward motion of the g e n e r a t i o n r e g i o n ( G e n d r i n et a l . , 1967; Heacock, 1967), westward d r i f t of hot p r o t o n s ( F u k u n i s h i , 1969), and i n c r e a s i n g background magnetic f i e l d s t r e n g t h (Roxburgh, 1970). I t has a l s o been observed t h a t more than one of t h e s e mechanisms may o p e r a t e a t once (Heacock, 1973; Kangas et a l . , 1974). U s i n g ground-based and s a t e l l i t e d a t a , t h i s t h e s i s w i l l p r e s e n t a q u a n t i t a t i v e assessment of the p o s s i b l e c o n t r i b u t i o n of each of t h e s e mechanisms t o the IPDP fr e q u e n c y r i s e i n the c o n t e x t of an o v e r a l l model f o r IPDP g e n e r a t i o n . Chapter Two w i l l d e s c r i b e the d a t a s o u r c e s and a n a l y s i s methods used h e r e , w h i l e Chapter Three i s an i n depth d e s c r i p t i o n of IPDPs and t h e i r r e l a t i o n s h i p s t o o t h e r geomagnetic phenomena. The g e n e r a t i o n p r o c e s s of IPDPs i s d i s c u s s e d i n Chapter Four, i n c l u d i n g the f r e q u e n c y s h i f t mechanisms, w h i l e Chapter F i v e p r e s e n t s the r e s u l t s of the e x p e r i m e n t a l t e s t s of these mechanisms, a l o n g w i t h a d i s c u s s i o n of t h e i r s i g n i f i c a n c e . CHAPTER 2 . DATA SOURCES AND ANALYSIS T h i s c h a p t e r o f f e r s a d e s c r i p t i o n of the dat a s e t s used i n t h i s t h e s i s , f o l l o w e d by a review of the t e c h n i q u e s used i n the a n a l y s i s of the IPDP d a t a . 2 . 1 . DATA SOURCES The r e s e a r c h work p r e s e n t e d i n C h a p t e r s Four and F i v e made use of i n f o r m a t i o n from f i v e s o u r c e s : the 1980 "Aurora-ULF-VLF" campaign m i c r o p u l s a t i o n r e c o r d s , GOES s a t e l l i t e magnetograms, magnetograms from a u r o r a l zone magnetic o b s e r v a t o r i e s , Rp i n d i c e s , and Dst i n d i c e s . The p r i m a r y d a t a s o u r c e , t h a t of the IPDP m i c r o p u l s a t i o n r e c o r d s , was the "Aurora-ULF-VLF" campaign (Oguti et a l . , 1982). As p a r t of t h i s p r o j e c t , t h i r t e e n ULF s t a t i o n s were o p e r a t e d i n western Canada a t a u r o r a l zone and plasmapause l a t i t u d e s d u r i n g J a nuary and F e b r u a r y of 1980. El e v e n of the t h i r t e e n s t a t i o n s were l o c a t e d at l a t i t u d e s s u i t a b l e f o r r e c o r d i n g IPDPs. These s t a t i o n s a r e l i s t e d , a l o n g w i t h t h e i r g e o g r a p h i c and c o r r e c t e d geomagnetic c o o r d i n a t e s ( G u s t a f s s o n , 1984), i n Tab l e I I I , and t h e i r l o c a t i o n s a r e p l o t t e d i n f i g u r e 3. The network they c o m p rised c o n s i s t e d e s s e n t i a l l y of t h r e e n o r t h - s o u t h l i n e s of s t a t i o n s ; one each i n B r i t i s h C olumbia, Saskatchewan, and Manitoba ( c f . f i g . 3 ) . Two eas t - w e s t l i n e s c o u l d a l s o be c o n s t r u c t e d from the network; a n o r t h e r n l i n e of SR, LR, and 8 9 Table III ULF Station Names and Coordinates Manitoba L i n e I s l a n d Lake ( I L ) G i m l i (GM) Geographic C o r r e c t e d Geomagnet i c Lat.(°N) Long.(°E) Lat.(°N) Long.(°E) 53.9 265.3 50.6 263.0 64.9 329.6 61.4 326.8 Saskatchewan L i n e R a b b i t Lake (RL) 58. 2 256. 3 67. 8 314.8 South End (SE) 56. 3 256. 5 66. 0 315.8 La Ronge (LR) 55. 2 254. 7 64. 6 313.7 Waskesiu (WS) 53. 9 253. 9 63. 1 313.1 Park S i t e (PS) 52. 2 252. 8 61 . 3 312.2 Lucky Lake (LL) 51 . 0 252. 9 60. 1 312.7 B.C. L i n e Steen R i v e r (SR) 59. 7 242. 8 66. 6 295.7 P r i n c e George (PG) 53. 9 237. 1 59. 6 292.4 V i c t o r i a (VC) 48. 3 236. 4 53. 8 294. 1 10 0) o C cn D E o Q> CD 72 70 68 66 64 62 60 58 56 54 . B.C. line OiSR -4-I J. • PGI 4V—-4~ Sask. line , RL, .4- - 4--V..4 4..... 1 <>"SE ILR I I <>WS| J. L K>PS 1 I O L L I 4- I. I I I I Man. line 4——-4- 4— ---I. 4- I IL o "IOGMI 4- l~. northern east-west line southern east-west line VC, 52 290 300 310 320 330 340 geomagnetic longitude (E) FIGURE 3. P l o t of ULF s t a t i o n l o c a t i o n s , i n geomagnetic c o o r d i n a t e s , f o r the "Aurora-ULF-VLF" campaign. The n o r t h - s o u t h and eas t - w e s t s t a t i o n l i n e s a r e a l s o shown. 11 I L , as w e l l as a s o u t h e r n l i n e of PG, PS and/or LL, and GM. The r e c o r d i n g systems a t these ground s t a t i o n s c o n s i s t e d of i n d u c t i o n magnetometers w i t h high-M m e t a l c o r e s , a m p l i f i e r s , and slow-speed FM analogue tape r e c o r d e r s . These systems were each c a p a b l e of r e c o r d i n g t h r e e o r t h o g o n a l components: X (magnetic n o r t h ) , Y (magnetic e a s t ) , and Z (downward). F u r t h e r i n f o r m a t i o n on the campaign, i n c l u d i n g the r e c o r d i n g systems used, can be o b t a i n e d from O g u t i et a l . (1982). The network of ULF s t a t i o n s was not w i t h o u t i t s problems. Depending on the r e c o r d i n g system, narrow band i n s t r u m e n t n o i s e was p r e s e n t w i t h i n the IPDP f r e q u e n c y band, at e i t h e r 0.5 or 0.7 Hz. Man-made i m p u l s i v e n o i s e a l s o i n t e r f e r e d w i t h some s t a t i o n s : t r a f f i c n o i s e a t GM, RL, PG, and SR; and r a d i o t r a n s m i s s i o n s a t I L and PG. In a d d i t i o n , WS r e c o r d e d broad band n o i s e below 0.2 Hz which was a t t r i b u t e d t o l a k e o s c i l l a t i o n s . A more s e r i o u s problem f o r the study of IPDPs proved t o be m i s s i n g d a t a i n t e r v a l s . For example, a t WS the X-component was not r e c o r d e d a t a l l , some of the t a p e s from PG and IL p r o v e d t o be u n r e a d a b l e , and almost a l l s t a t i o n s s u f f e r e d from i n c o m p l e t e coverage of the campaign p e r i o d . With t h e s e d i f f i c u l t i e s , i t was q u i t e r a r e t o have most of the s t a t i o n s o p e r a t i n g p r o p e r l y a t the time of an IPDP e v e n t , which l i m i t e d the c h o i c e of e v e n t s s u i t a b l e f o r d e t a i l e d a n a l y s i s . A l t o g e t h e r , t e n IPDPs were r e c o r d e d between J a n . 16 and 1 2 Feb. 24, 1980. These e v e n t s a re l i s t e d i n Ta b l e IV. A book of dynamic s p e c t r a from the Aurora-ULF-VLF campaign ( O g u t i et a l . , 1982) was used t o i d e n t i f y them. From th e s e t e n e v e n t s , t h r e e were s e l e c t e d f o r d e t a i l e d a n a l y s i s . These t h r e e , Feb. 14, Feb. 15, and Feb. 24c, w i l l be d i s c u s s e d e x t e n s i v e l y i n Chapter F i v e . The c r i t e r i a f o r s e l e c t i o n of the above e v e n t s i n c l u d e d t h a t they be r e c o r d e d a t more than one s i t e on a n o r t h - s o u t h l i n e and/or more than one s i t e on an e a s t - w e s t l i n e f o r a n a l y s i s purposes ( c f . Chapter F i v e ) , the q u a l i t y of the da t a o b t a i n e d , and the c l a r i t y of the IPDP, e n s u r i n g t h a t the event was unambiguously i d e n t i f i e d as an IPDP. Magnetograms from two geosynchronous s a t e l l i t e s , GOES 2 and GOES 3, were a l s o used. The magnetograms from both of these GOES s a t e l l i t e s c o n s i s t of 0000-2400 UT p l o t s of t h r e e o r t h o g o n a l components, H, D, and V, p l u s the t o t a l f i e l d s t r e n g t h , a l l b e i n g p l o t t e d i n gammas. The GOES 2 s a t e l l i t e o r b i t s near 251° E, and i s thus c l o s e t o the geomagnetic m e r i d i a n of the Saskatchewan n o r t h - s o u t h l i n e . D u r i n g the campaign p e r i o d , o n l y t w e l v e days of da t a a r e a v a i l a b l e from t h i s s a t e l l i t e , from Feb. 5 t o Feb. 16 i n c l u s i v e . The GOES 3 s a t e l l i t e o r b i t s near 225° E, c l o s e t o the geomagnetic m e r i d i a n of the B.C. n o r t h - s o u t h l i n e . Magnetograms from t h i s s a t e l l i t e a r e a v a i l a b l e f o r the e n t i r e campaign p e r i o d . The t h i r d d a ta s e t r e q u i r e d f o r the a n a l y s i s of IPDPs Table IV IPDP Events Event UT 1. J a n . 1 6 0255 - 031 5 2. J a n . 23 0535 - 0635 3. J a n . 27 2230 - 2320 4. J a n . 28 0000 - 0105 c J a n . 29 0150 - 0315 Feb. 1 4 0835 - 0940 Feb. 1 5 2145 - 2205 8. Feb. 24a 0000 - 01 30 9. Feb. 24b 0150 - 0300 10. Feb. 24c 0550 - 0650 (Events s e l e c t e d f o r d e t a i l e d a n a l y s i s u nder1ined.) 1 4 c o n s i s t s of magnetograms from an a r r a y of e i g h t a u r o r a l and s u b - a u r o r a l zone magnetic o b s e r v a t o r i e s (see T a b l e V ) . These magnetograms were o b t a i n e d from World Data Center A f o r s o l a r - t e r r e s t r i a l p h y s i c s i n B o u l d e r , C o l o r a d o (NOAA). The data a r e i n the form of one-minute v a l u e s g i v e n t o the ne a r e s t gamma f o r the magnetic n o r t h , magnetic e a s t , and v e r t i c a l components, as w e l l as f o r the t o t a l f i e l d s t r e n g t h . The l a s t two d a t a s e t s used here a r e the Kp and Dst i n d i c e s . Kp i n d i c e s were a v a i l a b l e from World Data Center A f o r s o l a r - t e r r e s t r i a l p h y s i c s , and Dst i n d i c e s from World Data C e n t e r A f o r r o c k e t s and s a t e l l i t e s i n G r e e n b e l t , M a r y l a n d (NASA). These two i n d i c e s a r e d e s c r i b e d i n d e t a i l i n Appendix C. 2 . 2 . DATA PROCESSING T h i s s e c t i o n p r o v i d e s a d e s c r i p t i o n of analogue and d i g i t a l p r o c e s s i n g t e c h n i q u e s employed d u r i n g the a n a l y s i s of the IPDP d a t a . The f i r s t s t e p i n the a n a l y s i s of an IPDP ev e n t , a f t e r i t s i d e n t i f i c a t i o n , i s s i m p l y t o look a t i t i n the form of a h i g h speed magnetogram or as a dynamic spectrum ( s p e c t r o g r a m ) . T h i s i s n e c e s s a r y both t o und e r s t a n d the gr o s s p r o p e r t i e s of the event and t o e s t a b l i s h the parameters f o r l a t e r d i g i t i z a t i o n and computer a n a l y s i s . Table V Magnetic Observatory Coordinates Geographic Lat.(°N) Long.(°E) S t . John's (STJ) 47. ,6 307. .4 Ottawa (OTT) 45. .4 284. .5 Great Whale R. (GWR) 55. .2 282, .3 W h i t e s h e l l (WHS) 40. .3 264. .8 F o r t C h u r c h i l l (FC) 58. ,8 265. .9 Meanook (ME) 54. .6 246. .7 Y e l l o w k n i f e (YEK) 62. ,4 245. ,6 V i c t o r i a (VC) 48. .5 236. .6 C o r r e c t e d  Geomagnet i c  Lat.(°N) Long.(°E 55.4 31.0 57.2 359.2 66.8 359.6 51.1 330.7 69.7 329.5 62.4 303.4 69.8 297.4 54.1 294.3 1 6 Each of t h e s e d i s p l a y s can be c r e a t e d from the analogue magnetic t a p e s ; d i r e c t l y i n the case of a magnetogram, and through a spectrum a n a l y s e r ( N i c o l e t 440B or S p e c t r a l Dynamics SD345) and f i b r e - o p t i c o s c i l l o g r a p h (Honeywell 1856A) f o r a dynamic spectrum. The IPDP events chosen f o r d e t a i l e d study r e q u i r e d d i g i t i z a t i o n p r i o r t o computer a n a l y s i s . The a n a l o g u e - t o - d i g i t a l c o n v e r s i o n system c o n s i s t e d of an analogue tape d r i v e , an analogue f i l t e r bank, and a Data T r a n s l a t i o n DT-2801-A A/D c a r d dumping the d i g i t i z e d d a t a d i r e c t l y onto an IBM PCAT computer. The s a m p l i n g f r e q u e n c y was set a t 3.75 Hz. P r i o r t o d i g i t i z a t i o n , 48 db/octave a n t i - a l i a s i n g f i l t e r s w i t h a c o r n e r f r e q u e n c y of 1.5 Hz were a p p l i e d . The d i g i t i z e d e v e n t s a r e then s u b j e c t e d t o d e t a i l e d a n a l y s i s i n o r d e r t o u n d e r s t a n d t h e i r f r e q u e n c y , a m p l i t u d e , and p o l a r i z a t i o n e v o l u t i o n . T h i s a n a l y s i s i s c a r r i e d out u s i n g programs f o r d i g i t a l f i l t e r i n g , f a s t F o u r i e r t r a n s f o r m s ( F F T s ) , and c r o s s - c o r r e l a t i o n s . The FFT r o u t i n e used f o r IPDP a n a l y s i s here i s a TM complex FFT r o u t i n e from the Microway 87FFT package. As p a r t of the pre-FFT p r o c e s s i n g , the d a t a were f i l t e r e d w i t h a B u t t e r w o r t h band-pass f i l t e r (Ranasewich, 1981) t o remove unwanted n o i s e , e s p e c i a l l y a t low f r e q u e n c i e s , o u t s i d e the IPDP's f r e q u e n c y range. The r o l l - o f f of t h i s f i l t e r i s 96 1 7 dB/octave. The FFT method f o r d e t a i l e d IPDP e v o l u t i o n a n a l y s i s r e q u i r e s t h a t the event be d i v i d e d i n t o a s e r i e s of r e l a t i v e l y s h o r t r e c o r d s , t y p i c a l l y of 512 or 1024 p o i n t s (2.27 or 4.55 minutes of d a t a ) , each of which i s then i n d i v i d u a l l y a n a l y s e d . W i t h i n t h e s e s h o r t d a t a segments the IPDP freq u e n c y i s assumed t o be c o n s t a n t f o r the purpose of a p p l y i n g an FFT. T h i s assumption has been t e s t e d by the a n a l y s i s of s y n t h e t i c s i g n a l s w i t h f r e q u e n c i e s i n c r e a s i n g a t r a t e s s i m i l a r t o those e n c o u n t e r e d i n IPDPs. For the segment l e n g t h s used, the FFT a n a l y s i s of these s i g n a l s reproduced t h e i r known a m p l i t u d e and f r e q u e n c y c h a r a c t e r i s t i c s v e r y w e l l , thus i n d i c a t i n g t h a t the assumption of c o n s t a n t f r e q u e n c y used here i s r e a s o n a b l e . The f r e q u e n c y and a m p l i t u d e e v o l u t i o n of an IPDP i s then found from the s p e c t r a computed from the FFTs of a s u c c e s s i o n of c o n s e c u t i v e d a t a segments c o m p r i s i n g the IPDP. The p o l a r i z a t i o n s p e c t r o g r a m s , from which the e v o l u t i o n of an e v e n t ' s p o l a r i z a t i o n i s found, a r e o b t a i n e d from the combined complex FFTs of c o i n c i d e n t X and Y component d a t a segments. P o l a r i z a t i o n s pectrograms appear as normal power s p e c t r a , except t h a t the d a t a p r e s e n t e d are f o r the g i v e n p o l a r i z a t i o n component o n l y . These spectrograms can be produced f o r r i g h t c i r c u l a r , l e f t c i r c u l a r , and l i n e a r p o l a r i z a t i o n s as shown below ( A r n o l d y et a l . , 1979). I f F 18 and fJ are the F o u r i e r t r a n s f o r m e d complex s e r i e s of the X and Y d a t a components F. = 2^=0 f e x p [ - i 2 7 r j k / N ] , then the r i g h t and l e f t c i r c u l a r p o l a r i z a t i o n components can be r e p r e s e n t e d a s : F r = ( Fx - i F^ )/v/2 (2.1a) J J J f o r the r i g h t component, and a s : Fl. = ( Fx + i F' )/v/2 (2.1b) J J J f o r the l e f t component. From th e s e c i r c u l a r components, the p o l a r i z a t i o n power s p e c t r a a r e c a l c u l a t e d as f o l l o w s : P c = I F r I 2 - I Fl. I 2 (2.2) J J J where p o s i t i v e r e p r e s e n t s power i n the r i g h t c i r c u l a r component, and n e g a t i v e P^ i n the l e f t component. L i n e a r p o l a r i z a t i o n spectrograms a r e c a l c u l a t e d from: 19 P L = [ ( | F r | 2 + | F / | 2 ) 2 - | P C | 2 ] 2 (2.3) . J ' J 1 1 ; 1 1 J ' F i n a l l y , c r o s s - c o r r e l a t i o n s a r e used t o compare r e c o r d i n g s of an event taken s i m u l t a n e o u s l y a t d i f f e r e n t s t a t i o n s . To f a c i l i t a t e t h i s , c r o s s - and a u t o - c o r r e l a t i o n TM r o u t i n e s from the Microway 87FFT package were used. In a d d i t i o n t o the above s i g n a l p r o c e s s i n g t e c h n i q u e s , some c u r v e - f i t t i n g i s a l s o r e q u i r e d f o r the IPDP a n a l y s e s . The c u r v e - f i t t i n g r o u t i n e employed h e r e , from the Laboratory Technol ogi es Inc. NOTEBOOK s o f t w a r e package, uses an i t e r a t i v e l e a s t - s q u a r e s r e g r e s s i o n t e c h n i q u e . CHAPTER 3. PROPERTIES OF IPDPS T h i s c h a p t e r w i l l r e v i ew the p h y s i c a l and o c c u r r e n c e c h a r a c t e r i s t i c s of IPDPs as observed by ground s t a t i o n s , and compare geosynchronous s a t e l l i t e o b s e r v a t i o n s t o ground o b s e r v a t i o n s . In a d d i t i o n , IPDP r e l a t i o n s h i p s w i t h o t h e r geomagnetic phenomena w i l l be d i s c u s s e d . 3.1. PHYSICAL CHARACTERISTICS IPDPs a re broad-band e v e n t s which e x h i b i t a p r o g r e s s i v e l y r i s i n g m id-frequency throughout t h e i r l i f e t i m e s . F i g u r e 4 shows a dynamic spectrum of a t y p i c a l IPDP e v e n t . Some of the b a s i c p h y s i c a l p r o p e r t i e s of IPDPs, as seen from ground s t a t i o n s , have been summarized i n Ta b l e V I . The parameters of most IPDPs w i l l f a l l w i t h i n the ranges g i v e n . However, i n extreme c o n d i t i o n s , some ev e n t s w i l l have some parameter v a l u e s o u t s i d e these ranges. I n i t i a l f r e q u e n c i e s as low as 0.05 Hz, which i s i n the Pc 3 fr e q u e n c y range, have been r e c o r d e d (Heacock, 1971). End f r e q u e n c i e s of up t o 2 Hz have a l s o been o b s e r v e d , e s p e c i a l l y a t lower l a t i t u d e s . The change i n frequ e n c y d u r i n g the c o u r s e of an event must be p o s i t i v e f o r the event t o be i d e n t i f i e d as an IPDP. A t y p i c a l i n c r e a s e i n f r e q u e n c y would be g r e a t e r than 1 o c t a v e , and sometimes as h i g h as 3 o c t a v e s ( S a i t o , 1969). Though the frequency s l o p e s which d i f f e r e n t IPDP e v e n t s can 20 21 PARK SITE • FIGURE 4 . Dynamic s p e c t r a of an IPDP r e c o r d e d on Feb. 14, 1980 a t Park S i t e and Lucky Lake, Saskatchewan. T h i s e v e n t , which o c c u r s near 0900UT, c l e a r l y shows the r i s i n g f r e q u e n c y t r e n d t y p i c a l of IPDPs. Table VI  IPDP Physical C h a r a c t e r i s t i c s I n i t i a l f r e q u e n c y (F;. ) End fr e q u e n c y (F ) Change i n frequ e n c y ( F e - F / ) Average s l o p e ((F -F.)/T) D u r a t i o n (T) Amp l i t u d e 0.1 - 0.3 Hz 0.5 - 1.0 Hz 0.2 - 0.7 Hz 0.2 - 1.0 Hz/h 20 min - 2 h 0.0! - 1.0 7 23 e x h i b i t may be q u i t e d i f f e r e n t , w i t h i n an i n d i v i d u a l event they tend t o be f a i r l y c o n s t a n t . An average s l o p e of 0.73 Hz/h was o b t a i n e d by Heacock (1971) from 130 e v e n t s , w h i l e Roxburgh (1970) found a t y p i c a l s l o p e t o be 0.3 Hz/h. In extreme c a s e s , the s l o p e may be much l a r g e r than 1 Hz/h. For example, s l o p e s of up t o 5 Hz/h have been r e p o r t e d (Roxburgh, 1970). The w i d t h of the n o i s e band of IPDPs i s u s u a l l y i n the range of 0.1 - 0.3 Hz. From a sample of 66 e v e n t s , an average l e n g t h f o r IPDPs of 39 minutes was found by F u k u n i s h i et a l . (1981). Most IPDP event d u r a t i o n s exceed 20 mi n u t e s , though events l o n g e r than 2 hours a r e q u i t e r a r e . A mean a m p l i t u d e of 0.17 f o r IPDP e v e n t s was g i v e n by Ge n d r i n (1970). However, IPDPs o f t e n c o n t a i n s h o r t , h i g h e r a m p l i t u d e i n t e r v a l s as w e l l . The c h a r t r e c o r d i n g i n f i g u r e 5 shows an example of such an i n t e r v a l . These s t r u c t u r e d e l ements, as the h i g h a m p l i t u d e i n t e r v a l s a r e o f t e n c a l l e d , t end t o oc c u r a t randomly spaced i n t e r v a l s d u r i n g the c o u r s e of an IPDP e v e n t . The p o l a r i z a t i o n shown by IPDPs can be r i g h t - h a n d e d or l e f t - h a n d e d e l l i p t i c a l , or l i n e a r . A r n o l d y et a l . (1979) r e p o r t e d a p r o g r e s s i o n of f i r s t r i g h t - h a n d e d , then l i n e a r , then l e f t - h a n d e d , then l i n e a r a g a i n , and l a s t l y r i g h t - h a n d e d p o l a r i z a t i o n a g a i n d u r i n g the c o u r s e of an IPDP event. 24 (/(.) ap'n^idujD FIGURE 5. Y component magnetogram of a part of an IPDP event (0905 - 0909 UT) recorded at Park S i t e , Sask. on Feb. 14, 1980. A 0.4 - 1.0 Hz bandpass f i l t e r has been a p p l i e d to the data. Note the higher amplitude i n t e r v a l near 0908UT. 25 3.2. OCCURRENCE OF IPDPS T a b l e V I I p r e s e n t s a b r i e f summary of the o c c u r r e n c e c h a r a c t e r i s t i c s of e v e n i n g - s i d e IPDPs. M o r n i n g - s i d e IPDPs ( F u k u n i s h i and Toya, 1981; Dovbnya et a l . , 1984), which t y p i c a l l y appear near 0500 geomagnetic l o c a l time (GMLT), a r e p o s s i b l y a d i s t i n c t c l a s s of m i c r o p u l s a t i o n from e v e n i n g - s i d e IPDPs and are not c o n s i d e r e d i n t h i s t h e s i s . As w i t h Table V I , the v a l u e s g i v e n here w i l l be t y p i c a l of most, but not a l l , IPDP e v e n t s . IPDPs a r e s t r o n g l y c o n c e n t r a t e d i n the e v e n i n g l o c a l time s e c t o r , w i t h the peak i n o c c u r r e n c e near 2000 GMLT as shown i n f i g u r e 6. The h e a v i e s t c o n c e n t r a t i o n of ev e n t s a l s o o c c u r s i n the geomagnetic l a t i t u d e (GM L a t . ) range of 60° t o 65°, the s u b - a u r o r a l zone. Very few have been o b s e r v e d a t l a t i t u d e s h i g h e r than 70°. Below 50° GM L a t . , IPDPs a r e a l s o l e s s common, r e a c h i n g t h e s e l a t i t u d e s o n l y t h r o u g h i o n o s p h e r i c duct p r o p a g a t i o n ( c f . Appendix B) or on days of v e r y h i g h magnetospheric a c t i v i t y . Most IPDPs o c c u r on mo d e r a t e l y a c t i v e days (20 < ZKp < 30 ) , though some a r e o c c a s i o n a l l y seen on r e l a t i v e l y q u i e t days (10 < ZKp < 20). Heacock (1967) found a median v a l u e of 3- f o r the 3 - h o u r l y Kp index c o r r e s p o n d i n g t o an IPDP e v e n t ' s o c c u r r e n c e t i m e . F i g u r e 7 shows when IPDPs o c c u r r e d on a Kp v e r s u s time p l o t c o v e r i n g 2y months ( G e n d r i n , 1970). Heacock (1967) a l s o found t h a t IPDPs o c c u r r e d a t the r a t e of a p p r o x i m a t e l y 12 per q u a r t e r , Table VII IPDP Occurrence Characteristics L o c a l time L a t i t u d e 3 - h o u r l y Kp 1600 - 0100 GMLT 55° - 65° GM L a t . 20 - 35 1 - 5 27 F e b 1 9 6 5 - D e c 1966 6 12 18 0 6 Local Time (120°W) FIGURE 6 . D i u r n a l d i s t r i b u t i o n of the o c c u r r e n c e of IPDPs, showing the peak i n o c c u r r e n c e i n the e v e n i n g h o u r s . These da t a were c o l l e c t e d a t S e a t t l e , Wash. (GM L a t . ^53°) by K n a f l i c h and Kenney (1967). 28 Kp. 9 6 J 0 2 f 1 0 70 60 55 T r 1 1 1 1 1 1 1 r 1 1 1 1 ~i 1 1 " .t. . . .tt. .i „ t l . , ! • 1 1 1 1 1 r 1 ; _ a  ,t..t.t. .t. ,f. , 15 20 2S, , ,- , .JO, , 1 . . . . 5 10' 15 March - 10 April 1964 i r 1 1 1 1 r— L . . • t. .f.t ~~I 1 1 1 1 1 1 T 1 J— 1 1 1 1 1 < 1 1 1 t . *_ . t t t. . . . . ,15. , . , ,20 25. . ' . , .30. \ , , , . 5 , 11 April — 07 May 1964 o 2 o 70 A C 6 S 60 55 , , 1 , , f.tl. ,t 25. • • . ,30. •' 08 May — 03 June 1964 FIGURE 7. Occurrence of IPDPs v e r s u s Kp index ( G e n d r i n , 1970). The v e r t i c a l arrows i n the c e n t r a l p a n e l s i n d i c a t e IPDPs, which tend t o occur i n more a c t i v e t i m e s ( h i g h e r K p ) . 29 i n c r e a s i n g t o s e v e r a l dozen per q u a r t e r i n the summer. F u k u n i s h i e t a l . (1981) o b t a i n e d the somewhat lower r a t e of 66 e v e n t s i n 25 months a t Syowa S t a t i o n , A n t a r c t i c a (GM L a t . = -65.9°). As i n d i c a t e d above, on days of h i g h magnetospheric a c t i v i t y IPDPs are obs e r v e d a t lower l a t i t u d e s , w h i l e h i g h l a t i t u d e s t a t i o n s d e t e c t n o t h i n g . These lower l a t i t u d e e v e n t s t e n d t o e x h i b i t h i g h e r f r e q u e n c i e s than the h i g h l a t i t u d e IPDPs. A c c o r d i n g t o Soraas et a l . (1980), the low l a t i t u d e , h i g h Kp e v e n t s a l s o tend t o occur a t e a r l i e r l o c a l t i m e s , though, f o r c o n s t a n t Kp, the maximum o c c u r r e n c e r a t e i s a t an e a r l i e r GMLT f o r h i g h l a t i t u d e IPDPs. Heacock e t a l . (1976) found the d i u r n a l peak t o be near 1700 GMLT f o r C o l l e g e , A l a s k a (64.5° GM L a t . ) and near 2000 GMLT f o r P a l o A l t o , C a l i f o r n i a . (43.5° GM L a t . ) . Other l a t i t u d e e f f e c t s t h a t have been noted i n c l u d e 0.17 a m p l i t u d e s a t lower l a t i t u d e s v e r s u s 17 a m p l i t u d e s a t h i g h l a t i t u d e s (Heacock, 1967) as w e l l as lower f r e q u e n c y s l o p e s a t h i g h l a t i t u d e s ( P i k k a r a i n e n e t a l . , 1983). Heacock (1971) found t h a t IPDP s l o p e v a r i e s w i t h GMLT, d e t e r m i n i n g an average s l o p e of 0.55 Hz/h from a s e t of 63 IPDPs o c c u r r i n g i n the 1200 t o 1600 GMLT s e c t o r , and an average s l o p e of 0.91 Hz/h from 67 ev e n t s o c c u r r i n g i n the 1700 t o 2300 GMLT s e c t o r . However, Roxburgh (1970) c l a i m e d t o f i n d no c o r r e l a t i o n between s l o p e and GMLT. Heacock e t 30 a l . (1976) a l s o compared the s l o p e s of IPDPs t o the AE index f o r l a t e - e v e n i n g s e c t o r e v e n t s , f i n d i n g t h a t h i g h AE c o r r e l a t e d w i t h h i g h s l o p e s and low AE w i t h low s l o p e s . These c o r r e l a t i o n s were not e v i d e n t i n the a f t e r n o o n s e c t o r . Note t h a t both the Kp and AE i n d i c e s a r e d e s c r i b e d i n Appendix C. V a r i o u s s t u d i e s comparing IPDPs r e c o r d e d a t g e o m a g n e t i c a l l y c o n j u g a t e s t a t i o n s have been c o n d u c t e d . G e n d r i n et a l . (1966) r e p o r t e d t h a t IPDP s t r u c t u r e d e l e m e n t s , or h i g h a m p l i t u d e i n t e r v a l s , appeared s i m u l t a n e o u s l y a t c o n j u g a t e s t a t i o n s and w i t h the same p o l a r i z a t i o n , t h a t i s , both d i s p l a y i n g the same sense of magnetic v e c t o r r o t a t i o n a t one t i m e . Both th e s e c h a r a c t e r i s t i c s a r e o p p o s i t e t h o s e shown by s t r u c t u r e d Pc 1 ( p e a r l s ) , whose elements appear a l t e r n a t e l y and w i t h o p p o s i t e senses of v e c t o r r o t a t i o n a t c o n j u g a t e s t a t i o n s . A r n o l d y e t a l . (1979) found t h a t an IPDP r e c o r d e d a t S i p l e , A n t a r c t i c a , and R o b e r v a l , Quebec, showed n e i t h e r l e f t - h a n d p o l a r i z a t i o n nor cosmic n o i s e a b s o r p t i o n which accompanies l e f t - h a n d p o l a r i z a t i o n ( c f . s e c . 3.5) s i m u l t a n e o u s l y a t each s i t e even though R o b e r v a l i s o n l y 40km from S i p l e ' s c o n j u g a t e p o i n t . T h i s i n d i c a t e s t h a t c a r e must be taken i n i n t e r p r e t i n g " c o n j u g a t e " p o i n t p o l a r i z a t i o n o b s e r v a t i o n s . Heacock et a l . (1976) found t h a t i n v i r t u a l l y a l l c a s e s IPDPs r e c o r d e d a t one s i t e were a l s o seen a t the c o n j u g a t e 31 s i t e , and e x h i b i t e d the same frequ e n c y s l o p e a t both s i t e s . I t was a l s o found, however, t h a t the o c c u r r e n c e of s t r u c t u r e d elements w i t h i n an IPDP were u n c o r r e l a t e d between the c o n j u g a t e s i t e s , which i s i n c o n t r a s t t o the r e s u l t mentioned above. I t must be noted t h a t , w i t h r e s p e c t t o both p o l a r i z a t i o n and element o c c u r r e n c e , there- appears t o be some u n c e r t a i n t y i n IPDP p r o p e r t i e s . 3.3. NETWORK OBSERVATIONS Networks of ground s t a t i o n s have o f t e n been employed t o study IPDP e v e n t s . These networks have g e n e r a l l y c o n s i s t e d of n o r t h - south l i n e s of s t a t i o n s ( L u k k a r i et a l . , 1977; M a l t s e v a e t a l . , 1981; P i k k a r a i n e n e t a l . , 1983; M a l t s e v a et a l . , 1985; P i k k a r a i n e n e t a l . , 1986), and/or e a s t - west s t a t i o n a r r a y s ( M a l t s e v a e t a l . , 1970; Heacock, 1973; Soraas et a l . , 1980; P i k k a r a i n e n e t a l . , 1983). Magnetograms and spectrograms of an IPDP event r e c o r d e d a t s t a t i o n s i n a n o r t h - so u t h l i n e g e n e r a l l y have s i m i l a r appearances a t each s i t e . I o n o s p h e r i c d u c t i n g of IPDP s i g n a l s causes an event r e c o r d e d s i m u l t a n e o u s l y a t l a t i t u d i n a l l y s e p a r a t e d s t a t i o n s t o show the same f r e q u e n c y , s l o p e , d u r a t i o n , and s t r u c t u r e d elements a t each l o c a t i o n . The a m p l i t u d e of an IPDP, however, w i l l v a r y a l o n g a n o r t h -sou t h l i n e of s t a t i o n s , w i t h the l o c a t i o n of the peak a m p l i t u d e moving southward d u r i n g the event (among o t h e r s ; 32 L u k k a r i e t a l . , 1977, M a l t s e v a et a l . , 1981, P i k k a r a i n e n e t a l . , 1986). F i g u r e 8 shows s i m u l t a n e o u s c h a r t r e c o r d s of an IPDP o b t a i n e d from two of the s t a t i o n s of the Saskatchewan n o r t h - south c h a i n (PS and LL) s e p a r a t e d by 1.2° of l a t i t u d e , d e m o n s t r a t i n g the s i m i l a r i t y of s i g n a l s from c o - m e r i d i o n a l s t a t i o n s . Somewhat l e s s a t t e n t i o n has been p a i d t o s i m u l t a n e o u s o b s e r v a t i o n s of IPDPs at s t a t i o n s s e p a r a t e d i n l o n g i t u d e . The s t u d i e s t h a t have been done i n d i c a t e t h a t the l o n g i t u d i n a l range of IPDP e v e n t s can v a r y w i d e l y ; Soraas et a l . (1980) found e v e n t s c o v e r i n g more than 140° geomagnetic l o n g i t u d e (GM Long.) are r a r e , w h i l e 30% of the e v e n t s o b s e r v e d spanned l e s s than 60° GM L o n g i t u d e . Though P i k k a r a i n e n e t a l . (1983) commented t h a t no d r a s t i c changes i n IPDP f r e q u e n c y - time c h a r a c t e r i s t i c s a r e n e c e s s a r i l y o b s e r v e d over the 100° l o n g i t u d e range of an event and Soraas e t a l . (1980) found t h a t IPDPs can be q u i t e s i m i l a r over ranges of l e s s than 60° GM Long., i t i s n e v e r t h e l e s s c l e a r t h a t some l o n g i t u d i n a l d i f f e r e n c e s do e x i s t w i t h i n an IPDP event as seen on an e a s t - west c h a i n of s t a t i o n s . M a l t s e v a et a l . (1970) found t h a t both the f r e q u e n c y and s l o p e of IPDPs tends t o be h i g h e r towards the e a s t , t h a t i s , towards m i d n i g h t . W h i l e Heacock (1973) c o u l d not c o n f i r m the t r e n d f o r IPDP s l o p e s , i t was noted t h a t a d e l a y i n onset t i m e s t o the west of 15 minutes t o 1 hour was o f t e n seen 33 2.0 3.0 4.0 5.0 6.0 t ime (min ) 2.0 ' 3 . 0 4.0 5.0 6.0 t ime (min ) - FIGURE 8 . Comparison of Y component r e c o r d segments (0902 t o 0906 UT) from two s t a t i o n s on the same m e r i d i a n (Park S i t e , 312.2° E, and Lucky Lake, 312.7° E ) , Feb. 14 e v e n t . Each segment has been n o r m a l i z e d and a 0.4 - 1.0 Hz bandpass f i l t e r has been a p p l i e d . Note the s i m i l a r i t y i n the s i g n a l s between these two s t a t i o n s . 34 between Meanook and C o l l e g e , 44.5° west (towards dusk) of Meanook. P i k k a r a i n e n e t a l . (1983) o b t a i n e d a much f a s t e r onset d r i f t of 5° - 6°/min t o the west from 23 e v e n t s . Three of t hese 23 ev e n t s were a l s o examined i n d e t a i l , w i t h a l l t h r e e showing l o n g e r d u r a t i o n s towards the west and l e s s i n t e n s e low f r e q u e n c i e s towards the e a s t . Two of the events d i s p l a y e d no change i n s l o p e w i t h l o n g i t u d e , w h i l e the t h i r d e x h i b i t e d lower s l o p e s towards the west. F i g u r e 9 shows s i m u l t a n e o u s c h a r t r e c o r d s of an IPDP from two s i t e s i n the sou t h e r n e a s t - west l i n e (PG and PS). Here, the s i g n a l s do not show the same degree of s i m i l a r i t y as those i n f i g u r e 8. The s t a t i o n s a r e s e p a r a t e d by 19.8° GM L o n g i t u d e . 3.4. SATELLITE OBSERVATIONS IPDPs have been s t u d i e d from geosynchronous s a t e l l i t e s by Bossen et a l . (1976), u s i n g ATS-1 d a t a , and McPherron (1981), u s i n g ATS-6 d a t a . Almost a l l e v e n t s seen a t geosynchronous o r b i t a r e a l s o seen a t a ground s t a t i o n near the f o o t of the s a t e l l i t e ' s f i e l d l i n e . For t h e s e IPDPs, the freque n c y spectrum seen a t the s a t e l l i t e i s narrower than t h a t on the ground, but i s c o n t a i n e d w i t h i n the same range. S a t e l l i t e s a l s o observe s m a l l e r changes i n fr e q u e n c y and s h o r t e r d u r a t i o n s than ground s t a t i o n s f o r IPDP events ( c f . f i g . 10). These d i f f e r e n c e s a r e l i k e l y due t o i o n o s p h e r i c d u c t i n g of the gro u n d - r e c o r d e d s i g n a l s ( c f . Appendix B ) . 35 40 41 42 43 44 45 time (min ) 40 41 42 43 44 45 time (min ) FIGURE 9. Comparison of Y component r e c o r d segments (0641 t o 0646 UT) from two s t a t i o n s near the same p a r a l l e l (Park S i t e , 61.3° N, and P r i n c e George, 59.6° N), Feb. 24c e v e n t . Each segment has been n o r m a l i z e d and a 0.2 - 0.6 Hz bandpass f i l t e r has been a p p l i e d . These l o n g i t u d i n a l y s e p a r a t e d s t a t i o n s e x h i b i t q u i t e d i f f e r e n t IPDP s i g n a l s . 36 FIGURE 1 0 . Comparison of s p e c t r a from an IPDP r e c o r d e d s i m u l t a n e o u s l y by s a t e l l i t e (ATS-1) and a t a ground s t a t i o n (Tungsten, NWT.) (Bossen e t a l . , 1976). Note the s h o r t e r event d u r a t i o n and s m a l l e r f r e q u e n c y r i s e seen by the s a t e l l i t e . 37 A m p l i t u d e s of about 57 have been r e c o r d e d i n o r b i t , which i s a p p r o x i m a t e l y 50 tim e s g r e a t e r than a t y p i c a l ground s t a t i o n a m p l i t u d e . The p o l a r i z a t i o n s o b s e r v e d a t thes e s a t e l l i t e s a r e l e f t - h a n d e d e l l i p t i c a l , and a t ATS-6, which i s 10° above the magnetic e q u a t o r , IPDP waves a r e always observed p r o p a g a t i n g away from the e q u a t o r . 