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An investigation of the frequency shift mechanisms of IPDP type pulsations Koleszar, Thomas W. 1980

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AN INVESTIGATION OF THE FREQUENCY SHIFT MECHANISMS OF IPDP TYPE PULSATIONS by \ c THOMAS W. KOLESZAR B.Sc. . (Hons) , U n i v e r s i t y o f B r i t i s h C o lumbia, 1978 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF f MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of Geo p h y s i c s and Astromony) We accept t h i s t e s as co n f o r m i n g t o t h e r e g u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA Octo b e r , 1980 © Thomas W. K o l e s z a r , 1980 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I ag ree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . It i s u n d e r s t o o d that c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f C, Bopuvstcs ~f A* Tfl-o A/ Ory V The U n i v e r s i t y o f B r i t i s h Co lumbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date O c-t . ~>-<-r / &>c ABSTRACT P o s s i b l e f r e g u e n c y s h i f t mechanisms f o r IPDP m i c r o p u l s a t i o n e v e n t s a r e examined here. M i c r o p u l s a t i o n data c o l l e c t e d from 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 i n B r i t i s h Columbia i s used f o r t h i s s t u d y , a l o n g w i t h normal-run magnetograms o b t a i n e d from o b s e r v a t o r i e s near t h i s c h a i n , from e g u a t o r i a l o b s e r v a t o r i e s , and from o b s e r v a t o r i e s t o the e a s t of t h e c h a i n . Four t h e o r i e s p r o p o s i n g t o e x p l a i n t h e IPDP f r e g u e n c y s h i f t have been advanced; the i n w a r d motion t h e o r y , the a z i m u t h a l d r i f t t h e o r y , the i n c r e a s i n g f i e l d t h e o r y , and the d e c r e a s i n g plasma d e n s i t y t h e o r y . I t i s found t h a t two of t h e s e mechanisms, as d e s c r i b e d i n the inward motion and a z i m u t h a l d r i f t t h e o r i e s , c a n, a c t i n g t o g e t h e r , a c c o u n t f o r t h e observed f r e g u e n c y s h i f t i n t h e e v e n t s d e t e c t e d on t h e B.C..chain. The g r e a t e r p a r t of t h e f r e q u e n c y r i s e i n t h e s e e v e n t s i s produced by t h e i n w a r d motion mechanism. I t i s a l s o noted t h a t t h e i o n o s p h e r i c duct s t r o n g l y a f f e c t s the p r o p a g a t i o n of t h e IPDP hydromagnetic waves through the upper atmosphere. i i i TABLE OF CONTENTS 1. . I n t r o d u c t i o n 1 2. Data C o l l e c t i o n And A n a l y s i s 7 2.1 M i c r o p u l s a t i o n And Magnetic F i e l d Data Sources .. 7 2.2 IPDP Event S e l e c t i o n .10 2.3 M i c r o p u l s a t i o n Data A n a l y s i s Methods .....13 3. . P r o p e r t i e s Of IPDPs 18 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 .18 3.2 O c c u r r e n c e Of IPDPs . . . 1 9 3.3 E e l a t i o n To Other Geomagnetic Phenomena .22 4. .IPDP G e n e r a t i o n Mechanisms 27 4.1 G e n e r a l G e n e r a t i o n P r o c e s s .27 4.2 Freguency S h i f t Mechanisms .34 4.3 D i s c u s s i o n Of Freguency S h i f t Mechanisms .........45 5. E x p e r i m e n t a l R e s u l t s .49 5.1 Inward Motion Of G e n e r a t i o n Region .,., 49 5.2 Freguency S h i f t From A z i m u t h a l D r i f t E f f e c t s .... 61 5.3 I n c r e a s i n g F i e l d and D e c r e a s i n g Plasma D e n s i t y P r o c e s s e s 65 5.4 D i s c u s s i o n 68 6 . . C o n c l u s i o n s And F u t u r e E x p e r i m e n t s .70 R e f e r e n c e s • .73 Appendix 1 Kp I n d i c e s For August 1979 , .77 Appendix 2 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 Freguency . 7 8 i v LIST OF TABLES Page T a b l e 1. C l a s s i f i c a t i o n o f Geomagnetic M i c r o p u l s a t i o n s 2 T a b l e 2. L o c a t i o n of M i c r o p u l s a t i o n S t a t i o n s 7 T a b l e 3 . L o c a t i o n o f Magnetic O b s e r v a t o r i e s 9 Table 4 . IPDP Events 13 V LIST OF FIGURES Page F i g . 1. . Dynamic spectrum of IPDP event r e c o r d e d at F o r t S t . . John, B.C. (L=4. 6) , on August 9, 1979. F i g . 2. Waveform of a s e c t i o n of t h e IPDP event r e c o r d e d at F o r t S t . . J o h n , B.C., on August 8, 1979. . F i g . 3. Dynamic s p e c t r a of a) IPDP, b) pp, and c) CE. 11 Note t h e d i f f e r e n c e s i n t h e r i s i n g .freguency s t r u c t u r e s o f IPDP and PP ( p a r t s b) and c) from Heacock, 1970). F i g . .4.. Dynamic spectrum and slow speed c h a r t 12 r e c o r d i n g of the IPDP event r e c o r d e d a t F o r t S t . John on August 9, 1979. F i g . . 5 . . Dynamic s p e c t r a o f t h e August 9, 1979 IPDP 14 event from a) F o r t S t . John, b) P r i n c e George, and c) W i l l i a m s Lake. F i g . .6.. The periodogram and maximum e n t r o p y s p e c t r a o f 16 a segment of the August 9 event a t F o r t S t . John.. Note the good agreement between t h e s e two methods. F i g . . 7 . The c o n s e c u t i v e IPDP e v e n t s a t F o r t S t . John 20 on August 6, 1979..Only the second of t h e s e two e v e n t s was e v i d e n t a t s t a t i o n s f u r t h e r s o u t h , i n d i c a t i n g t h a t they were p r o b a b l y s e p a r a t e o c c u r r e n c e s . F i g . . 8 . . D i u r n a l v a r i a t i o n o f o c c u r r e n c e of a l l IPDPs 21 observed a t S e a t t l e , Wash., over an 11 month p e r i o d ( K n a f l i c h and Kenney, 1967).. F i g . . 9 . . Magnetic f i e l d H component from G r e a t Whale 24 R i v e r and IPDP dynamic spectrum from F o r t S t . John. Note the s h a r p o n s e t of a n e g a t i v e bay s h o r t l y b e f o r e t h e IPDP event b e g i n s (August 8, 1979) . v i F i g . 10. IPDP event from c o n j u g a t e s t a t i o n s at 26 Macguarie I s . . and Kotzebue, A l a s k a . Note t h e P e l -*• Pc2 a c t i v i t y l e a d i n g up t o t h e event (Heacock e t a l . , 1976)., F i g . .11.. A model c u r r e n t system f o r a t y p i c a l p o l a r 29 magnetic substorm, showing t h e p a r t i a l r i n g c u r r e n t on t h e e v e n i n g s i d e (Kamide and Fukushima, 1972) . . F i g . 12.. Schematic i l l u s t r a t i o n of p a r t i c l e 31 a c c e l e r a t i o n , d r i f t , and p r e c i p i t a t i o n d u r i n g a substorm ( B o t e l e r , 1980). F i g . 13. Normal-run magnetogram from C o l l e g e , A l a s k a , 32 and IPDP dynamic spectrum from F o r t S t . .John. Note the p o s i t i v e bay o c c u r r i n g a t C o l l e g e . There i s a s l i g h t t i m e d i f f e r e n c e between t h e IPDP and t h e peak o f t h i s bay. F i g . . 1 4 . Diagram showing t h e i n w a r d motion of t h e 37 g e n e r a t i o n r e g i o n due t o t h e inward motion of the plasmapause. The plasmapause i s r e p r e s e n t e d by t h e s o l i d and ( l a t e r ) dashed c u r v e d l i n e s . . The ground s t a t i o n i s r e p r e s e n t e d by G, and L and T i n d i c a t e L s h e l l and t i m e , r e s p e c t i v e l y ( H o r i t a et a l . , 1979). F i g . . 