3.5. RELATION TO GEOMAGNETIC PHENOMENA I t i s w e l l e s t a b l i s h e d t h a t IPDPs occur i n a c t i v e p e r i o d s f o l l o w i n g storm sudden commencements. In p a r t i c u l a r , t h ey are always a s s o c i a t e d w i t h magnetospheric substorms, o c c u r r i n g i n the e x p a n s i o n and r e c o v e r y phases (Heacock et a l . , 1976). The onset of the ex p a n s i o n phase i s seen on the ground as a sharp n e g a t i v e bay i n the X component a t h i g h l a t i t u d e s t a t i o n s near m i d n i g h t . In the dusk s e c t o r , the X component o f t e n e x h i b i t s h i g h l a t i t u d e p o s i t i v e bays d u r i n g a substorm e x p a n s i o n phase. IPDPs can occur i n the a f t e r n o o n or e v e n i n g s e c t o r s f o l l o w i n g , u s u a l l y w i t h i n an hour, the onset of a sharp n e g a t i v e bay near m i d n i g h t . The d e l a y time i s g e n e r a l l y l o n g e r f o r IPDPs o c c u r r i n g a t e a r l i e r l o c a l t i m e s , and i t has been found t h a t the s l o p e of an event tends t o dec r e a s e as t h i s d e l a y time i n c r e a s e s ( F u k u n i s h i , 1969). IPDPs a r e a l s o known t o occ u r i n c o n j u n c t i o n w i t h the dusk s e c t o r h i g h l a t i t u d e p o s i t i v e bays. D u r i n g a substorm e x p a n s i o n phase, s a t e l l i t e s i n geosynchronous o r b i t observe 38 a d e p r e s s i o n i n the magnetic f i e l d s t r e n g t h , f o l l o w e d by a r e c o v e r y . A l t h o u g h Roxburgh (1970) found t h a t IPDPs o c c u r r e d d u r i n g t h i s r e c o v e r y phase, the r e s u l t s of Bossen et a l . (1976) i n d i c a t e d t h a t 83% of the 33 e v e n t s s t u d i e d o c c u r r e d when the magnetic f i e l d a t geosynchronous o r b i t was e i t h e r d e c r e a s i n g or c o n s t a n t . P r o t o n p r e c i p i t a t i o n and a s s o c i a t e d p r o t o n a u r o r a have been o b s e r v e d w i t h IPDP e v e n t s ( F u k u n i s h i , 1973), as has cosmic n o i s e a b s o r p t i o n (CNA). Note, however, t h a t CNA i s most l i k e l y not caused by p r e c i p i t a t i n g p r o t o n s , but r a t h e r by i n c r e a s e d i o n i z a t i o n i n the i o n o s p h e r e caused by p r e c i p i t a t i n g p r o t o n s ( F u k u n i s h i , 1973), or by r e l a t i v i s t i c e l e c t r o n s p r e c i p i t a t e d by p a r a s i t i c i n t e r a c t i o n s between IPDP waves and these e l e c t r o n s (Thorne and K e n n e l , 1971; Thorne and L a r s e n , 1976). A r n o l d y et a l . (1979) found t h a t the l e f t - h a n d p o l a r i z e d phase of IPDPs was c o r r e l a t e d w i t h the o c c u r r e n c e of CNA, p a r t i c l e p r e c i p i t a t i o n , and a u r o r a l l i g h t . In a d d i t i o n t o v i s u a l a u r o r a , IPDPs have been a s s o c i a t e d w i t h the a u r o r a l s p o r a d i c E - l a y e r and a u r o r a l X-ray b u r s t s . IPDPs have a l s o been a s s o c i a t e d w i t h o t h e r t y p e s of m i c r o p u l s a t i o n s . Heacock (1967) r e p o r t e d t h a t 4-second band p u l s a t i o n s sometimes t e r m i n a t e i n IPDPs, and Roxburgh (1970) found t h a t o c c a s i o n a l l y hm e m i s s i o n s i m m e d i a t e l y f o l l o w IPDP e v e n t s . M a l t s e v a et a l . (1981) r e p o r t e d o b s e r v a t i o n s of Pc 39 4-5 p u l s a t i o n s a t geosynchronous o r b i t o n l y w h i l e IPDPs were seen on the ground. P i b u r s t s ( P i 1) were s t u d i e d i n c o n j u n c t i o n w i t h IPDPs by Heacock (1971). I t was noted t h a t P i b u r s t s o c c u r b e f o r e and towards m i d n i g h t of almost a l l IPDPs. They appear a t h i g h e r l a t i t u d e s than IPDPs, and are accompanied by l a r g e s c a l e p a r t i c l e p r e c i p i t a t i o n i n t o the i o n o s p h e r e . CHAPTER 4. MAGNETOSPHERIC MODEL OF IPDP GENERATION I t i s now g e n e r a l l y a c c e p t e d t h a t IPDP m i c r o p u l s a t i o n s a r e produced by an i o n - c y c l o t r o n i n s t a b i l i t y i n v o l v i n g l e f t - h a n d p o l a r i z e d waves and westward d r i f t i n g p a r t i c l e s i n j e c t e d i n t o the i n n e r magnetosphere from the m a g n e t o t a i l d u r i n g magnetospheric substorms ( H o r i t a et a l . , 1979; P i k k a r a i n e n e t a l . , 1983). However, not a l l the a s p e c t s of t h i s p r o c e s s a re c o m p l e t e l y u n d e r s t o o d , t h i s b e i n g e s p e c i a l l y t r u e of the mechanism(s) r e s p o n s i b l e f o r the r i s i n g f r e q u e n c y t r e n d e x h i b i t e d by IPDPs. In t h i s c h a p t e r , the magnetospheric p r o c e s s e s r e s p o n s i b l e f o r the appearance of IPDPs a r e d e s c r i b e d ( s e c t i o n 4.1), f o l l o w e d by a d e s c r i p t i o n and d i s c u s s i o n 'of the fre q u e n c y s h i f t mechanisms ( s e c t i o n s 4.2 and 4.3). L a s t l y , the p r o c e s s e s d e s c r i b e d i n s e c t i o n s 4.1 through 4.3 are examined u s i n g a s i m p l e computer s i m u l a t i o n of IPDP freq u e n c y b e h a v i o u r ( s e c t i o n 4.4) . 4 . 1 . IPDP - SUBSTORM MODEL At t he onset of a magnetospheric substorm, hot p a r t i c l e s , which may e v e n t u a l l y become i n v o l v e d i n IPDP g e n e r a t i o n , a r e i n j e c t e d from the plasma sheet i n towards the n i g h t s i d e of the E a r t h . T h i s i n j e c t i o n i s d r i v e n by the substorm a s s o c i a t e d i n t e n s i f i e d westward e l e c t r i c f i e l d . Though the plasma h e a t i n g mechanism r e s p o n s i b l e f o r the h i g h 40 41 p a r t i c l e e n e r g i e s i s not y e t w e l l u n d e r s t o o d , i t i s l i k e l y r e l a t e d t o the r e c o n n e c t i o n p r o c e s s o c c u r r i n g i n the m a g n e t o t a i l a t magnetospheric substorm onset ( N i s h i d a , 1978). Some of the p a r t i c l e s i n v o l v e d i n the i n j e c t i o n p r e c i p i t a t e d i r e c t l y i n t o the i o n o s p h e r e near m i d n i g h t a t h i g h l a t i t u d e s . T h i s i s most l i k e l y the p r e c i p i t a t i o n o b served i n c o n j u n c t i o n w i t h the P i b u r s t s , which a re o f t e n seen near m i d n i g h t p r e c e e d i n g IPDPs ( c f . s e c t i o n 3.5). A sh a r p i n n e r boundary of the i n j e c t e d p a r t i c l e s has been o b s e r v e d or i n f e r r e d by some a u t h o r s (Mauk and M c l l w a i n , 1974; M c l l w a i n , 1974; Mauk and Meng, 1983). I f d i r e c t o b s e r v a t i o n of t h i s boundary i s not p o s s i b l e , i t s o r i g i n a l p o s i t i o n can be c a l c u l a t e d by b a c k t r a c k i n g the d r i f t motions of the p a r t i c l e s from where they were d e t e c t e d by s a t e l l i t e . Such c a l c u l a t i o n s r e s u l t i n the i d e n t i f i c a t i o n of a s h a r p l y d e f i n e d s p i r a l or double s p i r a l shaped boundary, as shown i n f i g u r e 11 (double s p i r a l ) and f i g u r e 12 ( s i n g l e s p i r a l ) . These b o u n d a r i e s a r e c l o s e s t t o E a r t h j u s t a f t e r m i d n i g h t , w i t h the cusp of a double - s p i r a l boundary u s u a l l y f a l l i n g near 0100-0200 GMLT. S i n g l e s p i r a l b o u n d a r i e s , which almost always s p i r a l out westward towards dusk, can have t h e i r c l o s e s t p o i n t as f a r ea s t w a r d (towards morning) as 0300-0400 GMLT. Note t h a t b e f o r e d r i f t motions and p a r t i c l e p r e c i p i t a t i o n d i s t u r b the i n j e c t e d plasma, p a r t i c l e s of a l l e n e r g i e s and p i t c h a n g l e s a r e p r e s e n t 42 FIGURE 1 1 . Diagram of a d o u b l e - s p i r a l i n j e c t i o n boundary (Mauk and Meng, 1983). 43 00 FIGURE 1 2 . Westward s i n g l e - s p i r a l i n j e c t i o n boundary (Mauk and M c l l w a i n , 1974). Note the boundary p o s i t i o n v a r i a t i o n w i t h m agnetospheric a c t i v i t y ( K p ) : i n n e r boundary, Kp = 5; o u t e r boundary, Kp = 2. 44 t o g e t h e r . I t has been found t h a t the p o s i t i o n of the i n j e c t i o n boundary i s dependent on the l e v e l of magnetospheric a c t i v i t y ( K p ) , w i t h the boundary o c c u r r i n g f u r t h e r inward d u r i n g more a c t i v e t i m e s , as i l l u s t r a t e d i n f i g u r e 12. Mauk and M c l l w a i n (1974) have p r e s e n t e d a fo r m u l a r e l a t i n g boundary p o s i t i o n t o Kp and GMLT f o r a s i n g l e westward s p i r a l boundary: 122 - 1OKp / A . b = GMLT - 7.3 U ' } ) where L^ i s the L s h e l l of the boundary (L = [ d i s t a n c e from c e n t e r of E a r t h ] / [ r a d i u s of E a r t h ] ) and Kp i s the " i n s t a n t a n e o u s " Kp v a l u e . Note t h a t i n e q u a t i o n 4.1, GMLT, which i s e x p r e s s e d i n h o u r s , i s a c t u a l l y e q u a l t o GMLT + 2400 a f t e r m i d n i g h t ( i . e . 0100 becomes 2500). A r n o l d y and Moore (1983) have suggested a l s o t h a t the boundary forms f i r s t near m i d n i g h t , then expands c o n t i n u o u s l y t o the west f o r m i n g a s i n g l e s p i r a l , or both t o the e a s t and t o the west f o r m i n g a double s p i r a l . T h e i r s t u d i e s i n d i c a t e t h a t i t t a k e s a p p r o x i m a t e l y 10 t o 15 minutes f o r the e n t i r e i n j e c t i o n boundary t o form, w i t h the f o r m a t i o n p r o c e e d i n g more q u i c k l y near m i d n i g h t than t o the west or e a s t . 45 Immediately a f t e r the hot p r o t o n s a r e i n j e c t e d i n t o the i n n e r magnetosphere, they b e g i n t o d r i f t westward under the i n f l u e n c e of the g r a d i e n t and c u r v a t u r e of the geomagnetic f i e l d . The g r a d i e n t d r i f t v e l o c i t y i s g i v e n by ( J a c k s o n , 1975): v = g 2a 1 x Vj_B (4.2a) and the c u r v a t u r e d r i f t v e l o c i t y by: v c where v_^ and v„ a r e the p a r t i c l e v e l o c i t i e s p e r p e n d i c u l a r and p a r a l l e l t o the magnetic f i e l d B. R" i s the r a d i u s v e c t o r from the e f f e c t i v e c e n t e r of c u r v a t u r e t o the f i e l d l i n e and u> i s the p a r t i c l e g y r o f r e q u e n c y . From J a c k s o n (1975), and u s i n g u> = qB/mc, R = r E / 3 a t equator of a d i p o l e f i e l d ( r E i s d i s t a n c e from c e n t e r of E a r t h ) , and B = B / L 3 (B i s e q e q f i e l d s t r e n g t h on E a r t h ' s s u r f a c e a t the e q u a t o r ) , e q u a t i o n s 4.2a and 4.2b above can be combined t o g i v e a t o t a l d r i f t v e l o c i t y o f : v 2 w R R x B RB (4.2b) 46 3Wc (1 + c o s 2 a ) L 2 . . , . v , = — — (4.3) ^ E eg where W i s the t o t a l p a r t i c l e k i n e t i c energy, a i s t h e p i t c h a n g l e , R_ i s the r a d i u s of the E a r t h , and c i s the speed of l i g h t . Note t h a t s i n c e u> i s p o s i t i v e because q i s p o s i t i v e f o r p r o t o n s , the d r i f t v e l o c i t y i s d i r e c t e d westward. I t i s apparent from t h i s e q u a t i o n t h a t the d r i f t v e l o c i t y i n c r e a s e s w i t h p a r t i c l e energy and w i t h d i s t a n c e from E a r t h ( i n c r e a s i n g L ) . The energy dependence of v^ i n d i c a t e s t h a t a s a t e l l i t e i n the e v e n i n g s e c t o r s h o u l d see a s o f t e n i n g p r o t o n energy spectrum as p r o g r e s s i v e l y s l o w e r , lower energy p a r t i c l e s a re en c o u n t e r e d d u r i n g the westward d r i f t . T h i s e f f e c t , which i s more pronounced i n the dusk r e g i o n f u r t h e r from the i n j e c t i o n boundary i s w e l l s u p p o r t e d by o b s e r v a t i o n ( M c l l w a i n , 1974; H o r i t a et a l . , 1979; Mauk and Meng, 1983). The d u r a t i o n of IPDPs i s a l s o w e l l matched by the d u r a t i o n of the enhanced f l u x of westward d r i f t i n g p r o t o n s as measured by s a t e l l i t e (Soraas et a l . , 1980). Though the p i t c h a n g l e d i s t r i b u t i o n a t i n j e c t i o n i s v i r t u a l l y i s o t r o p i c , l e a d i n g t o l a r g e s c a l e p r e c i p i t a t i o n i n t o the io n o s p h e r e a t h i g h e r l a t i t u d e s , i n s i d e and towards dusk of the i n j e c t i o n boundary the westward d r i f t i n g p r o t o n s show an 47 h i g h l y a n i s o t r o p i c d i s t r i b u t i o n w i t h an almost empty l o s s cone ( W i l l i a m s and Lyons, 1974a,b) (see f i g . 13). Though t h e r e i s a s t r o n g dawn t o dusk e l e c t r i c f i e l d a c r o s s the m a g n e t o t a i l d u r i n g substorms, t h i s does not seem to a f f e c t the d r i f t motions of h i g h energy p a r t i c l e s i n s i d e the plasma sheet i n n e r edge. T h i s i s p r i m a r i l y due t o the f o r m a t i o n of the A l f v e n l a y e r , a l a y e r h a v i n g a net p o s i t i v e charge on the e v e n i n g s i d e and a net n e g a t i v e charge on the morning s i d e , which i s c r e a t e d by the d i f f e r e n t i a l d r i f t motions of p r o t o n s and e l e c t r o n s i n the i n n e r magnetosphere. The p o l a r i z a t i o n e l e c t r i c f i e l d produced by t h e s e charged l a y e r s i s d i r e c t e d dusk t o dawn, o p p o s i t e the t a i l f i e l d , and s i g n i f i c a n t l y reduces the net e l e c t r i c f i e l d i n s i d e the A l f v e n l a y e r ( N i s h i d a , 1978). Thus, f o r h i g h e r energy p r o t o n s above a few keV which a r e r e s p o n s i b l e f o r IPDP g e n e r a t i o n , the e l e c t r i c f i e l d e f f e c t s on d r i f t motion a r e n e g l i g i b l e and the d r i f t p a t h s a r e c i r c u l a r . Lower energy p a r t i c l e s w i l l undergo E x B* d r i f t as w e l l as g r a d i e n t and c u r v a t u r e d r i f t s , w i t h the e l e c t r i c f i e l d e f f e c t s becoming dominant a t e n e r g i e s of l e s s than one keV ( N i s h i d a , 1982). S a t e l l i t e o b s e r v a t i o n s of s p a t i a l p r o t o n energy d i s p e r s i o n p a t t e r n s a l s o show t h a t the e l e c t r i c f i e l d component of the d r i f t v e l o c i t y must be q u i t e s m a l l f o r h i g h energy p r o t o n s ( M c l l w a i n , 1974; Mauk and Meng, 1983). T h i s p o l a r i z a t i o n e l e c t r i c f i e l d i s a l s o b e l i e v e d t o be 48 westward H + drift (a anisotropic) (empty loss cone) Sun Earth Injection Boundary H + injection ( a isotropic) FIGURE 13. /Proton i n j e c t i o n and westward d r i f t t r a j e c t o r i e s d u r i n g a substorm. Note the., d i f f e r e n t p i t c h angle (a) d i s t r i b u t i o n s p r e s e n t d u r i n g the i n j e c t i o n and westward d r i f t phases. 49 r e s p o n s i b l e f o r d r i v i n g the ea s t w a r d e l e c t r o j e t which i s sometimes, though not a l w a y s , observed w i t h i o n o s p h e r i c substorms ( N i s h i d a , 1978; B o t e l e r , 1980). T h i s e l e c t r o j e t c r e a t e s the dusk s e c t o r p o s i t i v e bays seen w i t h IPDPs ( c f . s e c t i o n 3.5), and i s con n e c t e d t o the p a r t i a l r i n g c u r r e n t produced by the westward p r o t o n d r i f t by an inward f i e l d a l i g n e d c u r r e n t (see f i g . 14). I t i s noteworthy t h a t n e i t h e r IPDPs nor the eastward e l e c t r o j e t - p a r t i a l r i n g c u r r e n t system appear w i t h e v e r y substorm. T h i s may be due t o the f a c t t h a t weak substorms have weak i n j e c t i o n s t h a t do not p e n e t r a t e d e e p l y i n t o the i n n e r magnetosphere, thus d e p r i v i n g b o t h IPDPs and the p a r t i a l r i n g c u r r e n t of t h e i r s o u r c e s . As the hot p r o t o n s c o n t i n u e t h e i r westward d r i f t , t hose on lower L s h e l l s w i l l e v e n t u a l l y meet the plasmapause, which i s a r e g i o n of s t e e p g r a d i e n t s i n c o l d plasma d e n s i t y s e p a r a t i n g the h i g h d e n s i t y t r a p p e d c o l d plasma i n s i d e the plasmaspause from the much lower d e n s i t y plasmas o u t s i d e of i t . I t i s here t h a t the d r i f t i n g p r o t o n s undergo the i o n - c y c l o t r o n i n s t a b i l i t y which t r a n s f e r s p a r t i c l e energy t o wave energy, thus g e n e r a t i n g an IPDP ev e n t . The i n s t a b i l i t y o c c u r s when a wave w i t h IPDP f r e q u e n c i e s , whose p r o p a g a t i o n v e c t o r i s o p p o s i t e l y d i r e c t e d t o the p a r t i c l e v e l o c i t y p a r a l l e l t o the background magnetic f i e l d , has i t s f r e q u e n c y d o p p l e r s h i f t e d i n the p r o t o n r e s t frame t o match the 50 FIGURE 14. M a g n e t o s p h e r i c and i o n o s p h e r i c substorm c u r r e n t systems. The system f e a t u r e s r e l a t i n g t o IPDP o c c u r r e n c e a r e the p a r t i a l r i n g c u r r e n t and the downward f i e l d - a l i g n e d c u r r e n t s l a b e l l e d c' and d' which feed the e a s t w a r d e l e c t r o j e t (Kamide et a l . , 1976). 51 p r o t o n ' s g y r o f r e q u e n c y . The opposed d i r e c t i o n s of t r a v e l mean t h a t o n l y l e f t - h a n d p o l a r i z e d waves can i n t e r a c t w i t h the p r o t o n s s i n c e the d i r e c t i o n of r o t a t i o n of the wave f i e l d must c o i n c i d e w i t h the d i r e c t i o n of p r o t o n g y r a t i o n about the magnetic f i e l d l i n e s . The above i m p l i e s t h a t the wave f r e q u e n c y , w, must be l e s s than the p r o t o n g y r o f requency, J2^, which i s as o b s e r v e d ( t y p i c a l l y cj ~ 0 . 1 0 ) . P The i n s t a b i l i t y o c c u r s p r e f e r e n t i a l l y a t the plasmapause because of i t s s h a r p l y i n c r e a s i n g c o l d plasma d e n s i t y (n ). C o r n w a l l e t a l . (1970) and P e r r a u t et a l . * c (1976) c a l c u l a t e d t h a t the peak growth r a t e of i o n - c y c l o t r o n waves (ICW) i s j u s t i n s i d e the plasmapause, and Gomberoff and Cuperman (1982) have shown t h a t the growth of ICW i n c r e a s e s as n /n i n c r e a s e s , which o c c u r s as the c w ' plasmapause i s c r o s s e d , u n t i l n^/n^ r e a c h e s an optimum v a l u e , and then growth d e c r e a s e s a g a i n . The plasmapause as the IPDP g e n e r a t i o n l o c a t i o n i s a l s o s u p p o r t e d by o b s e r v a t i o n ( H o r i t a et a l . , 1979). The growth of ICW depends c r i t i c a l l y on the a n i s o t r o p y (A) i n the hot p r o t o n d i s t r i b u t i o n as w e l l as on n £ . G e n d r i n et a l . (1971) have shown t h a t A > 1/[(A / u ) - 1 ] , where K P P p r o t o n g y r o f requency and A = [Tj_/T»] - 1, f o r ICW t o grow. Here, T, and T„ a r e d e f i n e d as T, = m < v 2 >/(2k) and T„ m < v 2 >/K where m i s the p r o t o n mass, < v 2 > and < v 2 > P " P j . " 52 are the averag e s of the squares of the speeds p e r p e n d i c u l a r and p a r a l l e l t o the magnetic f i e l d , and K i s Boltzmann's c o n s t a n t . For fi^/w = 10, t h i s means A must be g r e a t e r than 0.11. The hot p r o t o n p i t c h a n g l e d i s t r i b u t i o n w i l l have become a n i s o t r o p i c ( i . e . A > 0) d u r i n g the westward d r i f t . However, g i v e n the v e r y low n c found o u t s i d e the plasmapause, A does not become l a r g e enough f o r the i o n - c y c l o t r o n i n s t a b i l i t y t o oc c u r i n t h i s r e g i o n . T h i s i s c o n f i r m e d by C o r n w a l l and S c h u l z (1971), who found t h a t , o u t s i d e the plasmapause, the storm-time r i n g c u r r e n t i s s t a b l e w i t h r e s p e c t t o the i o n - c y c l o t r o n i n s t a b i l i t y . I t i s not u n t i l the plasmapause i s reached t h a t both the a n i s o t r o p y and n c f a v o u r wave growth. Once i n s i d e the plasmapause, however, wave growth a g a i n d e c r e a s e s due t o e l e c t r o n - i o n c o l l i s i o n s ( C o r n w a l l et a l . , 1970) and an a l t e r e d hot p r o t o n p o p u l a t i o n . S i n c e the i n s t a b i l i t y p r o c e s s t a k e s the p a r t i c l e energy from Vj_, i t a l s o reduces A s i n c e T^/T,, i s reduced. T h i s has the e f f e c t of s c a t t e r i n g p r o t o n s i n t o the p r e v i o u s l y empty l o s s cone of t h e i r p i t c h a n g l e d i s t r i b u t i o n , r e s u l t i n g i n a l o s s of p a r t i c l e s t o the i o n o s p h e r e . The lowered A and n^ then r e s u l t i n a d e c r e a s e d wave growth i n s i d e the plasmapause. A f t e r a m p l i f i c a t i o n , the ICW propagate down f i e l d l i n e s towards E a r t h ' s s u r f a c e . S i m i l a r i t i e s i n o c c u r r e n c e times and dynamic s p e c t r a of IPDPs as r e c o r d e d a t c o n j u g a t e 53 s t a t i o n s i n the n o r t h e r n and s o u t h e r n hemispheres, and as o b s e r v e d by s a t e l l i t e s and ground s t a t i o n s near the same f i e l d l i n e s , p r o v i d e s t r o n g e v i d e n c e f o r such f i e l d l i n e g u i d i n g ( c f . s e c t i o n s 3.2 and 3.4). The c o r r e l a t i o n s of p r o t o n p r e c i p i t a t i o n and CNA w i t h the l e f t - h a n d p o l a r i z e d waves ( c f . s e c t i o n 3.5), which a r r i v e a t the i o n o s p h e r e d i r e c t l y overhead of a ground s t a t i o n , p r o v i d e f u r t h e r c o n f i r m a t i o n of f i e l d l i n e g u i d i n g of the waves. T h i s p r o t o n p r e c i p i t a t i o n r e p r e s e n t s a t l e a s t a p o r t i o n of the downward f i e l d a l i g n e d c u r r e n t c o n n e c t i n g the p a r t i a l r i n g c u r r e n t and the e a s t w a r d e l e c t r o j e t mentioned e a r l i e r . The o b s e r v a t i o n t h a t the waves always propagate away from the equator ( c f . s e c t i o n 3.4) a l s o i n d i c a t e s t h a t a m p l i f i c a t i o n of the ICW t a k e s p l a c e p r i m a r i l y i n the e q u a t o r i a l r e g i o n . The shape of the plasmapause e x e r t s s t r o n g c o n t r o l over where and when IPDPs appear. F i g u r e 15 shows t h r e e e s t i m a t e s of the averaged plasmapause c o n f i g u r a t i o n . The westward p r o t o n d r i f t from the m i d n i g h t r e g i o n and the dusk s e c t o r bulge i n the plasmapause account f o r the o b s e r v a t i o n t h a t IPDPs occur p r e d o m i n a n t l y i n the e v e n i n g s e c t o r ( c f . s e c t i o n 3.2). T h i s a l s o c o n t r o l s the l o n g i t u d i n a l e x t e n t of i n d i v i d u a l IPDPs ( c f . s e c t i o n 3.3). As w e l l , the e q u a t o r i a l plasmapause d i s t a n c e c o n t r o l s the l a t i t u d e s of peak IPDP o b s e r v a t i o n by ground s t a t i o n s . The plasmapause shape p r o v i d e s an o b v i o u s l a t i t u d e GMLT c o r r e l a t i o n i n IPDP 54 FIGURE 15. Three average plasmapause L v e r s u s LT p r o f i l e s as d e t e r m i n e d from w h i s t l e r o b s e r v a t i o n s ( C a r p e n t e r , 1966), Ogo 5 i o n mass s p e c t r o m e t e r d a t a ( C h a p p e l l e t a l . , 1971), and E x p l o r e r 45 dc probe d a t a ( h i s t o g r a m ) (Maynard and Grebowsky, 1977). Note the i n c r e a s e d plasmapasue r a d i u s near 1800 LT which i s termed the dusk s e c t o r b u l g e . 55 o c c u r r e n c e , w i t h h i g h e r l a t i t u d e e v e n t s t e n d i n g t o occur a t e a r l i e r GMLT. S i n c e the plasmapause r a d i u s s h r i n k s w i t h h i g h e r magnetsopheric a c t i v i t y t h e r e i s a l s o a l a t i t u d e Kp c o r r e l a t i o n , w i t h h i g h e r l a t i t u d e e v e n t s o c c u r r i n g when Kp i s lower ( c f . s e c t i o n 3.2). Note t h a t t h e s e o b s e r v e d o c c u r r e n c e c h a r a c t e r i s t i c s and c o r r e l a t i o n s a l s o p r o v i d e c o n f i r m a t i o n t h a t IPDPs a r e g e n e r a t e d a t the plasmapause. 4.2. IPDP FREQUENCY SHIFT MECHANISMS The p r e c e d i n g s e c t i o n has d e s c r i b e d the g e n e r a l g e n e r a t i o n p r o c e s s e s which c r e a t e IPDPs, e x c e p t i n g those which produce the c h a r a c t e r i s t i c f r e q u e n c y r i s e . In t h i s s e c t i o n , t h r e e mechanisms which have been proposed t o account f o r the IPDP f r e q u e n c y s h i f t a r e r e v i e w e d . The p r i m a r y f a c t o r s c o n t r o l l i n g t he fre q u e n c y change of the i o n - c y c l o t r o n resonance g e n e r a t i n g IPDPs a r e the s t r e n g t h of the background magnetic f i e l d i n the g e n e r a t i o n r e g i o n and the energy of the hot r e s o n a t i n g p r o t o n s . In Appendix A ( e q u a t i o n A.4b), i t i s shown t h a t the fre q u e n c y ( f ) v a r i e s w i t h these parameters a s : The r i s i n g tone of IPDPs can t h e r e f o r e be caused by an 56 i n c r e a s i n g magnetic f i e l d B, or a d e c r e a s i n g p r o t o n energy W. Below, two p r o c e s s e s t h a t r e s u l t i n i n c r e a s i n g B, inward motion and i n c r e a s i n g background f i e l d , and one r e s u l t i n g i n d e c r e a s i n g W, a z i m u t h a l d r i f t , a r e d i s c u s s e d . 4.2.1. Inward Motion Inward motion of the IPDP g e n e r a t i o n r e g i o n from h i g h e r L s h e l l s i n towards the E a r t h , and thus t o r e g i o n s of h i g h e r magnetic f i e l d s t r e n g t h , was among the f i r s t mechanisms proposed t o account f o r the fr e q u e n c y r i s e of IPDPs (Gendrin et a l . , 1967; Heacock, 1967). T h i s inward motion was b e l i e v e d t o i n v o l v e the d i f f u s i o n inward a c r o s s f i e l d l i n e s i n the p r e m i d n i g h t - dusk s e c t o r of an hot p r o t o n c l o u d i n which the i o n - c y c l o t r o n i n s t a b i l i t y o c c u r r e d . The d i f f u s i o n was thought t o be d r i v e n by a westward e l e c t r i c f i e l d ( T r o i t s k a y a et a l . , 1968). r Roxburgh (1970) no t e d , however, t h a t the inward d i f f u s i o n v e l o c i t i e s (~6km/s) and e l e c t r i c f i e l d s (-6kV/R ) n e c e s s a r y f o r t h i s mechanism t o o p e r a t e a re not observed i n the IPDP g e n e r a t i o n r e g i o n . There i s , though, a way t o move the g e n e r a t i o n r e g i o n t o lower L s h e l l s w i t h o u t r e q u i r i n g a c r o s s L d r i f t of the hot p r o t o n s d u r i n g the ev e n t . As d i s c u s s e d i n s e c t i o n 4.1, IPDP g e n e r a t i o n o c c u r s a t the plasmapause a f t e r a westward d r i f t , i n c i r c u l a r o r b i t s , of the hot p r o t o n s . The r a d i a l p o s i t i o n of the g e n e r a t i o n 57 r e g i o n i s then c o n t r o l l e d by the plasmapause p o s i t i o n above, t h a t i s , i n the same m e r i d i a n a s , the ground s t a t i o n r e c o r d i n g the event. I f the plasmapause moves inw a r d , as i s observed t o happen d u r i n g magnetospheric s t o r m s , then the g e n e r a t i o n r e g i o n w i l l a l s o move inward, r e s u l t i n g i n the westward d r i f t i n g p r o t o n s meeting the plasmapause a t s u c c e s s i v e l y lower L s h e l l s i n the m e r i d i a n of the ground s t a t i o n , and c a u s i n g the IPDP e m i s s i o n f r e q u e n c y t o r i s e (Heacock, 1971; H o r i t a et a l . , 1979). I f i t i s assumed t h a t E a r t h ' s magnetic f i e l d i s a p p r o x i m a t e l y d i p o l a r (B L" 3) a t the s e s m a l l r a d i a l d i s t a n c e s , and a l s o t h a t W i s assumed t o be c o n s t a n t i n or d e r t o i s o l a t e the e f f e c t s of the inward motion r e l a t e d magnetic f i e l d changes, then e q u a t i o n 4.4 becomes: L. i_ fl . 5 (4.5) where X^ . and Xy a r e , r e s p e c t i v e l y , the i n i t i a l and f i n a l v a l u e s f o r each q u a n t i t y . Note t h a t the s t r o n g dependence of f on L (power of 4.5) i n d i c a t e s t h a t a r e l a t i v e l y s m a l l change i n L can produce a s i g n i f i c a n t f r e q u e n c y r i s e . O b s e r v a t i o n s of inward source movement have been made i n t h r e e ways. L u k k a r i e t a l . (1977) and M a l t s e v a et a l . (1981) o b s e r v e d the l a t i t u d e of peak IPDP a m p l i t u d e moving 58 southward a l o n g a n o r t h - s o u t h c h a i n of s t a t i o n s as the freque n c y r o s e , i m p l y i n g inward source motion i n the e q u a t o r i a l p l a n e , M a l t s e v a et a l . (1985) and P i k k a r a i n e n e t a l . (1986) used r i o m e t e r a b s o r p t i o n e v e n t s t o t r a c e inward source movements, and A r n o l d y e t a l . (1979) observed the RH - LH - RH p o l a r i z a t i o n sequence over a ground s t a t i o n , a l s o i m p l y i n g source motion. Though i t i s now g e n e r a l l y a greed t h a t inward motion can p l a y a r o l e i n c r e a t i n g the IPDP fr e q u e n c y s h i f t , the s i g n i f i c a n c e of t h i s r o l e i s not ye t w e l l u n d e r s t o o d . I t has been v a r i o u s l y c l a i m e d t h a t the r o l e i s minor (Heacock, 1971) or major ( P i k k a r a i n e n et a l . , 1 983) . 4.2.2. Increasing Background F i e l d An a l t e r n a t i v e p r o c e s s f o r i n c r e a s i n g the magnetic f i e l d s t r e n g t h i n the IPDP g e n e r a t i o n r e g i o n i s t o have the r e g i o n remain a t a c o n s t a n t r a d i a l d i s t a n c e w h i l e the background f i e l d s t r e n g t h i n c r e a s e s w i t h t i m e . T h i s mechanism was f i r s t proposed by Roxburgh (1970). I t r e q u i r e s t h a t the IPDP event occur d u r i n g . the p a r t i a l r i n g c u r r e n t decay phase a f t e r a magnetospheric substorm, when the c u r r e n t ' s e q u a t o r i a l magnetic f i e l d d e p r e s s i o n i n the IPDP g e n e r a t i o n r e g i o n i s weakening. I f we assume t h a t L and W are c o n s t a n t , the i n c r e a s i n g f i e l d e f f e c t on fr e q u e n c y would be (from e q u a t i o n 4.4): 59 r B B. . 5 ( 4 . 6 ) . Though Roxburgh (1970) r e p o r t e d IPDP e v e n t s whose fr e q u e n c y r i s e c o u l d be q u a n t i t a t i v e l y e x p l a i n e d by t h i s i n c r e a s i n g f i e l d mechanism, the r e l a t i o n s h i p between the magnetic f i e l d a t geosynchronous o r b i t and t h a t i n an IPDP source r e g i o n a t lower L may not be as s i m p l e .as was supposed. The a c t u a l f i e l d b e h a v i o u r w i l l depend c r i t i c a l l y not o n l y on the growth and r e c o v e r y of the r i n g c u r r e n t , but i t s p o s i t i o n and movement as w e l l . T h i s c o u l d cause the magnetic f i e l d b e h a v i o u r at geosynchronous o r b i t and a t a lower IPDP source r e g i o n t o be q u i t e d i f f e r e n t . Bossen et a l . ( 1976), u s i n g a geosynchronous s a t e l l i t e and a c o n j u g a t e ground s t a t i o n , found t h a t the IPDP and magnetic f i e l d d a t a c o u l d not support the i n c r e a s i n g f i e l d mechanism ( c f . s e c t i o n 3.5). 4.2.3. Azimuthal D r i f t The a z i m u t h a l d r i f t mechanism f o r IPDP f r e q u e n c y s h i f t s was f i r s t a r t i c u l a t e d by F u k u n i s h i (1969). T h i s t h e o r y s t i p u l a t e s t h a t the IPDP freq u e n c y r i s e s as the energy of the p r o t o n s i n v o l v e d i n the i o n - c y c l o t r o n i n s t a b i l i t y f a l l s . 60 The g r a d u a l l y s o f t e n i n g p r o t o n energy spectrum i s c r e a t e d by the energy dependent westward a z i m u t h a l d r i f t v e l o c i t y of the p r o t o n s . A f t e r the substorm plasma i n j e c t i o n , h i g h e r energy p r o t o n s d r i f t westward f a s t e r , r e a c h i n g the g e n e r a t i o n r e g i o n ahead of the lower energy p r o t o n s on the same L s h e l l . T h i s e f f e c t would cause a st e a d y f r e q u e n c y r i s e t h roughout an IPDP e v e n t . I f B i s assumed c o n s t a n t , t h e n , from e q u a t i o n 4.4, the d e c r e a s i n g energy e f f e c t i s g i v e n by: f x . W. "1 0 . 5 ( 4 . 7 ) . _i W Note t h a t the dependence of f on W i s r e l a t i v e l y weak (power of o n l y 0.5). The e x i s t e n c e of p r o t o n energy s o f t e n i n g as d e s c r i b e d above has been v e r i f i e d by c a l c u l a t i o n from ground o b s e r v a t i o n s , u s i n g the d e l a y time from substorm onset t o IPDP o c c u r r e n c e and p r o t o n d r i f t v e l o c i t i e s , by Kangas e t a l . (1974) and a l s o observed by s a t e l l i t e ( c f . s e c t i o n 4.1). D e s p i t e t h i s , t h e r e i s s t i l l c o n s i d e r a b l e u n c e r t a i n t y over the importance of the a z i m u t h a l d r i f t mechanism t o IPDP fre q u e n c y s h i f t s . Heacock (1971) a s c r i b e d t o i t the dominant r o l e , w h i l e P i k k a r a i n e n et a l . (1983) c o n c l u d e d t h a t i t s c o n t r i b u t i o n t o IPDPs must be minor and Soraas e t a l . (1980) 61 s t a t e d t h a t the observed energy d i s p e r s i o n was over too narrow a range t o p r o v i d e s i g n i f i c a n t f r e q u e n c y r i s e . Bossen et a l . (1976) noted t h a t the a z i m u t h a l d r i f t mechanism was a p l a u s i b l e mechanism t o e x p l a i n IPDPs. 4.3. DISCUSSION OF IPDP FREQUENCY SHIFT MECHANISMS I t i s c l e a r t h a t t he s t a t e of u n d e r s t a n d i n g of IPDP frequ e n c y s h i f t s i s f a r from complete s i n c e disagreement e x i s t s over the importance o f , and even the e x i s t e n c e o f , the mechanisms d e s c r i b e d i n s e c t i o n 4.2. I t s h o u l d a l s o be p o i n t e d out t h a t the r e l a t i v e importance of the r o l e s of the t h r e e mechanisms d i s c u s s e d here c o u l d p o s s i b l y change w i t h changing magnetospheric c o n d i t i o n s , and/or t h e i r s i g n i f i c a n c e c o u l d s i m p l y be d i f f e r e n t a t d i f f e r e n t GMLTs. The i n a d e q u a c i e s found i n each of the above mechanisms' a b i l i t y t o e x p l a i n the IPDP f r e q u e n c y s h i f t a l o n e has f o r c e d the c o n s i d e r a t i o n of the s u p e r p o s i t i o n of two or more of these mechanisms t o account f o r IPDP e v e n t s . Most of thes e h y b r i d models have i n v o l v e d the c o m b i n a t i o n of inward motion and a z i m u t h a l d r i f t e f f e c t s , w i t h the inward motion b e i n g due t o one of E x 1 d r i f t ( e . g . , F r a s e r and Wawryzniak, 1978), plasmapause motion ( e . g . , H o r i t a e t a l . , 1979), or s u c c e s s i v e i n j e c t i o n s p e n e t r a t i n g t o lower L b e f o r e t h e i r a z i m u t h a l d r i f t s t a r t s (Kangas et a l . , 1974). These h y b r i d models have not a c t u a l l y been q u a n t i t a t i v e l y t e s t e d a g a i n s t 62 IPDP d a t a , and r e p r e s e n t o n l y the g e n e r a l r e a l i z a t i o n t h a t some s o r t of s u p e r p o s i t i o n of mechanisms i s n e c e s s a r y t o e x p l a i n IPDPs. In t h i s t h e s i s , we w i l l t e s t an IPDP f r e q u e n c y s h i f t model i n v o l v i n g the a z i m u t h a l d r i f t and inward motion mechanisms which f o l l o w s l o g i c a l l y from the g e n e r a t i o n model d i s c u s s e d i n s e c t i o n 4.1. In t h i s model, the energy d i s p e r s i v e a z i m u t h a l d r i f t e f f e c t s o ccur d u r i n g the westward d r i f t of the hot p r o t o n s from the i n j e c t i o n boundary t o the plasmapause. The source r e g i o n inward motion r e s u l t s from the i n j e c t e d plasma c o v e r i n g a range i n L i n c o m b i n a t i o n w i t h plasmapause inward m o t i o n , w i t h the s l o w e r d r i f t i n g p r o t o n s a t lower L ( c f . e q u a t i o n 4.3) meeting a c o n t r a c t i n g plasmapause above a ground s t a t i o n a f t e r the f a s t e r d r i f t i n g p r o t o n s a t h i g h e r L i n t e r s e c t the plasmapause above the same ground s t a t i o n (see f i g . 16 ( t o p ) ) . In a d d i t i o n , the model a l s o i n c o r p o r a t e s a new inward motion p r o c e s s due t o plasmapause geometry. Even i f the plasmapause motion i s not s i g n i f i c a n t d u r i n g an e v e n t , the IPDP g e n e r a t i o n r e g i o n , as seen by a ground s t a t i o n , can s t i l l appear t o move t o lower L s h e l l s due t o the shape of the plasmasphere dusk s e c t o r b u l g e . As the E a r t h ' s r o t a t i o n c a r r i e s the ground s t a t i o n from dusk towards m i d n i g h t , the slowe r d r i f t i n g lower L p r o t o n s w i l l meet the plasmapause a t a s t e a d i l y d e c r e a s i n g r a d i a l d i s t a n c e overhead of the ground s t a t i o n (see f i g . 16 63 FIGURE 16. TOP: Diagram showing inward source motion due t o L-dependent a z i m u t h a l d r i f t v e l o c i t y v a r i a t i o n s and a c o n t r a c t i n g plasmapause. BOTTOM: Diagram showing t h a t inward motion of the IPDP so u r c e r e g i o n , due t o E a r t h ' s r o t a t i o n and the plasmapause bulge shape, s t i l l e x i s t s even when t h e r e i s no c o n t r a c t i o n of the plasmapause. The t i m e s t , and t 2 c o r r e s p o n d t o the tim e s of g e n e r a t i o n (plasmapause i n t e r s e c t i o n ) on the r e s p e c t i v e L s h e l l s . 64 ( b o t t o m ) ) . From e q u a t i o n 4.4, assuming a d i p o l a r f i e l d , and u s i n g e q u a t i o n 4.3 t o account f o r the v a r y i n g d r i f t v e l o c i t i e s a t d i f f e r e n t L, the fre q u e n c y s h i f t becomes: f . ALT ALT f 0 . 5 r L 7 (4.8) where ALT i s the a r c through which the p r o t o n s d r i f t , t h a t i s , the d i s t a n c e of d r i f t = ALT-L (ALT i n r a d i a n s ) , and t ^ i s the d r i f t time of the p r o t o n s from i n j e c t i o n t o plasmapause f o r each L s h e l l . The p r o t o n energy (W) has been r e p l a c e d i n t h i s e q u a t i o n by ALT and t ^ s i n c e we are no l o n g e r s a m p l i n g one stream of p r o t o n s on one L s h e l l w i t h i t s s i m p l e s o f t e n i n g spectrum, but c r o s s i n g L s h e l l s i n t o d i f f e r e n t p r o t o n streams which c o u l d r e s u l t i n a more c o m p l i c a t e d energy e v o l u t i o n . The d r i f t t i m e s and a r c s now c h a r a c t e r i z e the p r o t o n energy v a r i a t i o n seen at the plasmapause above a ground s t a t i o n as the s t a t i o n i s c a r r i e d eastward d u r i n g an IPDP e v e n t . E q u a t i o n 4.8 shows a s l i g h t l y reduced dependence on L compared t o e q u a t i o n 4.5, and a l s o t h a t i n c r e a s i n g d r i f t t i m e s and d e c r e a s i n g d r i f t a r c s w i l l r e s u l t i n f r e q u e n c y r i s e s . The f r e q u e n c y s h i f t model d e s c r i b e d here w i l l be t e s t e d by computer s i m u l a t i o n ( s e c t i o n 4.4), and the r e s u l t s of the 65 a n a l y s i s of data from a network of ground s t a t i o n s w i l l a l s o be i n t e r p r e t e d i n terms of t h i s model ( c f . Chapter F i v e ) . I f any t e m p o r a l changes, p o s i t i v e or n e g a t i v e , o c c u r i n the background magnetic f i e l d s t r e n g t h d u r i n g an IPDP e v e n t , the e f f e c t would be superimposed on the o t h e r mechanisms a l r e a d y o p e r a t i n g , enhancing or d e p r e s s i n g the fr e q u e n c y r i s e c r e a t e d by these o t h e r mechanisms. However, i n t h i s model, such f i e l d changes a re not e s s e n t i a l t o the development of an IPDP. 4.4. IPDP FREQUENCY BEHAVIOUR SIMULATION The magnetospheric p r o c e s s e s d e s c r i b e d i n s e c t i o n s 4.1 thr o u g h 4.3 can be s i m u l a t e d by computer. The purpose of t h i s s i m u l a t i o n i s t o q u a n t i t a t i v e l y t e s t the model t o see i f , s t a r t i n g from magnetospheric c o n d i t i o n s o b s e r v e d t o be a s s o c i a t e d w i t h IPDP o c c u r r e n c e , i t can reproduce IPDP f r e q u e n c y b e h a v i o u r as seen by ground s t a t i o n s . T h i s t e s t i s d i r e c t e d p r i m a r i l y a t IPDP f r e q u e n c y e v o l u t i o n s i n c e t h i s i s the o u t s t a n d i n g u n e x p l a i n e d f e a t u r e of IPDP-type m i c r o p u l s a t i o n s and the p r i n c i p a l f o c u s of t h i s t h e s i s . In a d d i t i o n t o f r e q u e n c i e s , however, the s i m u l a t i o n a l s o y i e l d s i n f o r m a t i o n on l o c a l t i m e s and l a t i t u d e s of IPDP o c c u r r e n c e , event d u r a t i o n s , and the e v o l u t i o n of the hot p r o t o n e n e r g i e s . 66 4.4.1. Computational Procedure The model c o n s i d e r e d here b e g i n s a t the f o r m a t i o n of the i n j e c t i o n boundary, f o l l o w s the d r i f t of the i n j e c t e d p r o t o n s from t h e r e t o the plasmapause where the IPDPs a r e g e n e r a t e d , and f i n a l l y d e t e r m i n e s what a ground s t a t i o n would see d u r i n g an e v e n t . The i n i t i a l s t e p of t h i s m o d e l l i n g p r o c e s s i n v o l v e s d e f i n i n g the s t a r t i n g c o n f i g u r a t i o n . T h i s r e q u i r e s s p e c i f y i n g the plasmapause and i n j e c t i o n boundary p o s i t i o n s . The l o c a t i o n of the i n j e c t i o n boundary i s c a l c u l a t e d as d i s c u s s e d i n s e c t i o n 4.1 ( c f . e q u a t i o n 4.1). Note t h a t the parameters i n t h i s e q u a t i o n can v a r y (Mauk and Meng, 1983), thus c h a n g i n g the form of the i n j e c t i o n boundary. The plasmapause p o s i t i o n i s d e t e r m i n e d from a s i m p l e t e a r d r o p model of the plasmapause shape, the f o r m u l a f o r which i s ( K i v e l s o n , 1976): L 2 R E E = C{[1 - (1 + s i n ( 0 ) ) * ] / s i n U ) } 2 (4.9) where E i s the magnetospheric e l e c t r i c f i e l d s t r e n g t h i n the e q u a t o r i a l p l a n e , C i s the c o r o t a t i o n p o t e n t i a l (- 90kV), and ^ ( r a d i a n s ) = 7r«LT/l2 (LT = l o c a l time i n h o u r s ) . In e q u a t i o n 4.9, the r e f e r e n c e m e r i d i a n from which 4> i s measured i s the m e r i d i a n of the apex of the dusk s e c t o r b u l g e . 67 In the dusk s e c t o r , where most IPDPs o c c u r , the plasmapause shape produced by t h i s model i s q u i t e s i m i l a r t o the average plasmapause shape of Maynard and Grebowsky (1977) ( c f . f i g . 15). The o r i e n t a t i o n of the dusk s e c t o r b u l g e ( i . e . LT p o s i t i o n of the apex of the b u l g e ) and the a c t u a l r a d i u s of the plasmapause, i n the e q u a t o r i a l p l a n e , a r e known t o be v a r i a b l e . Here, these parameters are c a l c u l a t e d from s t a t i s t i c a l r e l a t i o n s found by H i g e l and L e i (1984). The o r i e n t a t i o n of the plasmapause bulge i s g i v e n by: LT = 23.45 - 0 . 6 i - L 9 h r K p ( 4 . 1 0 ) . The r a d i u s of the plasmapause i s c o n t r o l l e d by E ( c f . e q u a t i o n 4.9), which i s g i v e n by: E(kV/Rg) = 0.88 + 0.12Kp + 0.019Kp 2 ( 4 . 1 1 ) . The v a l i d i t y of t h i s r e l a t i o n i s l i m i t e d t o v a l u e s of E < 2kV/R E and Kp < 6. By u s i n g e q u a t i o n s 4.1 and 4.9 t o 4.11 f o r , r e s p e c t i v e l y , the plasmapause and i n j e c t i o n boundary, the model s t a r t i n g c o n f i g u r a t i o n can be produced by i n p u t t i n g o n l y the GMLT range of the i n j e c t i o n boundary and the Kp i n d i c e s f o r the p r e c e d i n g n i n e hours ( t h r e e 3 - h o u r l y 68 v a l u e s ) . At t h i s p o i n t , a p l o t of the model s t a r t i n g c o n f i g u r a t i o n can be produced, as shown i n the model f l o w c h a r t i n f i g u r e 17. The next s t e p of the m o d e l l i n g p r o c e s s i n v o l v e s c a l c u l a t i n g the i n j e c t e d p r o t o n d r i f t m o t i o n s . However, b e f o r e t h i s s t e p , both the energy range and increment ( i n keV) must be i n p u t i n t o the c o m p u t a t i o n ( c f . f i g . 17). For s i m p l i c i t y , i t i s assumed t h a t a l l the p r o t o n s , which a r e i n i t i a l l y a t r e s t , s t a r t d r i f t i n g from p o s i t i o n s on the i n j e c t i o n boundary. For co m p a r i s o n , however, some t e s t s have been c a r r i e d out under the assumption t h a t the i n j e c t e d plasma o c c u p i e s a l i m i t e d a r e a b e h i n d the boundary upon i n j e c t i o n (see s e c t i o n 4.4.3). At each (L,LT) p o i n t a l o n g the i n j e c t i o n boundary, t h e n , t h e r e e x i s t s a common range of energy v a l u e s . For each energy l e v e l (W) a t each (L,LT) p o i n t , the westward d r i f t motion of a p r o t o n of t h a t energy can now be c a l c u l a t e d . The p r o t o n d r i f t p a t h s a re assumed t o be c i r c u l a r ( c f . s e c t i o n 4.1), and the changing LT p o s i t i o n s of each p r o t o n a re f o l l o w e d u s i n g the westward d r i f t v e l o c i t y of e q u a t i o n 4.3. A new LT v a l u e i s c a l c u l a t e d f o r each p r o t o n a t each time s t e p of one minute d u r i n g the d r i f t phase of the model. Note t h a t the p i t c h a n g l e (a) used i n the v e l o c i t y c a l c u l a t i o n s was 60°. T h i s would, assuming t h a t a l l p r o t o n s i n a d i s t r i b u t i o n had the same a, c o r r e s p o n d t o an a n i s o t r o p y of 69 INPUTS CALCULATIONS OUTPUTS activity (Kps) proton energy boundary type run.tiie plasiapause noveaent ground stations Initial •odei configuration plasiapause Intersection points frequency and latitude calculations ground station assignment initial--•odel plot-3 proton drift tables * frequency, latitude, tite, + energy tables ground observations FIGURE 17. Flow c h a r t f o r computer s i m u l a t i o n of m i c r o p u l s a t i o n s (see t e x t f o r d e t a i l e d d e s c r i p t i o n ) . IPDP 70 A = 2. G e n d r i n e t a l . (1971) found ( f o r Pc 1) t h a t A was g e n e r a l l y between 1 (a = 55°) and 2 (a 60°). Note a l s o t h a t the s t a r t of the d r i f t p r o c e s s i s d e l a y e d a t the western end of the i n j e c t i o n boundary i n accordance w i t h the f i n i t e boundary f o r m a t i o n time found by A r n o l d y and Moore (1983) ( c f . s e c t i o n 4.1). D u r i n g the d r i f t phase of the model, f o r each p r o t o n energy on each L s h e l l a t each time s t e p , the LT c o o r d i n a t e of the p r o t o n i s t e s t e d t o see i f i t i s l e s s than the plasmapause LT c o o r d i n a t e on the same L s h e l l a t t h a t time ( i e , LT (L,W,t) < LT ( L , t ) , where LT i s the d r i f t i n g P PP P p r o t o n ' s LT and L T ^ i s the plasmapause L T ) . For each c a s e , the f i r s t time s t e p a t which LT (L,W,t) < LT ( L , t ) d e f i n e s P PP when plasmapause i n t e r s e c t i o n i s s a i d t o have o c c u r r e d ( c f . f i g . 17). The p a r t i c l e d r i f t motions a re not f o l l o w e d a f t e r t h i s t i m e , s i n c e t h i s i s the p o i n t a t which IPDP g e n e r a t i o n i s s a i d t o take p l a c e . The i n t e r s e c t i o n p o i n t d e t e r m i n e s the LT and time ( t ) of IPDP g e n e r a t i o n f o r p r o t o n s of energy W d r i f t i n g a l o n g a p a t h of r a d i u s L. The model p r o v i d e s an o p t i o n f o r the inward movement of the plasmapause, due t o plasmasphere c o n t r a c t i o n , d u r i n g the d r i f t phase. I f t h i s o p t i o n i s s e l e c t e d , the plasmapause i s moved inward a t each time s t e p by d e c r e a s i n g the LT c o o r d i n a t e of each (L,LT) p a i r d e f i n i n g the plasmapause i n the a f t e r n o o n - e v e n i n g s e c t o r (see s e c t i o n 4.4.3). Because of the shape of the 71 plasmapause dusk s e c t o r bulge ( c f . f i g . 16 ( t o p ) ) , t h i s has the same e f f e c t as d e c r e a s i n g the r a d i a l d i s t a n c e L a t a f i x e d m e r i d i a n . Once the plasmapause i n t e r s e c t i o n p o i n t i s known, i t i s p o s s i b l e t o c a l c u l a t e the i o n - c y c l o t r o n wave fr e q u e n c y f o r t h a t p o i n t , r e l a t i v e t o a r e f e r e n c e f r e q u e n c y ^ r^> a s f o l l o w s (from e q u a t i o n 4.4 i n a d i p o l a r f i e l d ) : r L i H . 5 r w i r r L W (4.12) where i s the L v a l u e of the e a s t e r n ( l o w e r ) end of the i n j e c t i o n boundary and W i s the h i g h e s t p r o t o n energy v a l u e b e i n g c o n s i d e r e d . Assuming a d i p o l a r f i e l d , the geomagnetic l a t i t u d e can a l s o be found from the L v a l u e of the i n t e r s e c t i o n p o i n t as f o l l o w s : XGM = c o s " 1 ( ]M L) (4.13). W i t h d a t a from each i n t e r s e c t i o n p o i n t , i t i s now p o s s i b l e t o produce a t a b l e of r e s u l t s which i n c l u d e s the l a t i t u d e , t i m e , energy, l o c a l t i m e , and r e l a t i v e f r e q u e n c y f o r each plasmapause i n t e r s e c t i o n p o i n t , the p o i n t a t which IPDP wave a m p l f i c a t i o n i s s a i d t o occur (see f i g . 17). T h i s , however, does not y e t r e p r e s e n t an IPDP event. In 72 o r d e r t o o b t a i n a r e p r e s e n t a t i o n of an IPDP event as seen by a ground s t a t i o n , we must f i r s t d e f i n e a s e t of ground s t a t i o n s , each of which "sees" o n l y a l i m i t e d LT s e c t o r of the plasmapause "above" i t , t h a t i s , near i t s own m e r i d i a n . The model a l l o w s s p e c i f i c a t i o n of an a r r a y of up t o ten ground s i t e s spaced by h a l f an hour i n LT (7.5° l o n g . ) . The s t a t i o n a r r a y can be p o s i t i o n e d over any l o c a l time range. Only the LT c o o r d i n a t e of a ground s i t e i s n e c e s s a r y s i n c e n o r t h - s o u t h i o n o s p h e r i c d u c t i n g i s c o n s i d e r e d t o be v e r y good, and a s i g n a l r e a c h i n g the io n o s p h e r e on one m e r i d i a n w i l l be d e t e c t e d a t any ground s t a t i o n i n the a u r o r a l and s u b - a u r o r a l zones a l o n g t h a t m e r i d i a n . The LT range of the plasmapause t h a t each ground s t a t i o n " s e e s " has been s e t a t ±0.15h (or ±2.25° Long.) f o r most r u n s . T h i s i s e q u i v a l e n t t o a 250km range a t 60° L a t . , and i s c o n s i s t e n t w i t h the Pc 1 source s i z e r e s u l t s of Hayashi e t a l . (1981). The LT c o o r d i n a t e of each i n t e r s e c t i o n p o i n t i s t e s t e d t o see i f i t f a l l s w i t h i n the LT range of a ground s t a t i o n . I f so, i t i s a s s i g n e d t o t h a t ground s t a t i o n and the r e l a t i v e f r e q u e n c y , l a t i t u d e , t i m e , and p r o t o n energy a s s o c i a t e d w i t h i t are s a i d t o be ob s e r v e d a t t h a t s t a t i o n . I t s h o u l d be noted t h a t the l o c a l time of each ground s i t e changes throughout the event as E a r t h ' s r o t a t i o n c a r r i e s the s t a t i o n e a s t w a r d . I t i s now p o s s i b l e t o w r i t e out a t a b l e f o r each s t a t i o n c o n t a i n i n g the 73 f r e q u e n c i e s , t i m e s , l a t i t u d e s , and e n e r g i e s "observed" a t each s t a t i o n (see f l o w c h a r t i n f i g . 17). These (f,t,X,W) d a t a s e t s a r e c h r o n o l o g i c a l l y a r r a n g e d , i n o r d e r of i n c r e a s i n g time ( t ) , and now r e p r e s e n t an IPDP event as observed by t h a t ground s t a t i o n . 4.4.2. Model IPDPs versus Observed IPDPs The model d e s c r i b e d above has been run w i t h a l l v a r i a b l e s e x t e n d i n g t h r o u g h o u t , and sometimes beyond, t h e i r normal ranges a s s o c i a t e d w i t h IPDP a c t i v i t y . The Kp index a s s o c i a t e d w i t h the IPDP o c c u r r e n c e i n t e r v a l v a r i e d from 1 t o 7, w h i l e I ^ ^ K p v a r i e d from 1 t o 19. The p r o t o n energy ranges (W - W . ) used i n the runs extended from 10 t o 80 max mi n keV, and a l l the v a l u e s used f e l l w i t h i n the energy span of 10 t o 340 keV. Most runs used an i n j e c t i o n boundary c a l c u l a t e d from e q u a t i o n 4.1, however, some t e s t s were a l s o done w i t h d i f f e r e n t parameters s u b s t i t u t e d i n t o e q u a t i o n 4.1 ( c f . s e c t i o n 4.4.1) t o produce s t e e p e r or f l a t t e r boundary shapes. The r e s u l t s of these numerous runs can now be compared w i t h the p r o p e r t i e s of IPDPs d e s c r i b e d i n Chapter Three. However, the model produces o n l y r e l a t i v e f r e q u e n c y i n f o r m a t i o n ( f / f ^ . , c f . e q u a t i o n 4.12), which r e s t r i c t s the comparisons t h a t can be made. T h i s d i f f i c u l t y can be p a r t i a l l y c i r c u m v e n t e d by comparing the known IPDP 74 f r e q u e n c i e s t o f r e q u e n c i e s produced by models h a v i n g the most common Kps (near 3) and p r o t o n e n e r g i e s (40 t o 100 keV) a s s o c i a t e d w i t h o b s e r v e d IPDPs. The median f r e q u e n c y produced by thes e model runs i s assumed t o be the same as the median observed IPDP f r e q u e n c y , a l l o w i n g a v e r y rough adjustment t o be made t o t h e model f r e q u e n c i e s so t h a t they are comparable t o ob s e r v e d f r e q u e n c i e s . T h i s e n a b l e s the freq u e n c y ranges and s l o p e s d e r i v e d from th e s e a d j u s t e d model f r e q u e n c i e s t o be compared w i t h a c t u a l v a l u e s . I t must be emphasized, however, t h a t no comparison of a b s o l u t e f r e q u e n c i e s i s made h e r e , and t h a t a l l q u a n t i t a t i v e f r e q u e n c y - r e l a t e d i n f o r m a t i o n must be reg a r d e d as o n l y rough e s t i m a t e s when b e i n g compared t o ob s e r v e d v a l u e s . W i t h t h i s i n mind, we can then examine the r e s u l t s p r e s e n t e d i n Table V I I I . These r e s u l t s , which a re a summary of the p r o p e r t i e s of model IPDPs computed w i t h parameters most commonly a s s o c i a t e d w i t h r e a l e v e n t s , a re compared t o observe d IPDP c h a r a c t e r i s t i c s (from T a b l e s VI and V I I i n Chapter T h r e e ) . Though the ranges of the model r e s u l t s do not always e x a c t l y match the IPDP o b s e r v a t i o n s , i n g e n e r a l the agreement between the two i s q u i t e good. Note t h a t though no GMLT of peak o c c u r r e n c e can be a s s i g n e d from the model r e s u l t s s i n c e the a c t u a l r a t e s of IPDP o c c u r r e n c e v e r s u s the i n p u t parameters a r e not w e l l u n d e r s t o o d , the c e n t e r of the GMLT range of the model r e s u l t s l i e s a t 2030 Table VIII IPDP Characteristics Model R e s u l t s Observat i o n s I n i t i a l f r e q u e n c y 0.1 - 0.6 Hz (F. ) End f r e q u e n c y (F ) 0.2 - 1.1 Hz AF (Fe~F. ) 0.1 - 0.6 Hz S l o p e ( ( F -F )/T) 0.1 - 0.6 Hz/h D u r a t i o n (T) L o c a l time L a t i t u d e 0.25 - 1.75 h 1800 - 2300 GMLT 60° - 65.5° 0.1 - 0.3 Hz 0.5 - 1.0 Hz 0.2 - 0.7 Hz 0.2 - 1.0 Hz/h 0.33 - 2.0 h 1600 - 0100 GMLT 55° - 65° 76 GMLT, which compares w e l l w i t h the ob s e r v e d peak a t 2000 GMLT ( c f . s e c t i o n 3.2). The l a t i t u d e f r e q u e n c y and l a t i t u d e s l o p e c o r r e l a t i o n s mentioned i n s e c t i o n 3.2 (paragraph two) a r e a l s o produced by the model runs (see f i g . 18). I t i s i n t e r e s t i n g t o n o t e , however, t h a t a p o s s i b l e GMLT s l o p e r e l a t i o n s h i p about which c o n f l i c t i n g s t a t e m e n t s have appeared ( c f . s e c t i o n 3.2, par a g r a p h t h r e e ) , i s not c l e a r l y s u p p o r t e d by the model r e s u l t s . The Kp GMLT and Kp GM L a t . c o r r e l a t i o n s noted i n s e c t i o n 3.2 a r e a l s o r e p r o d u c e d by the model, though not i n p r e c i s e l y the same manner. P r e v i o u s comparisons have o n l y been concerned w i t h the s i n g l e Kp v a l u e a s s o c i a t e d w i t h the IPDP o c c u r r e n c e i n t e r v a l . W h i l e t h i s s i n g l e index can be used f o r the l a t i t u d e c o m p a r i s o n , s i n c e t h i s index c o n t r o l s the plasmapause r a d i a l d i s t a n c e ( c f . e q u a t i o n s 4.9 and 4.11) ( f i g . 19), i t i s by i t s e l f not e n t i r e l y a p p r o p r i a t e f o r the Kp GMLT r e l a t i o n . S i n c e L ^ ^ K p c o n t r o l s the GMLT o r i e n t a t i o n of the plasmapause ( c f . e q u a t i o n 4.10), i t i s t h i s parameter t h a t a c c o u n t s f o r the Kp GMLT r e l a t i o n t h a t i s both reproduced by the model and observ e d ( f i g . 19). Most of the m o d e l l e d IPDPs c o v e r e d 45°-65° GM Long., though i t i s p o s s i b l e t o gen e r a t e e v e n t s spanning much g r e a t e r r a n g e s , such as 100° or more, examples of which have been r e p o r t e d ( c f . s e c t i o n 3.3). I t i s a l s o q u i t e c l e a r t h a t d i f f e r e n c e s can be seen w i t h i n m o d e l l e d IPDP e v e n t s 4.0 3.5 3.0 77 -P 2.5 cr 2.0 h N X 1.5 1.0 0.5 0.0 2.0 1.6 1.2 0) CL " i 0.8 Q_ £ 0.4 0.0 52 52 56 . 60 64 GM lot. (deg.) 68 • + • + • • J — J 1 I I * 56 60 64 GM lot. (deg.) 68 FIGURE 18. S i m u l a t i o n r e s u l t s d e m o n s t r a t i n g the r e p r o d u c t i o n of the IPDP f r e q u e n c y - GM L a t . ( t o p ) and s l o p e - GM L a t . (bottom) c o r r e l a t i o n s . 78 0 4 Kp 7 8 24 4 23 _ • • 22 • •f • Kp = 3 21 • + t i 20 -+ • O 19 • 18 17 16 1 1 1 8 10 *9hrKp 12 14 16 FIGURE 19. S i m u l a t i o n r e s u l t s showing the GM L a t . - Kp ( Z p ^ K p c o n s t a n t ) (top) and GMLT - Zp/^Kp (Kp = c o n s t a n t ) (bottom) c o r r e l a t i o n s produced. 79 "observed" a t ground s i t e s spaced q u i t e c l o s e l y i n l o n g i t u d e (AGMLT = 0.5h). These d i f f e r e n c e s can become v e r y o b v i o u s over spans of 60° GM Long., a range over which l o n g i t u d i n a l v a r i a t i o n s have been r e p o r t e d i n observed IPDPs ( c f . s e c t i o n 3.3). The model r e s u l t s agree w i t h the r e p o r t e d l a t e r GMLT h i g h e r f r e q u e n c y c o r r e l a t i o n ( f i g . 20, top) and a l s o show a l a t e r GMLT s t e e p e r s l o p e c o r r e l a t i o n ( f i g . 20, bottom), though not always i n a c l e a r f a s h i o n . Most model event d u r a t i o n s a r e e i t h e r l o n g e r t o the west or a p p r o x i m a t e l y the same a t a l l s t a t i o n s s e e i n g the event, though o n l y c a s e s of lo n g e r d u r a t i o n s t o the west have been r e p o r t e d i n the l i t e r a t u r e ( c f . s e c t i o n 3.3). The event onset d r i f t r a t e s from the model can d i f f e r s i g n i f i c a n t l y from those d i s c u s s e d i n s e c t i o n 3.3. For model IPDPs on l e s s a c t i v e days ( I ^ ^ K p < 10), onset d r i f t s g e n e r a l l y agree w i t h r e p o r t e d o b s e r v a t i o n s , f a l l i n g i n the 2-5°/min. range. However, on more a c t i v e days ( I p ^ K p > 10), the onset d r i f t s tend t o be n e g a t i v e , as shown i n f i g u r e 21, r e p r e s e n t i n g events d e v e l o p i n g from the west r a t h e r than the e a s t . Such eastward development i s c o n t r a r y t o what has p r e v i o u s l y been thought t o be the c a s e . T h i s problem w i l l be d i s c u s s e d i n more d e t a i l i n a subsequent s e c t i o n . > 2.0 •P 1.5 o cr <D £ 0.5 o.o -. model D / model C / model B i i ^ ^ ^ ^ - ^ m o ^ e l A 80 16 18 20 GMLT (h) 22 24 N X 1.0 0.8 0.6 h CL ° ^ * w 0.4 Q_ £ 0.2 0.0 _ model 0 / / model C model B 1 — i i i ^ — model A i I I 16 18 20 GMLT (h) 22 24 FIGURE 20. S i m u l a t i o n r e s u l t s showing the frequ e n c y - GMLT ( t o p ) and s l o p e - GMLT (bottom) c o r r e l a t i o n s . 81 c o - 2 0 FIGURE 21. S i m u l a t i o n r e s u l t s : onset d r i f t v e r s u s Ep/^Kp, i n d i c a t i n g the appearance of both westward and eastward d e v e l o p i n g IPDPs. 82 4.4.3. Other Model Results and Predictions T h i s s e c t i o n w i l l p r e s e n t some new r e s u l t s produced by the model c a l c u l a t i o n s . There has been some u n c e r t a i n t y c o n c e r n i n g the p o s s i b l e r o l e of inward motion of the plasmapause i n c r e a t i n g the IPDP frequency s h i f t . Here, the e f f e c t s of t h i s movement have been e x p l o r e d by model c a l c u l a t i o n . S i m u l a t i o n s have been c a r r i e d out kee p i n g a l l parameters t h e same except f o r the r a t e of plasmapause inward motion. F i g u r e 22 (top) shows the plasmapause p o s i t i o n , as seen by the same ground s t a t i o n , f o r f o u r c a s e s w i t h d i f f e r i n g plasmapause movement r a t e s {dLT) r a n g i n g from z e r o t o dLT = -0. 01 0h/[ t ime s t e p ] ( c f . s e c t i o n 4.4.1). The f o u r c a s e s a r e ; Model A: dLT = 0, Model B: dLT ='-0.002h, Model C: dLT = -0.005h, and Model D: dLT = -O.OlOh. The e f f e c t s of t h i s inward movement on IPDP f r e q u e n c y - t i m e c h a r a c t e r i s t i c s f o r the same f o u r c a ses are a l s o i l l u s t r a t e d i n f i g u r e 22 (bottom). Note t h a t the g r e a t e r inward movements, towards lower L s h e l l s and c o r r e s p o n d i n g l y lower l a t i t u d e s , r e s u l t i n h i g h e r f r e q u e n c i e s and h i g h e r f r e q u e n c y s l o p e s due t o the s t r o n g e r magnetic f i e l d B and h i g h e r dB/dt "observed" by the ground s t a t i o n . The r e s u l t s of the s e c a l c u l a t i o n s c l e a r l y demonstrate t h a t w h i l e an inward moving plasmapause has the p o t e n t i a l t o change the c h a r a c t e r i s t i c s of an IPDP, i n c l u d i n g d r a m a t i c a l l y enhancing the fr e q u e n c y r i s e , i t i s 83 4.0 3.5 8 3.0 § 2.5 o 2.0 c 1.5 S" i.oh 0.5 h 0.0 0 model A model B J I I I L 40 80 120 160 200 time (min.) model D model C model B model A 40 80 120 time (min ) 160 200 FIGURE 22. E f f e c t s of plasmapause inward motion on IPDPs. Top: L s h e l l of the plasmapause over a ground s t a t i o n f o r 4 ca s e s of inward m o t i o n , i n c r e a s i n g from A (no inward motion) t o D (see t e x t ) . Bottom: f r e q u e n c y - t i m e p l o t s f o r each of the above c a s e s f o r an IPDP event as seen by the same ground s t a t i o n . Note t h a t the zero-movement case (Model A) s t i l l shows s i g n i f i c a n t inward motion and fre q u e n c y r i s e . 84 c l e a r l y not a r e q u i r e d c o n d i t i o n f o r the appearance of an IPDP e v e n t , s i n c e the zero-movement case (Model A i n f i g . 22) shows a s i g n i f i c a n t f r e q u e n c y r i s e . The GMLT range over which the i n j e c t i o n boundary forms i s a p r i m a r y f a c t o r c o n t r o l l i n g the l o n g i t u d i n a l range over which an IPDP i s seen on the ground, s i n c e , a l o n g w i t h the plasmapause o r i e n t a t i o n and r a d i a l p o s i t i o n , i t de t e r m i n e s over what GMLT range the i o n - c y c l o t r o n i n s t a b i l i t y can occur a l o n g the plasmapause. As noted i n s e c t i o n 4.4.2, the most common span of m o d e l l e d events was 45° t o 65° GM Long.; f o r these models, the i n j e c t i o n boundary GMLT span from which p r o t o n s i n v o l v e d i n the IPDP g e n e r a t i o n d r i f t e d ranged from 1.9 t o 3.8 h o u r s . In or d e r t o reproduce the v e r y wide GM Long, e x t e n t s of over 140° o c c a s i o n a l l y o b s e r v e d i n IPDPs ( c f . s e c t i o n 3.4), i n j e c t i o n boundary spans of s i g n i f i c a n t l y g r e a t e r than 4 hours GMLT a r e r e q u i r e d . I t was mentioned i n s e c t i o n 4.4.1 t h a t some models were run w i t h the p r o t o n d r i f t s t a r t i n g not o n l y on the i n j e c t i o n boundary, but a l s o from a l i m i t e d a r e a b e h i n d i t . For thes e r u n s , the model was a l t e r e d such t h a t the p r o t o n d r i f t began on and from an ar e a of up t o 10° behi n d the boundary, t h a t i s , on a g i v e n L s h e l l , the p r o t o n s can b e g i n t h e i r d r i f t anywhere on an a r c b e g i n n i n g a t the i n j e c t i o n boundary and e x t e n d i n g up t o 10° t o the e a s t . The IPDPs seen on the ground r e s u l t i n g from these model runs e x h i b i t o n l y v e r y 85 minor d i f f e r e n c e s from e v e n t s whose d r i f t s t a r t e d on the i n j e c t i o n boundary o n l y , thus the d i s p a r i t i e s between the two model t y p e s a re i n s u f f i c i e n t t o d e t e r m i n e , by way of comparisons t o r e a l e v e n t s , which i s the more a p p r o p r i a t e . As mentioned p r e v i o u s l y ( c f . s e c t i o n 4.4.2), an i n t e r e s t i n g outcome of the IPDP m o d e l l i n g has been the appearance of eas t w a r d d e v e l o p i n g e v e n t s . Eastward d e v e l o p i n g IPDPs a re ob s e r v e d f i r s t a t more w e s t e r l y ground s t a t i o n s , then appear l a t e r a t s i t e s p r o g r e s s i v e l y f u r t h e r e a s t . T h i s e f f e c t , which has been r e p o r t e d o n l y v e r y r e c e n t l y (Hayashi et a l . , 1988), i s r e f e r r e d t o here as a n e g a t i v e , or eastward, onset d r i f t v e l o c i t y , as opposed t o the normal p o s i t i v e , or westward, onset d r i f t . The geometry of the plasmapause and the i n j e c t i o n boundary determine whether a mode l l e d ' e v e n t w i l l d e v e l o p eastward or westward. For an eastward IPDP, the geometry must be such t h a t the hot p r o t o n s d r i f t i n g westward on h i g h e r L s h e l l s meet the plasmapause b e f o r e those on lower L s h e l l s . T h i s r e q u i r e s t h a t the d r i f t time a t h i g h e r L must be l e s s than t h a t a t lower L. The d r i f t time i n t u r n depends on the d r i f t v e l o c i t y ( v ^ ) , which i s h i g h e r a t h i g h e r L, and on the l e n g t h of the d r i f t p a t h , t h a t i s , the l o c a l time range AGMLT through which the p r o t o n s d r i f t . The major f a c t o r s c o n t r o l l i n g how AGMLT v a r i e s between h i g h and low L are the o r i e n t a t i o n of the plasmapause, or the GMLT p o s i t i o n 86 of the bu l g e apex, and the shape, or s t e e p n e s s , of the i n j e c t i o n boundary. In g e n e r a l , s t e e p e r b o u n d a r i e s , t h o s e which c u r v e more r a p i d l y away from E a r t h , produce westward d e v e l o p i n g e v e n t s , w h i l e f l a t t e r b o u n d a r i e s , those whose d i s t a n c e from E a r t h i n c r e a s e s more s l o w l y , t e n d t o r e s u l t i n eastward d e v e l o p i n g e v e n t s . A l s o , eastward e v e n t s t e n d t o occur on more a c t i v e days when the plasmapause i s g e n e r a l l y lower and has i t s bulge apex a t e a r l i e r GMLTs and the i n j e c t i o n boundary i s a l s o lower and i s s h i f t e d toward e a r l i e r GMLTs ( c f . f i g . 14). F i g u r e 23 shows examples of the d i f f e r e n t plasmapause i n j e c t i o n boundary g e o m e t r i e s n e c e s s a r y t o produce eastward and westward IPDP e v e n t s . As a r e s u l t of the m o d e l l i n g c o n d u c t e d , the major d i f f e r e n c e s between eastward and westward d e v e l o p i n g IPDPs, as observed from the ground, appear i n the onset d r i f t s , d u r a t i o n s , and hot p r o t o n energy s p e c t r a . As mentioned above, the onset times a re l a t e r f o r more e a s t e r l y s i t e s f o r eastward e v e n t s , o p p o s i t e t o the case f o r westward d e v e l o p i n g e v e n t s . The t r e n d i n d u r a t i o n s of eastward IPDPs i s a l s o o p p o s i t e t o t h a t of westward e v e n t s , w i t h e v e n t s . l a s t i n g l o n g e r a t the more e a s t e r l y ground s t a t i o n s . The energy s p e c t r a of the p r o t o n s i n v o l v e d i n the g e n e r a t i o n of the IPDP waves observed by a ground s t a t i o n a r e b e l i e v e d t o show a s o f t e n i n g energy t r e n d . T h i s e f f e c t i s b e l i e v e d t o proceed more s l o w l y t o the west, and model c a l c u l a t i o n s a r e 87 t Sun Earth t Sun Earth FIGURE 23. Model diagrams f o r a westward d e v e l o p i n g IPDP ( L ^ = 30/(LT-17.5)) (top) and an eastward d e v e l o p i n g IPDP (Lb = 6 0 / ( L T - l 2 ) ) ( b o t t o m ) . Both models used Kp = 3 and Ip/^Kp = 9. The plasmapause p r o f i l e s aire" c a l c u l a t e d from e q u a t i o n s 4.9 t h r o u g h 4.11. 88 i n agreement w i t h t h i s r e s u l t f o r westward d e v e l o p i n g e v e n t s . However, f o r eastward IPDPs, the model r e s u l t s show the s o f t e n i n g p r o c e e d i n g more s l o w l y t o the e a s t . F i g u r e 24 demonstrates these model r e s u l t s . These p r e d i c t i o n s c o n c e r n i n g e a s t w a r d IPDPs a w a i t v e r i f i c a t i o n by o b s e r v a t i o n . However, the model parameters p r o d u c i n g the eastward e v e n t s seem q u i t e p l a u s i b l e , and, as mentioned, r e c e n t l y the appearance of e a s t w a r d e v e n t s has been i n d i c a t e d by Hayashi et a l . (1988). S t i l l , even i f they do e x i s t , the absence or s c a r c i t y of e a s t w a r d e v e n t s can t e l l us something of the i n j e c t i o n boundary shape, i n d i c a t i n g perhaps t h a t i t i s more commonly of the s t e e p e r form r a t h e r than h a v i n g a f l a t t e r p r o f i l e . I t i s e v i d e n t t h a t most IPDPs occur a t e v e n i n g s e c t o r l o c a l t imes when the plasmapause bulge i s l o c a t e d near dusk or l a t e r . T h i s may a l s o account f o r the l a c k of eastward e v e n t s , which m o d e l l i n g shows would t e n d t o occur more r e a d i l y a t the e a r l i e r l o c a l t i m e s a c c e s s i b l e when the b u l g e i s l o c a t e d a t e a r l i e r GMLTs. 4.4.4. Model Versus Real GMLTs Comparison of the IPDP model c o n s i d e r e d here t o r e a l IPDP e v e n t s can be a c h i e v e d by e n t e r i n g measured magnetospheric parameters a s s o c i a t e d w i t h o b s e r v e d IPDPs i n t o the model and c h e c k i n g the r e s u l t s a g a i n s t the observed r ^ 75 c £ 7 0 o> 65 £ ~ 60 v> 55 r ° 50 89 6 - 8-station-ano. 6 8 station no. £ a> •o 0.0 -0.2 -0.4 -0.6 6 8 station no. 10-10 - WEST EAST ^ ^ " ** —r* — I I I I 10 FIGURE 24. S i m u l a t i o n r e s u l t s : westward v e r s u s e a s t w a r d d e v e l o p i n g IPDPs. Onset t i m e s ( t o p ) , d u r a t i o n s ( m i d d l e ) , and p r o t o n e n e r g i e s (bottom) a re compared f o r an e a s t - west l i n e of s t a t i o n s (models as i n f i g . 2 3 ) . The s t a t i o n s a r e s e p a r a t e d by 7j° l o n g . ( y h ) . The s o l i d l i n e s a r e f o r the westward d e v e l o p i n g event and the dashed l i n e s f o r the eastward d e v e l o p i n g e v e n t . 90 event. Due t o the n a t u r e of the model and t h e r e a l event a n a l y s i s r e q u i r e m e n t s , however, o n l y the GMLT range of o c c u r r e n c e can be compared f o r a l l t e n IPDPs i n the da t a s e t under c o n s i d e r a t i o n . For the ten events a v a i l a b l e , the GMLT span over which each o c c u r r e d has been d e t e r m i n e d . - The GMLT range of p o s s i b l e IPDP o c c u r r e n c e a l l o w e d by the model was found, f o r each e v e n t , by a s i m u l a t i o n run u s i n g the Kp i n d i c e s a s s o c i a t e d w i t h t h a t e v e n t . Such a run d e t e r m i n e s the plasmapause p o s i t i o n and, assuming an i n j e c t i o n boundary easternmost end of 0200 GMLT, the lo w e s t L s h e l l of hot pr o t o n d r i f t . The L range c o v e r e d by the westward d r i f t i s determined by t h i s lower l i m i t and an upper l i m i t g i v e n by the plasmapause bulge apex L. T h i s L range combined w i t h the plasmapause p o s i t i o n then g i v e s the GMLT range of p o s s i b l e IPDP g e n e r a t i o n . For seven of the ten IPDPs s t u d i e d , the observed GMLT span f a l l s w i t h i n the range a l l o w e d by the model, and one o t h e r e v e n t s ' s GMLT span l i e s m a i n l y (more than 50%) w i t h i n the p e r m i t t e d range. In the case of o n l y two e v e n t s does the observ e d GMLT range not c o r r e s p o n d t o the model r e s u l t s at a l l . F i g u r e 25 shows a s u c c e s s f u l match, the Feb. 15 e v e n t , and a f a i l e d match, the Feb. 14 event. These model r e s u l t s i n d i c a t e t h a t the model i s r e a s o n a b l y s u c c e s s f u l i n p r e d i c t i n g the p o t e n t i a l GMLT IPDPX Plasmapause t Sun 91 Feb. 15 event X \ Earth U FIGURE 25. M o d e l l e d v e r s u s observed IPDP GMLT co m p a r i s o n s . The plasmapause s e c t i o n p l o t t e d i n d i c a t e s where the model p r e d i c t e d an IPDP c o u l d o c c u r , and the ob s e r v e d IPDP GMLTs are marked by the dashed l i n e s . Here, a s u c c e s s f u l p r e d i c t i o n i s shown (Feb. 15 e v e n t , t o p ) , a l o n g w i t h an u n s u c c e s s f u l one (Feb. 14 e v e n t , bottom). 92 p o s i t i o n s of IPDPs. The s t a t i s t i c a l n a t u r e of the r e l a t i o n s d e t e r m i n i n g the plasmapause s i z e and o r i e n t a t i o n and the i n j e c t i o n boundary p o s i t i o n may be the cause of the two f a i l e d GMLT p r e d i c t i o n s , though a l a r g e r IPDP d a t a s e t would be n e c e s s a r y f o r a prop e r e v a l u a t i o n of the performance of these r e l a t i o n s as combined i n the c o n t e x t of t h i s IPDP model. 4.4.5. Discussion of IPDP Simulation Model As mentioned a t the o u t s e t of the d e s c r i p t i o n of t h i s IPDP model, the model i s q u i t e s i m p l e and of l i m i t e d purpose. I t c a l c u l a t e s o n l y r e l a t i v e f r e q u e n c i e s , and the plasmapause and i n j e c t i o n boundary p o s i t i o n s a r e d e t e r m i n e d from s t a t i s t i c a l r e l a t i o n s which w i l l not always be a p p l i c a b l e t o i n d i v i d u a l e v e n t s . Furthermore t h e s e r e l a t i o n s ar e not v a l i d f o r a l l Kps ( c f . s e c t i o n 4.4.1). Another l i m i t a t i o n of the model i s i t s l a c k of f a c i l i t y t o a l l o w f o r the e f f e c t s of tempor a l changes i n the geomagnetic f i e l d s t r e n g t h , a t a f i x e d L, on IPDP f r e q u e n c y e v o l u t i o n . T h i s was not i n c l u d e d s i n c e the i n c r e a s i n g background f i e l d mechanism i s not b e l i e v e d t o be n e c e s s a r y f o r p r o d u c i n g IPDP frequ e n c y b e h a v i o u r ( c f . s e c t i o n 4.3). The assumption of good i o n o s p h e r i c d u c t i n g a p p l i e s o n l y a l o n g the geomagnetic m e r i d i a n , and not t o d u c t i n g i n the east-west d i r e c t i o n , p e r p e n d i c u l a r t o the geomagnetic 93 m e r i d i a n . That good n o r t h - s o u t h d u c t i n g of IPDP s i g n a l s i n the s u b - a u r o r a l zone i o n o s p h e r e o c c u r s i s w e l l known, but the r o l e of e a s t - w e s t d u c t i n g i s l e s s w e l l u n d e r s t o o d ( c f . Appendix B ) . I f e a s t - w e s t d u c t i n g does e x i s t , i t s p r i m a r y e f f e c t would be t o i n c r e a s e the f r e q u e n c y band-width of an IPDP as observed a t the l a t i t u d e of the source f i e l d l i n e s by a d d i n g , a t g e n e r a l l y lower a m p l i t u d e s , lower or h i g h e r f r e q u e n c i e s d u cted from the west or e a s t r e s p e c t i v e l y , t o the g e n e r a l l y h i g h e r a m p l i t u d e s i g n a l s o b s e r v e d from i t s own m e r i d i a n by a ground s t a t i o n . An a d d i t i o n a l a ssumption used t o f a c i l i t a t e the c a l c u l a t i o n of the change i n IPDP fr e q u e n c y due t o a change i n L, and a l s o the geomagnetic l a t i t u d e from L, i s t h a t of a d i p o l a r geomagnetic f i e l d . W i t h i t s framework of l i m i t a t i o n s and assumptions d i s c u s s e d above, t h i s model may be c o n s i d e r e d t o be a " f i r s t a p p r o x i m a t i o n " a t t e m p t . To d e v e l o p i t f u r t h e r would r e q u i r e the i n c l u s i o n of a more s o p h i s t i c a t e d geomagnetic f i e l d model, i n c l u d i n g r i n g c u r r e n t and t e m p o r a l e f f e c t s , b e t t e r i n f o r m a t i o n on the f o r m a t i o n and p o s i t i o n of the i n j e c t i o n boundary and the n a t u r e of the plasma b e h i n d i t , improved knowledge of the shape and movement of the plasmapause, and a more d e t a i l e d t r e a t m e n t of the i o n - c y c l o t r o n i n s t a b i l i t y g e n e r a t i n g the IPDP and the subsequent p r o p a g a t i o n of the HM waves th r o u g h the magnetcsphere and i o n o s p h e r e t o the ground s t a t i o n s . 