1 5 . Growth r a t e c o n t o u r s f o r s t a t i c c o l d plasma 43 d e n s i t y w i t h d r i f t e f f e c t s i n c l u d e d ( t o p ) , and d e c r e a s i n g c o l d plasma d e n s i t y w i t h no d r i f t (bottom) ( L i n and P a r k s , 1976) . F i g . .16. Growth r a t e c o n t o u r s f o r v a r i o u s c o l d plasma 44 d e n s i t y p r o f i l e s , a l l w i t h d r i f t e f f e c t s i n c l u d e d . Note the r i s i n g t o n e s f o r the c o n s t a n t and d e c r e a s i n g c o l d plasma d e n s i t y p l o t s ( L i n and P a r k s , 1976). F i g . 17. The f r e g u e n c y (top) and power (bottom) 51 p r o f i l e s o f an IPDP event r e c o r d e d on t h e B.C. n o r t h - s o u t h c h a i n . F i g . .18.. F o r t S t . . John power p r o f i l e s f o r the H 53 component ( s o l i d l i n e ) and the t o t a l h o r i z o n t a l component (H+D) (dashed l i n e ) . S i n c e t h i s r e l a t i v e r e l a t i o n s h i p between H v i i ' and H+D appeared t o be the same a t a l l t h r e e s t a t i o n s , i t i s f e a s i b l e t o use the H component a l o n e . F i g . 19.. The power r a t i o p r o f i l e s f o r each p o s s i b l e 54 s t a t i o n p a i r i n g f o r an IPDP observed on t h e B.C. c h a i n . Note the r e g u l a r changes i n d i c a t i n g a n o n - s t a t i o n a r y g e n e r a t i o n r e g i o n . . F i g . 20.. The i n w a r d motion of the IPDP g e n e r a t i o n 58 r e g i o n i n terms of L v a l u e s , and the f r e g u e n c y s h i f t p r e d i c t e d from t h e s e values..The a c t u a l f r e g u e n c y s h i f t i s i n c l u d e d f o r c omparison. P a r t (a) , August 6 event; p a r t (b) , August 8 e v e n t ; and p a r t ( c ) , August 9 event ( f o l l o w i n g page) . F i g . 20. P a r t (c) . 59 F i g . . 21.. The f r e g u e n c y s h i f t due t o t h e a z i m u t h a l d r i f t 62 mechanism as c o r r e c t e d f o r t h e i n w a r d motion of t h e g e n e r a t i o n r e g i o n , and the t o t a l s h i f t due t o t h e c o m b i n a t i o n of t h e s e two mechanisms (as g i v e n by ( 2 1 ) ) . The r e a l f r e g u e n c y s h i f t i s i n c l u d e d f o r c o m p a r i s o n . P a r t ( a ) , August 6 e v e n t ; p a r t (b) , August 8 e v e n t ; and p a r t (c) , August 9 event ( f o l l o w i n g page). F i g . .21.. P a r t (c) . . 63 F i g . 22. A p o s i t i v e bay r e c o r d e d a t C o l l e g e 66 s i m u l t a n e o u s l y w i t h t h e o b s e r v a t i o n of an IPDP event on the B.C. c h a i n . The t i m e of o c c u r r e n c e of the IPDP i s marked on t h e magnetogram by t h e v e r t i c a l l i n e s . Note t h a t t h e IPDP does not o c c u r on t h e r e c o v e r y s i d e of the bay. v i i i ACKNOWLEDGEMENTS I would l i k e t o thank 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 d u r i n g the c o u r s e o f t h i s work. Many o t h e r people have a l s o c o n t r i b u t e d t o the s u c c e s s of t h i s p r o j e c t . Dr. R.E.. H o r i t a o f the P h y s i c s department, U n i v e r s i t y of V i c t o r i a , and f e l l o w g r a d u a t e s t u d e n t David B o t e l e r h e l p e d w i t h the s e t t i n g up and o p e r a t i o n of the B.C. n o r t h - s o u t h c h a i n and p r o v i d e d many u s e f u l d i s c u s s i o n s on t h e t o p i c i n q u e s t i o n . I am a l