94 Where i t was p o s s i b l e t o make com p a r i s o n s , the model r e s u l t s a greed q u i t e w e l l w i t h 'the known IPDP o b s e r v a t i o n s ( c f . s e c t i o n 4.4.2). A check of mo d e l l e d IPDP GMLTs v e r s u s o b s e r v e d IPDP GMLTs f o r t e n events a l s o r e v e a l e d a good match (75%, c f . s e c t i o n 4.4.4). These r e s u l t s , w h i l e not p r o v i n g the c o r r e c t n e s s of the model, r a i s e c o n f i d e n c e i n i t s u s e f u l n e s s and i n d i c a t e t h a t the new r e s u l t s produced by i t m e r i t c o n s i d e r a t i o n and i n v e s t i g a t i o n . In summary, the s e new r e s u l t s i n c l u d e the s i g n i f i c a n t a pparent inward motion p o s s i b l e w i t h o u t a c t u a l plasmapause inward motion and the p o s s i b i l i t y of eastward d e v e l o p i n g IPDP e v e n t s . CHAPTER 5. EXPERIMENTAL RESULTS Three IPDPs, the Feb. 14, Feb. 15, and Feb. 24c ev e n t s ( c f . s e c . 2.1), have been a n a l y s e d i n d e t a i l ( c f . s e c . 2.2). The r e s u l t s of t h e s e a n a l y s e s a r e used here t o study the causes of the IPDP freq u e n c y r i s e and the l o n g i t u d i n a l development of IPDPs. The p r i m a r y aim of t h i s work i s t o p r o v i d e some e x p e r i m e n t a l i n d i c a t i o n of the r e l a t i v e i m p o r t a n c e , or even e x i s t e n c e , of the v a r i o u s f r e q u e n c y s h i f t mechanisms d i s c u s s e d i n s e c t i o n s 4.2 and 4.3. S e c t i o n 5.1 examines the inward motion mechanism's e f f e c t on the Feb. 14 and Feb. 15 IPDPs ( c f . s e c t i o n 4.2.1), w h i l e s e c t i o n 5.2 p r e s e n t s a study of the i n c r e a s i n g background magnetic f i e l d mechanism ( c f . s e c t i o n 4.2.2). In s e c t i o n 5.3, the c o n t r i b u t i o n s of the a z i m u t h a l d r i f t mechanism ( c f . s e c t i o n 4.2.3) t o the fre q u e n c y s h i f t s of the two ev e n t s s t u d i e d i n s e c t i o n 5.1 a r e examined. The l o n g i t u d i n a l development r e s u l t s a r e p r e s e n t e d i n s e c t i o n 5.4, and s e c t i o n 5.5 c o n t a i n s a d i s c u s s i o n of a l l the e x p e r i m e n t a l r e s u l t s w i t h r e f e r e n c e t o the IPDP model d e s c r i b e d i n Chapter F o u r . 5.1. INWARD MOTION OF IPDP SOURCE REGION In o r d e r t o u n d e r s t a n d the fre q u e n c y e f f e c t s of the inward motion mechanism, the inward motion of the IPDP sour c e r e g i o n must be d e t e r m i n e d . T h i s can be a c h i e v e d t h r o u g h the a n a l y s i s of the e v o l u t i o n of a m p l i t u d e 95 96 v a r i a t i o n s as observed a l o n g a n o r t h - s o u t h l i n e of s t a t i o n s d u r i n g an IPDP event. Such a n a l y s e s have been c a r r i e d out f o r the Feb. 14 and Feb. 15 IPDPs, and a r e d e s c r i b e d below. The Feb. 24c event i s not s u i t a b l e f o r such a n a l y s i s s i n c e o n l y one of the s t a t i o n s s i t u a t e d t o r e c o r d the event on each n o r t h - s o u t h l i n e was o p e r a t i n g . 5.1.1. Feb. 14 Event The IPDP event of Feb. 14 was ob s e r v e d by the t h r e e s t a t i o n s a t the s o u t h e r n end of the Saskatchewan l i n e ; WS, PS, and LL ( c f . s e c t i o n 2.1, f i g . 3 ) . From each of these t h r e e s t a t i o n s , d a t a b l o c k s c e n t e r e d e v e r y f i v e minutes from 0835 t o 0940 UT, are a n a l y z e d ( c f . s e c t i o n 2.2) i n o r d e r t o f o l l o w the f r e q u e n c y , a m p l i t u d e , and p o l a r i z a t i o n e v o l u t i o n of the e v e n t . The p o l a r i z a t i o n s pectrograms from PS and LL p r o v i d e i n f o r m a t i o n on the p r o p a g a t i o n c h a r a c t e r i s t i c s of the IPDP waves i n the ionos p h e r e n e c e s s a r y f o r the u n d e r s t a n d i n g of t h e i r a m p l i t u d e v a r i a t i o n s a l o n g a n o r t h - s o u t h s t a t i o n l i n e . The l e f t - h a n d (LH) p o l a r i z e d f i e l d - l i n e g u i d e d waves from the magnetospheric IPDP sou r c e r e g i o n e n t e r the io n o s p h e r e and p e n e t r a t e through the F - l a y e r . Some of the wave energy may become t r a p p e d i n the i o n o s p h e r i c F - l a y e r waveguide i f the wave fr e q u e n c y i s above a lower c u t - o f f f r e q u e n c y d e t e r m i n e d by the i o n o s p h e r i c plasma c h a r a c t e r i s t i c s . The 97 waveguide i s formed i n the A l f v e n v e l o c i t y minimum c r e a t e d by the peak i n i o n i z a t i o n i n the F 2 - l a y e r ( c f . Appendix B ) . The t r a p p e d wave energy, which i s c o n v e r t e d from LH t o RH ( r i g h t - h a n d p o l a r i z a t i o n ) , can then propagate h o r i z o n t a l l y a l o n g the geomagnetic m e r i d i a n f o r l o n g d i s t a n c e s . T h e r e f o r e , IPDPs s u b j e c t t o i o n o s p h e r i c p r o p a g a t i o n w i l l show LH p o l a r i z a t i o n i f the f i e l d l i n e s g u i d i n g the waves from the magnetospheric source r e g i o n e n t e r the i o n o s p h e r e overhead of the ground s i t e and RH p o l a r i z a t i o n i f they a r e t o the n o r t h or s o u t h of the ground s t a t i o n ( G r e i f i n g e r , 1972; A r n o l d y e t a l . , 1979). I f no such i o n o s p h e r i c p r o p a g a t i o n i s o c c u r r i n g , then o n l y LH p o l a r i z a t i o n s h o u l d be o b s e r v e d . A study of the appearance of RH p o l a r i z a t i o n then t e l l s us whether i o n o s p h e r i c p r o p a g a t i o n i s o c c u r r i n g and below which f r e q u e n c y t h i s e f f e c t i s c u t o f f , and thus i n d i c a t e s whether or not wave a m p l i t u d e v a r i a t i o n w i t h d i s t a n c e from the wave e n t r y p o i n t i n t o the i o n o s p h e r e i s a f f e c t e d by i o n o s p h e r i c p r o p a g a t i o n . Note t h a t the p o i n t , or a r e a , on each m e r i d i a n a t which the IPDP waves e n t e r the i o n o s p h e r e i s o f t e n termed the "secondary s o u r c e " . In the p o l a r i z a t i o n s pectrograms from the Feb. 14 e v e n t , RH p o l a r i z a t i o n appears o n l y above ^0.5Hz, thus i n d i c a t i n g the lower c u t - o f f f r e q u e n c y of i o n o s p h e r i c p r o p a g a t i o n e f f e c t s d u r i n g t h i s IPDP ( f o r example, see f i g . 26 and 27). The p a t t e r n of appearance of RH p o l a r i z a t i o n 98 ^ ° - 8 0.4 a £ o 0.0 c « - 0 . 4 o CL —0.8 RH power 0840UT LH power 0.2 0.4 0.6 0.8 frequency (Hz) 1.0 0.4 0.6 0.8 frequency (Hz) FIGURE 26. P o l a r i z a t i o n s p e c t r o g r a m ( t o p ) and power spectrum ( t o t a l h o r i z o n t a l component) (bottom) from PS f o r 0840UT, Feb. 14. The p o l a r i z a t i o n spec txojg ram i s a c t u a l l y p r e s e n t e d as [ p o l a r i z e d power ]/[ h o r i z o n t a l . : component power]. The change- from LH p o l a r i z a t i o n at lower f r e q u e n c i e s t o RH p o l a r i z a t i o n j u s t above ^0. 5Hz"In'ajtS'ates the p o s i t i o n of the lower c u t - o f f f r e q u e n c y of i o n o s p h e r i c p r o p a g a t i o n . 99 d u r i n g t h i s IPDP i s a l s o c o n s i s t e n t w i t h waves t r a v e l l i n g w i t h i n the io n o s p h e r e from a southward moving secondary s o u r c e . At PS, f i r s t RH p o l a r i z a t i o n appears a t 0840UT, i n the band above 0.5Hz ( c f . f i g . 2 6 ) , then LH i s dominant i n the c e n t e r of the freq u e n c y band a t 0900UT ( f i g . 2 7 ) , and l a s t l y we see o n l y RH a g a i n a t 0940UT ( f i g . 27). The p o l a r i z a t i o n spectrograms from LL i n f i g u r e 28 a l s o support t h i s p i c t u r e , w i t h the s i g n a l showing RH p o l a r i z a t i o n a t 0900UT when the secondary source i s t o the n o r t h , near PS, and LH p o l a r i z a t i o n i n the upper p a r t of the f r e q u e n c y band a t 0940UT as the secondary s o u r c e approaches LL. S i n c e v i r t u a l l y a l l of t h i s event i s a t f r e q u e n c i e s >0.5Hz, p r o p a g a t i o n i n the i o n o s p h e r i c waveguide i s t a k i n g p l a c e . Thus, when comparing IPDP power l e v e l s o b s e r v e d a t the t h r e e s t a t i o n s f o r the purpose of d e t e r m i n i n g the secondary source p o s i t i o n , the energy a t t e n u a t i o n between s i t e s can be t r e a t e d as a d u c t e d wave problem. I t s h o u l d be p o i n t e d out t h a t the s i m u l t a n e o u s appearance of both LH and RH bands i n the IPDP s p e c t r a ( c f . f i g . 26, 27) i n d i c a t e s t h a t the magnetospheric s o u r c e r e g i o n i s not a o n e - d i m e n s i o n a l l i n e a l o n g the plasmapause, but o c c u p i e s a more extended t w o - d i m e n s i o n a l a r e a i n the v i c i n i t y of the plasmapause (Hayashi et a l . , 1988). I f the g e n e r a t i o n r e g i o n were p u r e l y o n e - d i m e n s i o n a l , then we s h o u l d see o n l y one p o l a r i z a t i o n , LH or RH, a t a t i m e . 100 N o o c o 0.8 0.4 0.0 •0.4 - 0 . 8 h 0.0 ^ 0.8 X> <u •5 0.4 o E o c 0.0 « - 0 . 4 o CL - 0 . 8 0.0 RH power 0900UT LH power 0.4 0.8 frequency (Hz) 1.2 RH power 0940UT LH power 0.4 0.8 frequency (Hz) 1.2 FIGURE 27. P o l a r i z a t i o n spectrograms from PS f o r 0900UT and 0940UT ( p r e s e n t e d as i n f i g . 2 6). The RH - LH - RH p r o f i l e a t 0900UT i n d i c a t e s t h a t the secondary source (LH waves) i s a p p r o x i m a t e l y overhead of PS at-., t h i s t i m e , w h i l e the p r e d o m i n a n t l y RH p o l a r i z a t i o n e v i d e n t a t 0940UT i s a r e s u l t of waves d u c t e d from a secondary...source d i s t a n t from PS. The RH bands i n the low and. h i g h f r e q u e n c y s e c t i o n s of the 0900UT spe c t r o g r a m r e p r e s e n t - s i g n a l s d u c t e d t o the s i t e from j u s t n o r t h and south of i t , r e s p e c t i v e l y . 101 a> N "6 E t_ o c o CL 0) N o c =: o CL 0.8 0.4 0.0 -0.4 -0.8 h 0.0 0.8 0.4 0.0 0.0 RH power 0900UT LH power 0.4 0.8 frequency (Hz) 1.2 RH power w 0940UT ' V" LH power i i i i i 0.4 0.8 frequency (Hz) 1.2 FIGURE 28. P o l a r i z a t i o n s p e c t r o g r a m s ' f r o m LL f o r 0900UT and 0940UT ( p r e s e n t e d as i n f i g . 2 7 ) . Here, the p o l a r i z a t i o n i s RH a t 0900UT s i n c e the secondary source i s near PS ( c f . f i g . 27) and i s p r e d o m i n a n t l y LH i n the---upper p a r t of the IPDP f r e q u e n c y band a t 0940UT, i n d i c a t i n g t h a t the secondary source has moved southward and i s a p p r o a c h i n g LL. 1 02 Due t o r e c o r d i n g system problems i n the X component a t WS, IPDP s i g n a l power i n o n l y the Y da t a component can be compared between a l l t h r e e s t a t i o n s . These d i f f i c u l t i e s a l s o e l i m i n a t e the p o s s i b i l i t y of s t u d y i n g p o l a r i z a t i o n s pectrograms from WS. However, as p a r t of a study of IPDP s i g n a l power v a r i a t i o n s a l o n g a n o r t h - s o u t h l i n e of s t a t i o n s , the problem of d i f f e r i n g power v a r i a t i o n s between the X and Y components a l o n g the l i n e was examined by K o l e s z a r (1980). The r e s u l t was t h a t the X and Y component v a r i a t i o n s were s u f f i c i e n t l y s i m i l a r t o j u s t i f y t he use of one component o n l y , though the d i s t a n c e s from the secondary s o u r c e concerned were l e s s than 1.6° of l a t i t u d e . T h i s i s c o n f i r m e d by the s i m i l a r i t y of the X and Y component power v a r i a t i o n s a t LL d u r i n g the Feb. 14 IPDP, as shown i n f i g u r e 29. The l i k e n e s s of the X and Y component power v a r i a t i o n s may, however, break down a t l a r g e r d i s t a n c e s from the secondary source s i n c e the p o l a r i z a t i o n below the duct becomes l i n e a r a l o n g the m e r i d i a n , or i n the X - d i r e c t i o n , w i t h the Y component t h e r e f o r e becoming v e r y s m a l l . Note t h a t LL and WS are s e p a r a t e d by ^3° of l a t i t u d e . A l t h o u s e and D a v i s (1978) showed t h a t the Y component i s much weaker r e l a t i v e t o the X component a t a low l a t i t u d e s i t e than i t i s a t s i t e s =*l000km t o the n o r t h which a r e c l o s e r t o the secondary s o u r c e . In o r d e r t o q u a n t i t a t i v e l y d etermine the l a t i t u d i n a l 1 03 FIGURE 29. P l o t s of t h e X and Y component peak power v a r i a t i o n s f o r the Feb. 14 IPDP. For ease of comp a r i s o n , each component i s n o r m a l i z e d t o i t s 0940UT-- l e v i l v " T h e p l o t s a r e g e n e r a l l y q u i t e s i m i l a r , though the s t r o n g e r . X component b e f o r e 0845UT may be i n d i c a t i n g the b e g i n n i n g of _the presence of l i n e a r p o l a r i z a t i o n below the duct (see t e x t ) . 1 04 p o s i t i o n of the secondary s o u r c e , we must know the a t t e n u a t i o n f a c t o r f o r the d u c t e d waves. T h i s can be d e t e r m i n e d e x p e r i m e n t a l l y from the power r a t i o s between ground s t a t i o n s and the known i n t e r - s t a t i o n d i s t a n c e s i f the secondary s o u r c e i s known not t o be between the two s i t e s i n q u e s t i o n . T h i s r e l a t i v e secondary s o u r c e p o s i t i o n c an, i n t u r n , be e s t a b l i s h e d from the p o l a r i z a t i o n s pectrograms and a q u a l i t a t i v e e x a m i n a t i o n of i n t e r - s t a t i o n power r a t i o s . For the Feb. 14 IPDP, the p o l a r i z a t i o n spectrograms from PS e x h i b i t the c h a r a c t e r i s t i c RH - LH - RH time p r o f i l e of a southward moving secondary source w i t h t h i s s o u r c e b e i n g n o r t h o f , or i n the v i c i n i t y o f , PS u n t i l =* 0910UT, and south of PS t h e r e a f t e r . An e x a m i n a t i o n of the i n t e r - s t a t i o n power r a t i o s can, under • some c i r c u m s t a n c e s , p r o v i d e c o n f i r m a t i o n as t o whether or not the secondary source i s a c t u a l l y between any two s i t e s . For example, i f the power r a t i o LL/WS = 1, then the secondary source would be a p p r o x i m a t e l y h a l f way between WS and LL. T h i s would be c o n f i r m e d by h a v i n g the r a t i o s PS/WS and PS/LL both s i g n i f i c a n t l y g r e a t e r than one (see f i g . 35 f o r s t a t i o n l o c a t i o n s ) , and would p l a c e the secondary source somewhere between PS and WS. T h i s type of c o n f i r m a t i o n can be i m p o r t a n t , s i n c e near the secondary s o u r c e , the p o l a r i z a t i o n p a t t e r n can sometimes be more complex than the s i m p l e s i t u a t i o n d e s c r i b e d above ( c f . Appendix B ) . 1 05 U s i n g the PS/LL power r a t i o s b e f o r e 091 OUT (see a b o v e ) , we can then c a l c u l a t e the a t t e n u a t i o n as f o l l o w s : A = 1000 1 39 10 Log PS LL (5.1) where A i s the a t t e n u a t i o n i n dB/1000km, which i s the form commonly used t o e x p r e s s duct a t t e n u a t i o n (Manchester, 1966; G r e i f i n g e r and G r e i f i n g e r , 1973; A l t h o u s e and D a v i s , 1978), and 139 i s the PS - LL s e p a r a t i o n d i s t a n c e i n k i l o m e t e r s . The r e s u l t i n g a t t e n u a t i o n f a c t o r i s 21.5 ± 2.4 dB/l000km. Due t o v e r y weak s i g n a l s t r e n g t h s at WS a f t e r 091 OUT, no a t t e n u a t i o n c a l c u l a t i o n s were p o s s i b l e u s i n g the PS/WS power r a t i o s . There was no n o t i c e a b l e f r e q u e n c y dependence of the a t t e n u a t i o n , though the f r e q u e n c y range c o v e r e d i n the above c a l c u l a t i o n s was q u i t e narrow (0.15Hz) as compared t o some duct model c a l c u l a t i o n s ( c f . Appendix B ) . T h i s a t t e n u a t i o n f a c t o r may now be used t o c a l c u l a t e the p o s i t i o n , a l o n g the m e r i d i a n , of the secondary source when t h i s source i s between two s t a t i o n s . To f a c i l i t a t e t h i s , t h e o r e t i c a l power r a t i o v e r s u s n o r t h - s o u t h p o s i t i o n p r o f i l e s were c a l c u l a t e d f o r each of the t h r e e s t a t i o n p a i r s of the Saskatchewan c h a i n (PS/WS, PS/LL, and LL/WS) u s i n g A f o r the Feb. 14 event as c a l c u l a t e d above. These p r o f i l e s a r e shown i n f i g u r e 30. For c o m p a r i s o n , the e x p e r i m e n t a l south north 0 I i i i i i i i i - 2 0 0 - 1 0 0 0 100 2 0 0 position (km) FIGURE 30. T h e o r e t i c a l power r a t i o v e r s u s p o s i t i o n c u r v e s f o r the PS/WS, PS/LL, and LL/WS s t a t i o n p a i r s . The A v a l u e used here i s t h a t c a l c u l a t e d from the Y component of the Feb. 14 event. The l e t t e r s (a-h) i n d i c a t e the e x p e r i m e n t a l p o i n t s w i t h t i m e s (UT) and fr e q u e n c y (Hz) as f o l l o w s : a-0835,0.50; b-0840,0.56; c-0850,0.59; d-0915,0.75; e-0920,0.84; f-0930,0.87; g-0935,0.89; h-0940,0.89. The p o i n t s i n d i c a t e d by x, *, and + are a l s o from 0840UT, but d i f f e r e n t from the p o i n t s l a b e l l e d b above by b e i n g from a lower f r e q u e n c y band (< 0.5Hz) (see t e x t ) . The p o s i t i o n s f o r the p o i n t s on the h o r i z o n t a l branch a re d e t e r m i n e d from the o t h e r power r a t i o ( s ) f o r t h a t t i m e . P o s i t i o n i n t h i s p l o t i s c e n t e r e d a t PS. 1 07 power r a t i o s a r e a l s o marked i n f i g u r e 30. Note t h a t the t h e o r e t i c a l p l o t shows t h a t the PS/LL power r a t i o i s c o n s t a n t w h i l e the secondary source i s n o r t h of PS, and t h a t the e x p e r i m e n t a l PS/LL r a t i o s are a l s o r e l a t i v e l y c o n s t a n t u n t i l =*091 OUT, thus c o n f i r m i n g the p o l a r i z a t i o n s p e ctrogram r e s u l t t h a t the secondary source i s n o r t h o f , or i n the v i c i n i t y o f , PS u n t i l =0910UT. That th e s e power r a t i o s l i e on or near the h o r i z o n t a l branch of the t h e o r e t i c a l c u r v e a l s o demonstrates t h a t the e x p o n e n t i a l s i g n a l decay model ( c f . e q u a t i o n 5.1) i s a p p r o p r i a t e f o r the . a n a l y s i s of t h i s e v e n t , or a t l e a s t f o r the m a j o r i t y of i t which has f r e q u e n c i e s above 0.5Hz. I f s i g n a l decay were due t o g e o m e t r i c a l s p r e a d i n g as e x p r e s s e d i n e q u a t i o n 5.2, no such h o r i z o n t a l branch would e x i s t and the PS/LL power, r a t i o s s h o u l d d e c r e a s e w i t h i n c r e a s i n g secondary source d i s t a n c e n o r t h of PS. F i g u r e 30 a l s o i n c l u d e s power r a t i o s c a l c u l a t e d from the s i g n a l band below 0.5Hz at 0840UT and i n d i c a t e d by x (PS/WS), * ( P S / L L ) , and + (LL/WS). S i n c e t h e s e s i g n a l s are below 0.5Hz, they s h o u l d not be a f f e c t e d by i o n o s p h e r i c p r o p a g a t i o n . Thus, as e x p e c t e d , they do not l i e on the t h e o r e t i c a l c u r v e s , e x c e p t f o r the LL/WS r a t i o p o i n t . In the case of t h i s LL/WS p o i n t , the secondary so u r c e p o s i t i o n happens t o be almost e x a c t l y h a l f way between LL and WS r e s u l t i n g i n a power r a t i o near 1 and a r a t i o p o s i t i o n near the t h e o r e t i c a l c u r v e . The p o s i t i o n e s t i m a t e from t h i s low 108 f r e q u e n c y p o i n t i s 27km n o r t h of PS f o r 0840UT, j u s t s l i g h t l y d i f f e r e n t than the 23km n o r t h e s t i m a t e made from the s i g n a l band above 0.5Hz. The method used f o r e s t i m a t i n g secondary source p o s i t i o n s when IPDP s i g n a l decay i s due t o g e o m e t r i c a l s p r e a d i n g i s d e s c r i b e d i n d e t a i l i n the d i s c u s s i o n of the Feb. 15 event below ( c f . s e c t i o n 5.1.2). I t s h o u l d a l s o be noted here t h a t the power and frequency v a l u e s used i n the secondary s o u r c e p o s i t i o n a n a l y s i s a re taken from the peaks i n the s p e c t r a , the f r e q u e n c i e s of which a r e g e n e r a l l y near the IPDP m i d - f r e q u e n c y . The secondary source p o s i t i o n can now be d e t e r m i n e d by matching the t h r e e s t a t i o n p a i r power r a t i o s , when each i s a v a i l a b l e , t o the t h e o r e t i c a l c u r v e s , and r e a d i n g the p o s i t i o n a s s o c i a t e d w i t h t h a t r a t i o from these c u r v e s . T h i s method assumes t h a t , on each m e r i d i a n , the secondary source can be ap p r o x i m a t e d by a p o i n t s o u r c e . T h i s i s r e a s o n a b l e s i n c e the plasmapause, the p r i m a r y source r e g i o n ( c f . s e c t i o n 4.1), i s p r o b a b l y l e s s than 0.15R„ a c r o s s , w i t h the plasma d e n s i t y i n c r e a s i n g from 1 t o 100 cm" 3 over t h i s d i s t a n c e ( J a c o b s , 1970). The main r e g i o n of IPDP wave growth, ( i . e . t h a t p a r t r e s p o n s i b l e f o r the s p e c t r a l p e a k ) , l i k e l y c o v e r s o n l y a s m a l l p o r t i o n of t h i s 0.15R E range. I f i t c o v e r e d o n l y — of t h i s range, the r a d i a l d i m e n s i o n of t h i s p a r t of the magnetospheric g e n e r a t i o n r e g i o n would be ^lOOkm. When t h i s range i s mapped down the c o n v e r g i n g f i e l d 109 l i n e s t o E a r t h ' s s u r f a c e , the range a l o n g the m e r i d i a n becomes o n l y -6km, or 0.05°, a t the l a t i t u d e of PS. For the Feb. 14 IPDP, secondary s o u r c e p o s i t i o n s have been d e t e r m i n e d b e f o r e 0900UT u s i n g both the PS/WS and LL/WS power r a t i o s . Reasonable agreement was o b t a i n e d between the p o s i t i o n s found from each of thes e two r a t i o s a t each p o i n t (see f i g . 3 0 ) . A f t e r 0910UT, however, o n l y the PS/LL r a t i o was a v a i l a b l e , s i n c e the s i g n a l s t r e n g t h a t WS was too weak to produce r e l i a b l e r e s u l t s . Though s p e c t r a l e s t i m a t e s were made from d a t a b l o c k s c e n t e r e d every f i v e minutes thr o u g h o u t the e v e n t , source l o c a t i o n p o i n t s do not appear a t each of these t i m e s . T h i s i s due t o i n t e r v a l s of v e r y low s i g n a l / n o i s e r a t i o , and a l s o t o p e r i o d s of mismatched, or d i s s i m i l a r s p e c t r a a t the v a r i o u s s t a t i o n s . These p e r i o d s a r e p o s s i b l y i n d i c a t i v e of temporary poor s i g n a l p r o p a g a t i o n , s l i g h t s i g n a l d i f f e r e n c e s caused by the s m a l l l o n g i t u d i n a l d i f f e r e n c e s between the s t a t i o n s ( c f . s e c . 5.4), or the L-s p r e a d of the IPDP sou r c e r e g i o n mentioned e a r l i e r . The p o s i t i o n s of the IPDP secondary s o u r c e , as deter m i n e d by the above method, f o r the Feb. 14 IPDP a r e p r e s e n t e d i n f i g u r e 31 i n terms of c o r r e c t e d geomagnetic l a t i t u d e ( G u s t a f s s o n , 1984). A l s o shown a r e the e q u i v a l e n t e q u a t o r i a l r a d i a l p o s i t i o n s , i n L, of the magnetospheric source r e g i o n . In a d d i t i o n t o thes e d a t a p o i n t s , a p o i n t a t 1 10 CM CD LO 63.0 1 — US u s -CO \ r LflT. 62.0 1 GM L a t . / / / CD CD " o CD - P S / / ^ / • -— \ / \ \ / w ' w * w P S - cn O O - L L ^ L L - CD CD 1 ' 1 :' 1 ' 8.0 8 .5 9 .0 UT (H) 9 .5 10.0 FIGURE 31. Geomagnetic l a t i t u d e and e q u a t o r i a l r a d i a l p o s i t i o n ( L ) , r e s p e c t i v e l y f o r the secondary and magnetospheric s o u r c e s ; Feb. 14 IPDP. S t a t i o n l o c a t i o n s a r e a l s o shown. The source r e g i o n inward motion i s c l e a r l y e v i d e n t . 111 0900UT has been added d i r e c t l y over PS. The PS p o l a r i z a t i o n s p ectrograms show LH p o l a r i z a t i o n i n the c e n t e r of the IPDP fr e q u e n c y band a t t h i s t i m e , which i n d i c a t e s t h a t the secondary s o u r c e i s overhead of the s i t e . These r e s u l t s show a c l e a r inward motion t r e n d f o r the magnetospheric source r e g i o n of t h i s IPDP e v e n t . The e f f e c t of t h i s inward motion on the IPDP e v e n t ' s f r e q u e n c y e v o l u t i o n can be e s t i m a t e d u s i n g e q u a t i o n 4.5 ( c f . s e c t i o n 4.2.1). The f r e q u e n c y r i s e due t o d e c r e a s i n g L p r e d i c t e d by t h i s i s shown i n f i g u r e 32, a l o n g w i t h the a c t u a l f r e q u e n c y r i s e o b s e r v e d d u r i n g the Feb. 14 e v e n t . In t h i s f i g u r e , and i n a l l the f o l l o w i n g f r e q u e n c y s h i f t a n a l y s e s , we use freq u e n c y n o r m a l i z e d t o the i n i t i a l v a l u e of the event under s t u d y ( f / f ). I t i s e v i d e n t t h a t the inward motion e f f e c t produces ' a s i g n i f i c a n t amount, a p p r o x i m a t e l y •§-, of the freq u e n c y r i s e of t h i s IPDP, but c e r t a i n l y cannot be s a i d t o account f o r i t a l l . 5.1.2. Feb. 15 Event The second event s t u d i e d , t h a t of Feb. 15, was a l s o o bserved on the t h r e e southernmost s t a t i o n s of the Saskatchewan l i n e . The a n a l y s i s p r o c e d u r e f o r t h i s IPDP i s g e n e r a l l y t h e same as t h a t f o r the Feb. 14 e v e n t , i n c l u d i n g the n e c e s s i t y of u s i n g the Y component d a t a o n l y . However, some p r o c e d u r a l adjustment i s r e q u i r e d by the d i f f e r e n t 1 1 2 2.0 1.8 <D N ~5 E i _ 1.6 o c o 1.4 c 0J Z3 cr a) 1.2 observed frequency 1.0 8 .0 predicted frequency 8.4 8.8 9.2 UT (h) 9 .6 10.0 FIGURE 32. Observed and inward motion p r e d i c t e d f r e q u e n c y p r o f i l e s f o r the Feb. 14 ev e n t . The f r e q u e n c i e s a r e n o r m a l i z e d t o the observed i n i t i a l f r e q u e n c y of 0.50Hz a t 0835UT. The inward motion p r e d i c t e d f r e q u e n c y r i s e a c c o u n t s f o r of the observed r i s e . Note t h a t the forms of the two c u r v e s a r e q u i t e s i m i l a r , however. 1 13 s i g n a l c h a r a c t e r i s t i c s of t h i s e v e nt. The i n s p e c t i o n of p o l a r i z a t i o n s pectrograms f o r t h i s event i n d i c a t e s t h a t the lower c u t - o f f f r e q u e n c y f o r i o n o s p h e r i c p r o p a g a t i o n i s =0.25Hz ( f o r example, see f i g . 3 3 ) , r a t h e r than =0.5Hz as f o r the p r e v i o u s e v e n t . F i g u r e 34 shows p o l a r i z a t i o n s pectrograms from PS and LL a t 2201UT, a t which time the IPDP s i g n a l o c c u p i e s the f r e q u e n c y band from =0.35 t o =0.5 Hz. These s p e c t r a show t h a t both e v e n t s a r e RH a t t h i s t i m e , thus i n d i c a t i n g t h a t the secondary source i s over n e i t h e r s i t e . ( I t i s a c t u a l l y r o u g h l y h a l f way between them, see b e l o w ) . In s p i t e of t h i s lower c u t - o f f , the e n t i r e event cannot be t r e a t e d as a ducted wave problem s i n c e the i n i t i a l IPDP f r e q u e n c y i s <0.25Hz. For the i n i t i a l low f r e q u e n c y p o i n t , a t 2149UT, the power d e c r e a s e w i t h d i s t a n c e from the secondary source i s then l i k e l y due t o g e o m e t r i c a l s p r e a d i n g . In such a s i t u a t i o n , w i t h no p r o p a g a t i o n e f f e c t s from the i o n o s p h e r e or the E a r t h , the s i g n a l power (P) s h o u l d depend on d i s t a n c e (d) a s : P 1= ( 5 . 2 ) . The exponent x would be 2 f o r a p o i n t s o u r c e and 1 f o r an i n f i n i t e l y l o n g l i n e s o u r c e . S i n c e each s t a t i o n i s l i k e l y t o 1 1 4 ^ 0.8 X) 0.4 D o c 0.0 I - 0 . 4 o Q. - 0 . 8 h RH power 2157UT LH power 0.0 0.2 0.4 0.6 frequency (Hz) 0.8 1.0 0.4 0.6 frequency (Hz) 0.8 1.0 FIGURE 33. P o l a r i z a t i o n s p e c trogram ( t o p ) and power spectrum ( t o t a l h o r i z o n t a l component) (bottom) from PS f o r 2157UT, Feb. 15. The p o l a r i z a t i o n s p e c t r o g r a m i s a g a i n p r e s e n t e d as [ p o l a r i z e d power ]/[horizontal"..component power]. The change from LH p o l a r i z a t i o n a t lower f r e q u e n c i e s t o RH p o l a r i z a t i o n a t =0.25Hz i n d i c a t e s the p o s i t i o n of the duct lower c u t - o f f f r e q u e n c y . 1 15 N £ 0.4 o £ o c o CL X) N E o c 0) o 0.0 •0.4 •0.8 - RH power A PS : 2201UT LH power i i i i 0.8 0.4 0.0 - 0 . 4 - 0 . 8 0.0 0.2 0.4 0.6 frequency (Hz) 0.8 0.0 0.2 0.4 0.6 frequency (Hz) 0.8 1.0 - RH power LL -2201UT U power i i i i 1.0 FIGURE 34. P o l a r i z a t i o n spectrograms from PS (top) and LL (bottom) f o r 2201UT, Feb. 15. These spectrograms a re p r e s e n t e d as i n f i g u r e 33. The secondary source i s over n e i t h e r s i t e a t t h i s t i m e . 1 16 be r e c e i v i n g s i g n a l s from more than j u s t i t s own m e r i d i a n f o r non-ducted waves (see f i g . 3 5 ) , the a c t u a l exponent w i l l f a l l i n the range of 1 < x < 2, t h a t i s , the source can be a p p r o x i m a t e d by a l i n e of f i n i t e l e n g t h . Assuming a p a r t i c u l a r s o u r c e l o c a t i o n w i t h r e s p e c t t o the s t a t i o n s a l o n g the s t a t i o n s ' m e r i d i a n , i t i s p o s s i b l e t o w r i t e t h r e e equations, f o r the secondary s o u r c e p o s i t i o n u s i n g the t h r e e power r a t i o s . These e q u a t i o n s e x p r e s s secondary s o u r c e p o s i t i o n i n terms of d i s t a n c e n o r t h or s o u t h of PS. The f o l l o w i n g e q u a t i o n s are f o r the geometry of f i g u r e 35: 209 / _ _ * d, = (5.3a) (PS/WSK + 1 1 39 d 2 = (5.3b) ( P S / L L ) y - 1 d 3 = - 139 (5.3c) (LL/WS ) y + 1 where y = 1/x and the d.'s r e p r e s e n t d i s t a n c e n o r t h of PS. For each x between 0.20 and 4.00 (increment s i z e = 0.01), each d. above, p l u s the sum of the e r r o r s 1 17 CO i _ (D -*-» (D E o 250 200 150 100 50 0 - 5 0 - 1 0 0 - 1 5 0 - 2 0 0 -\ — secondary source - p s o -1 1 1 1 i i i 100 0 100 kilometers 200 FIGURE 3 5 . Source - s t a t i o n geometry f o r the Feb. 15 IPDP a t 2149UT. The secondary s o u r c e — l i n e i s a segment of the plasmapause mapped down, f i e l d , . l i n e s t o the ground. The segment i s assumed t o be c e n t e r e d on the s t a t i o n s ' m e r i d i a n so the sou r c e d i s t a n c e c a l c u l a t i o n s y i e l d p o s i t i o n s d i r e c t l y n o r t h or south of PS. The p o s i t i o n ..of PS i s c e n t e r e d a t Okm, w i t h LL 139km south and WS 209km-north. 118 e - C ( d 1 - d m ) 2 + ( d 2 - d m ) 2 + ( d 3 - d m ) a ) * (where d^ = ( d , + d 2 + d 3 ) / 3 ) , were c a l c u l a t e d . The r e s u l t i s shown i n f i g u r e 36, i n d i c a t i n g v e r y good convergence of the t h r e e p o s i t i o n e s t i m a t e s a t x = 1.44 and d = 152km n o r t h of PS. No convergence of the t h r e e p o s i t i o n e s t i m a t e s o c c u r s w i t h o t h e r s o u r c e - s t a t i o n g e o m e t r i e s . For example, h a v i n g the secondary source n o r t h of WS or south of LL, f o r which the e q u a t i o n s 5.3a,b,c must be m o d i f i e d s l i g h t l y , y i e l d s no c o n s i s t e n t p o s i t i o n e s t i m a t e . A l s o shown i n f i g u r e 36 are the r e s u l t s of the same c a l c u l a t i o n s c a r r i e d out u s i n g the power r a t i o s from 2157UT, a time when the IPDP s i g n a l i s p r o p a g a t i n g i n the i o n o s p h e r i c waveguide. Here, the exponent (x) g i v i n g the bes t d. convergence i s 0.76, o u t s i d e the e x p e c t e d range, and e a t t h i s p o i n t (e . ) i s 12.42km, 20 t i m e s g r e a t e r than ^ mi n e . f o r the 2149UT c a l c u l a t i o n . I t s h o u l d be noted a t the mi 7? e . p o i n t f o r the 2157UT c a s e , two of the d.'s a r e mi n ^ i v i r t u a l l y i d e n t i c a l , w h i l e the t h i r d i s s i g n i f i c a n t l y (=*15km) d i f f e r e n t . For t h i s 2157UT c a l c u l a t i o n , when x 1.44 (the 2149UT e . p o i n t ) , e = 130km. These r e s u l t s , which a r e t y p i c a l of a l l the d a t a p o i n t s a f t e r 2149UT, demonstrate t h a t t h i s method of secondary source d e t e r m i n a t i o n i s not a p p r o p r i a t e when d e a l i n g w i t h d u c t e d waves. 119 FIGURE 36. Sum of the e r r o r s (e) v e r s u s exponent (x) f o r 2149UT (top) and 2157UT (bottom); Feb. 15 ev e n t . At 2149UT, e i s minimum a t x = 1.44, c o r r e s p o n d i n g t o a source p o s i t i o n 152km n o r t h of PS (from e q u a t i o n s 5.3a - 5.3c). 1 20 The above method was then n e c e s s a r y f o r o n l y the f i r s t p o i n t of the Feb. 15 IPDP, a t 2149UT. For the r e m a i n i n g f o u r p o i n t s , a t 2152 t o 2205 UT ( c f . f i g . 37 c a p t i o n ) , the secondary s o u r c e p o s i t i o n was found u s i n g the same method as f o r the Feb. 14 event. The a t t e n u a t i o n f a c t o r d e t e r m i n e d here was 30.6 ± 2.8 dB/l000km. I t i s i n t e r e s t i n g t o note t h a t the i o n o s p h e r i c p r o p a g a t i o n c o n d i t i o n s a r e q u i t e d i f f e r e n t f o r t h i s IPDP than f o r the Feb. 14 e v e n t . The a t t e n u a t i o n i s 50% g r e a t e r h e r e , and the lower c u t - o f f f r e q u e n c y o n l y y t h a t f o r the p r e v i o u s e v e n t . T h i s may be a r e s u l t of the d i f f e r e n t l o c a l t i mes of the two e v e n t s ; the Feb. 14 event o c c u r r e d d u r i n g the n i g h t , w h i l e the Feb. 15 event appeared w h i l e the ion o s p h e r e was i n s u n l i g h t , which can s u b s t a n t i a l l y a l t e r the i o n o s p h e r i c plasma c h a r a c t e r i s t i c s i n c l u d i n g the d u c t i n g p a r a m e t e r s . F i g u r e 37 shows the power r a t i o p r o f i l e s f o r A = 30.6 dB/1000km p l u s the e x p e r i m e n t a l p o i n t s f o r the Feb. 15 IPDP. As i n the Feb. 14 e v e n t , the p o i n t s on or near the h o r i z o n t a l branches i n f i g u r e 37 show t h a t the e x p o n e n t i a l decay model ( c f . e q u a t i o n 5.1) i s a p p r o p r i a t e a t f r e q u e n c i e s above the c u t - o f f of =0.25Hz f o r t h i s e v e n t . That the p o i n t s f o r 2149UT i n t h i s f i g u r e a r e not on the t h e o r e t i c a l power r a t i o c u r v e s a l s o i n d i c a t e s t h a t t h i s low fr e q u e n c y p o i n t cannot be t r e a t e d i n t h i s manner.. I f we were t o i n t e r p r e t 121 position (km) FIGURE 37. Power r a t i o v e r s u s p o s i t i o n p r o f i l e s f o r the PS/WS, PS/LL, and LL/WS s t a t i o n p a i r s . The A v a l u e used here i s t h a t c a l c u l a t e d from the Feb. 15 e v e n t . The l e t t e r s (a,b,c,d) i n d i c a t e the e x p e r i m e n t a l p o i n t s w i t h t imes (UT) and f r e q u e n c i e s (Hz) as f o l l o w s : a-2152,0.27; b-2157,0.32; c-2201,0.47; d-2205,0.50. The p o i n t s marked w i t h x (PS/WS), * ( P S / L L ) , and + (LL/WS) a r e from 21.49UT ( f r e q . =0 . 22Hz ) , when the IPDP freq u e n c y was below the i o n o s p h e r i c p r o p a g a t i o n c u t - o f f f o r t h i s day. The p o s i t i o n s of the p o i n t s on the h o r i z o n t a l branches a r e d e t e r m i n e d as i n the Feb. 14 event ( c f . f i g . 3 0 ) . P o s i t i o n i n t h i s p l o t i s c e n t e r e d a t PS. 122 the 2149UT p o i n t i n terms of e x p o n e n t i a l decay, the secondary s o u r c e p o s i t i o n e s t i m a t e s would be somewhere n o r t h of PS, j u s t s o u th of WS, or somewhere n o r t h of WS, depending on the i n t e r - s t a t i o n power r a t i o s used. The secondary s o u r c e p o s i t i o n r e s u l t s from the above a n a l y s e s a r e shown i n f i g u r e 38, a l o n g w i t h the c o r r e s p o n d i n g L p o s i t i o n s of the magnetospheric g e n e r a t i o n r e g i o n . The inward motion of the g e n e r a t i o n r e g i o n i s a g a i n c l e a r from t h i s p l o t . The r e a l f r e q u e n c y r i s e and t h a t p r e d i c t e d from the inward motion a r e p r e s e n t e d i n f i g u r e 39. Inward s o u r c e motion a c c o u n t s f o r a l i t t l e more than h a l f , =60% i n t h i s c a s e , of the t o t a l f r e q u e n c y r i s e of t h i s IPDP. In summary, t h e n , i n t h i s s e c t i o n two new methods f o r d e t e r m i n i n g IPDP source r e g i o n inward motion u s i n g a m p l i t u d e v a r i a t i o n s a l o n g a n o r t h - s o u t h l i n e of ground s t a t i o n s have been p r e s e n t e d . These methods have been a p p l i e d t o two e v e n t s , w i t h the r e s u l t s showing t h a t the inward motion mechanism i s c a p a b l e of p r o d u c i n g a major p o r t i o n of an IPDP's f r e q u e n c y r i s e , though i t i s not always s u f f i c i e n t , of i t s e l f , t o e x p l a i n the e n t i r e observed r i s e of an ev e n t . 5.2. MAGNETIC FIELD CHANGES IN IPDP SOURCE REGION I t i s e v i d e n t from s e c t i o n 5.1 t h a t the two IPDPs s t u d i e d i n d e t a i l r e q u i r e one or more a d d i t i o n a l f r e q u e n c y s h i f t mechanisms c o n t r i b u t i n g t o t h e i r f r e q u e n c y r i s e s 1 23 FIGURE 38. Geomagnetic l a t i t u d e and e q u a t o r i a l r a d i a l p o s i t i o n ( L ) , r e s p e c t i v e l y f o r the secondary and magnetospheric s o u r c e s ; Feb. 15 IPDP. S t a t i o n l o c a t i o n s a r e a l s o shown. As w i t h the Feb. 14 e v e n t , t h i s IPDP a l s o shows c l e a r s o u r c e r e g i o n i n w a rd motion. 124 FIGURE 39. Observed and inward motion p r e d i c t e d f r e q u e n c y p r o f i l e s f o r the Feb. 15 event. The f r e q u e n c i e s a r e n o r m a l i z e d t o the i n i t i a l f r e q u e n c y of 0.22Hz at 2149UT. Here, the inward motion mechanism a c c o u n t s f o r o n l y =*60% of the observed f r e q u e n c y r i s e , though, as i n the Feb. 14 e v e n t , the forms of the two c u r v e s are q u i t e s i m i l a r . 1 25 beyond the inward motion mechanism a l r e a d y d i s c u s s e d . In t h i s s e c t i o n , the p o t e n t i a l c o n t r i b u t i o n s of the i n c r e a s i n g magnetic f i e l d mechanism t o IPDP frequency s h i f t s w i l l be a s s e s s e d , both i n g e n e r a l and f o r the s p e c i f i c e v e n t s examined i n s e c t i o n 5.1. The magnetospheric p r o c e s s e s p r o d u c i n g the magnetic f i e l d changes i n the IPDP sou r c e r e g i o n a r e d e s c r i b e d below. The a n a l y s i s of the s e p r o c e s s e s here r e p r e s e n t s a more s o p h i s t i c a t e d approach than t h a t d i s c u s s e d b r i e f l y i n s e c t i o n 4.2.2, though the dependence of IPDP f r e q u e n c y on magnetic f i e l d s t r e n g t h i s the same ( c f . e q u a t i o n 4.6). Comparisons of geosynchronous s a t e l l i t e magnetograms, from GOES 2 and 3 (whose m e r i d i a n s c o r r e s p o n d a p p r o x i m a t e l y t o the Saskatchewan and B r i t i s h Columbia l i n e s , r e s p e c t i v e l y ; c f . s e c t i o n 2.1), and Dst i n d i c e s ( c f . Appendix C) w i t h the ground s t a t i o n IPDP r e c o r d s a r e used t o g a i n some u n d e r s t a n d i n g of the e f f e c t s of t h i s f r e q u e n c y s h i f t mechanism. 5.2.1. Ring Current Versus IPDPs The IPDP g e n e r a t i o n r e g i o n i s t y p i c a l l y i n the e v e n i n g s e c t o r between L 3 and 5y. The source of magnetic f i e l d v a r i a t i o n s i n t h i s r e g i o n c o n s i d e r e d here i s the r i n g c u r r e n t s i n c e t h i s c u r r e n t can s t r o n g l y i n f l u e n c e magnetic f i e l d b e h a v i o u r i n the IPDP sou r c e r e g i o n and i t s f o r m a t i o n i s d i r e c t l y r e l a t e d t o the substorm p r o c e s s e s which a r e a l s o 1 26 n e c e s s a r y t o c r e a t e IPDPs ( c f . s e c t i o n 4.1). T h i s r i n g c u r r e n t forms d u r i n g magnetospheric storms and i s c a r r i e d by westward d r i f t i n g p r o t o n s . S i n c e the r i n g c u r r e n t i s d i r e c t e d westward, the magnetic f i e l d i s d e p r e s s e d e a r t h w a r d of the c u r r e n t and enhanced o u t s i d e of i t . The magnetic e f f e c t s of the r i n g c u r r e n t can be mo n i t o r e d both a t geosynchronous o r b i t (L = 6.6) and a t e q u a t o r i a l ground s t a t i o n s (L = 1 ) . These r e c o r d s c l e a r l y show the magnetic f i e l d a t L = 6.6 becoming d e p r e s s e d e a r l i e r than a t the ground, and then r e c o v e r i n g t o near q u i e t time l e v e l s w h i l e the ground s t a t i o n s s t i l l show a s t r o n g l y d e p r e s s e d f i e l d . T h i s i n d i c a t e s t h a t the r i n g c u r r e n t i n i t i a l l y forms o u t s i d e L = 6.6, and t h e n , over the co u r s e of s e v e r a l h o u r s , moves inward d u r i n g the storm t o L < 6.6 ( N i s h i d a , 1978). T h i s r e s u l t i s a l s o s u p p o r t e d by the r i n g c u r r e n t o b s e r v a t i o n s and g e n e r a t i o n model of Lyons and W i l l i a m s (1980). On the n i g h t s i d e , the e f f e c t of the c r o s s - t a i l c u r r e n t f i e l d , which i s o p p o s i t e l y d i r e c t e d t o the r i n g c u r r e n t f i e l d o u t s i d e of the r i n g c u r r e n t , p r e v e n t s the magnetic f i e l d a t geosynchronous o r b i t from r i s i n g much above the q u i e t day l e v e l as the r i n g c u r r e n t moves i n s i d e L = 6.6. The magnetic f i e l d e f f e c t of t h i s c r o s s - t a i l c u r r e n t , i s , however, s m a l l compared t o the r i n g c u r r e n t f i e l d a t lower L (Kawasaki and A k a s o f u , 1971). T h e r e f o r e , i t i s the growth, movement, and decay of the r i n g c u r r e n t which 1 27 c o n t r o l s magnetic f i e l d changes i n the IPDP source r e g i o n , and i t i s t h e s e p r o c e s s e s which are examined i n o r d e r t o u n d e r s t a n d the r o l e of the i n c r e a s i n g background magnetic f i e l d f r e q u e n c y s h i f t mechanism. Though IPDPs u s u a l l y o ccur w i t h i n L = 6.6, geosynchronous s a t e l l i t e magnetograms, a l o n g w i t h the Dst index which r e f l e c t s the e f f e c t of the r i n g c u r r e n t magnetic f i e l d a t n e a r - e q u a t o r i a l ground s t a t i o n s (L = 1 ) , can be u s e f u l i n e s t i m a t i n g the magnetic f i e l d b e h a v i o u r i n the IPDP g e n e r a t i o n r e g i o n . As the r i n g c u r r e n t forms o u t s i d e L = 6.6, the f i e l d a t L = 6.6 w i l l be d e c r e a s i n g , though t h i s c u r r e n t may not y e t show up as a n e g a t i v e e x c u r s i o n of the ground-based Dst i n d e x . S i n c e the magnetic f i e l d i s e i t h e r d e c r e a s i n g or c o n s t a n t a t v i r t u a l l y a l l L's a t which an IPDP c o u l d be g e n e r a t e d , an event o c c u r r i n g a t t h i s time s h o u l d not take p l a c e d u r i n g an i n t e r v a l of i n c r e a s i n g magnetic f i e l d . T h e r e f o r e , the i n c r e a s i n g f i e l d mechanism c o u l d not account f o r the o b s e r v e d f r e q u e n c y r i s e of e v e n t s o c c u r r i n g under t h e s e c o n d i t i o n s . Even as the r i n g c u r r e n t moves e a r t h w a r d towards L = 6.6, the f i e l d a t the lower L's where most IPDPs a r e g e n e r a t e d s h o u l d not be i n c r e a s i n g and the above c o n c l u s i o n h o l d s t r u e here as w e l l . These t y p e s of c o n d i t i o n s were q u i t e l i k e l y i n e f f e c t f o r those 83% of h i g h l a t i t u d e IPDP e v e n t s which were observed by Bossen et a l . (1976) s i m u l t a n e o u s l y at the geosynchronous s a t e l l i t e ATS-1 1 28 and Tungsten, Northwest T e r r i t o r i e s , which i s near the same f i e l d l i n e as ATS-1, when the magnetic f i e l d a t ATS-1 was e i t h e r d e c r e a s i n g or c o n s t a n t ( c f . s e c t i o n 3.5). P a r t (a) of f i g u r e 40 shows a s k e t c h of the magnetic f i e l d changes t h a t would o c c u r as the r i n g c u r r e n t forms o u t s i d e L = 6.6; i n t h i s example, a t L = 7 . Note t h a t the changes from the p r e - r i n g c u r r e n t f o r m a t i o n l e v e l , r e p r e s e n t e d by the s o l i d l i n e l a b e l l e d tO i n f i g u r e 40, t o the p o i n t where the r i n g c u r r e n t has formed a t L — 7, shown by the dashed l i n e l a b e l l e d t 1 , are n e g a t i v e a t a l l L's on which IPDPs a r e commonly g e n e r a t e d . Though the diagrams i n f i g u r e 40 a r e o n l y s k e t c h e s r e p r e s e n t i n g a rough guide t o r i n g c u r r e n t magnetic f i e l d b e h a v i o u r , the p r o f i l e shapes f o l l o w a p p r o x i m a t e l y t h o s e c a l c u l a t e d by Kawasaki and A k a s o f u (1971) and Berko e t a l . (1975). I f the r i n g c u r r e n t has moved i n s i d e L = 6.6, i t becomes more d i f f i c u l t t o f o l l o w the magnetic f i e l d b e h a v i o u r i n the IPDP g e n e r a t i o n r e g i o n . In t h i s c a s e , an i n c r e a s i n g f i e l d a t geosynchronous o r b i t does not n e c e s s a r i l y imply an i n c r e a s i n g f i e l d everywhere E a r t h w a r d of L = 6.6. The r i s e a t L = 6.6 may s i m p l y be due t o b e i n g on the outward s i d e of the r i n g c u r r e n t , where the magnetic f i e l d i s r e c o v e r i n g back towards i t s normal l e v e l (see f i g . 40, p a r t ( b ) ) . Some l i g h t can s t i l l be shed on t h i s s i t u a t i o n w i t h the use of the Dst i n d e x , however. Note t h a t 129 ~5 E i_ o c CD <D _ N ~5 £ o c CD 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 0.2 0.0 -0,2 -0.4 -0.6 -0.8 -1.0 \ -to t1 • / / - A B \ - ( a ) i i 1 2 3 4 5 6 7 8 t2 •s _ N - A B / / \ / +AB A t 1 - (b) \ v. • "* -J 1 ~" 1 1 1 8 9) N £ o C m < FIGURE 40. Sk e t c h e s o u t l i n i n g the magnetic f i e l d changes d u r i n g r i n g c u r r e n t e v o l u t i o n , i n c l u d i n g the f o r m a t i o n ( a ) , the inward movement ( b ) , and the decay of the r i n g c u r r e n t ( c ) . The r e l a t i v e t imes of each of the AB p r o f i l e s a re l a b e l e d , w i t h t 0 < t 1 < t 2 < t 3 . The o v e r a l l time s c a l e f o r the magnetic f i e l d v a r i a t i o n s shown here i s g e n e r a l l y s e v e r a l hours t o s e v e r a l days, depending on the storm c o n d i t i o n s . The r e g i o n s where the magnetic f i e l d i s i n c r e a s i n g or d e c r e a s i n g d u r i n g each stage a r e a l s o l a b e l l e d . 130 the Dst index i s composed of h o u r l y v a l u e s , which i s a l s o the time s c a l e of many IPDP e v e n t s . T h i s does not pose a problem, however, because of the slow v a r i a t i o n of the r i n g c u r r e n t , the p r i m a r y source of l o n g e r term v a r i a t i o n s a t the lower L - s h e l l s (Kawasaki and A k a s o f u , 1971) on which most IPDPs a r e g e n e r a t e d , which makes h o u r l y i n t e r v a l s s u f f i c i e n t t o c h a r a c t e r i z e i t (Mayaud, 1980). I f o t h e r , s h o r t e r p e r i o d (<1 hour) magnetic f i e l d v a r i a t i o n s e x i s t , they c o u l d a d v e r s e l y a f f e c t t h i s type of IPDP a n a l y s i s , though magnetograms from geosynchronous o r b i t showed no v a r i a t i o n s of t h i s type l a r g e enough t o s i g n i f i c a n t l y a f f e c t IPDP f r e q u e n c y d u r i n g the events s t u d i e d . D i s c u s s e d below a r e f o u r p o s s i b l e Dst v e r s u s IPDP c a s e s i l l u s t r a t i n g magnetic f i e l d b e h a v i o u r i n the IPDP source r e g i o n d u r i n g d i f f e r e n t phases of r i n g c u r r e n t e v o l u t i o n . I. I f the Dst index i s p o s i t i v e , or n e g a t i v e but s t i l l near z e r o h a v i n g j u s t begun i t s stormtime d e c r e a s e , then i t i s l i k e l y t h a t the r i n g c u r r e n t i s c o m p a r a t i v e l y f u r t h e r out and i s s t i l l d e v e l o p i n g . An IPDP o c c u r r i n g a t t h i s time would most l i k e l y see a d e c r e a s i n g o r , i f a t low L where the c u r r e n t e f f e c t s a r e not yet s t r o n g l y f e l t , p o s s i b l y c o n s t a n t magnetic f i e l d . II. I f the Dst index i s w e l l i n t o i t s d e c r e a s e , then the r i n g c u r r e n t s h o u l d be f u r t h e r inward as w e l l . E q u a t o r i a l ground s t a t i o n s do not show a s t r o n g f i e l d 131 d e p r e s s i o n u n t i l the r i n g c u r r e n t has moved i n s i d e geosynchronous o r b i t (L = 6.6) ( N i s h i d a , 1978), and Lyons and W i l l i a m s (1980) a l s o i n f e r r i n g c u r r e n t inward motion as the Dst d e p r e s s i o n i s formed* IPDPs a t h i g h e r l a t i t u d e s , t h a t i s , h i g h e r L, would then be, i f the r i n g c u r r e n t has a l r e a d y moved pa s t t h e i r g e n e r a t i o n r e g i o n , i n an a r e a of i n c r e a s i n g magnetic f i e l d s t r e n g t h . Lower l a t i t u d e IPDPs would s t i l l see a d e c r e a s i n g f i e l d as the c u r r e n t d e v e l o p s and moves inward towards, but not p a s t , t h e i r magnetospheric source r e g i o n s . P a r t (b) of f i g u r e 40 shows the e f f e c t s of moving the r i n g c u r r e n t from L = 7 ( t l ) t o L = 5 ( t 2 ) , where the f i e l d d e p r e s s i o n reaches L = 1 i m p l y i n g t h a t the Dst index i s a l s o d e p r e s s e d . Between ti m e s t1 and t2 the magnetic f i e l d has r i s e n over the L range of 5 t o 7, p r o v i d i n g an i n c r e a s i n g f i e l d d u r i n g h i g h L IPDPs, and dropped f o r L < 5, showing a d e c r e a s i n g f i e l d t o any IPDPs g e n e r a t e d w i t h i n t h i s range. III. I f the Dst index has completed i t s drop and i s r e l a t i v e l y s t a b l e , t h a t i s , the index changes r e l a t i v e l y l i t t l e d u r i n g the event and any s m a l l changes which do o c c u r are not p a r t of a g e n e r a l i n c r e a s i n g or d e c r e a s i n g t r e n d , then the magnetic f i e l d w i l l be e s s e n t i a l l y c o n s t a n t i n a l l r e g i o n s dominated by the r i n g c u r r e n t . IV. I f the Dst index i s undergoing a g e n e r a l r e c o v e r y back towards q u i e t time l e v e l s , then the f i e l d , which has 1 32 been s e v e r e l y d e p r e s s e d out t o L =* 5-6, w i l l be r i s i n g i n the IPDP g e n e r a t i o n r e g i o n . T h i s i s i l l u s t r a t e d i n p a r t (c) of f i g u r e 40. As the r i n g c u r r e n t weakens between ti m e s t2 and t 3 , the magnetic f i e l d r e c o v e r s towards q u i e t time l e v e l s a t a l l a f f e c t e d L s h e l l s , i n c l u d i n g the Dst index a t ground l e v e l (L = 1). F i g u r e 41 demonstrates t h e s e f o u r c a s e s , p l u s the i n i t i a l r i n g c u r r e n t f o r m a t i o n phase, i n d i c a t i n g the f i e l d b e h a v i o u r a t the ground (Dst) and a t f o u r L s h e l l s as the r i n g c u r r e n t forms, moves inw a r d , and decays. T h i s f i g u r e s h o u l d be r e g a r d e d o n l y as an approximate and q u a l i t a t i v e guide t o r i n g c u r r e n t magnetic f i e l d b e h a v i o u r . F i e l d p r o f i l e s r e l e v a n t t o i n d i v i d u a l s i t u a t i o n s may v a r y t o some degree from t h e s e c a s e s . A l s o , the d i v i s i o n s among the case t y p e s a r e o n l y r o u g h l y d e f i n e d , and i n t e r p o l a t i o n between the s e d e s c r i b e d s i t u a t i o n s would be n e c e s s a r y f o r a f u l l u n d e r s t a n d i n g of a l l magnetic f i e l d b e h a v i o u r p a t t e r n s p o s s i b l e d u r i n g IPDP e v e n t s . I t must be emphasized t h a t t h i s system of s o r t i n g IPDP e v e n t s i n t o these c a s e s i s i n t e n d e d f o r r e s e a r c h c o n v e n i e n c e o n l y , and does not i n d i c a t e any fundamental d i f f e r e n c e s i n IPDPs a c r o s s case b o u n d a r i e s . In each of the ca s e s I th r o u g h IV above, the magnetic f i e l d a t geosynchronous o r b i t w i l l be seen t o be i n c r e a s i n g or c o n s t a n t ( c f . f i g . 4 1 ) , y e t o n l y i n ca s e s I I and IV i s i t p o s s i b l e t h a t the f i e l d i n an IPDP's g e n e r a t i o n r e g i o n i s RING CURRENT FIELD F I II III IV L SHELL 5 \ \ , > > / * 6.6 \ / / (geosynchronous orbit) F. ring current forming I. moving inward (early stage) II. moving inward (later stage) III. static IV. ring current decaying FIGURE 4 1 . R i n g c u r r e n t r e l a t e d magnetic f i e l d b e h a v i o u r i n the IPDP g e n e r a t i o n r e g i o n . The s l o p e of the arrows i n d i c a t e s whether the f i e l d i s d e c r e a s i n g , c o n s t a n t , or i n c r e a s i n g a t each L s h e l l f o r each c a s e . Case F i s the r i n g c u r r e n t f o r m a t i o n a l phase, and ca s e s I through IV c o r r e s p o n d t o th o s e d i s c u s s e d i n the t e x t . 1 34 a c t u a l l y r i s i n g as w e l l , t h e r e b y c o n t r i b u t i n g t o the e v e n t ' s f r e q u e n c y r i s e . T h i s c l e a r l y d emonstrates the u n r e l i a b i l i t y of u s i n g geosynchronous s a t e l l i t e magnetograms a l o n e f o r a s s e s s i n g the i n c r e a s i n g f i e l d mechanism f o r IPDP freq u e n c y s h i f t s , as has p r e v i o u s l y been done, u n l e s s the secondary s o u r c e s of the events c o n s i d e r e d a r e a t v e r y h i g h l a t i t u d e , t h a t i s , near 67° GM L a t . or L = 6.6 (geosynchronous o r b i t ) . F i g u r e 42 i s a p l o t of Dst v e r s u s IPDP o c c u r r e n c e f o r the p e r i o d of January 15 t o F e b r u a r y 25, 1980. Ten IPDPs o c c u r r e d d u r i n g t h i s p e r i o d , i n c l u d i n g examples of a l l of the f o u r c a s e s d e s c r i b e d above. F i g u r e 43 shows a sample of each of t h e s e cases w i t h an expanded s c a l e . Even w i t h o u t f u r t h e r a n a l y s i s i t i s o b v i o u s t h a t an i n c r e a s i n g magnetic f i e l d cannot be c o n s i d e r e d a n e c e s s a r y c o n d i t i o n f o r IPDP frequ e n c y s h i f t s t o o c c u r , because of the e x i s t e n c e of case I and I I I e v e n t s . The case IV e v e n t s make i t e q u a l l y o b v i o u s , however, t h a t t h e r e a r e s i t u a t i o n s where the i n c r e a s i n g f i e l d mechanism can c o n t r i b u t e t o the IPDP frequ e n c y r i s e . 5.2.2. Individual IPDP Event Assessments U s i n g the f o u r e v e n t s from f i g u r e 43, a more d e t a i l e d d i s c u s s i o n of i n d i v i d u a l IPDP e v e n t s , which e x e m p l i f y each of the f o u r IPDP v e r s u s Dst c a s e s d e s c r i b e d above, f o l l o w s . Feb. 14 Event. The IPDP of Feb. 14 (event no. 6, 135 O'Sfr O'O O'St?- 0 '06- 0 ' 9 G l -(UNNdO) i s a FIGURE 42. IPDP o c c u r r e n c e v e r s u s the Dst index f o r the p e r i o d January 15.to F e b r u a r y 25, 1980. IPDPs occur i n a l l phases of the r i n g c u r r e n t development and decay c y c l e . The IPDP events a r e numbered as l i s t e d i n T a b l e IV (Chapter Two). 1 36 UT (h) UT (h) FIGURE 43. Examples of each of the f o u r IPDP v e r s u s Dst cases i n l a r g e r s c a l e ; a ) c a s e I ; Feb. 14 e v e n t , b) case I I ; Feb. 15 ev e n t , c) case I I I ; J a n . 29 e v e n t , and d) case IV; Feb. 24c event. The IPDP events o c c u r r e d i n the i n t e r v a l s marked by the boxes. 1 37 f i g . 42) i s an example of a case I e v e n t , as are two o t h e r e v e n t s , J a n . 28 and Feb. 24b. In f i g u r e 44, i t can be seen t h a t the Dst index i s above z e r o f o r most of the IPDP e v e n t , b e g i n n i n g t o f a l l i n t o i t s l a r g e r i n g c u r r e n t c r e a t e d n e g a t i v e d e p r e s s i o n o n l y near the e v e n t ' s end (see Appendix C f o r a d i s c u s s i o n of the Dst z e r o l e v e l ) . Meanwhile, the f i e l d ( t o t a l f i e l d s t r e n g t h ) a t geosynchronous o r b i t i s r i s i n g t h roughout the IPDP e v e n t . T h i s c o m b i n a t i o n , a c c o r d i n g t o f i g u r e 41, i n d i c a t e s a case I event w i t h the r i n g c u r r e n t l o c a t e d j u s t e a r t h w a r d of L = 6.6 and not y e t w e l l d e v e l o p e d a t lower L s h e l l s . Ground based o b s e r v a t i o n s of t h i s event i n d i c a t e t h a t i t was g e n e r a t e d w i t h i n the L range of 4 t o 4y ( c f . s e c t i o n 5.1), which i s most l i k e l y w i t h i n the d e c r e a s i n g f i e l d regime f o r a case I event ( c f . f i g . 41). For an event a t t h i s low L t o see a r i s i n g magnetic f i e l d , the r i n g c u r r e n t would have t o be a t v e r y low L, such as L < 4y, and moving inw a r d , which would c r e a t e a l a r g e Dst d e p r e s s i o n . R e c a l l t h a t f i g u r e 40b, w i t h the r i n g c u r r e n t moving i n t o L ^ 5, showed AB t o be s t i l l n e g a t i v e a t L = 4 - 4y w h i l e a l s o i n d i c a t i n g a s i g n i f i c a n t f i e l d d e p r e s s i o n a t ground l e v e l ( D s t ) . S i n c e such a d e p r e s s i o n i s not p r e s e n t d u r i n g t h i s IPDP, i t i s e v i d e n t t h a t the i n c r e a s i n g f i e l d mechanism does not c o n t r i b u t e t o the f r e q u e n c y r i s e of t h i s e v e n t . I t i s even p o s s i b l e t h a t the background magnetic f i e l d i s 1 38 FIGURE 44. D s t p r o f i l e a n d G O E S 2 m a g n e t b g r a m ( " t o t a l f i e l d s t r e n g t h , B T ) f o r t h e F e b . 14 I P D P , w i t h t h e ' I P D P o c c u r r e n c e t i m e i n d i c a t e d b y t h e b o x . T h i s i s a c a s e I e v e n t . 1 39 d e c r e a s i n g a l i t t l e i n the IPDP source r e g i o n , a c t u a l l y s u p r e s s i n g the f r e q u e n c y r i s e s l i g h t l y , though due t o the low L t h i s i s u n l i k e l y t o be a s i g n i f i c a n t e f f e c t f o r t h i s e v e n t. Feb. 15 Event. Case I I i s a l s o seen i n t h r e e e v e n t s ; J a n . 16, J a n . 23, and Feb. 15 (event no. 7, f i g . 42). F i g u r e 45 shows the Dst index and geosynchronous s a t e l l i t e magnetograms f o r the Feb. 15 e v e n t . Here, both the Dst and magnetogram a r e s t r o n g l y d e p r e s s e d , though the magnetogram shows the b e g i n n i n g of a f i e l d r e c o v e r y a t L = 6.6 w h i l e the Dst c o n t i n u e s t o d r o p . T h i s s i t u a t i o n i m p l i e s a case I I e v e n t , w i t h the r i n g c u r r e n t f u r t h e r i n than the case I event d i s c u s s e d above. Note t h a t the magnetogram i s c o m p l i c a t e d by the onset of a second substorm d u r i n g the IPDP as shown by the Great Whale R i v e r X-component magnetogram i n f i g u r e 46. T h i s second substorm causes the magnetic f i e l d a t L = 6.6 t o b e g i n d r o p p i n g a g a i n a f t e r o n l y a s l i g h t r e c o v e r y s i n c e the r i n g c u r r e n t i s s t r e n g t h e n e d o u t s i d e L = 6.6 i n the e a r l y phase of the substorm ( N i s h i d a , 1978). I t s h o u l d be noted t h a t the o c c u r r e n c e of the second substorm makes the p r o p e r case assignment l e s s o b v i o u s f o r t h i s e v e n t , though s i n c e the s i t u a t i o n began as a t y p i c a l case I I type b e f o r e the c o m p l i c a t i o n s o c c u r r e d , t h i s (case I I ) assignment has been made. 1 40 FIGURE 45. Dst p r o f i l e and GOES 2 magnetogram f o r the Feb. 15 IPDP, w i t h the IPDP o c c u r r e n c e time i n d i c a t e d by the box. T h i s i s a case I I event. 141 10400 9800 ' 1 1 1 '— 1 1 1 1 16 18 20 22 24 UT (h) FIGURE 46. X component magnetogram from Great Whale R i v e r , 1600 -2400 UT, F e b r u a r y 1 5 , 1980. Note the onset of a second substorm d u r i n g the IPDP e v e n t . 1 42 The Feb. 15 IPDP was g e n e r a t e d w i t h i n the L range of 4.1 t o 4.8 ( c f . sec. 5.1). In t h i s s i t u a t i o n , however, w i t h the r i n g c u r r e n t a t lower L (case I I e v e n t , c f . f i g . 40, 41) , i t i s v e r y d i f f i c u l t t o e s t i m a t e the magnetic f i e l d b e h a v i o u r i n the IPDP g e n e r a t i o n r e g i o n , and t h e r e f o r e the e f f e c t i v e n e s s of the i n c r e a s i n g f i e l d mechanism, w i t h o u t h a v i n g f u r t h e r d a t a on the r i n g c u r r e n t d i s t r i b u t i o n . I f the r i n g c u r r e n t i s a t v e r y low L, i t i s p o s s i b l e t h a t the magnetic f i e l d i s i n c r e a s i n g i n the IPDP sou r c e r e g i o n , though i t i s more p r o b a b l e ( c f . f i g . 41) t h a t the magnetic f i e l d i s d e c r e a s i n g or c o n s t a n t d u r i n g t h i s IPDP. In any c a s e , the Feb. 15 IPDP i s v e r y s h o r t , w i t h o n l y a 16 minute i n t e r v a l s t u d i e d i n d e t a i l , and any magnetic f i e l d changes i n t h i s b r i e f time are l i k e l y t o be q u i t e s m a l l , m i n i m i z i n g the e f f e c t of the i n c r e a s i n g f i e l d mechanism. J a n . 29 Event. The o n l y event observed t h a t q u a l i f i e d as a case I I I IPDP o c c u r r e d on J a n . 29 (event no. 5, f i g . 42) . Both the Dst and geosynchronous s a t e l l i t e magnetograms were s t r o n g l y d e p r e s s e d and had not y e t begun t h e i r g e n e r a l r e c o v e r y phases. S i n c e they were each r e l a t i v e l y s t a b l e (see f i g . 4 7 ) , the f i e l d i n the IPDP g e n e r a t i o n r e g i o n s h o u l d have been s i m i l a r l y s t a b l e . T h e r e f o r e the i n c r e a s i n g f i e l d mechanism c o u l d not be r e s p o n s i b l e f o r t h i s IPDP's f r e q u e n c y r i s e . Feb. 24c Event. Three e v e n t s , J a n . 27, Feb. 24a, and 143 FIGURE 47. Dst p r o f i l e and GOES 3 magnetogram f o r the J a n . 29 IPDP, w i t h the IPDP o c c u r r e n c e time i n d i c a t e d by the box. T h i s i s a case I I I e v e n t . 1 44 Feb. 24c (event no. 10, f i g . 4 2 ) , o c c u r r e d when Dst i s r i s i n g back towards z e r o . The t h i r d of the t h r e e IPDPs r e c o r d e d on Feb. 24, event Feb. 24c, i s shown i n f i g u r e 48, a l o n g w i t h i t s c o r r e s p o n d i n g Dst i n d i c e s and geosynchronous s a t e l l i t e magnetogram. The r e c o v e r i n g Dst and geosynchronous magnetic f i e l d i n d i c a t e a case IV e v e n t . The magnetic f i e l d s h o u l d then a l s o be i n c r e a s i n g i n the IPDP g e n e r a t i o n r e g i o n . T h e r e f o r e , f o r t h i s e v ent, the i n c r e a s i n g f i e l d mechanism s h o u l d c o n t r i b u t e t o the IPDP f r e q u e n c y s h i f t . Of the i n d i v i d u a l e v e n t s d i s c u s s e d above, o n l y the Feb. 24c event shows good i n d i c a t i o n t h a t the i n c r e a s i n g f i e l d mechanism c o n t r i b u t e s t o i t s f r e q u e n c y r i s e . The q u e s t i o n i s how much of t h i s e v e n t ' s f r e q u e n c y r i s e i s a t t r i b u t a b l e t o t h i s mechanism? In o r d e r t o a s c e r t a i n t h i s , we must know the L s h e l l of both the IPDP g e n e r a t i o n r e g i o n and the r i n g c u r r e n t . The secondary source p o s i t i o n c o u l d not be de t e r m i n e d f o r t h i s event ( c f . s e c t i o n 5.1), however, the p o l a r i z a t i o n spectrograms from PG (L - 3.9), f i r s t r i g h t - h a n d and then l e f t - h a n d at the v e r y end of the e v e n t , i n d i c a t e t h a t most of the event o c c u r r e d t o the n o r t h of the s t a t i o n (L 4 + ? ) . Though the p r e c i s e d i s t r i b u t i o n of the r i n g c u r r e n t d u r i n g t h i s IPDP i s unknown, models such as t h a t of Kawasaki and A k a s o f u (1971), and measurements (Berko et a l . , 1975), show t h a t t h i s p o s i t i o n i s near the p o i n t of the g r e a t e s t magnetic f i e l d d e p r e s s i o n of a t y p i c a l r i n g 145 FIGURE 48. Dst p r o f i l e and GOES 3 magnetogram f o r the Feb. 24c IPDP, w i t h the IPDP o c c u r r e n c e time i n d i c a t e d by the box. T h i s i s a case IV event. 1 46 c u r r e n t . T h i s demonstrates t h a t the f i e l d r e c o v e r y i n the IPDP g e n e r a t i o n r e g i o n has the p o t e n t i a l t o be q u i t e l a r g e . For t h i s e v e n t , though, the s m a l l Dst d e p r e s s i o n i n d i c a t e s t h a t the r i n g c u r r e n t may have been weaker and/or f u r t h e r out than normal. Note t h a t W i l l i a m s (1985) showed t h a t the amount of Dst d e p r e s s i o n i s r e l a t e d t o r i n g c u r r e n t p a r t i c l e f l u x , and Lyons and W i l l i a m s (1980) i n d i c a t e d t h a t o n l y l a r g e storms have s i g n i f i c a n t r i n g c u r r e n t f l u x e s a t lower L's. T h i s s i t u a t i o n i n d i c a t e s a c o r r e s p o n d i n g l y s m a l l e r f i e l d r e c o v e r y i n the IPDP g e n e r a t i o n r e g i o n . I f a v a l u e f o r the f i e l d d e p r e s s i o n a t L = 4 of - I O O 7 were chosen f o r t h i s e v e n t , then the f i e l d r e c o v e r y i n the IPDP g e n e r a t i o n r e g i o n c o u l d be c r u d e l y e s t i m a t e d . Note t h a t t h i s f i e l d d e p r e s s i o n v a l u e i s p r o b a b l y an o v e r e s t i m a t e f o r t h i s weak D s t ; Berko et a l . , (1975) obse r v e d v a l u e s of - 1 2 O 7 near L = 3 T and - I O O 7 near L = 4 f o r a Dst of - 8 O 7 . The magnetic f i e l d r e c o v e r y d u r i n g the IPDP can be gauged from the degree of r e c o v e r y back towards t h e i r q u i e t time l e v e l s of the f i e l d a t geosynchronous o r b i t , r o u g h l y - 6 5 7 t o - 4 5 7 , or =30%, and of the Dst i n d e x , r o u g h l y - 2 O 7 t o - 1 6 7 , or =20%. The f i e l d a t L = 4 would most l i k e l y r e c o v e r by a s i m i l a r p r o p o r t i o n d u r i n g t h i s t i m e , assuming t h a t the r i n g c u r r e n t changes o n l y i n s t r e n g t h and not i n s p a t i a l d i s t r i b u t i o n . Assuming E a r t h ' s magnetic f i e l d t o be d i p o l a r , i t s s t r e n g t h i n q u i e t t i m e s a t L = 4 s h o u l d be: 1 47 B B 0 = - 4 8 4 7 ( 5 . 4 ) . U s i n g the - I O O 7 d e p r e s s i o n d i s c u s s e d above and a 30% r e c o v e r y e s t i m a t e , the magnetic f i e l d i n the g e n e r a t i o n r e g i o n s h o u l d then r i s e from 3847 t o 4147 d u r i n g the IPDP. U s i n g e q u a t i o n 4.6 from s e c t i o n 4.2.2, the f r e q u e n c y s h i f t can then be e s t i m a t e d a s : For t h i s e v e n t , however, the a c t u a l v a l u e i s f y / f j = 2.62. Thus, i n t h i s crude e s t i m a t e , the i n c r e a s i n g f i e l d mechanism acco u n t e d f o r o n l y -7% of the t o t a l f r e q u e n c y r i s e f o r t h i s IPDP. Though the f i e l d r e c o v e r y f i g u r e s used f o r t h i s e s t i m a t e a r e o n l y v e r y rough e s t i m a t e s , i t i s v e r y u n l i k e l y t h a t they c o u l d be a l t e r e d enough t o account f o r a l a r g e p r o p o r t i o n of the f r e q u e n c y s h i f t o bserved h e r e . I n c r e a s i n g the i n i t i a l d e p r e s s i o n t o -1507 and the r e c o v e r y f a c t o r t o 50% would s t i l l o n l y y i e l d 22% of the o b s e r v e d f r e q u e n c y r i s e . Note t h a t here the f r e q u e n c y r i s e r e f e r e d t o i s a r e l a t i v e f r e q u e n c y r i s e from 1 ( i . e . i./i.) t o f , / f .. f. L 3847 . 5 = 1.12 ( 5 . 5 ) . 1 48 5.2.3. Ring Current and Inward Motion Mechanism The c a l c u l a t i o n s p r e s e n t e d above f o r the i n c r e a s i n g magnetic f i e l d e f f e c t on the Feb. 24c event assume t h a t the IPDP sou r c e r e g i o n i s a t c o n s t a n t L ( c f . s e c t i o n 4.2.2). However, the p a t t e r n of p o l a r i z a t i o n v a r i a t i o n s (see above) i n d i c a t e s t h a t t h i s i s not the t r u e s i t u a t i o n . T h e r e f o r e , i n a d d i t i o n t o the i n c r e a s i n g f i e l d mechanism, i t i s a l s o n e c e s s a r y t o c o n s i d e r the e f f e c t of the d e p r e s s e d magnetic f i e l d environment i n the IPDP sou r c e r e g i o n on the inward motion f r e q u e n c y s h i f t mechanism. The e x a m i n a t i o n of the f r e q u e n c y e f f e c t of the inward motion mechanism under these c o n d i t i o n s shows t h a t t h e r e i s another manner i n which the r i n g c u r r e n t magnetic f i e l d can a f f e c t an IPDP's f r e q u e n c y r i s e independent of t e m p o r a l changes i n the r i n g c u r r e n t . I f the r i n g c u r r e n t i s i n a s t a t e such t h a t i t s magnetic f i e l d d e p r e s s e s the background magnetic f i e l d , t h i s f i e l d d e p r e s s i o n w i l l c r e a t e a h i g h e r magnetic f i e l d s t r e n g t h r a t i o B y / B j - than normal f o r a d i p o l a r c o n f i g u r a t i o n . T h i s then s e r v e s t o i n c r e a s e the f r e q u e n c y s h i f t e f f e c t due t o the inward motion mechanism, as i s i l l u s t r a t e d below. For the purpose of d i s c u s s i o n o n l y , we can assume r e a s o n a b l e c h o i c e s f o r the amount of source inward movement, from, say, L = 4.5 t o 3.9 d u r i n g the Feb. 24c IPDP. In the absence of any r i n g c u r r e n t e f f e c t s ( f i e l d d e p r e s s i o n s ) , t h i s motion would y i e l d , from e q u a t i o n 4.5, f f / i . = 1.90. 1 49 F u r t h e r , we can assume a f i e l d d e p r e s s i o n of -8O7 a t L = 4.5 and -IOO7 a t L = 3.9 and a r e c o v e r y f a c t o r of 25% d u r i n g the IPDP. A g a i n , t h e s e a re r e a s o n a b l e c h o i c e s made f o r the sake of d i s c u s s i o n o n l y . U s i n g t h e s e v a l u e s , the inward motion mechanism, i n the dep r e s s e d f i e l d environment (but w i t h no f i e l d r e c o v e r y ) , would produce a fre q u e n c y r i s e as f o l l o w s (from e q u a t i o n 4.6): Ll. f . 1 where 5237 and 34O7 are the d i p o l a r f i e l d s t r e n g t h s (from e q u a t i o n 5.4) a t 3.9L and 4.5L, r e s p e c t i v e l y , and 1OO7 and 8O7 are the f i e l d d e p r e s s i o n s d i s c u s s e d above. T h i s i s an i n c r e a s e of 20% over the case w i t h no r i n g c u r r e n t e f f e c t s , d e m o n s t r a t i n g t h a t , even w i t h no te m p o r a l changes i n the r i n g c u r r e n t f i e l d d u r i n g an IPDP, i t i s s t i l l p o s s i b l e f o r the r i n g c u r r e n t t o have an im p o r t a n t e f f e c t on an IPDP's f r e q u e n c y r i s e , and i t t h e r e f o r e cannot be i g n o r e d . F i n a l l y , t he combined e f f e c t of the i n c r e a s i n g magnetic f i e l d mechanism, u s i n g the 25% r e c o v e r y f a c t o r , and the inward motion mechanism would y i e l d t he f o l l o w i n g f r e q u e n c y r i s e : (523-100)7 (340-80)7 1 . 5 = 2.08 (5.6a) 1 50 " (523-75)7 " (340-80)7 . . 5 = 2.26 ( 5 . 