s o i n d e b t e d t o Dr. S. , Watanabe and B r i a n C h a p e l f o r t h e i r h e l p w i t h the f i e l d o p e r a t i o n s , and t o Dr. K . . H a y a s h i , D r . . R . D . . R u s s e l l , and the t e c h n i c a l s t a f f of the department f o r t h e i r h e l p w i t h the i n s t r u m e n t a t i o n used i n th e s e o p e r a t i o n s . . I must a l s o o f f e r my t h a n k s t o my mother, Mrs. S. K o l e s z a r , and t o Mi s s Sandy P a t i e n c e f o r c o n t i n u a l l y c o r r e c t i n g t h e E n g l i s h o f t h i s m a n u s c r i p t . S u p p o r t f o r t h e f i e l d o p e r a t i o n s was p r o v i d e d by t h e Canadian M i n i s t r y of T r a n s p o r t a t the F o r t S t . John, P r i n c e George, and W i l l i a m s Lake a i r p o r t s , as w e l l as by t h e P r i n c e George Aero C l u b , and by t h e B.C. F o r e s t S e r v i c e at Pemberton. F a c i l i t i e s and eguipment were a l s o p r o v i d e d by t h e Defence Research E s t a b l i s h m e n t P a c i f i c i n E s g u i m a l t B.C., and t h e P a c i f i c G e o s c i e n c e C e n t r e i n S i d n e y , B.C. F i n a n c i a l s u p p o r t came from t h e 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 g r a n t s numbered A3564 and D6409. 1 ii-INTRODUCTION Geomagnetic m i c r o p u l s a t i o n s a r e s m a l l , t r a n s i t o r y f l u c t u a t i o n s i n E a r t h ' s magnetic f i e l d which propagate t h r o u g h t h e magnetosphere i n t h e form of hydromagnetic waves. The p e r i o d s o f these p u l s a t i o n s , t y p i c a l l y between 0.1 seconds and 10 m i n u t e s , are s h o r t when compared t o o t h e r magnetospheric phenomena, such as s t o r m - t i m e and d i u r n a l v a r i a t i o n s . The a m p l i t u d e s d i s p l a y e d range from l e s s than one gamma (10 - < > t e s l a ) t o , on r a r e o c c a s i o n s , as h i g h as a few hundreds of gammas, t h u s seldom e x c e e d i n g one p a r t i n 10 3 o f the s t r e n g t h of E a r t h ' s main f i e l d . . L i k e magnetospheric substorms, m i c r o p u l s a t i o n s have an e x t e r n a l , or s o l a r , o r i g i n , as opposed t o the i n t e r n a l o r i g i n of main f i e l d and s e c u l a r v a r i a t i o n s . 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 , and t h e energy r e g u i r e d f o r t h e i r g e n e r a t i o n i s s u p p l i e d by the s o l a r wind. . Geomagnetic m i c r o p u l s a t i o n s l e a v e no l a s t i n g e f f e c t s i n t h e magnetosphere, but t h e y can be very u s e f u l as n a t u r a l probes i n t o m a gnetospheric p r o c e s s e s . S a i t o (1976) d i v i d e d m i c r o p u l s a t i o n s i n t o two broad c a t e g o r i e s ; c o n t i n u o u s p u l s a t i o n s (denoted P c ) , and i r r e g u l a r p u l s a t i o n s (denoted P i ) (see Table 1 ) . F o l l o w i n g an e a r l i e r c l a s s i f i c a t i o n scheme by Jacobs e t a l . (1964), t h e Pc s e c t i o n i s f u r t h e r d i v i d e d i n t o s i x subgroups, and the P i s e c t i o n i n t o t h r e e subgroups. These s u b d i v i s i o n s a r e based on major m o r p h o l o g i c a l p r o p e r t i e s of t h e m i c r o p u l s a t i o n s , such as p e r i o d , a m p l i t u d e , and t i m e of o c c u r r e n c e . S a i t o has o f f e r e d an even 2 T a b l e j k C l a s s i f i c a t i o n o f Geo magnetic M i c r o p u i s a t i o n s C o n t i n u o u s P u l s a t i o n s JPcJ_ P e r i o d Jsec|_ Type Sub-type 0. 