6 b ) . T h i s i s o n l y a 17% i n c r e a s e i n the f r e q u e n c y r i s e over the inward motion o n l y case d i s c u s s e d above ( e q u a t i o n 5.6a). W h i l e some of the numbers used here r e p r e s e n t assumptions o n l y and may bear l i t t l e r e l a t i o n t o the a c t u a l parameters c o n c e r n i n g t h i s IPDP, parameters f o r which we have i n s u f f i c i e n t i n f o r m a t i o n t o p r o p e r l y d e t e r m i n e , they cannot be r e a s o n a b l y a l t e r e d t o produce a s i g n i f i c a n t l y l a r g e r i n c r e a s i n g f i e l d mechanism c o n t r i b u t i o n . T h e r e f o r e , whether the IPDP g e n e r a t i o n r e g i o n i s ' assumed t o be s t a t i o n a r y or no t , the i n c r e a s i n g f i e l d mechanism makes o n l y a r e l a t i v e l y minor c o n t r i b u t i o n t o the f r e q u e n c y r i s e of the Feb. 24c IPDP. In s e c t i o n 5.1 i t was shown t h a t , f o r both the Feb. 14 and Feb. 15 IPDPs, the inward motion mechanism was i n s u f f i c i e n t t o account f o r the obse r v e d f r e q u e n c y r i s e of the IPDPs. Here, i t has a l s o been demonstrated t h a t the i n c r e a s i n g f i e l d mechanism makes o n l y a minor, i f any, c o n t r i b u t i o n t o the f r e q u e n c y s h i f t s of t h e s e e v e n t s ( c f . s e c t i o n 5.2.2). However, the p o s s i b l e e f f e c t s of the r i n g c u r r e n t c r e a t e d magnetic f i e l d d e p r e s s i o n on the inward motion mechanism's f r e q u e n c y s h i f t c o n t r i b u t i o n t o these 151 events must s t i l l be c o n s i d e r e d . For the Feb. 14 event t h i s r i n g c u r r e n t e f f e c t i s l i k e l y t o be s m a l l s i n c e the r i n g c u r r e n t i s p r o b a b l y not yet w e l l d e v e l o p e d i n the source r e g i o n L s h e l l s . The c u r r e n t i s r e l a t i v e l y weak i n any c a s e , as i s demonstrated by the f a c t t h a t the maximum f i e l d d e p r e s s i o n s o b s e r v e d d u r i n g the e n t i r e magnetospheric storm p e r i o d a r e o n l y - 5 O 7 a t L = 6.6 and o n l y - 3 5 t a t L = 1 ( D s t ) . C a l c u l a t i o n s s i m i l a r t o t h a t of e q u a t i o n 5.6a show t h a t a u n i f o r m f i e l d d e p r e s s i o n of —115-y would be n e c e s s a r y i n o r d e r t o enhance the inward motion produced f r e q u e n c y s h i f t s u f f i c i e n t l y t o account f o r the e n t i r e f r e q u e n c y r i s e of t h i s e v e nt. Such d e p r e s s i o n s a r e v e r y u n l i k e l y t o be p r e s e n t i n such a case I event g e n e r a t e d a t low L ( c f . s e c t i o n 5.2.1). Even w i t h a c o n s t a n t f i e l d d e p r e s s i o n of - 5 O 7 i n the g e n e r a t i o n r e g i o n , p r o b a b l y s t i l l much l a r g e r than would be r e a l i s t i c , the inward motion mechanism c o u l d account f o r o n l y ^77% of the IPDP's o v e r a l l f r e q u e n c y r i s e , as opposed t o =*66% w i t h no r i n g c u r r e n t induced magnetic f i e l d d e p r e s s i o n . I t has a l r e a d y been noted t h a t d u r i n g the Feb. 15 event the magnetic f i e l d s t r e n g t h i s u n l i k e l y t o change much a t c o n s t a n t L. I t w i l l , however, be s t r o n g l y d e p r e s s e d i n the IPDP sou r c e r e g i o n , as i n d i c a t e d by the s t r o n g Dst d e p r e s s i o n ( c f . f i g . 45) and the form of t y p i c a l r i n g c u r r e n t f i e l d p r o f i l e s ( c f . f i g . 40, a l s o Kawasaki and 152 A k a s o f u , 1971; Berko e t a l . , 1975). I t has been found t h a t a s o u r c e r e g i o n f i e l d d e p r e s s i o n of -1057 would be n e c e s s a r y t o enhance the inward motion produced f r e q u e n c y r i s e so t h a t i t would best match the observed r i s e of t h i s IPDP. A f i e l d d e p r e s s i o n of t h i s magnitude i s q u i t e p o s s i b l e f o r t h i s event (see above), though i t cannot be d i r e c t l y c o n f i r m e d by o b s e r v a t i o n . However, the d e p r e s s i o n s h o u l d be g r e a t e r than the Dst d e p r e s s i o n of = - 5 5 7 . U s i n g t h i s - 5 5 7 v a l u e as a lower l i m i t on the source r e g i o n f i e l d d e p r e s s i o n , the enhanced inward motion mechanism f r e q u e n c y s h i f t can account f o r >75% of the IPDP's o v e r a l l f r e q u e n c y r i s e , compared t o =60% w i t h no r i n g c u r r e n t f i e l d i n f l u e n c e . F i g u r e 49 compares the r e a l f r e q u e n c y r i s e t o those enhanced inward motion c r e a t e d f r e q u e n c y s h i f t s c a l c u l a t e d f o r source r e g i o n magnetic f i e l d d e p r e s s i o n s of -1057 and - 5 5 7 . 5.2.4. Discussion of Ring Current Ef f e c t s on IPDPs A much l a r g e r number of IPDPs must be s t u d i e d i n o r d e r t o g a i n a c l e a r e r p i c t u r e of the p r o p o r t i o n of e v e n t s t o which the i n c r e a s i n g f i e l d mechanism i s i m p o r t a n t . Here, based on the IPDP - r i n g c u r r e n t c l a s s i f i c a t i o n scheme d i s c u s s e d i n s e c t i o n 5.2.1, t h i s mechanism may have c o n t r i b u t e d t o the f r e q u e n c y r i s e of between t h r e e , the c l a s s IV e v e n t s , and s i x , the c l a s s I I and IV e v e n t s , of the te n IPDPs s t u d i e d , w i t h the c o n t r i b u t i o n b e i n g e i t h e r s m a l l 153 2.4 ^ 2 - 2 <D 2.0 o E o 1.8 >s 1.6 o •c 3 1 4 <u 1.2 1.0 observed frequency AB=-557 AB=0y A B = - 1 0 5 r 21.6 21.8 22.0 UT (h) 22.2 22.4 FIGURE 49. F e b r u a r y 15 IPDP: o b s e r v e d f r e q u e n c y r i s e and enhanced inward motion r i s e s w i t h magnetic f i e l d d e p r e s s i o n s - ( A B ) of O7 (no r i n g c u r r e n t ) , - 5 5 7 , and - 1 0 5 7 . T h i s f i g u r e a l s o c l e a r l y demonstrates how even s t a t i c r i n g c u r r e n t i n d u c e d f i e l d d e p r e s s i o n s can a f f e c t IPDP f r e q u e n c y s h i f t s . 1 54 (Feb. 24c event) or unknown. The s m a l l c o n t r i b u t i o n of the i n c r e a s i n g f i e l d mechanism to the frequency s h i f t of the Feb. 24c event i s a t l e a s t p a r t i a l l y due t o i t s low L and weak r i n g c u r r e n t , however. I t i s c l e a r , though, t h a t the i n c r e a s i n g background magnetic f i e l d mechanism i s not r e q u i r e d i n o r d e r t o produce IPDP f r e q u e n c y s h i f t s . For the two IPDPs b e i n g s t u d i e d i n d e t a i l , the Feb. 14 and Feb. 15 e v e n t s , the i n c r e a s i n g f i e l d mechanism has been shown t o have o n l y a v e r y minor i n f l u e n c e , i f any a t a l l . For t h e s e e v e n t s , the magnitude of the r i n g c u r r e n t induced f i e l d i s more i m p o r t a n t than i t s changes. Though t h i s e f f e c t i s r e l a t i v e l y minor i n the Feb. 14 IPDP, r a i s i n g the inward motion mechanism's c o n t r i b u t i o n t o <77% from =66%, i t may be an i m p o r t a n t f a c t o r i n e x p l a i n i n g the Feb. 15 e v e n t , a l l o w i n g the inward motion mechanism t o account f o r >75%, and p o s s i b l y up t o 100%, of the f r e q u e n c y r i s e . W i t h r e s p e c t t o these two IPDPs, however, the c o n c l u s i o n i s t h a t we must l o o k s t i l l f u r t h e r than the inward motion and i n c r e a s i n g f i e l d mechanisms i n o r d e r t o f u l l y u n d e r s t a n d the e n t i r e f r e q u e n c y s h i f t s of these e v e n t s . 1 55 5.3. AZIMUTHAL DRIFT EFFECTS ON IPDP FREQUENCY EVOLUTION The t h i r d of the t h r e e IPDP f r e q u e n c y s h i f t mechanisms c o n s i d e r e d i n t h i s t h e s i s i s the a z i m u t h a l d r i f t e f f e c t ( c f . s e c t i o n 4.2.3). From s e c t i o n 5.2, i t i s e v i d e n t t h a t c o n t r i b u t i o n s from t h i s mechanism are r e q u i r e d by a t l e a s t one, and p o s s i b l y b o t h , of the IPDPs s t u d i e d i n o r d e r t o f u l l y account f o r t h e i r f r e q u e n c y s h i f t s . T h i s s e c t i o n w i l l then examine the e f f e c t s of the a z i m u t h a l d r i f t mechanism on the Feb. 14 and Feb. 15 IPDPs. A n a l y s i s of the a z i m u t h a l d r i f t mechanism's e f f e c t r e q u i r e s a knowledge of the e v o l u t i o n of the e n e r g i e s of the p r o t o n s i n v o l v e d i n the i o n - c y c l o t r o n i n s t a b i l i t y i n the IPDP magnetospheric source r e g i o n above a ground s t a t i o n ' s m e r i d i a n . E q u a t i o n 4.3 ( s e c t i o n 4.1) shows t h a t i n o r d e r t o deter m i n e the energy (W) of the i n t e r a c t i n g p r o t o n s , both L and the p r o t o n d r i f t v e l o c i t y ( v^) must be known. Though the L v a l u e s were d e t e r m i n e d i n s e c t i o n 5.1, v^ i s unknown, and cannot be c a l c u l a t e d w i t h o u t the time and p o s i t i o n of the i n j e c t i o n boundary f o r m a t i o n b e i n g known. The time of f o r m a t i o n can be e s t i m a t e d from a u r o r a l - z o n e ground s t a t i o n magnetograms (see b e l o w ) , but the boundary shape remains unknown. Note t h a t the s t a t i s t i c a l r e l a t i o n d e s c r i b i n g i n j e c t i o n boundary shape p r e s e n t e d i n s e c t i o n 4.1 ( e q u a t i o n 4.1) c a n n o t , i n the form g i v e n , be f i t s a t i s f a c t o r a l l y i n t o the d e s c r i p t i o n of the IPDP e v e n t s c o n s i d e r e d h e r e . T h i s i s 156 e s p e c i a l l y t r u e i n the case of the Feb. 14 ev e n t , s i n c e the boundary shape produced would not rea c h t o low enough L t o form the event as observ e d ( f o r example, see f i g . 55 ( b o t t o m ) ) . C o n s e q u e n t l y , a method by which the boundary p o s i t i o n and t h e r e f o r e the p r o t o n energy can be e s t i m a t e d f o r each IPDP i s r e q u i r e d . Such a method i s d e s c r i b e d - b e l o w . S i n c e i t was shown i n s e c t i o n 5.2 t h a t a r i n g c u r r e n t magnetic f i e l d d e p r e s s i o n i n the IPDP g e n e r a t i o n r e g i o n can have an im p o r t a n t i n f l u e n c e on an IPDP's f r e q u e n c y r i s e , t h i s method a l l o w s f o r the e f f e c t of such a d e p r e s s i o n and y i e l d s an e s t i m a t e of i t s magnitude. In o r d e r t o e s t i m a t e the i n j e c t i o n boundary p o s i t i o n from IPDP d a t a , the p o s i t i o n of the source r e g i o n (L,GMLT) and the westward d r i f t a r c of the p r o t o n s between the i n j e c t i o n boundary and the plasmapause (ALT) must be known. The source r e g i o n GMLT i s e q u i v a l e n t t o the GMLT of the o b s e r v i n g ground s t a t i o n , and L i s found as i n s e c t i o n 5.1. The r e l a t i v e d r i f t a r c s ALT/ALT ^. can be found from a m o d i f i e d form of e q u a t i o n 4.8 ( c f . s e c t i o n 4.3) as f o l l o w s : ALT ALT. i f . i f 2 r L. / L ODS (5.7a) where f ^ r e p r e s e n t s the observ e d IPDP fr e q u e n c y and L i s as found i n s e c t i o n 5.1. T h i s e q u a t i o n y i e l d s t he ALT/ALT^. 157 n e c e s s a r y f o r the f r e q u e n c y r i s e p r e d i c t i o n s of the combined a z i m u t h a l d r i f t and inward motion mechanisms t o match the observed f r e q u e n c y s h i f t of an IPDP. Note t h a t e q u a t i o n 5.7a assumes a d i p o l a r magnetic f i e l d c o n f i g u r a t i o n . The p r o t o n d r i f t t i m e s ( t ^ ) r e q u i r e d by e q u a t i o n 5.7a are e s t i m a t e d from a u r o r a l - z o n e s t a t i o n magnetograms and the i n j e c t i o n e x p a n s i o n t i m e s of A r n o l d y and Moore (1983) ( c f . s e c t i o n 4.1). The substorm*s onset time i s d e t e r m i n e d from the magnetograms of the a u r o r a l - z o n e s t a t i o n which f i r s t sees a l a r g e n e g a t i v e bay i n i t s X-component, a s i g n of the s t a r t of a new substorm, p r e c e d i n g the IPDP e v e n t , and i s a l s o c o n f i r m e d by the o c c u r r e n c e of P i 2 p u l s a t i o n s . The time of the b e g i n n i n g of the bay a t t h i s f i r s t s t a t i o n g i v e s the onset of the substorm, and t h e r e f o r e the b e g i n n i n g of i n j e c t i o n boundary f o r m a t i o n ( A r n o l d y and Moore, 1983), near the s t a t i o n ' s m e r i d i a n . T h i s p r o c e d u r e then a l s o p r o v i d e s a t e n t a t i v e e s t i m a t e of the m e r i d i a n of the i n i t i a l i n j e c t i o n a t substorm o n s e t . S i n c e the boundary t a k e s 10 t o 15 minutes a f t e r substorm onset t o complete i t s e x p a n s i o n t o the west ( c f . s e c t i o n 4.1), p r o t o n d r i f t from the boundary s h o u l d begin w i t h i n 15 minutes a f t e r substorm o n s e t . The a c t u a l time of d r i f t onset f o r an IPDP's p r o t o n s depends on how f a r t o the west of the m e r i d i a n of i n i t i a l i n j e c t i o n the s e c t i o n of the i n j e c t i o n boundary forms from which t h e s e p r o t o n s d r i f t . The c o n c l u s i o n of the westward d r i f t phase of the 1 58 p r o t o n s concerned i s marked by t h e i r i n v o l v m e n t i n the i o n - c y c l o t r o n i n s t a b i l i t y a t the plasmapause g e n e r a t i n g the IPDP. The d r i f t t i m e s t o be used i n e q u a t i o n 5.7a can then be found from the d i f f e r e n c e between the e s t i m a t e d i n j e c t i o n time and the measured g e n e r a t i o n t i m e . E q u a t i o n 5.7a can a c t u a l l y be r e p l a c e d by a more v e r s a t i l e form by r e p l a c i n g L w i t h the magnetic f i e l d s t r e n g t h (B) i n the inward motion f a c t o r o n l y . Thus, e q u a t i o n 5.7a then becomes: ALT ALT. di L L~ r f - i 2 ' B " f obs B. L i J (5.7b) where B can now be c a l c u l a t e d from L as B = (B / L 3 ) . + AB. eq' The replacement of L by B i n the inward motion f a c t o r and the i n c l u s i o n of the AB term i n c a l c u l a t i n g B now p e r m i t s the e f f e c t of magnetic f i e l d d e p r e s s i o n s , which a l t e r the p u r e l y d i p o l e f i e l d p r o f i l e g i v e n by B / L 3 by an assumed e q c o n s t a n t amount AB, on the inward motion mechanism t o be ta k e n i n t o a c c o u n t . The s i m p l i f y i n g assumption of c o n s t a n t AB i n the IPDP g e n e r a t i o n r e g i o n d u r i n g the event i s made h e r e . I t must a l s o be noted t h a t t h i s form of e q u a t i o n 5.7 assumes t h a t the f i e l d d e p r e s s i o n a f f e c t s o n l y the inward 159 motion mechanism, and does not i n f l u e n c e the a z i m u t h a l d r i f t p r o c e s s ( i . e . AB = 0 d u r i n g the d r i f t p h a s e ) . At the b e g i n n i n g of the d r i f t phase, AB can g e n e r a l l y be assumed s m a l l s i n c e the r i n g c u r r e n t i s o f t e n not w e l l d e v e l o p e d a t t h i s t i m e . However, as the r i n g c u r r e n t d e v e l o p s ( c f . s e c t i o n 5.2), the AB l a t e r i n the d r i f t phase may become l a r g e r . D e t e r m i n i n g d r i f t v e l o c i t i e s f o r t h i s type of s i t u a t i o n i s q u i t e d i f f i c u l t , e s p e c i a l l y s i n c e the i n f o r m a t i o n needed t o e s t i m a t e the AB's a f f e c t i n g the p r o t o n d r i f t i s l a c k i n g . T h e r e f o r e , the p r o c e s s has been i d e a l i z e d by s e t t i n g AB = 0 d u r i n g the d r i f t phase, then a l l o w i n g AB to be non-zero (but u n i f o r m ) d u r i n g IPDP g e n e r a t i o n a t the plasmapause. I f non-zero AB i s p r e s e n t d u r i n g the d r i f t phase, a reduced magnetic f i e l d s t r e n g t h (B) w i l l i n c r e a s e d r i f t v e l o c i t e s somewhat ( c f . e q u a t i o n 4.2a), though t h i s c o u l d be p a r t i a l l y o f f s e t by an i n c r e a s e d f i e l d l i n e r a d i u s of c u r v a t u r e near the e q u a t o r ( c f . e q u a t i o n 4.2b). A v e r y l a r g e AB would have t o e x i s t over most of the westward d r i f t range i n o r d e r t o s i g n i f i c a n t l y a f f e c t the e n e r g i e s of the p r o t o n s i n v o l v e d i n IPDP g e n e r a t i o n , i n which case the IPDP p r o t o n e n e r g i e s s h o u l d be somewhat lo w e r . E q u a t i o n 5.7b now produces the n e c e s s a r y ALT/ALT^. f o r the combined fre q u e n c y s h i f t s from a z i m u t h a l d r i f t and A B - a d j u s t e d inward motion mechanisms t o match the o b s e r v e d f r e q u e n c y r i s e . However, s i n c e AB i s not known w i t h any 1 60 p r e c i s i o n , a number of c a l c u l a t i o n s must be c a r r i e d out f o r a range of AB v a l u e s , g i v i n g many p o s s i b l e ALT/ALTV s e t s f o r a s i n g l e IPDP. The next s t e p r e q u i r e d i s the s e l e c t i o n of the energy of the i n i t i a l p r o t o n s i n v o l v e d i n the IPDP g e n e r a t i o n (VI.), a l l o w i n g the c a l c u l a t i o n of ALT. (ALT. t,.W.L.). Here 3 i i di i i a g a i n , the a c t u a l i n i t i a l energy i s unknown, so we must repeat the c a l c u l a t i o n over a range of v a l u e s . Once ALT^. i s known, a l l the ALTs can be de t e r m i n e d from the r a t i o s found from e q u a t i o n 5.7b above. These ALTs p l u s the source r e g i o n GMLTs then y i e l d the i n j e c t i o n boundary l o c a l t i m e s at the L v a l u e s of the IPDP sou r c e r e g i o n . The net r e s u l t of a l l t h e s e c a l c u l a t i o n s i s t h a t , f o r each p a i r of (W;. ,AB) v a l u e s s e l e c t e d , we have a s e r i e s . of (L,LT) p o i n t s which d e f i n e a segment of an i n j e c t i o n boundary which g i v e s , f o r t h a t and AB, an e x a c t match of the combined a z i m u t h a l d r i f t and A B - a d j u s t e d inward motion p r e d i c t e d f r e q u e n c i e s , h e n c e f o r t h termed the "combined mechanisms" p r e d i c t e d f r e q u e n c i e s , t o the observed IPDP f r e q u e n c i e s . I t must now be d e t e r m i n e d which of the s e (VI. ,AB) p a i r s and c o r r e s p o n d i n g i n j e c t i o n boundary segments best r e p r e s e n t s the a c t u a l magnetospheric s i t u a t i o n i n v o l v i n g the IPDP event i n o r d e r t o e s t i m a t e the prop e r i n j e c t i o n boundary p o s i t i o n . The boundary segments c a l c u l a t e d by the above method 161 co v e r l i m i t e d spans i n L and LT compared t o an e n t i r e i n j e c t i o n boundary. C o n s i d e r : i f t h e s e p r o s p e c t i v e b o u n d a r i e s a r e extended t o co v e r the f u l l LT range t y p i c a l of an i n j e c t i o n boundary, do they resemble the d e s c r i p t i o n s p r o v i d e d by Mauk and Meng (1983) ( c f . s e c . 4.1)? T h i s can be t e s t e d by f i t t i n g the boundary p o i n t s t o the e x p r e s s i o n f o r a s i n g l e , duskward s p i r a l i n j e c t i o n boundary (Mauk and Meng, 1983): LT = £l + K 2 (5.8) L where K , and K2 a r e c o n s t a n t s t o be d e t e r m i n e d by the c u r v e - f i t t i n g p r o c e s s . Note t h a t t h i s r e l a t i o n i s e s s e n t i a l l y the same as t h a t of e q u a t i o n 4.1, except t h a t the c o n s t a n t s remain t o be d e t e r m i n e d . I t i s now p o s s i b l e t o p l o t a f u l l i n j e c t i o n boundary f o r each (VI. ,AB) p a i r f o r which boundary p o i n t s were d e t e r m i n e d . The new c u r v e - f i t i n j e c t i o n b o u n d a r i e s a l l o w us to r e c a l c u l a t e the p r e d i c t e d f r e q u e n c y r i s e u s i n g t h e s e new boundary shapes from each (VI. ,AB) p a i r , and t o p r e s e n t some c r i t e r i a f o r s e l e c t i n g the (W^ . ,AB) p a i r which b e s t c h a r a c t e r i z e s each IPDP e v e n t . These c r i t e r i a , a l o n g w i t h a few o t h e r s , a r e : Boundary shape. Does the i n j e c t i o n boundary, i n terms of 162 the v a l u e s of K , and ic2 i n e q u a t i o n 5.8, approximate the d e s c r i p t i o n s d e r i v e d from o b s e r v a t i o n , and does i t s eastward end c o r r e s p o n d t o the i n j e c t i o n onset GMLT observed by a u r o r a l - z o n e s t a t i o n s ? Frequency match. How w e l l do the combined mechanisms p r e d i c t i o n s , u s i n g the new c u r v e - f i t boundary shape, match the o b s e r v e d f r e q u e n c y r i s e ? Boundary match. How w e l l does the new i n j e c t i o n boundary f i t the o r i g i n a l boundary p o i n t s , t h a t i s , what i s the e r r o r between the o r i g i n a l p o i n t s and the new boundary as c a l c u l a t e d i n the c u r v e - f i t t i n g p r o c e s s ? Note t h a t t h i s i s s e p a r a t e from the boundary shape c r i t e r i o n s i n c e a good f i t of the d a t a t o e q u a t i o n 5.8 does not n e c e s s a r i l y imply t h a t the shape of the boundary produced i s r e a s o n a b l e . AB range. Does the AB f o r t h i s boundary f a l l w i t h i n a r e a s o n a b l e range? T h i s range i s d e t e r m i n e d by c o n s i d e r i n g t y p i c a l r i n g c u r r e n t AB p r o f i l e s a l o n g w i t h the d e p r e s s i o n s of the Dst index and the geosynchronous s a t e l l i t e magnetograms a s s o c i a t e d w i t h an IPDP, and can be d i f f e r e n t f o r each IPDP. W range. Do the p r o t o n e n e r g i e s f o r the whole event l i e w i t h i n the broad range of =10 t o =300 keV w i t h i n which IPDPs a r e thought t o o c c u r ? These s e l e c t i o n c r i t e r i a can now be a p p l i e d t o the 163 r e s u l t s of the i n j e c t i o n boundary c a l c u l a t i o n s f o r each (VI.,&B) p a i r i n o r d e r t o choose the b e s t p a i r . The f i r s t s e r i e s of c a l c u l a t i o n s performed f o r t h i s purpose used a l a r g e ,AB g r i d s p a c i n g , w i t h v a r y i n g by 20-30 keV and AB by 10-20 7, i n o r d e r t o i s o l a t e the range of i n t e r e s t f o r each of the pa r a m e t e r s . Then p r o g r e s s i v e l y f i n e r g r i d s , down t o a g r i d s p a c i n g of 2keV by 27, are used u n t i l the best p a i r i s o b t a i n e d . The s e l e c t i o n c r i t e r i a d i s c u s s e d above a r e used t o determine the b e s t (VI. ,AB) p a i r as f o l l o w s . F i r s t , they a r e employed i n a g e n e r a l manner t o det e r m i n e where t o make c a l c u l a t i o n s over f i n e r g r i d s , then i n a more d e t a i l e d manner on the r e s u l t s of the c a l c u l a t i o n s from the f i n e s t g r i d s p a c i n g i n o r d e r t o s e l e c t the b e s t (W;. ,AB) p a i r . T h i s d e t a i l e d e v a l u a t i o n of the s e l e c t i o n c r i t e r i a i s performed i n a q u a n t i t a t i v e manner u s i n g the boundary shape, f r e q u e n c y match, and boundary match c r i t e r i a o n l y . For the AB and W range c r i t e r i a , the AB and W ranges f o r each IPDP a r e s i m p l y judged e i t h e r a c c e p t a b l e or u n a c c e p t a b l e , w i t h the u n a c c e p t a b l e p a i r s b e i n g r e j e c t e d . For the q u a n t i t a t i v e e v a l u t i o n , each of the t h r e e c r i t e r i a f o r a p a r t i c u l a r (vr ,AB) p a i r a r e r a t e d r e l a t i v e t o t h a t c r i t e r i a from the o t h e r p a i r c a l c u l a t i o n s . For example, the (W^ . ,AB) p a i r w i t h the b e s t f r e q u e n c y match would be a s s i g n e d t e n r a t i n g p o i n t s , w h i l e t h a t w i t h the worst match, c o n s i d e r i n g o n l y the p a i r s f o r which d e t a i l e d e v a l u a t i o n s a r e b e i n g done, 1 64 would be g i v e n z e r o p o i n t s . The o t h e r (W. ,AB) p a i r s c o n s i d e r e d would be a s s i g n e d i n t e r m e d i a t e v a l u e s w i t h i n t h i s range depending on the q u a l i t y of t h e i r f r e q u e n c y matches. The same scheme i s a p p l i e d t o the o t h e r two c r i t e r i a . F i n a l l y , the r a t i n g p o i n t s from each c r i t e r i o n f o r each (W;. ,AB) p a i r a r e summed, and t h a t p a i r w i t h the l a r g e s t sum i s deemed t o be the p a i r b e s t d e s c r i b i n g the IPDP e v e n t ' s s i t u a t i o n i n t h a t i t has the b e s t c o m b i n a t i o n of i n j e c t i o n boundary and f r e q u e n c y match. Note t h a t the boundary shape and f r e q u e n c y match c r i t e r i a a r e g i v e n double weight i n the summing p r o c e s s . F i g u r e 50 c o n t a i n s a f l o w c h a r t which summarizes the e n t i r e p r o c e s s , as d e s c r i b e d above, f o r d e t e r m i n i n g the e f f e c t s the a z i m u t h a l d r i f t and A B - a d j u s t e d inward motion mechanisms have on an IPDP's f r e q u e n c y s h i f t . T h i s p r o c e s s r e p r e s e n t s an i n t u i t i v e , p r a c t i c a l approach t o the problem of u n d e r s t a n d i n g IPDP f r e q u e n c y s h i f t s , and, though s t i l l q u i t e s i m p l e , i s the b e s t a v a i l a b l e and does g i v e r e a s o n a b l e f r e q u e n c y s h i f t e s t i m a t e s . 5.3.1. Feb. 14 Event The above boundary s e l e c t i o n p r o c e s s can now be a p p l i e d t o the two e v e n t s s t u d i e d i n d e t a i l i n s e c t i o n s 5.1 and 5.2. F i r s t , we w i l l l o o k a t the Feb. 14 IPDP. B e f o r e the boundary c a l c u l a t i o n can be made, however, 165 f r e q u e n c i e s (observed) s o u r c e L.LT (sec. 5.1) d r i f t time i n i t i a l U i . e s t i m a t e s ? i n j e c t i o n boundary ( • d e l t a - B p a i r s p o i n t s e s t i m a t e new d r i f t t imes T I I no A. f i t p o i n t s t o boundary e q u a t i o n i i n j e c t i o n boundary e s t i m a t e I c a l c u l a t e delta-ni.M.+delta-B) a n d d e l T a - f l f i . D . ) i i a p p l y s e l e c t i o n c r i t e r i a a r e o r i g i n a l b e s t i n j e c t i o n d r i f t time boundary e s t i m a t e s O K ? yes -~A f i n a l i n j e c t i o n boundary e s t i m a t e - a z i m u t h a l d r i f t f r e q u e n c y e f f e c t - delta-B a d j u s t e d inward motion e f f e c t FIGURE 50. Flow c h a r t f o r the e s t i m a t i o n of i n j e c t i o n boundary p o s i t i o n and the a z i m u t h a l d r i f t and A B - a d j u s t e d inward motion f r e q u e n c y s h i f t e f f e c t s (see t e x t f o r d e t a i l e d d e s c r i p t i o n ) . 166 the d r i f t t i m e s ( t ^ ) must be e s t i m a t e d . For t h i s e v e n t , the Great Whale R i v e r (GWR) magnetogram showed the substorm onset e a r l i e r than s t a t i o n s t o the e a s t or west, and t h e r e f o r e i n d i c a t e s t h a t t h i s substorm, and thus the plasma i n j e c t i o n , s t a r t near 0807UT (see f i g . 5 1 ) , a t 27.35 GMLT. The onset time i s a l s o c o n f i r m e d by P i 2 o b s e r v a t i o n s . For t h i s IPDP t h e n , the p r o t o n d r i f t must s t a r t w e l l a f t e r m i d n i g h t , s i n c e the IPDP o c c u r s a f t e r m i d n i g h t . The d r i f t i s e s t i m a t e d t o be g i n a p p r o x i m a t e l y 1±1 minutes a f t e r t he i n j e c t i o n s t a r t s . T h i s e s t i m a t e i s based on an i n j e c t i o n boundary f o r m a t i o n time of 12 m i n u t e s , s t a r t i n g from 27.35 GMLT and then expanding t o the west t h r o u g h 10 hours of GMLT, w i t h the IPDP d r i f t onset time e s t i m a t e b e i n g made by i n t e r p o l a t i o n w i t h i n t h i s i n t e r v a l u s i n g a f o r m a t i o n r a t e which i s t e n times f a s t e r a t the e a s t e r n end than a t the western end ( c f . s e c t i o n 4.1). The u n c e r t a i n t y i n d r i f t s t a r t t i m e s i s q u i t e s m a l l when compared t o the a c t u a l d r i f t t imes of 27 t o 92 mi n u t e s . The AB f o r t h i s event i s l i k e l y t o be f a i r l y s m a l l ( c f . s e c t i o n 5.2), and t h e r e f o r e boundary c a l c u l a t i o n s w i l l be c a r r i e d out over the range 0 < AB < - 6 O 7 . The W;. range used f o r the s e c a l c u l a t i o n s i s 10 < W.' < 140 keV. With t h e s e p a r a m e t e r s , the b e s t - f i t i n j e c t i o n boundary f o r the Feb. 14 IPDP was t h a t c a l c u l a t e d from the s t a r t i n g p o i n t of W. = 14keV and AB = -14-y. T h i s (W^ . ,AB) p a i r 1 67 10100 9 2 0 0 ' 1 1 1 1 1 1 0 2 4 6 8 10 12 UT (h) FIGURE 51. X-component magnetogram from Great Whale R i v e r , 0000-1200UT, Feb. 14, 1980. Note the l a r g e n e g a t i v e bay b e g i n n i n g a t 0807UT, s h o r t l y b e f o r e the IPDP event s t a r t s . produced the best c o m b i n a t i o n of boundary shape and fre q u e n c y match compared t o the r e s u l t s f o r these c r i t e r i o n f o r the o t h e r (VI. ,AB) p a i r c a l c u l a t i o n s . The W and AB range c r i t e r i a a r e a l s o s a t i s f i e d , w i t h the W v a l u e s b e i n g w i t h i n the range n o r m a l l y a s s o c i a t e d w i t h IPDPs and the AB v a l u e b e i n g q u i t e a c c e p t a b l e when compared t o the Dst index and geosynchronous s a t e l l i t e magnetogram f o r Feb. 14 ( c f . s e c t i o n 5.2). In a d d i t i o n , the boundary match (LT e r r o r between d a t a p o i n t s and c u r v e : 0.l63h) i s a l s o a c c e p t a b l e , f a l l i n g a p p r o x i m a t e l y i n the mi d d l e of the range of boundary c u r v e - f i t e r r o r s of 0.161 t o 0.166 h produced by b o u n d a r i e s f o r which r a t i n g s sums were c a l c u l a t e d . T h i s i n j e c t i o n boundary and the c a l c u l a t e d plasmapause p o i n t s a s s o c i a t e d w i t h the IPDP are shown i n f i g u r e 52. F i g u r e 53 i l l u s t r a t e s the change i n p r o t o n energy d u r i n g the IPDP. T h i s energy p r o f i l e i s found u s i n g the new boundary, as shown i n f i g u r e 52, thus W^. = 16keV, not 14keV, due t o the d i f f e r e n c e between the new c u r v e - f i t boundary and the o r i g i n a l boundary p o i n t s . Note t h a t VI. , and not t^., i s a l t e r e d t o accomodate the new c u r v e - f i t boundary shape s i n c e t^. as e s t i m a t e d from the boundary f o r m a t i o n time cannot change. The obser v e d f r e q u e n c y r i s e and t h a t p r e d i c t e d by the p r o t o n energy change (or a z i m u t h a l d r i f t ) e f f e c t , b oth n o r m a l i z e d , a r e a l s o shown i n f i g u r e 53. The f r e q u e n c y s h i f t s due t o the hot p r o t o n energy changes are c a l c u l a t e d 169 H 1 1 1 1 1 1-Earth i 1 H - 8 . - 6 . - 4 . - 2 . 2.--plasmapause segment injection boundary •6.-L FIGURE 52. Model p l o t f o r Feb. 14 e v e n t , showing the i n j e c t i o n boundary s e l e c t e d and the plasmapause segment d e f i n e d by the IPDP g e n e r a t i o n r e g i o n (L,GMLT) c o o r d i n a t e s . The r e g i o n t h r o u g h which the p r o t o n s d r i f t e d f o r t h i s IPDP (as observed on the Saskatchewan l i n e ) i s e n c l o s e d by the dashed l i n e s . The sun i s towards the t o p of the page, and the d i s t a n c e l a b e l s on the axes a r e i n L ( E a r t h r a d i i ) . Note t h a t the source r e g i o n GMLTs of =0100-0200 a r e q u i t e l a t e compared t o t y p i c a l IPDPs. 1 70 UT -(H) FIGURE 53. Top: p r o t o n energy p r o f i l e p l u s the obse r v e d ( s o l i d l i n e ) and a z i m u t h a l d r i f t mechanism p r e d i c t e d (dashed l i n e ) f r e q u e n c y p r o f i l e s ( n o r m a l i z e d ) f o r the Feb. 14 IPDP. Bottom: magnetic f i e l d s t r e n g t h p r o f i l e p l u s the o b s e r v e d ( s o l i d l i n e ) and A B - a d j u s t e d inward motion mechanism p r e d i c t e d (dashed l i n e ) f requency p r o f i l e s f o r the Feb. " 14 IPDP. 171 from e q u a t i o n 4.7. I t s h o u l d be p o i n t e d out here t h a t the f r e q u e n c y e f f e c t s of c h a n g i n g p r o t o n e n e r g i e s and inward s o u r c e motion cannot r e a l l y be i s o l a t e d i n t h i s manner, s i n c e inward motion o c c u r s s i m u l t a n e o u s l y w i t h the p r o t o n energy changes. The c a l c u l a t i o n u s i n g e q u a t i o n 4.7 f o r the energy change f r e q u e n c y s h i f t i s then an h y p o t h e t i c a l case o n l y i n which, f o r the purpose of d i s c u s s i o n , inward motion i s assumed t o be z e r o . In t h i s d i s c u s s i o n we have a l s o used the terms " a z i m u t h a l d r i f t e f f e c t " and "hot p r o t o n energy change e f f e c t " i n t e r c h a n g a b l y . Though the a z i m u t h a l d r i f t e f f e c t c r e a t e s hot p r o t o n energy changes ( c f . s e c t i o n 4.2), i t i s not the o n l y e f f e c t c a u s i n g t h e s e changes s i n c e IPDP g e n e r a t i o n , as seen from a ground s t a t i o n , i n v o l v e s p r o t o n s d r i f t i n g on d i f f e r e n t L - s h e l l s a t d i f f e r e n t t i m e s . The p r o t o n streams on t h e s e d i f f e r e n t L - s h e l l s have d i f f e r e n t v e l o c i t i e s and d i f f e r e n t d r i f t s t a r t and end t i m e s , and can t h e r e f o r e have d i f f e r e n t p r o t o n e n e r g i e s a t any one t i m e , d e m o n s t r a t i n g t h a t c r o s s i n g L - s h e l l s i n t o t h e s e d i f f e r e n t streams can a l s o cause p r o t o n energy changes. Thus, h e n c e f o r t h we w i l l use terms such as "hot p r o t o n energy change e f f e c t " i n s t e a d of " a z i m u t h a l d r i f t e f f e c t " when d i s c u s s i n g energy change f r e q u e n c y s h i f t s . D u r i n g the Feb. 14 IPDP, as shown i n f i g u r e 53, the p r o t o n energy drops r a p i d l y and the hot p r o t o n energy change 1 72 e f f e c t f r e q u e n c y s h i f t i n c r e a s e s s i g n i f i c a n t l y a t the b e g i n n i n g of the e v e n t , and then they have l i t t l e net change over the f i n a l -| of the IPDP. T h i s r e d u c t i o n , and temporary r e v e r s a l , of the r a t e of change of t h e s e p r o f i l e s c o u l d be a t t r i b u t e d t o r a p i d inward motion of the plasmapause d u r i n g the c e n t r a l p a r t of the IPDP, r e q u i r i n g the p r o t o n s t o be more e n e r g e t i c i n o r d e r t o r e a c h i t w i t h i n the d r i f t time a v a i l a b l e . F i g u r e 53 a l s o shows the magnetic f i e l d p r o f i l e a l o n g w i t h i t s p r e d i c t e d f r e q u e n c y r i s e and the obse r v e d r i s e f o r the Feb. 14 IPDP. The f r e q u e n c y r i s e due t o the i n c r e a s i n g magnetic f i e l d i s d e t e r m i n e d by e q u a t i o n 4.6. The f r e q u e n c y r i s e p r e d i c t e d here i s v e r y s i m i l a r t o t h a t shown i n f i g u r e 32 f o r inward motion w i t h o u t a AB a d j u s t m e n t , though the i n c r e a s e i s s l i g h t l y l a r g e r i n t h i s c a s e ; 68% of the observed end f r e q u e n c y , up from 66%. The combined e f f e c t s of the i n c r e a s i n g B and g e n e r a l l y d e c r e a s i n g W can be c a l c u l a t e d from a r e a r r a n g e d v e r s i o n of e q u a t i o n 5.7b: f_ f . r ALT. L_ L. o . 5 B_ B. . 5 ALT ( 5 . 9 ) . T h i s combined frequency r i s e i s compared t o the obse r v e d frequency i n f i g u r e 54. The r e l a t i v e l y good match between the two i s , of c o u r s e , a r e s u l t of the (W ,AB) p a i r 1 73 2.0 1.8 <D N ~o E 1.6 o c o 1.4 c Q) 3 cr Q) 1.2 1.0 8.0 predicted frequency 8.4 observed frequency 8.8 9.2 UT (h) 9.6 10.0 FIGURE 54. The f r e q u e n c y r i s e s as o b s e r v e d and as c a l c u l a t e d f o r the combined a z i m u t h a l d r i f t - A B - a d j u s t e d inward motion mechanisms f o r the Feb. 14 e v e n t , showing the good match between the two c u r v e s . 174 o r i g i n a l l y chosen. In c o n t r a s t t o the be s t p a i r r e s u l t s d i s c u s s e d above, f i g u r e 55 shows the r e s u l t s of c a l c u l a t i o n s u s i n g two d i f f e r e n t (VI.,AB) p a i r s . The t o p p o r t i o n of t h i s f i g u r e compares the p r e d i c t e d f r e q u e n c y r i s e found f o r W;. = lOkeV and AB = - I O 7 t o the obser v e d r i s e f o r the Feb. 14 IPDP. I t i s apparent t h a t t h i s f r e q u e n c y match i s much po o r e r than f o r the be s t case p a i r , w i t h the p r e d i c t e d f r e q u e n c y r i s e b e i n g g e n e r a l l y much h i g h e r than the o b s e r v a t i o n s . The lower p o r t i o n of f i g u r e 55 shows the i n j e c t i o n boundary as c a l c u l a t e d from. W. = 22KeV and AB = - 3 O 7 . The boundary shape produced by t h i s p a i r c o u l d not a c t u a l l y y i e l d the Feb. 14 IPDP when and where i t was observed s i n c e i t does not rea c h low enough L a t i t s eastward end ( c f . f i g . 55) as d e t e r m i n e d by the m e r i d i a n of substorm o n s e t . Problems such as the s e two i l l u s t r a t e d above appear c o n s i s t e n t l y f o r boundary c a l c u l a t i o n s u s i n g (W;. ,AB) p a i r v a l u e s which a r e not c l o s e t o those p r o d u c i n g the best c a s e . The r a t i n g s sums f o r the s e c a l c u l a t i o n s , r e s p e c t i v e l y 18 and 20, a r e u n d e r s t a n d a b l y q u i t e poor when compared to the best case sum of 3 4 , though on the o t h e r hand, they c e r t a i n l y do not r e p r e s e n t the worst c a s e s e i t h e r . For the Feb. 14 IPDP, we can now c o n c l u d e t h a t , o v e r a l l , the dominant r o l e i n c r e a t i n g the e v e n t ' s f r e q u e n c y s h i f t i s taken by the inward motion mechanism, which i s 175 TJ 2.0 Q) N "5 P 1.8 norr 1.6 1.4 o c <D 3 cr 1.2 a> l k. 1.0 8.0 predicted frequency observed frequency 8.4 8.8 9.2 UT (h) 9.6 10.0 injection boundary Earth -6 i FIGURE 55. Top: P r e d i c t e d f r e q u e n c y r i s e f o r W/ = lOkeV and AB -IO7 f o r the Feb. 14 ev e n t . Bottom: I n j e c t i o n boundary f o r Wz- = 22keV and AB = -3O7. These parameters produce r e s u l t s much worse than t h o s e f o r the b e s t c a s e . 176 f u r t h e r enhanced somewhat by a d e p r e s s e d (-147) magnetic f i e l d i n the IPDP g e n e r a t i o n r e g i o n . T h i s cannot account f o r the e n t i r e f r e q u e n c y r i s e , though, and a secondary r o l e i s p l a y e d by hot p r o t o n energy changes. However, f o r the f i r s t •j of the e v e n t , t h i s hot p r o t o n energy change e f f e c t i s a c t u a l l y the dominant f a c t o r i n p r o d u c i n g the f r e q u e n c y s h i f t , w i t h the inward motion mechanism o c c u p y i n g a secondary r o l e . R e c a l l t h a t i t was shown i n s e c t i o n 5.2 t h a t the i n c r e a s i n g f i e l d mechanism i s not i m p o r t a n t h e r e . 5.3.2. Feb. 15 Event As w i t h the Feb. 14 e v e n t , b e f o r e the i n j e c t i o n boundary p o s i t i o n i s c a l c u l a t e d the p r o t o n d r i f t t i m e s must be e s t i m a t e d . For t h i s e v e n t , the substorm and i n j e c t i o n onset o c c u r r e d e a s t of the a u r o r a l - z o n e s t a t i o n s a v a i l a b l e t o us. However, the substorm e f f e c t s were obse r v e d t o b e g i n i n the a f t e r n o o n s e c t o r a t GWR (GMLT = 1533) a t 2036UT ( f i g . 56). From the onset of P i 2 p u l s a t i o n s , though, the a c t u a l substorm onset o c c u r r e d near 2028UT. The westward d r i f t of the p r o t o n s i n v o l v e d i n the IPDP would then have s t a r t e d sometime a f t e r t h i s t i m e . In a d d i t i o n , the d r i f t of the IPDP p r o t o n s s t a r t e d from a boundary segment a t lower L - s h e l l s , and t h e r e f o r e l a t e r GMLTs, than GWR, l i k e l y from the dusk s e c t o r . Based on a boundary f o r m a t i o n time of a p p r o x i m a t e l y 8 minutes t o the m e r i d i a n of GWR and u s i n g a s i m i l a r 1 77 10400 9800 L ' ' » L _ 1 I 12 14 16 18 20 22 24 UT (h) FIGURE 56. X-component magnetogram from Great Whale R i v e r , 1200-2400UT, Feb. 15, 1980. Note the l a r g e n e g a t i v e bay b e g i n n i n g a t 2036UT, when the s t a t i o n i s a t 1533GMLT. 178 i n t e r p o l a t i o n p r o c e s s as f o r the Feb. 14 ev e n t , the d r i f t s t a r t time i s e s t i m a t e d a t =3±1 minutes a f t e r substorm o n s e t . Note t h a t i n the absence of an e s t i m a t e of the substorm onset m e r i d i a n , a t y p i c a l onset GMLT of 0130 ( c f . s e c t i o n 4.1) has been used. The one minute u n c e r t a i n t y i s s t i l l q u i t e s m a l l when compared t o the d r i f t t i m e s f o r t h i s event of 78 t o 94 m i n u t e s , and t e s t s have a l s o shown t h a t the c a l c u l a t e d boundary shapes a r e not s e n s i t i v e t o s m a l l (<5 min) changes i n the d r i f t time e s t i m a t e s . S i n c e the Dst index and the geosynchronous s a t e l l i t e r e c o r d s i n d i c a t e a much deeper AB f o r t h i s event than f o r the Feb. 14 IPDP, a range of 0 ^ AB < -I6O7 i s used i n the boundary e s t i m a t i o n c a l c u l a t i o n s . The VI. range c o v e r e d i s 10 < VI. < 300 keV, v i r t u a l l y the e n t i r e range of e n e r g i e s p o s s i b l y r e l a t e d t o IPDPs. From a l l the c a l c u l a t i o n s over t h e s e parameter ranges, the optimum c u r v e - f i t boundary emerges as t h a t c a l c u l a t e d u s i n g W;. = 30KeV and AB = -13O7. T h i s i n j e c t i o n boundary produced the best r a t i n g s sum; 38 out of a maximum of 50. The boundary c a l c u l a t e d from t h i s p a i r had each of the boundary shape, f r e q u e n c y match, and boundary match c r i t e r i a r a t e d as among the b e s t , r e s u l t i n g i n the h i g h e s t r a t i n g s sum. The AB and W v a l u e s a s s o c i a t e d w i t h the b e s t case boundary a r e w i t h i n the a c c e p t a b l e ranges f o r t h i s IPDP. The model p l o t of the s e l e c t e d boundary i s shown i n f i g u r e 57. 1 79 5.T injection boundary -5.-L FIGURE 5 7 . Model p l o t f o r Feb. 15 e v e n t , showing the i n j e c t i o n boundary s e l e c t e d and the plasmapause segment d e f i n e d by the IPDP g e n e r a t i o n r e g i o n (L,GMLT) c o o r d i n a t e s . The r e g i o n t h r ough which the p r o t o n s d r i f t e d f o r t h i s IPDP (as obser v e d on the Saskatchewan l i n e ) i s e n c l o s e d by the dashed l i n e s . The sun i s towards the t o p of the page, and the d i s t a n c e l a b e l s on the axes a r e i n L ( E a r t h r a d i i ) . Note t h a t the source r e g i o n GMLTs (near 1400) a r e q u i t e e a r l y compared t o t y p i c a l IPDPs. 180 Note t h a t the IPDP p r o t o n s b e g i n t h e i r d r i f t from a boundary segment i n the l a t t e r p a r t of the dusk s e c t o r , c o n f i r m i n g the d r i f t s t a r t time e s t i m a t e s d i s c u s s e d above. The p r o t o n energy e v o l u t i o n f o r the Feb. 15 IPDP i s shown i n f i g u r e 58. For t h i s IPDP, the energy i s i n c r e a s i n g w i t h t i m e , r a t h e r than d e c r e a s i n g as would have p r e v i o u s l y been e x p e c t e d ( c f . s e c t i o n 4.2.3). As w i t h the Feb. 14 e v e n t , a r a p i d inward movement of the plasmapause d u r i n g the IPDP may be r e s p o n s i b l e f o r t h i s u nusual b e h a v i o u r . C o r r e s p o n d i n g l y , the f r e q u e n c y s h i f t due t o the hot p r o t o n energy change e f f e c t , a l s o p l o t t e d i n f i g u r e 58, must show a s l i g h t decreasing f r e q u e n c y t r e n d . The magnetic f i e l d s t r e n g t h p r o f i l e and i t s c o r r e s p o n d i n g f r e q u e n c y s h i f t a r e a l s o i l l u s t r a t e d i n f i g u r e 58, a l o n g w i t h the o b s e r v e d f r e q u e n c y r i s e f o r c o m p a r i s o n . In t h i s c a s e , the AB adjustment t o the inward motion mechanism makes t h i s f r e q u e n c y r i s e much l a r g e r than t h a t f o r the u n a l t e r e d , or AB = 0, inward motion mechanism ( c f . f i g . 3 9 ) ; here i t a c t u a l l y reaches 116% of the t o t a l o b s e r v e d IPDP f r e q u e n c y s h i f t , as opposed t o o n l y 60% w i t h o u t the AB a d j u s t m e n t . The combined f r e q u e n c y e f f e c t s of p r o t o n energy and magnetic f i e l d v a r i a t i o n s i n the IPDP source r e g i o n a r e p l o t t e d i n f i g u r e 59, showing t h a t the n e g a t i v e a z i m u t h a l d r i f t e f f e c t b r i n g s the A B - a d j u s t e d inward motion f r e q u e n c y r i s e down i n t o l i n e w i t h the eg 21.6 21.8 22.0 22.2 22.4 UT (H) FIGURE 58. Top: p r o t o n energy p r o f i l e p l u s the obse r v e d ( s o l i d l i n e ) and a z i m u t h a l d r i f t mechanism p r e d i c t e d (dashed l i n e ) f r e q u e n c y p r o f i l e s ( n o r m a l i z e d ) f o r the Feb. 15 IPDP. Bottom: magnetic f i e l d s t r e n g t h p r o f i l e p l u s the o b s e r v e d ( s o l i d l i n e ) and A B - a d j u s t e d inward motion mechanism p r e d i c t e d (dashed l i n e ) f r e q u e n c y p r o f i l e s f o r the Feb. 15 IPDP. 182 o b s e r v e d f r e q u e n c y s h i f t of t h i s e v e n t . I t can be c o n c l u d e d , t h e n , t h a t the Feb. 15 IPDP's fr e q u e n c y r i s e i s produced s o l e l y by the inward motion mechanism o p e r a t i n g i n a de p r e s s e d (-13O7) magnetic f i e l d e n vironment. The hot p r o t o n energy change e f f e c t does not c o n t r i b u t e a t a l l ; i n s t e a d , i t a c t u a l l y d e p r e s s e s the fre q u e n c y r i s e somewhat. A g a i n , r e c a l l t h a t the i n c r e a s i n g f i e l d mechanism i s l i k e l y a v e r y minor p l a y e r i n t h i s event ( c f . s e c t i o n 5.2). In summary, t h i s s e c t i o n has p r e s e n t e d a method f o r e s t i m a t i n g the i n j e c t i o n boundary p o s i t i o n u s i n g ground based IPDP d a t a , and then used i t t o a s s e s s the fr e q u e n c y e f f e c t s of p r o t o n energy changes f o r two IPDPs. The r e s u l t s show t h a t p r o t o n energy changes have a c o m p a r a t i v e l y minor e f f e c t on the fr e q u e n c y r i s e s of th e s e e v e n t s . 5 . 4 . LONGITUDINAL IPDP DEVELOPMENT In the p r e v i o u s s e c t i o n s of t h i s c h a p t e r , IPDPs have been s t u d i e d u s i n g a n o r t h - s o u t h l i n e of s t a t i o n s . In t h i s s e c t i o n , d a t a from the s o u t h e r n e a s t - w e s t l i n e ( c f . s e c t i o n 2.1, f i g . 3) i s a n a l y s e d i n o r d e r t o g a i n f u r t h e r i n s i g h t i n t o the l o n g i t u d i n a l c h a r a c t e r i s t i c s of the IPDP g e n e r a t i o n r e g i o n . In a d d i t i o n t o the two eve n t s s t u d i e d i n s e c t i o n s 5.1 and 5.3, a t h i r d IPDP i s a l s o a n a l y s e d h e r e ; the Feb. 24c e v e n t . W h i l e d a t a f o r the o r i g i n a l two IPDPs a re 183 2.4 21.6 21.8 22.0 22.2 22.4 UT (h) FIGURE 59. The f r e q u e n c y r i s e s as o b s e r v e d and as c a l c u l a t e d f o r the combined a z i m u t h a l d r i f t - A B - a d j u s t e d inward motion mechanisms f o r the Feb. 15 e v e n t , showing the e x c e l l e n t agreement between the two c u r v e s . 184 a v a i l a b l e o n l y from GM and PS, the e a s t e r n and c e n t r a l s i t e s i n the s o u t h e r n e a s t - w e s t l i n e , the Feb. 24c event has d a t a a v a i l a b l e from a l l t h r e e s i t e s i n t h i s l i n e . Note t h a t the l o n g i t u d i n a l d i f f e r e n c e between GM and PS i s o n l y 14.6°, but t h a t the l o n g i t u d i n a l span of the l i n e expands t o 34.6° when PG, the westernmost s t a t i o n , i s i n c l u d e d . The d e t a i l e d l o n g i t u d i n a l a n a l y s e s a r e p r e s e n t e d below f o r each e v e n t . They a r e f o l l o w e d by a d i s c u s s i o n of the r e s u l t s of t h e s e a n a l y s e s . 5.4.1. Feb. 14 Event The f i r s t IPDP d i s c u s s e d i s the Feb. 14 e v e n t . F i g u r e 60 demonstrates the f r e q u e n c y e v o l u t i o n of t h i s event at b o t h GM and PS. Note t h a t the f r e q u e n c y i s g e n e r a l l y h i g h e r t o the e a s t , a t GM, a v e r a g i n g =0.06Hz above PS. The f r e q u e n c y s l o p e s are s i m i l a r , w i t h t h a t f o r GM, 0.43Hz/h, b e i n g s l i g h t l y h i g h e r than the 0.36Hz/h s l o p e a t PS. However, as can be seen i n f i g u r e 60, t h e r e are some s h o r t e r term v a r i a t i o n s i n f r e q u e n c y s l o p e which a r e not s h a r e d by b o t h s t a t i o n s . The event was o b s e r v e d t o b e g i n a t a p p r o x i m a t e l y the same time a t GM and PS, =0835UT, but i t l a s t e d =10 minutes l o n g e r , u n t i l 0950UT, a t GM, the e a s t e r n s t a t i o n . Comparisons between the IPDP s i g n a l s as o b s e r v e d a t GM and PS a r e made u s i n g c r o s s - c o r r e l a t i o n s . A s e r i e s of 2048 185 FIGURE 60. Frequency e v o l u t i o n a t both GM and PS f o r the Feb. 14 event. Note the h i g h e r f r e q u e n c i e s a t GM and the d i f f e r e n t l o c a l v a r i a t i o n s i n s l o p e a t the two s t a t i o n s . 186 p o i n t (9.1 min) d a t a windows, s t a r t i n g e v e r y f i v e m i n u t e s , from GM were c o r r e l a t e d w i t h a 8192 p o i n t (36.4 min) d a t a window, s t a r t i n g a t 0845UT, from PS. The r e s u l t s show c o r r e l a t i o n c o e f f i c i e n t s t o be <0.2 a t a l l time s h i f t s f o r each window, i n d i c a t i n g no s i g n i f i c a n t c o r r e l a t i o n between t h e s e s t a t i o n s . For c o m p a r i s o n , s t a t i o n s on the same m e r i d i a n , PS and LL, have r e c o r d s which appear t o be v e r y s i m i l a r , w i t h a c o r r e l a t i o n c o e f f i c i e n t of 0.36 f o r a l e a d of o n l y 1.3 seconds a t LL u s i n g the same d a t a window as above f o r PS c o r r e l a t e d w i t h a 9.1 minute window s t a r t i n g a t 0855UT from LL. Note, however, t h a t PS and LL a r e s e p a r a t e d o n l y by 1.2° of l a t i t u d e ( c f . s e c t i o n 2.1). An e x a m i n a t i o n of power s p e c t r a computed from the same time i n t e r v a l s a t GM and PS shows the d i f f e r e n c e s i n the IPDP s i g n a l as observed by these two s t a t i o n s (see f i g . 6 1 ) ; t h e s p e c t r a not o n l y c o v e r somewhat d i f f e r e n t bands, but the d i s t r i b u t i o n of power w i t h i n the bands i s a l s o d i s s i m i l a r . 5.4.2. Feb. 15 Event The f r e q u e n c y e v o l u t i o n of the Feb. 15 event i s shown i n f i g u r e 62, d e m o n s t r a t i n g t h a t the f r e q u e n c y i s a g a i n h i g h e r t o the e a s t , a t GM, though by o n l y an average of -0.02Hz. As w e l l , the s l o p e s a r e v e r y s i m i l a r h e r e , though the average s l o p e i s s l i g h t l y h i g h e r a t PS, 1.06Hz/h, than a t GM, 1.0!Hz/h. As f o r the Feb. 14 IPDP, the event onset 187 250 0.0 0.2 0.4 0.6 0.8 frequency (Hz) 250 0.0 0.2 0.4 0.6 0.8 frequency (Hz) FIGURE 61. Top: Power s p e c t r a from PS f o r 0910UT, F e b r u a r y 14. Bottom: Power s p e c t r a from GM f o r same time p e r i o d . Both s p e c t r a a r e of the t o t a l h o r i z o n t a l component from a""*4.6 minute d a t a window. Note the d i f f e r e n t s i g n a l bands and the d i f f e r e n t power d i s t r i b u t i o n s i n the s e two s p e c t r a . 188 FIGURE 62. Frequency e v o l u t i o n f o r GM and PS, Feb. 15 event. GM has the h i g h e r f r e q u e n c i e s , but the s l o p e i s s l i g h t l y lower than a t PS. 189 t i m e s a r e e s s e n t i a l l y the same; 2147UT a t GM and 2148UT a t PS. However, i n t h i s c a s e , the d u r a t i o n was l o n g e r a t the western s t a t i o n , PS, a t 25 m i n u t e s , as compared t o 20 minutes a t GM. Note t h a t the d e t a i l e d a n a l y s i s of t h i s IPDP i n the p r e v i o u s s e c t i o n s was o n l y c a r r i e d out t o 2205UT, s i n c e a v e r y weak s i g n a l , and c o n s e q u e n t l y poor s i g n a l / n o i s e r a t i o , made the a n a l y s i s r e s u l t s of the l a s t s e c t i o n v e r y d i f f i c u l t t o i n t e r p r e t and t h e r e f o r e u n r e l i a b l e . A comparison of the appearance of the IPDP s i g n a l as seen a t GM and PS a l s o y i e l d s a r e s u l t u n l i k e t h a t f o r the Feb. 14 e v e n t . Here, each s t a t i o n e x h i b i t s s i m i l a r h i g h a m p l i t u d e i n t e r v a l s on the magnetograms, though these i n t e r v a l s do not n e c e s s a r i l y occur p r e c i s e l y s i m u l t a n e o u s l y . C r o s s - c o r r e l a t i o n a l a n a l y s i s shows t h a t each i n t e r v a l a t GM l e a d s the c o r r e s p o n d i n g one a t PS by between 54 and 4 seconds, w i t h the l a r g e s t l e a d s b e i n g e a r l i e r i n the e v e n t . In c o n t r a s t t o t h i s , t h e s e h i g h a m p l i t u d e i n t e r v a l s appear n e a r l y s i m u l t a n e o u s l y , the time s h i f t always b e i n g <5 seconds, at PS and LL, which a r e s e p a r a t e d o n l y i n l a t i t u d e . The c o r r e l a t i o n c o e f f i c i e n t s of up t o 0.60 a r e a l s o much h i g h e r between PS and LL than between PS and GM, which show c o e f f i c i e n t s of up t o o n l y 0.39. For t h i s e v e n t , the c o r r e l a t i o n s are done u s i n g 1024 p o i n t (4.6 min) d a t a windows from a l l s t a t i o n s . Note t h a t the h i g h a m p l i t u d e i n t e r v a l s a r e s h o r t compared t o the 4.6 minute d a t a windows. 190 C o r r e l a t i o n s were performed on f o u r windows w i t h s t a r t t i m e s of 2150, 2154, 2158, and 2203 UT. F i g u r e 63 shows sample c o r r e l a t i o n s between PS and GM and between PS and LL from the 2154UT window. D i f f e r e n t background n o i s e c o n d i t i o n s a t each s i t e and low a m p l i t u d e s a r e b e l i e v e d t o be r e s p o n s i b l e f o r the r e l a t i v e l y low l e v e l s of the c o r r e l a t i o n c o e f f i c i e n t s . The i n d i v i d u a l power s p e c t r a e x h i b i t the same k i n d s of d i f f e r e n c e s between GM and PS as they d i d f o r the Feb. 14 IPDP, even though the magnetograms from t h e s e two s t a t i o n s appear, a t l e a s t a t f i r s t g l a n c e , t o be q u i t e s i m i l a r i n t h i s c a s e . 5.4.3. Feb. 24c Event T h i s event was o b s e r v e d a t a l l t h r e e s t a t i o n s i n the s o u t h e r n e a s t - w e s t l i n e (GM, PS, and PG). The f r e q u e n c y p r o f i l e s from th e s e s t a t i o n s are shown i n f i g u r e 64. Though the PS and GM f r e q u e n c i e s appear t o be q u i t e s i m i l a r , t o the west the PG s t a t i o n o b s e r v e d f r e q u e n c i e s a v e r a g i n g 0.07Hz lower than the o t h e r s t a t i o n s . The average f r e q u e n c y s l o p e s a t each s i t e a r e s i m i l a r , l y i n g near 0.3Hz/h, w i t h PG b e i n g s l i g h t l y h i g h e r and GM somewhat lower than t h i s v a l u e . However, as f i g u r e 64 shows, t h e r e a r e d i f f e r e n t s h o r t e r term v a r i a t i o n s i n s l o p e w i t h i n the event a t each s i t e which can make the s l o p e s q u i t e d i f f e r e n t between s t a t i o n s f o r -100 - 5 0 0 50 100 time shift (s) 1.01 — — -100 - 5 0 0 50 100 time shift (s) FIGURE 63. Top: Sample c r o s s - c o r r e l a t i o n between LL and PS from the Feb. 15 e v e n t , showing t h a t the good c o r r e l a t i o n between the s e two s i t e s , which a r e on the same m e r i d i a n , i s near z e r o l a g . Bottom: C r o s s - c o r r e l a t i o n between GM and PS from the same time i n t e r v a l . Both c o r r e l a t i o n s use the Y component o n l y ( w i t h a 0.2-0.6 Hz bandpass f i l t e r ) . Note the s i g n i f i c a n t l y p o o r e r c o r r e l a t i o n t h e s e two l o n g i t u d i n a l l y s e p a r a t e d s i t e s . Here, GM l e a d s PS by 22 seconds. 1 92 FIGURE 64. Frequency e v o l u t i o n f o r a l l t h r e e s t a t i o n s o b s e r v i n g the Feb. 24c IPDP. PG, i n .the west, has the l o w e s t f r e q u e n c i e s . Note a l s o t h a t t h e r e are s i g n i f i c a n t l o c a l v a r i a t i o n s i n s l o p e between the s t a t i o n s . 193 some i n t e r v a l s d u r i n g the IPDP. The event i n t e r v a l s o b s e r v e d a t each s i t e a r e : GM, 0550 t o 0630 UT; PS, 0554 t o 0650 UT; and PG, 0558 t o 0700 UT. Note t h a t the GM d a t a were v e r y n o i s y and d i f f i c u l t t o i n t e r p r e t , making c o n c l u s i o n s based on i t l e s s r e l i a b l e . As w i t h the Feb. 14 e v e n t , but u n l i k e the Feb. 15 IPDP, t h e r e does not appear t o be any s i g n i f i c a n t c o r r e l a t i o n of the s i g n a l s between any of the t h r e e s t a t i o n s i n the e a s t - w e s t l i n e , s i n c e a l l c o r r e l a t i o n c o e f f i c i e n t s were a g a i n <0.2. No o t h e r r e c o r d i n g s i t e s on any of the n o r t h - s o u t h l i n e s are a v a i l a b l e f o r comparison f o r t h i s e v e n t . The power s p e c t r a f o r t h i s event behave much as has been d e s c r i b e d f o r the p r e v i o u s two c a s e s , w i t h the f r e q u e n c y bands c o v e r e d and the power d i s t r i b u t i o n w i t h i n the bands b e i n g n o t a b l y d i f f e r e n t a t each s i t e f o r the same time i n t e r v a l s . 5.4.4. Discussion A l l t h r e e e v e n t s d i s c u s s e d here e x h i b i t g e n e r a l l y h i g h e r f r e q u e n c i e s t o the e a s t . T h i s i m p l i e s g e n e r a t i o n on lower L - s h e l l s t o the e a s t , and thus i n d i c a t e s t h a t the g e n e r a t i o n r e g i o n f o l l o w s the plasmapause shape which i s a t lower L a t l a t e r , or more e a s t e r l y GMLTs. Two of the t h r e e IPDPs, Feb. 15 and Feb. 24c, show l o n g e r d u r a t i o n s t o the 1 94 west and e a r l i e r onset t i m e s t o the e a s t . T h i s i s c o n s i s t e n t w i t h the model d i s c u s s e d i n s e c t i o n 4.1, i n which the l a t e r o n s e t s imply l o n g e r d r i f t t i m e s which c r e a t e a l a r g e r GMLT spread i n the d r i f t i n g p r o t o n c l o u d , g i v i n g l o n g e r event d u r a t i o n s . Note t h a t v e r y low a m p l i t u d e s a t the s t a r t or end of an event can make i t v e r y d i f f i c u l t t o c o r r e c t l y p i c k the s t a r t or end t i m e s , which may be why the d u r a t i o n and/or onset time of the Feb. 14 IPDP does not f i t the above p a t t e r n . For a l l t h r e e e v e n t s , i n d i v i d u a l power s p e c t r a c a l c u l a t e d from i d e n t i c a l time i n t e r v a l s show major d i f f e r e n c e s between s i t e s on the e a s t - w e s t l i n e , but not f o r n o r t h - s o u t h l i n e s t a t i o n s . Each event a l s o shows temporary d i f f e r e n c e s i n s l o p e e x h i b i t e d by the s t a t i o n s on the east-west l i n e . Two of the t h r e e IPDPs s t u d i e d , Feb. 14 and Feb. 24c, show no s i g n i f i c a n t c o r r e l a t i o n between s t a t i o n s on the e a s t - w e s t l i n e , though the t h i r d e v e n t , the Feb. 15 IPDP, does show a weak ea s t - w e s t c o r r e l a t i o n . These r e s u l t s imply t h a t each s t a t i o n r e c e i v e s the IPDP s i g n a l s from a d i f f e r e n t p a r t of the magnetospheric s o u r c e r e g i o n . The e a s t - w e s t c o r r e l a t i o n s e x h i b i t e d by the Feb. 15 event c o u l d be caused by the magnetospheric s o u r c e r e g i o n s "above" each s t a t i o n r e c e i v i n g s i m i l a r " p a c k e t s " of d r i f t i n g p r o t o n s n e a r l y s i m u l t a n e o u s l y , thus c r e a t i n g s i m i l a r h i g h a m p l i t u d e i n t e r v a l s a t each s t a t i o n w i t h time s e p a r a t i o n s of 195 l e s s than one minute. Note t h a t good c o r r e l a t i o n s a r e o b s e r v e d between s t a t i o n s s e p a r a t e d i n l a t i t u d e o n l y , i l l u s t r a t i n g good n o r t h - s o u t h d u c t i n g from a common secondary s o u r c e . In summary, the p r i m a r y p o i n t of t h i s a n a l y s i s i s t o show t h a t t h e r e are s i g n i f i c a n t d i f f e r e n c e s w i t h i n an IPDP as ob s e r v e d on an e a s t - w e s t l i n e of s t a t i o n s . These d i f f e r e n c e s , which i n c l u d e v a r i a t i o n s i n magnetograms, f r e q u e n c y , s l o p e , and s p e c t r a , can be seen over as l i t t l e as 15° GM Long., and i m p l y t h a t each s i t e i s s e e i n g a s e p a r a t e magnetospheric s o u r c e . The e a s t - w e s t p a t t e r n of these d i f f e r e n c e s , which a l s o i n c l u d e onset times and d u r a t i o n s , i s c o n s i s t e n t w i t h the model d i s c u s s e d i n s e c t i o n 4.1, w i t h s i m u l t a n e o u s IPDP g e n e r a t i o n over a l o n g i t u d i n a l l y extended a r e a of the plasmapause a f t e r westward d r i f t of the p r o t o n s on d i f f e r e n t L - s h e l l s . Each ground s t a t i o n on the east-west l i n e i s then s e e i n g the IPDP as g e n e r a t e d on a d i f f e r e n t s e c t i o n of the plasmapause c l o s e t o t h a t s t a t i o n ' s m e r i d i a n , r e s u l t i n g i n the i n t e r - s t a t i o n v a r i a t i o n s i n the IPDP s i g n a l d e s c r i b e d above. Good n o r t h - s o u t h p r o p a g a t i o n w i t h i n the i o n o s p h e r e ensures t h a t a l l s i t e s on one m e r i d i a n see the same s i g n a l s from the same s o u r c e , w i t h o n l y the p o l a r i z a t i o n c h a r a c t e r i s t i c s and a m p l i t u d e s a l t e r e d by t h i s i o n o s p h e r i c p r o p a g a t i o n . 196 5.5. DISCUSSION OF EXPERIMENTAL RESULTS In s t u d y i n g the f r e q u e n c y r i s e of IPDPs, we have t e s t e d t h r e e mechanisms c a p a b l e of p r o d u c i n g t h i s e f f e c t ; the inward motion of the magnetospheric s o u r c e r e g i o n , an i n c r e a s i n g background magnetic f i e l d s t r e n g t h i n the s o u r c e r e g i o n , and the p r o t o n energy v a r i a t i o n s produced d u r i n g the a z i m u t h a l d r i f t of the hot p r o t o n s . The assessment of t h e s e mechanisms has been c a r r i e d out i n the c o n t e x t of the model d e s c r i b e d i n Chapter Four. In s e c t i o n s 5.1 t h r o u g h 5.3, i t was shown t h a t the inward motion was, f o r the e v e n t s a n a l y z e d , the p r i m a r y , though not always the e n t i r e , cause of the IPDPs' f r e q u e n c y r i s e . I t i s i m p o r t a n t t o note t h a t , f o r a p r o p e r assessment of t h i s mechanism, the e f f e c t of the r i n g c u r r e n t magnetic f i e l d on the r a d i a l geomagnetic f i e l d p r o f i l e must be t a k e n i n t o a c c o u n t , s i n c e i t can, i f the r i n g c u r r e n t i s w e l l d e v e l o p e d , s i g n i f i c a n t l y enhance the magnitude of the f r e q u e n c y r i s e a t t r i b u t a b l e t o inward motion of the IPDP g e n e r a t i o n r e g i o n . T h i s r e p r e s e n t s a f i r s t , i f s i m p l e , s t e p beyond the p u r e l y d i p o l e f i e l d model d i s c u s s e d i n Chapter Four. The inward motion of the source r e g i o n has e a r l i e r been d e s c r i b e d as b e i n g due t o the shape of the plasmapause, w i t h the p o s s i b l e a d d i t i o n of inward motion of the plasmapause i t s e l f ( c f . Chapter F o u r ) . The inward motion d e t e r m i n e d here 1 97 would be the sum of the s e two e f f e c t s , i f both a r e p r e s e n t . The i r r e g u l a r r a t e of inward motion demonstrated by both IPDPs s t u d i e d c o u l d then be i n t e r p r e t e d t o mean t h a t the plasmapause shape i t s e l f i s somewhat i r r e g u l a r w i t h the plasmapause moving e i t h e r v e r y l i t t l e or a t a c o n s t a n t r a t e d u r i n g t h e s e e v e n t s . A l t e r n a t e l y , d u r i n g the p e r i o d s of f a s t e r motion e x h i b i t e d d u r i n g t h e i r c e n t r a l time spans by bot h IPDPs ( c f . f i g . 31, 3 8 ) , a d d i t i o n a l plasmapause inward d i s p l a c e m e n t c o u l d be superimposed on a r e l a t i v e l y smooth inward motion due t o a smoother plasmapause shape. That the plasmapause would move most d u r i n g the m i d d l e of an IPDP event may not be unexpected, s i n c e the e l e c t r i c and magnetic f i e l d s which c o n t r o l the plasmapause p o s i t i o n may a l s o be chan g i n g a t t h i s time due t o magnetospheric substorm e f f e c t s . These' e f f e c t s , which i n c l u d e the ch a n g i n g plasma and f i e l d e nvironments a s s o c i a t e d w i t h the p r o t o n westward d r i f t p r o c e s s , c o u l d have an e f f e c t on the plasmapause p o s i t i o n , and i f so then may a f f e c t the plasmapause most when the p r o t o n s g e n e r a t i n g the IPDP are a r r i v i n g t h e r e . The r i n g c u r r e n t - IPDP model d i s c u s s e d i n s e c t i o n 5.2, though s i g n i f i c a n t l y improved over p r e v i o u s models, i s s t i l l q u i t e s i m p l e . N e v e r t h e l e s s , the c o n c l u s i o n can be drawn from i t t h a t the i n c r e a s i n g magnetic f i e l d mechanism f o r the IPDP f r e q u e n c y r i s e i s not a n e c e s s a r y c o n d i t i o n f o r IPDPs t o o c c u r , s i n c e case I and I I I e v e n t s do occur ( c f . s e c t i o n 198 5.2). I t can, however, under c e r t a i n c i r c u m s t a n c e s , s t i l l c o n t r i b u t e t o the f r e q u e n c y s h i f t of seme IPDPs, such as case I I and IV e v e n t s . I t i s a l s o shown t h a t the geosynchronous s a t e l l i t e magnetograms a l o n e cannot be used as a method of d e t e r m i n i n g IPDP sou r c e r e g i o n f i e l d b e h a v i o u r u n l e s s the IPDP i s b e i n g g e n e r a t e d i n the v i c i n i t y of L = 6.6. The i n c r e a s i n g f i e l d mechanism does not appear t o have c o n t r i b u t e d s i g n i f i c a n t l y t o the IPDPs examined h e r e . For t h i s mechanism, however, the assessment remains o n l y a q u a l i t a t i v e one due t o the d i f f i c u l t y i n q u a n t i t a t i v e l y d e t e r m i n i n g any changes i n magnetic f i e l d s t r e n g t h i n the IPDP s o u r c e r e g i o n from the i n f o r m a t i o n a v a i l a b l e . Lower a l t i t u d e , t h a t i s , L < 6.6, s a t e l l i t e magnetic f i e l d measurements i n the g e n e r a t i o n r e g i o n d u r i n g an IPDP would be n e c e s s a r y t o e v a l u a t e q u a n t i t a t i v e l y the i n c r e a s i n g f i e l d mechanism e f f e c t on IPDP f r e q u e n c y s h i f t s . The hot p r o t o n energy change e f f e c t p l a y e d a secondary r o l e i n c r e a t i n g the IPDP f r e q u e n c y s h i f t s o b s e r v e d h e r e . In one e v e n t , i t a c t u a l l y had the unusual e f f e c t of s u p p r e s s i n g the f r e q u e n c y r i s e . S e c t i o n 5.3 showed t h a t both the r i n g c u r r e n t i n d u c e d magnetic f i e l d d e p r e s s i o n and the i n j e c t i o n boundary p o s i t i o n must be e s t i m a t e d i n o r d e r t o f i n d the e n e r g i e s of the p r o t o n s g e n e r a t i n g the IPDP. T h i s e s t i m a t i o n p r o c e s s r e q u i r e s the assumption t h a t o n l y the p r o t o n energy 199 e f f e c t and the A B - a d j u s t e d inward motion mechanism a r e o p e r a t i n g , and would be i n a p p r o p r i a t e i f a p p l i e d t o an IPDP t o which the i n c r e a s i n g f i e l d mechanism was b e l i e v e d t o be making a s i g n i f i c a n t c o n t r i b u t i o n . I t s h o u l d a l s o be p o i n t e d out t h a t the s e l e c t i o n p r o c e s s by which the b e s t f i e l d d e p r e s s i o n v a l u e and i n j e c t i o n boundary p o s i t i o n a r e chosen i s p a r t i a l l y s u b j e c t i v e , e s p e c i a l l y w i t h r e g a r d s t o the w e i g h t s a s s i g n e d t o each of the s e l e c t i o n c r i t e r i a . The a n a l y s i s of the l o n g i t u d i n a l s t r u c t u r e and development of IPDPs p r e s e n t e d i n s e c t i o n 5.4 i n d i r e c t l y s u p p o r t s the f r e q u e n c y r i s e r e s u l t s d i s c u s s e d above by s u p p o r t i n g the model from which they are produced. In a d d i t i o n , the d e t a i l e d a n a l y s e s of the IPDPs showed t h a t l o n g i t u d i n a l v a r i a t i o n s w i t h i n IPDP e v e n t s e x i s t over much s m a l l e r l o n g i t u d i n a l s e p a r a t i o n s than p r e v i o u s l y r e p o r t e d ( c f . s e c t i o n 3.3). In c o n s i d e r i n g the o v e r a l l s i g n i f i c a n c e of the r e s u l t s d i s c u s s e d above, i t must be remembered t h a t o n l y two IPDP ev e n t s have been s t u d i e d i n d e t a i l . From j u s t two e v e n t s , s t r o n g c o n c l u s i o n s • r e g a r d i n g the r e l a t i v e importance of the d i f f e r e n t f r e q u e n c y s h i f t mechanisms cannot be extended t o r e l i a b l y a p p l y t o a l l IPDP e v e n t s . For example, the degree of i n f l u e n c e of each mechanism may change w i t h v a r y i n g m agnetospheric c o n d i t i o n s and/or IPDP source r e g i o n 200 l o c a t i o n s . I t i s i n t e r e s t i n g t o note t h a t the two IPDPs s t u d i e d here d i d occur a t d i s p a r a t e GMLT l o c a t i o n s and under d i v e r s e l e v e l s of magnetospheric a c t i v i t y . W h i l e both e x h i b i t e d s t r o n g inward motion mechanism c o n t r i b u t i o n s , t h e i r hot p r o t o n energy change e f f e c t s were of o p p o s i t e s i g n , i n d i c a t i n g t h a t such s y s t e m a t i c v a r i a t i o n s i n the f r e q u e n c y s h i f t mechanisms' c o n t r i b u t i o n s a r e a t l e a s t a p o s s i b i l i t y . To study p o t e n t i a l t r a i t s such as t h e s e , the a n a l y s i s of many more e v e n t s would be r e q u i r e d . The n e g a t i v e f r e q u e n c y s h i f t from the hot p r o t o n energy change e f f e c t d i s p l a y e d by one IPDP here ( c f . f i g . 58) has not been p r e v i o u s l y r e p o r t e d and was termed u n u s u a l above, y e t , w i t h o u t an extended s t u d y c o v e r i n g many e v e n t s , i t i s not r e a l l y known how r a r e such b e h a v i o u r a c t u a l l y i s . I t i s a l s o n e c e s s a r y t o be somewhat c a u t i o u s when c o n s i d e r i n g the d e t a i l s of the i n d i v i d u a l r e s u l t s . We must bear i n mind such t h i n g s as the i n c o m p l e t e d a t a s e t on which the a n a l y s e s were performed, the somewhat s i m p l i s t i c a p p l i c a t i o n of i o n o s p h e r i c duct t h e o r y n e c e s s a r y , and the s i m p l i f y i n g assumptions i n v o l v e d i n the IPDP g e n e r a t i o n model. These a s p e c t s can a f f e c t not o n l y the a c c u r a c y of the IPDP s o u r c e p o s i t i o n d e t e r m i n a t i o n and inward motion f r e q u e n c y s h i f t e s t i m a t e , but a l s o the a z i m u t h a l d r i f t f r e q u e n c y s h i f t e s t i m a t e , s i n c e t h i s depends, i n p a r t , on the s o u r c e inward motion r e s u l t s . The a z i m u t h a l d r i f t 201 e s t i m a t e a l s o depends on the assumption t h a t a l l i n j e c t i o n b o u n d a r i e s t a k e the form e x p r e s s e d by e q u a t i o n 5.8. However, b a r r i n g any major s h i f t s i n our g e n e r a l u n d e r s t a n d i n g of such p r o c e s s e s as i n j e c t i o n boundary f o r m a t i o n , r i n g c u r r e n t development, or i o n o s p h e r i c duct p r o p a g a t i o n , the g e n e r a l c o n c l u s i o n s r e g a r d i n g the r e l a t i v e importance of each of the f r e q u e n c y s h i f t mechanisms t o the e v e n t s s t u d i e d here s h o u l d be v a l i d . CHAPTER 6 . CONCLUSION We have made a q u a n t i t a t i v e study of two IPDP f r e q u e n c y s h i f t mechanisms, s u p p o r t e d by a q u a l i t a t i v e assessment of the r o l e of a p o t e n t i a l t h i r d mechanism. W i t h i n the framework of a magnetospheric IPDP g e n e r a t i o n model, i t has become e v i d e n t t h a t the inward motion of the magnetospheric source r e g i o n i s the dominant cause of the IPDP f r e q u e n c y r i s e , w i t h the hot p r o t o n energy v a r i a t i o n s c o n t r i b u t i n g t o a l e s s e r degree. The model c o n s i d e r e d c o n s i s t s of a westward d r i f t of e n e r g e t i c p r o t o n s from a substorm i n j e c t i o n boundary and subsequent wave a m p l i f i c a t i o n by t h e s e p r o t o n s at the plasmapause t h r o u g h the p r o t o n - c y c l o t r o n i n s t a b i l i t y . These c o n c l u s i o n s a r e the outcome of the d e t a i l e d a n a l y s e s of the two e v e n t s s t u d i e d h e r e . These r e s u l t s a r e s u p p o r t e d by model c a l c u l a t i o n s ( s e c t i o n 4.4), which a l s o show the inward motion mechanism g e n e r a l l y c o n t r i b u t i n g s i g n i f i c a n t l y more than the hot p r o t o n energy change e f f e c t . In a d d i t i o n , model c a l c u l a t i o n s show t h a t the inward motion can be l a r g e l y due t o the shape of the plasmapause, as opposed t o inward d i s p l a c e m e n t of the plasmapause. These model c a l c u l a t i o n s a l s o show t h a t the p o s s i b i l i t y e x i s t s t h a t e a stward d e v e l o p i n g IPDPs, o p p o s i t e to what i s now c o n s i d e r e d the normal t r e n d , may o c c u r . We have shown t h a t p r e v i o u s methods of i n t e r p r e t i n g the i n c r e a s i n g magnetic f i e l d mechanism's e f f e c t on IPDPs gave 202 203 i n s u f f i c i e n t a t t e n t i o n t o the d i f f e r e n c e s i n t e m p o r a l f i e l d b e h a v i o u r between geosynchronous o r b i t and the somewhat lower IPDP source r e g i o n s as caused by the dynamic n a t u r e of the storm time r i n g c u r r e n t . When even a s i m p l e d e s c r i p t i o n of r i n g c u r r e n t dynamics i s used, i n c l u d i n g the r i n g c u r r e n t ' s growth, inward d i s p l a c e m e n t , and decay d u r i n g the c o u r s e of a magnetic storm, i t becomes e v i d e n t t h a t the i n c r e a s i n g f i e l d mechanism may enhance, s u p p r e s s , or have no e f f e c t on an IPDP's f r e q u e n c y r i s e depending on the e v e n t ' s source r e g i o n l o c a t i o n and the storm phase d u r i n g which i t o c c u r s . However, t h i s mechanism i s never a r e q u i r e d p r o c e s s upon which an IPDP's e x i s t e n c e depends. In c o n t r a s t t o t h i s , due t o plasmapause geometry, some inward motion of the IPDP so u r c e r e g i o n w i l l always e x i s t . However, a c t u a l plasmapause inward d i s p l a c e m e n t w i l l not n e c e s s a r i l y always t a k e p l a c e . T h i s inward motion mechanism i s , though, the o n l y mechanism which w i l l always be p r e s e n t , as shown by the f a c t t h a t one of the two e v e n t s s t u d i e d d i s p l a y e d hot p r o t o n energy v a r i a t i o n s which r e s u l t e d i n a s l i g h t s u p p r e s s i o n of the f r e q u e n c y r i s e . In s p i t e of the f a c t t h a t a z i m u t h a l d r i f t v e l o c i t e s w i l l always produce a s o f t e n i n g p r o t o n energy spectrum as observed a t c o n s t a n t L, r a p i d c r o s s - L motion of the s o u r c e can r e v e r s e t h i s t r e n d , as "seen" by a ground s t a t i o n , y i e l d i n g an i n c r e a s i n g energy t r e n d whose e f f e c t a c t s t o d e p r e s s an IPDP's f r e q u e n c y r i s e . 204 Due t o l i m i t a t i o n s of the 1980 IPDP d a t a s e t used here ( c f . s e c . 2.1), o n l y two events were s t u d i e d i n d e t a i l and even t h e s e s u f f e r e d from i n c o m p l e t e s t a t i o n c o v e r a g e . D e s p i t e t h i s , i t has s t i l l been p o s s i b l e t o g a i n new i n s i g h t s i n t o the g e n e r a t i o n p r o c e s s e s of IPDPs. In a d d i t i o n , new methods f o r the stu d y of IPDPs have a l s o been d e v e l o p e d , as d e s c r i b e d i n s e c t i o n s 4.4 th r o u g h 5.4, which p r o v i d e a good b a s i s f o r f u t u r e work u s i n g more complete d a t a s e t s . As noted i n Chapter One, IPDPs have o f t e n been t o u t e d as a p o t e n t i a l l y u s e f u l t o o l f o r the d i a g n o s i s of magnetospheric c o n d i t i o n s . U n f o r t u n a t e l y , t h i s has not been r e a l i z e d t o any l a r g e e x t e n t as y e t . Now, however, w i t h a b e t t e r u n d e r s t a n d i n g of the f r e q u e n c y s h i f t mechanisms, we can b e g i n t o r e a l i z e some of the p o t e n t i a l of the stu d y of IPDPs. I t has been demonstrated here t h a t the d e t a i l e d s t u d y of i n d i v i d u a l IPDP events can y i e l d i n f o r m a t i o n on plasmapause p o s i t i o n and movement, d r i f t i n g p r o t o n e n e r g i e s , i n j e c t i o n boundary shapes, and r i n g - c u r r e n t c r e a t e d magnetic f i e l d d e p r e s s i o n s i n the IPDP g e n e r a t i o n r e g i o n . T h i s i s o n l y a b e g i n n i n g , however. The q u a l i t y and r e l i a b i l i t y of such i n f o r m a t i o n c o u l d be improved and o t h e r uses of IPDPs made i f our u n d e r s t a n d i n g of t h e s e m i c r o p u l s a t i o n s were t o be s o l i d i f i e d and extended. To do t h i s would r e q u i r e the a n a l y s i s of many w e l l r e c o r d e d e v e n t s from s t a t i o n networks 205 which i n c l u d e two or more a d j a c e n t n o r t h - s o u t h c h a i n s of s i t e s , a l l o w i n g the development of a t w o - d i m e n s i o n a l p i c t u r e of IPDP g e n e r a t i o n founded on e x p e r i m e n t . I t would a l s o be n e c e s s a r y t o i n c l u d e s a t e l l i t e magnetograms from L < 6.6 and/or a much more s o p h i s t i c a t e d r i n g c u r r e n t model t o q u a n t i t a t i v e l y u n d e r s t a n d the r o l e of t e m p o r a l magnetic f i e l d v a r i a t i o n s i n IPDP g e n e r a t i o n . I f such c o n c e r n s can be s a t i s f i e d by f u t u r e work, IPDPs may f i n a l l y t a k e t h e i r p l a c e as a u s e f u l type of m i c r o p u l s a t i o n i n magnetospheric p h y s i c s . REFERENCES A l t h o u s e , E.L., and J.R. 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Lyons, 1974b, F u r t h e r a s p e c t s of the p r o t o n r i n g c u r r e n t i n t e r a c t i o n w i t h the plasmapause: main and r e c o v e r y phases: J . Geophys. Res. 79, 4791-4798. W i l l i a m s , D.J., 1985, Dynamics of E a r t h ' s r i n g c u r r e n t : t h e o r y and o b s e r v a t i o n : Space S c i . Rev. 42, 375-396. APPENDIX A. THE ION-CYCLOTRON INSTABILITY AND IPDP FREQUENCY In o r d e r t o comprehend how the IPDP f r e q u e n c y r i s e i s produced, we must u n d e r s t a n d which p h y s i c a l f a c t o r s a f f e c t the f r e q u e n c y of waves a m p l i f i e d by the i o n - c y c l o t r o n i n s t a b i l i t y mechanism as w e l l as the magnitude of the e f f e c t of each of th e s e f a c t o r s . The d i s p e r s i o n r e l a t i o n f o r a l e f t hand p o l a r i z e d i o n - c y c l o t r o n wave p r o p a g a t i n g p a r a l l e l t o the background magnetic f i e l d i n a two component, p r o t o n and e l e c t r o n , plasma i s ( J a c o b s , 1 9 7 0 ) : ( k / c ) 2 c 2 = 1 - "P* - "PP ( A . 1 ) u>(u>+ S2 ) o n c o - f l ; 1 e 1 p where u>^ i s the plasma f r e q u e n c y , fl i s the g y r o f r e q u e n c y , and the s u b s c r i p t s { g) and ( ) r e f e r , r e s p e c t i v e l y , t o the e l e c t r o n and p r o t o n components. For a c o l d plasma, the p r o t o n - c y c l o t r o n resonance o c c u r s when the phase v e l o c i t y v ^ = cj/k = 0 . From e q u a t i o n A . 1 , t h i s happens when (w - fl ) = 0 , or OJ = 0 . For the IPDP P P c a s e , however, i n which the i n t e r a c t i o n i s between waves and warm p r o t o n s w i t h a ,non-zero s t r e a m i n g v e l o c i t y v„, the resonance c o n d i t i o n can be e x p r e s s e d as ( J a c o b s , 1 9 7 0 ) : 2 1 4 215 a) , - kv„ - co = 0 or CJ - kv» - U = 0 (A. 2) obs em p where w , i s the o b s e r v e d f r e q u e n c y and w i s the e m i t t e d obs ^ * em frequency i n the p r o t o n " r e s t frame", s i n c e the wave frequency (" 0^ 5 ° r must be d o p p l e r s h i f t e d , i n the p r o t o n " r e s t frame", t o match the p r o t o n g y r o f r e q u e n c y i^em or 0 ^ ) . The p r o t o n r e s t frame mentioned above i s t h a t r e f e r e n c e frame moving w i t h v e l o c i t y v« a l o n g the background magnetic f i e l d l i n e i n such a way t h a t the p r o t o n p a r a l l e l v e l o c i t y i s z e r o w i t h i n the r e f e r e n c e frame. By s u b s t i t u t i n g the above IPDP resonance c o n d i t i o n i n t o e q u a t i o n A.1, we can e l i m i n a t e the k dependence, and t h e r e f o r e study the e f f e c t s on the resonance f r e q u e n c y (w) of p arameters such as background magnetic f i e l d s t r e n g t h ( B 0 ) , and hot p r o t o n d e n s i t y ^ n p ^ a n < ^ energy (W) . In o r d e r to do t h i s , we c o n s i d e r the f o l l o w i n g : m^  i s n e g l i g i b l e as compared t o m^ , u> i s n e g l i g i b l e as compared t o u p e i the plasma i s n e u t r a l ( n ^ = n ), and the p r o t o n " p a r a l l e l energy" i s g i v e n by W» = m^v 2/2. The r e s u l t i s : * - - i 3 2 B ° q 2 n W« 87T m2 c 2 P P 1 " (2 P (A.3) where q r e p r e s e n t s the e l e c t r i c charge of the r e s o n a t i n g 216 p a r t i c l e s . S i n c e co < fl^, e q u a t i o n A.3 can be f u r t h e r s i m p l i f i e d t o (Roxburgh, 1970): Bo C J = * K* j (A.4a) (n W „ ) 2 P i where K = ( q 2 / ( 8 7 r m^ c 2 ) ) 2 . Another common s i m p l i f y i n g assumption i s t h a t n^ B 0 (Roxburgh, 1970; G e n d r i n e t a l . , 1971; P e r r a u t e t a l . , 1984). In a d d i t i o n , the t o t a l p r o t o n energy W can be r e l a t e d t o W« by W„ = Wcos 2a, where a i s the p r o t o n p i t c h a n g l e . Then, s u b s t i t u t i n g f o r n^ and VI,,, e q u a t i o n A.4a becomes: 3. ( B 0 ) 2 w X (A.4b) W2 E q u a t i o n A.4b c l e a r l y shows the e f f e c t s of background magnetic f i e l d s t r e n g t h and hot p r o t o n energy on IPDP f r e q u e n c y , and thus a l l o w s us t o examine the problem of IPDP frequency s h i f t s i n terms of changes i n t h e s e p a r a m e t e r s . T h i s r e s u l t i s used i n the study of IPDPs i n C h a p t e r s Four and F i v e . APPENDIX B. THE IONOSPHERIC WAVEGUIDE M i c r o p u l s a t i o n s w i t h f r e q u e n c i e s i n the upper p a r t of the Pc 1 range, which i n c l u d e s many IPDPs, a re commonly ob s e r v e d a t low l a t i t u d e s even though t h e i r s o u r c e f i e l d l i n e s a r e u s u a l l y a t L > 4, i n d i c a t i n g t h a t they r e a c h the s u r f a c e a t ^60° GM l a t i t u d e . S i n c e t h e s e waves propagate down t o the io n o s p h e r e as f i e l d - g u i d e d l e f t - h a n d (LH) p o l a r i z e d hydromagnetic waves, a l s o termed slow mode hm waves, they must r e a c h t h e s e lower l a t i t u d e s t h r ough h o r i z o n t a l p r o p a g a t i o n from h i g h e r l a t i t u d e s i n the i o n o s p h e r i c waveguide. C o n s i d e r a b l e e x p e r i m e n t a l e v i d e n c e e x i s t s f o r p r o p a g a t i o n i n such a waveguide a l o n g the geomagnetic m e r i d i a n , though the presence of d u c t i n g i n o f f - m e r i d i a n d i r e c t i o n s i s l e s s c l e a r . ( T e p l e y and L a n d s h o f f , 1966; Campbell and T h o r n b e r r y , 1972; F r a s e r , 1975a,b; A l t h o u s e and D a v i s , 1978; Hayashi e t a l . , 1981). The a b i l i t y of the io n o s p h e r e t o t r a p and guide hm waves i s due t o i t s height-dependent i o n i z a t i o n s t r u c t u r e (see f i g . 6 5 ) . The pronounced peak i n i o n i z a t i o n c r e a t e s an A l f v e n v e l o c i t y minimum t h e r e , and i t i s w i t h i n t h i s l a y e r t h a t d u c t i n g can ta k e p l a c e . Note t h a t f i g u r e 65 a l s o shows t h a t the i o n i z a t i o n peak i s s h a r p e r a t n i g h t , r e s u l t i n g i n lower duct a t t e n u a t i o n than d u r i n g the day. As mentioned above, slow, or o r d i n a r y , mode waves a r e f i e l d g u i d e d , and so cannot c r o s s the magnetic f i e l d l i n e s . 217 218 6 7 8 9 10 11 12 13 electron density (log c m " 3 ) FIGURE 65. E l e c t r o n d e n s i t y p r o f i l e s f o r both day and n i g h t sunspot maximum c o n d i t i o n s ( P r i n c e and B o s t i c k , 1964). Note t h a t a t n i g h t , the F2 l a y e r i o n i z a t i o n i s , r e l a t i v e t o the daytime p r o f i l e , much s t r o n g e r than the l a y e r s beneath i t . 219 T h i s , t h e r e f o r e , cannot be the mode p r o p a g a t i n g h o r i z o n t a l l y i n the i o n o s p h e r i c d u c t , s i n c e , except near the e q u a t o r , the geomagnetic f i e l d l i n e s c u t o b l i q u e l y a c r o s s the d u c t . The mode b e l i e v e d t o c a r r y the energy h o r i z o n t a l l y i n the duct i s t he f a s t , or e x t r a o r d i n a r y , mode. P r o p a g a t i o n of t h i s f a s t mode i s i s o t r o p i c , and s i n c e i t i s not g u i d e d by the ambient magnetic f i e l d , i t can t r a v e l h o r i z o n t a l l y w i t h i n the d u c t . The c o u p l i n g between th e s e two modes, which i s n e c e s s a r y f o r energy i n j e c t i o n i n t o the d u c t , has been a t t r i b u t e d t o the f i n i t e e x t e n t of the a r e a of i o n o s p h e r i c i n c i d e n c e , a l s o termed the secondary s o u r c e , by Jacobs and Watanabe (1962). I t i s a l s o s a i d t o be a consequence of a l t i t u d e - d e p e n d e n t v a r i a t i o n s i n p o l a r i z a t i o n of the incoming slow mode wave as i t t r a v e r s e s the F - l a y e r (Altman and F i j a l k o w , 1980). N u m e r i c a l a n a l y s i s p r e s e n t e d i n the l a t t e r work a l s o s u g g e s t s t h a t energy i n j e c t i o n i n t o the duct i s most e f f i c i e n t a t h i g h e r l a t i t u d e s (>45°), and t h a t i t t a k e s p l a c e over the e n t i r e a l t i t u d e range of the F 2 - l a y e r d u c t . Other i o n o s p h e r i c waveguide models (such as Manchester, 1966,1968; G r e i f i n g e r and G r e i f i n g e r , 1968) have not s p e c i f i c a l l y t r e a t e d the problem of i n j e c t i o n i n t o the duct o t h e r than t o say t h a t mode c o u p l i n g t a k e s p l a c e i n the lower i o n o s p h e r e . Once i n the i o n o s p h e r i c d u c t , the t r a p p e d wave 220 p r o p a g a t e s h o r i z o n t a l l y i n a s e r i e s of r e f l e c t i o n s from the upper and lower duct w a l l s , as i l l u s t r a t e d i n f i g u r e 66. T h i s f i g u r e shows t h a t most of the energy i s r e f l e c t e d from narrow a l t i t u d e ranges a t both the t o p and bottom of the d u c t , g i v i n g a w e l l d e f i n e d duct r e g i o n . The r e f l e c t i o n c o e f f i c i e n t s a t thes e w a l l s f o r the t r a p p e d f a s t mode wave a r e t y p i c a l l y 0.5 - 0.85 (Altman and F i j a k o w , 1980) (see f i g . 6 6 ) . E s t i m a t e s of a t t e n u a t i o n i n the duct v a r y somehat depending on the i o n o s p h e r i c waveguide model c o n s i d e r e d ; Manchester (1968), a t t r i b u t i n g a t t e n u a t i o n p r i m a r i l y t o a b s o r p t i o n , e s t i m a t e d ^4 db/1000km, w h i l e Altman and F i j a l k o w (1980) found a r a t e of 6-9 db/l000km due t o f a s t - t o - s l o w mode c o u p l i n g i n the d u c t . A d i u r n a l v a r i a t i o n i n duct a t t e n u a t i o n i s a l s o produced by thos e models c o n s i d e r i n g the d a i l y v a r i a t i o n s i n i o n o s p h e r i c s t r u c t u r e . The appearance of the E r e g i o n i n the daytime i o n o s p h e r e s t r o n g l y a f f e c t s the i o n i z a t i o n p r o f i l e ( c f . f i g . 6 5 ) , r e s u l t i n g i n i n c r e a s e d duct a t t e n u a t i o n d u r i n g the day. T h i s i n c r e a s e , r e l a t i v e t o n i g h t i m e a t t e n u a t i o n , has been c a l c u l a t e d t o be of r o u g h l y an o r d e r of magnitude ( G r e i f i n g e r and G r e i f i n g e r , 1968) or more (Manchester, 1966). The e x p e r i m e n t a l r e s u l t s of A l t h o u s e and D a v i s (1978) y i e l d e d a t y p i c a l a t t e n u a t i o n of =*6.5 db/1000km d u r i n g the e a r l y morning h o u r s , though the v a l u e s were q u i t e v a r i a b l e from day t o day and reached as n i g h as 13 db/1000km. I I I f = 1Hz NIGHT SUNSPOT MAX. 0.2 0.4 0.6 0.8 REFLECTION COEFFICIENTS FIGURE 66. Top: T y p i c a l p r o p a g a t i o n p a t h s f o r t r a p p e d f a s t mode ( l a b e l l e d E ( e x t r a o r d i n a r y ) mode i n the diagram) waves i n the F2 r e g i o n duct ( a f t e r Manchester, 1966). Bottom: H e i g h t p r o f i l e of R-mode r e f l e c t i o n c o e f f i c i e n t s f o r d i f f e r e n t v a l u e s of S n e l l ' s c o n s t a n t S (=n«sin0) ( a f t e r Altman and F i j a l k o w , 1980). 222 F i n a l l y , i t s h o u l d be p o i n t e d out t h a t the a t t e n u a t i o n v e r s u s f r e q u e n c y p r o f i l e s produced by the d i f f e r e n t waveguide models d i f f e r s i g n i f i c a n t l y . The i o n o s p h e r i c waveguide a l s o appears t o e x h i b i t a lower c u t - o f f f r e q u e n c y near 0.5Hz. T h i s c u t - o f f f r e q u e n c y v a r i e s w i t h duct c o n d i t i o n s and has been v a r i o u s l y c a l c u l a t e d a t 0.45Hz by Manchester (1968), w i t h the c u t - o f f b e i n g due t o a t t e n u a t i o n , and depending on the i o n i z a t i o n c o n d i t i o n s between 0.10 and 0.36 Hz by G r e i f i n g e r and G r e i f i n g e r (1968), w i t h the c u t - o f f b e i n g due t o boundary c o n d i t i o n s . One a s p e c t on which the d i f f e r e n t models agree f a i r l y w e l l , b o th among themselves and w i t h o b s e r v a t i o n s , i s the group v e l o c i t y of f a s t mode p r o p a g a t i o n w i t h i n the d u c t , which i s t y p i c a l l y 300-800 km/sec, depending on i o n o s p h e r i c c o n d i t i o n s ( T e p l e y and L a n d s h o f f , 1966; Manchester, 1966, 1968; G r e i f i n g e r and G r e i f i n g e r , 1968; Altman and F i j a l k o w , 1980). Note t h a t two of the most i m p o r t a n t f a c t o r s c o n t r o l l i n g i o n i z a t i o n c o n d i t i o n s i n the i o n o s p h e r i c waveguide a r e the l o c a l time and the sunspot number. The events s t u d i e d i n t h i s t h e s i s were r e c o r d e d near sunspot maximum. The waveguide r e s u l t s d i s c u s s e d so f a r have been f o r m e r i d i o n a l p r o p a g a t i o n o n l y , s i n c e a common s i m p l i f y i n g assumption i n duct models, j u s t i f i e d by some e x p e r i m e n t a l r e s u l t s , has been t o c o n s i d e r o n l y p r o p a g a t i o n i n t h i s 223 d i r e c t i o n . G r e i f i n g e r and G r e i f i n g e r (1973) showed t h a t , f o r o f f - m e r i d i a n d i r e c t i o n s , c o u p l i n g between the d u c t e d f a s t mode wave and the f i e l d g u i d e d slow mode wave produces g e n e r a l l y two t o f o u r l a r g e peaks i n a t t e n u a t i o n w i t h i n the IPDP f r e q u e n c y band. The f r e q u e n c y ranges c o v e r e d by t h e s e peaks, each of which i s = 0.1 t o 0.3 Hz wide, a r e dependent on geomagnetic l a t i t u d e . Thus, f o r any o f f - m e r i d i a n d i r e c t i o n e x cept p u r e l y e a s t - w e s t , each f r e q u e n c y component of a wave w i l l e ncounter a r e g i o n of h i g h a t t e n u a t i o n as the l a t i t u d e v a r i e s a l o n g the wave's p a t h , e f f e c t i v e l y e l i m i n a t i n g o f f - m e r i d i o n a l d u c t i n g ( G r e i f i n g e r and G r e i f i n g e r , 1973). The t r e a t m e n t of Altman and F i j a l k o w (1980) i n c l u d e d d u c t i n g i n both the n o r t h - s o u t h and e a s t - w e s t d i r e c t i o n s , and found t h a t a t t e n u a t i o n of waves t r a v e l l i n g i n the e a s t - w e s t d i r e c t i o n t o be g e n e r a l l y o n l y s l i g h t l y l a r g e r than f o r those t r a v e l l i n g a l o n g the m e r i d i a n . E x p e r i m e n t a l l y , the Pc 1 o b s e r v a t i o n s of Hayashi et a l . (1981) a l s o i n d i c a t e t h a t d u c t i n g o c c u r s p r e f e r e n t i a l l y i n the e a s t - w e s t and n o r t h - s o u t h d i r e c t i o n s . The p o l a r i z a t i o n c h a r a c t e r i s t i c s of some Pc 1 band m i c r o p u l s a t i o n s , i n c l u d i n g IPDPs, can be v e r y u s e f u l i n u n d e r s t a n d i n g these e v e n t s . As s t a t e d above, the i n i t i a l i ncoming slow mode wave has LH p o l a r i z a t i o n . However, the d u c t e d mode i n t o which i t i s c o n v e r t e d , the f a s t mode, has RH p o l a r i z a t i o n . T h i s c o u l d be e x p e c t e d t o l e a d t o 224 o b s e r v a t i o n s of LH p o l a r i z a t i o n a t ground s t a t i o n s below the incoming f i e l d g uided wave, and RH p o l a r i z a t i o n a t s t a t i o n s beneath the d u c t e d wave. However, i t has been shown t h a t the h o r i z o n t a l component p e r p e n d i c u l a r t o the d i r e c t i o n of p r o p a g a t i o n i s not t r a n s m i t t e d t o the s u r f a c e , so t h a t , a t l a r g e d i s t a n c e s from the source f i e l d l i n e s , the p o l a r i z a t i o n s h o u l d be n e a r l y l i n e a r w i t h the e l l i p s e a x i s a l i g n e d w i t h the d i r e c t i o n of p r o p a g a t i o n ( G r e i f i n g e r and G r e i f i n g e r , 1968; Rudenko et a l . , 1985). The v e r t i c a l component of the wave f i e l d w i l l v a n i s h a t the s u r f a c e , assuming i n f i n i t e ground c o n d u c t i v i t y ( G r e i f i n g e r , 1972). In r e g i o n s near but not under the incoming wave, the p o l a r i z a t i o n s can be complex, w i t h the d i r e c t wave, here a p p e a r i n g as RH ( G r e i f i n g e r , 1972), superimposed on the l i n e a r appearance of the d u c t e d wave. E x p e r i m e n t a l l y , A l t h o u s e and D a v i s (1978) and Hayashi et a l . (1981) o b t a i n e d mixed r e s u l t s from Pc 1 p o l a r i z a t i o n s t u d i e s , though i n the former case s t a t i o n s f a r from the source d i d show m a i n l y l i n e a r p o l a r i z a t i o n . These r e s u l t s may be due t o the near source complex r e g i o n noted above and/or t o the s u p e r p o s i t i o n of two or more waves a r r i v i n g a t the same s i t e from d i f f e r e n t d i r e c t i o n s as a r e s u l t of h o r i z o n t a l g r a d i e n t s i n i o n o s p h e r i c d e n s i t i e s a f f e c t i n g wave p r o p a g a t i o n p a t h s (Altman and F i j a l k o w , 1980). In g e n e r a l t h e r e i s a r e a s o n a b l y good q u a l i t a t i v e match 225 between most model c a l c u l a t i o n r e s u l t s and duct p r o p a g a t i o n o b s e r v a t i o n s . Examples of t h i s i n c l u d e the e x i s t e n c e of a c u t - o f f f r e q u e n c y , g e n e r a l p o l a r i z a t i o n p a t t e r n s , d i u r n a l v a r i a t i o n s i n duct a t t e n u a t i o n , and l a c k of a s i g n i f i c a n t v e r t i c a l wave component. However, on a more d e t a i l e d l e v e l , i n c l u d i n g q u a n t i t a t i v e a s p e c t s , the models' p r e d i c t i o n s do not always agree w e l l w i t h each o t h e r or w i t h e x p e r i m e n t a l r e s u l t s . T h i s i s q u i t e l i k e l y due t o the d i f f e r e n t approaches taken by some a u t h o r s , and, perhaps more i m p o r t a n t l y , the v a r i a n t assumptions used i n t h e i r d i f f e r e n t works. These assumptions i n c l u d e , among o t h e r a s p e c t s ; v e r t i c a l s t r a t i f i c a t i o n s of the i o n o s p h e r e , wave i n c i d e n c e a n g l e s , h o r i z o n t a l homogeneity i n the i o n o s p h e r e , c o l l i s i o n s , mode c o u p l i n g , background magnetic f i e l d s , and ground c o n d u c t i v i t y . Such d i s a g r e e m e n t s make i t i m p r a c t i c a l t o use any s p e c i f i c r e s u l t s as an a i d t o IPDP i n t e r p r e t a t i o n . T h e r e f o r e , the c h a r a c t e r i s t i c s of i o n o s p h e r i c p r o p a g a t i o n r e q u i r e d i n t h i s t h e s i s have been o b t a i n e d from the d a t a a n a l y s e d f o r the Feb. 14 and Feb. 15 IPDPs. A t t e n u a t i o n has been c a l c u l a t e d from the measured s i g n a l l e v e l s from s t a t i o n s on a n o r t h - s o u t h l i n e , and proved t o be g r e a t e r than most model r e s u l t s . W h i l e the a t t e n u a t i o n found from the daytime e v e n t , the Feb. 15 e v e n t , was l a r g e r than t h a t f o r the n i g h t e v e n t , the Feb. 14 IPDP, the d i f f e r e n c e was 226 not as extreme as p r e d i c t e d . The p o l a r i z a t i o n p a t t e r n seen i n t h e s e IPDPs of LH below the secondary source and RH elsewhere was as e x p e c t e d . In a d d i t i o n , t h e r e were i n t e r v a l s of LH p o l a r i z a t i o n c o v e r i n g the low f r e q u e n c y b e g i n n i n g s of the e v e n t s , i n d i c a t i n g the presence of non-ducted waves a t f r e q u e n c i e s below the duct c u t - o f f f r e q u e n c y . These c u t - o f f f r e q u e n c i e s were g e n e r a l l y s i m i l a r t o , though somewhat h i g h e r t h a n , the e x p e c t e d v a l u e s . The p a t t e r n of t h e i r d i u r n a l v a r i a t i o n , lower d u r i n g the day, was as p r e d i c t e d . APPENDIX C. GEOMAGNETIC INDICES A geomagnetic index i s a system which a t t e m p t s t o p r o v i d e summarized i n f o r m a t i o n c o n c e r n i n g the b e h a v i o u r of a s p e c i f i c geomagnetic v a r i a t i o n . I n d i c e s a re g e n e r a l l y p r e s e n t e d as d i s c r e t e v a l u e s c a l c u l a t e d from a c e r t a i n time i n t e r v a l u s i n g d a t a from one or more geomagnetic o b s e r v a t o r i e s . There a r e a number of d i f f e r e n t k i n d s of geomagnetic i n d i c e s r e l a t e d t o v a r i o u s geomagnetic phenomena of both l o c a l and p l a n e t a r y s c a l e . An index i s not o n l y u s e f u l f o r s t u d y i n g the s p e c i f i c geomagnetic v a r i a t i o n from which i t i s c a l c u l a t e d , but can a l s o be h e l p f u l i n u n d e r s t a n d i n g r e l a t e d geomagnetic phenomena. In t h i s t h e s i s , we have used or mentioned t h r e e i n d i c e s i n the l a t t e r manner. These a r e the Dst index ( r i n g c u r r e n t ) , the Kp index (magnetospheric a c t i v i t y ) , and the AE index ( a u r o r a l e l e c t r o j e t s ) . A d e s c r i p t i o n of each of the s e i s p r e s e n t e d below. I f more i n f o r m a t i o n on t h e s e , or o t h e r , i n d i c e s i s d e s i r e d , the re a d e r s h o u l d r e f e r t o the monograph of Mayaud (1980). Dst Index The magnetic f i e l d of the, r i n g c u r r e n t , which f l o w s westward around E a r t h i n the e q u a t o r i a l p l a n e , has the e f f e c t of d e p r e s s i n g the d i p o l e f i e l d a t E a r t h ' s magnetic e q u a t o r . The Dst index i s i n t e n d e d t o mon i t o r t h i s e f f e c t , and t h e r e f o r e a l s o monitor the i n t e n s i t y of the r i n g c u r r e n t 227 228 i t s e l f . I t does t h i s q u i t e w e l l , and i s p r o b a b l y the most a c c u r a t e of a l l the geomagnetic i n d i c e s i n r e p r e s e n t i n g the phenomenon f o r which i t i s d e r i v e d . There a r e , however, some d i f f i c u l t i e s i n d e t e r m i n i n g the Dst i n d e x ; most i m p o r t a n t l y , s e p a r a t i n g r i n g c u r r e n t v a r i a t i o n s from o t h e r t r a n s i e n t v a r i a t i o n s and from s e c u l a r v a r i a t i o n s . Some t r a n s i e n t v a r i a t i o n s a r e averaged out by the one hour i n t e r v a l over which each v a l u e of the Dst index i s c a l c u l a t e d . O t h e r s , such as the f i r s t phase of a storm, t h a t i s , the p e r i o d of i n c r e a s e d H-component which may precede the main phase of a storm, can c o n t r i b u t e t o the i n d e x , however. The e f f e c t of the DP 2 i r r e g u l a r v a r i a t i o n , q u a s i - p e r i o d i c f l u c t u a t i o n s w i t h a p e r i o d of =1 hour, c o u l d s i g n i f i c a n t l y i n t e r f e r e w i t h the Dst index near the e q u a t o r , but i t s e f f e c t i s m i n i m i z e d by not u s i n g e q u a t o r i a l s t a t i o n s i n the c a l c u l a t i o n of the i n d e x . A u r o r a l d i s t u r b a n c e s c o u l d a l s o a f f e c t t h i s i n d e x , though, the e f f e c t of the westward e l e c t r o j e t i s minor a t low l a t i t u d e s , and the eastward e l e c t r o j e t i s r e c o g n i z e d as b e i n g due t o the p a r t i a l r i n g c u r r e n t a l l o w i n g i t s e f f e c t s t o be c o n s i d e r e d p a r t of the phenomenon b e i n g m o n i t o r e d (Mayaud, 1980). The r e g u l a r d a i l y v a r i a t i o n s must a l s o be removed i n o r d e r t o a c c u r a t e l y c a l c u l a t e the Dst i n d e x . T h i s i s a c c o m p l i s h e d by computing a s t a t i s t i c a l v e r s i o n of t h i s d a i l y v a r i a t i o n from the f i v e q u i e t e s t days of each month, and then s u b t r a c t i n g t h i s from 229 the observed d a t a f o r each day of t h a t month. S i n c e the d a i l y v a r i a t i o n s are not c o n s t a n t from day t o day, t h e r e are n e c e s s a r i l y e r r o r s i n t r o d u c e d by t h i s p r o c e s s though these s h o u l d be reduced somewhat when a l l the s t a t i o n s a r e averaged t o g e t h e r t o produce the a c t u a l Dst i n d e x . Note a l s o t h a t these d a i l y v a r i a t i o n s do not a f f e c t the s t a t i o n s when they are on the n i g h t s i d e of E a r t h . L a s t l y , s e c u l a r v a r i a t i o n s must a l s o be removed i f the Dst index i s t o be u s e f u l f o r l o n g term s t u d i e s . B e f o r e a c t u a l c a l c u l a t i o n of the Dst index can b e g i n , a r e f e r e n c e l e v e l must be s e t . T h i s i s d e t e r m i n e d from the H-component annual means c a l c u l a t e d from the f i v e q u i e t e s t days of each month (Mayaud, 1980). Note t h a t t h i s r e f e r e n c e l e v e l i s not a z e r o l e v e l , s i n c e the r i n g c u r r e n t always e x i s t s , and t h e r e f o r e o n l y p r o v i d e s a r e f e r e n c e t o r i n g c u r r e n t i n t e n s i t y i n v e r y q u i e t t i m e s . For each s t a t i o n , a raw Dst e s t i m a t e i s then c a l c u l a t e d as f o l l o w s : Dst = H o b s - S q ( t ) - H 0 ( t ) (C.I) where H ^ i s the o b s e r v e d H-component of the magnetic f i e l d , S q ( t ) i s the e s t i m a t e d d a i l y v a r i a t i o n , and H 0 ( t ) i s the r e f e r e n c e l e v e l . These Dst e s t i m a t e s from each s t a t i o n a r e averaged t o remove l o c a l e f f e c t s and then c o r r e c t e d f o r l a t i t u d e i n o r d e r t o y i e l d the r i n g c u r r e n t e f f e c t a t the 230 e q u a t o r . T h i s l a s t s t e p r e q u i r e s t h a t the s t a t i o n s a l l be a t s i m i l a r l a t i t u d e s . The a c t u a l o b s e r v a t o r i e s used a r e H o n o l u l u ( H a w a i i ) , San Juan ( P u e r t o R i c o ) , Hermanus (South A f r i c a ) , and K a k i o k a ( J a p a n ) . They a r e w e l l s p r e a d out i n l o n g i t u d e i n o r d e r t o m i n i m i z e l o c a l e f f e c t s , and average about 28° from the geomagnetic e q u a t o r . T h i s i s a t a low enough l a t i t u d e t o be near the r i n g c u r r e n t and t o m i n i m i z e a u r o r a l e f f e c t s , and s t i l l f a r enough from the e q u a t o r t o a v o i d DP 2 i n t e r f e r e n c e . W i t h t h i s p r o c e s s , a f i n a l Dst i s c a l c u l a t e d , i n 7, f o r each h o u r l y i n t e r v a l , l e a v i n g a s i m p l e s e t of 24 Dst v a l u e s per day. The index can be e i t h e r p o s i t i v e or n e g a t i v e . Large n e g a t i v e v a l u e s are i n d i c a t i v e of l a r g e magnetic f i e l d d e p r e s s i o n s a t the e q u a t o r , common d u r i n g storm t i m e s when the r i n g c u r r e n t becomes s t r o n g l y enhanced by substorm plasma i n j e c t i o n s . Kp Index The Kp index c o n s i s t s of a q u a s i - l o g a r i t h m i c s c a l e i n d i c a t i v e of mid t o h i g h l a t i t u d e geomagnetic a c t i v i t y on a p l a n e t - w i d e b a s i s . I t i s d e r i v e d from l o c a l K i n d i c e s c a l c u l a t e d a t 11 geomagnetic o b s e r v a t o r i e s r a n g i n g from 45° t o 63° c o r r e c t e d geomagnetic l a t i t u d e (Hakura, 1965). The K index a t each o b s e r v a t o r y i s d e t e r m i n e d f o r each 3-hour p e r i o d , f o r example, 0000-0300 UT, from the component, e i t h e r H or D, showing the l a r g e r range of 231 i r r e g u l a r v a r i a t i o n s w i t h i n t h a t p e r i o d . The index i s i n t e n d e d t o be s e n s i t i v e t o i r r e g u l a r v a r i a t i o n s o n l y and, as w i t h the Dst i n d e x , the r e g u l a r d a i l y v a r i a t i o n must be removed. The range from the chosen component, the d i f f e r e n c e between the maximum and minimum l e v e l s of t h a t component w i t h i n the s p e c i f i e d i n t e r v a l , i s then a s s i g n e d t o a c l a s s of ranges, each w i t h an a s s o c i a t e d number from 0 t o 9. The d i v i d i n g l i n e s between th e s e range c l a s s e s i n c r e a s e q u a s i - l o g a r i t h m i c a l l y and a r e a d j u s t e d by l a t i t u d e , s i n c e the a m p l i t u d e of the ranges d i s p l a y e d v a r i e s s t r o n g l y w i t h l a t i t u d e . T h i s adjustment makes the d i s t r i b u t i o n of K i n d i c e s u n i f o r m a t each o b s e r v a t o r y . B e f o r e the Kp index can be d e t e r m i n e d from the K i n d i c e s produced by the 11 o b s e r v a t o r i e s , f u r t h e r s t a n d a r d i z a t i o n of the v a r i o u s K's must t a k e p l a c e . Beyond l a t i t u d i n a l e f f e c t s , t h e r e e x i s t f u r t h e r d i f f e r e n c e s i n the K's from each of the o b s e r v a t o r i e s , and a l s o from a s i n g l e o b s e r v a t o r y i n d i f f e r e n t seasons. These a r e removed by d e t e r m i n i n g c o n v e r s i o n t a b l e s f o r each o b s e r v a t o r y which enable t h e i r K's t o be c o n v e r t e d i n t o a s t a n d a r d i z e d form, termed Ks. The Kp index i s then j u s t an average of the Ks i n d i c e s f o r each 3-hour p e r i o d from the 11 o b s e r v a t o r i e s d i s t r i b u t e d around the g l o b e . The Kp s c a l e i s a c t u a l l y d i v i d e d i n t o f i n e r i n t e r v a l s than the whole numbers mentioned above. Each K range c l a s s i s s p l i t i n t o t h i r d s , 232 g i v i n g a s c a l e where the Kp = 2 range, f o r example, i s d i v i d e d e q u a l l y i n t o Kp = 2 . , 2 0 , and 2 + s e c t i o n s . A c t i v e storm t i m e s t y p i c a l l y have Kp's of between 3 and 6, w h i l e Kp's of =8 or more, r e p r e s e n t i n g e x t r e m e l y a c t i v e t i m e s , a re q u i t e r a r e . C o n v e r s e l y , v e r y q u i e t p e r i o d s , which a r e much more common than Kp > 6 t i m e s , have Kp's of l e s s than 1. AE Index The AE index i s d e s i g n e d t o be a measure of g l o b a l a u r o r a l e l e c t r o j e t a c t i v i t y . The e l e c t r o j e t s a r e the predominant form of a u r o r a l - z o n e magnetic v a r i a t i o n . Thus, as i n the case of the Dst index but d i f f e r e n t from the Kp in d e x , a w e l l d e f i n e d c l a s s of i r r e g u l a r v a r i a t i o n s i s b e i n g m o n i t o r e d . A g l o b a l network of up t o 13 o b s e r v a t o r i e s a t or near a u r o r a l zone l a t i t u d e s , of =70° c o r r e c t e d GM L a t . , i s used t o d e t e r m i n e the AE i n d e x . The c u r r e n t d i r e c t i o n s of the eastward and westward e l e c t r o j e t s make the H-component the l o g i c a l one t o use i n d e t e r m i n i n g t h i s i n d e x , w i t h the eastward e l e c t r o j e t p r o d u c i n g p o s i t i v e AH d e v i a t i o n s and the westward e l e c t r o j e t n e g a t i v e AH d e v i a t i o n s . For each month, the r e f e r e n c e l e v e l from which th e s e d e v i a t i o n s a r e c a l c u l a t e d i s de t e r m i n e d u s i n g an average of the H-component of the f i v e q u i e t e s t days of t h a t month. A f t e r removal of the r e f e r e n c e l e v e l , the H-component t r a c e s from a l l of thes e s t a t i o n s a re superimposed, y i e l d i n g upper and lower 233 e n v e l o p e s . The upper envelope i s the AU i n d e x , and m o n i t o r s the eastward e l e c t r o j e t , w h i l e the lower envelope i s the AL i n d e x , which m o n i t o r s the westward e l e c t r o j e t . T h i s envelope t e c h n i q u e means t h a t , f o r any s p e c i f i c t i m e , each index i s a c t u a l l y g i v e n by the one s t a t i o n b e s t s i t u a t e d t o observe t h a t e l e c t r o j e t a t t h a t t i m e . Note t h a t t h e s e i n d i c e s a r e produced i n a d i g i t a l form w i t h a 2.5 minute sam p l i n g r a t e . The AE index i s s i m p l y the d i f f e r e n c e between the AU and AL i n d i c e s , t h a t i s : AE = AU - AL. T h i s o p e r a t i o n removes r i n g c u r r e n t c o n t a m i n a t i o n , which i s s i g n i f i c a n t o n l y i n v e r y a c t i v e t i m e s , from the AU and AL i n d i c e s , l e a v i n g the AE index dependent o n l y on the e l e c t r o j e t s . A c t u a l l y , the r e g u l a r d a i l y v a r i a t i o n s t i l l i n t e r f e r s w i t h the AE i n d e x , but i s q u i t e s m a l l , =*10S of 7, compared t o e l e c t r o j e t AH a m p l i t u d e s of -100s of 7. Other d i f f i c u l t i e s which can i n t e r f e r e w i t h t h i s index i n c l u d e v a r i o u s , and unknown, ground i n d u c t i o n e f f e c t s a t the o b s e r v a t o r i e s , the H-component not b e i n g n e c e s s a r i l y p r e c i s e l y normal t o the c u r r e n t d i r e c t i o n s , and a l e s s than i d e a l d i s t r i b u t i o n w i t h r e s p e c t t o l a t i t u d e and l o n g i t u d e of the o b s e r v a t o r y network as caused l a r g e l y by the uneven d i s t r i b u t i o n of l a n d masses. S i n c e the a u r o r a l e l e c t r o j e t s a r e a d i r e c t r e s u l t of magnetospheric storms, the AE index reaches l a r g e v a l u e s , o f t e n >10007, i n stormy p e r i o d s , w h i l e v e r y q u i e t t i m e s can have AEs of <1007. 

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