2- 5 P e l PP HMC IPDP CE Name P e a r l p u l s a t i o n Hydromagnetic chorous I n t e r v a l o f p u l s a t i o n o f d i m i n i s h i n g p e r i o d C o n t i n u o u s e m i s s i o n O t h e r s 5- 10 Pc2 AIP A u r o r a l i r r e g u l a r p u l s a t i o n Others 10- 45 Pc3 Pc3 Pc3 Others 45- 150 Pc4 Pc4 Pg Pc4 G i a n t p u l s a t i o n Others 150-600 Pc5 Pc5 Pc5 Others 600- Pc6 TF T a i l f l u t t e r i n g O thers 1-40 I r r e g u l a r P u l s a t i o n s J P i J _ P i 1 Spt P i B P i c PiD Psc1,2, 3 P s i 1 , 2 , 3 S h o r t - p e r i o d Pt P i b u r s t P i (continuous) Daytime P i Sc ( S i ) - a s s o c i a t e d Pc1,2,3 Others 40-150 P i 2 P i 2 P s f e Psc4 P s i 4 P i 2 ( f o r m e r l y Pt) S f e - a s s o c i a t e d p u l s a t i o n Sc ( S i ) - a s s o c i a t e d Pc4 Others 150- Pi3 Psc5,6 P s i 5 , 6 P i p Ps6 Sc ( S i ) - a s s o c i a t e d Pc5,6 P o l a r i r r e g u l a r p u l s a t i o n S u b s t o r m - a s s o c i a t e d l o n g - p e r i o d p u l s a t i o n Others 3 more d e t a i l e d c l a s s i f i c a t i o n w i t h i n t h e s e subgroups which i s based l a r g e l y on the dynamic s p e c t r a o f the p u l s a t i o n s c o n c e r n e d . M i c r o p u l s a t i o n s of t h e P e l subgroup have been s e p a r a t e d i n t o f o u r c a t e g o r i e s ; p e a r l p u l s a t i o n s , hydromagnetic c h o r o u s , c o n t i n u o u s e m i s s i o n , and 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 . . While a l l t h e s e p u l s a t i o n s e x h i b i t s i m i l a r m o r p h o l o g i c a l c h a r a c t e r i s t i c s , the dynamic s p e c t r a o f the 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 (IPDPs) are e a s i l y d i s t i n g u i s h e d by t h e c o n t i n u o u s r i s e i n f r e g u e n c y of t h e p u l s a t i o n t h r o u g h o u t th e event (see F i g . 1). I t i s t h i s t y p e of m i c r o p u l s a t i o n t h a t w i l l be t h e s u b j e c t o f t h i s t h e s i s . . T r o i t s k a y a (1961) was t h e f i r s t t o study t h e IPDP phenomenon i n depth. S i n c e t h e n t h e s u b j e c t has a t t r a c t e d much a t t e n t i o n , l e a v i n g us w i t h a w e l l founded knowledge of the m o r p h o l o g i c a l p r o p e r t i e s of IPDPs, and a number of t h e o r i e s c o n c e r n i n g t h e i r o r i g i n s . . IPDPs c o n s i s t of a more or l e s s narrow n o i s e band w i t h i n which o c c a s i o n a l elements of h i g h e r i n t e n s i t y a r e i n t e r s p e r s e d (see F i g . .2). Though the IPDP waveform g e n e r a l l y resembles more s t r o n g l y t h e P e l t y p e o f waveform, Roxburgh (1970) has s u g g e s t e d t h a t i t a l s o shows many of t h e c h a r a c t e r i s t i c s of the more i r r e g u l a r P i 1 waveforms. The mid-freguency of both the n o i s e band and t h e h i g h e r i n t e n s i t y s t r u c t u r a l elements of an IPDP i n c r e a s e s over the c o u r s e of each e v e n t , though the r a t e o f t h i s i n c r e a s e v a r i e s w i d e l y between e v e n t s . A t y p i c a l event may l a s t anywhere from 20 minutes t o as l o n g as two hours. IPDPs u s u a l l y occur i n t h e r— U3 to a m n ro a a a t 0.0 0 . 4 0 . 8 1 . 2 TIME (HRS) • • M M J . 6 2 . 0 F i g . 1. Dynamic spectrum of IPDP event r e c o r d e d at F o r t John, B.C. (L=4.6), on August 9, 1979. St, 5 s u b - a u r o r a l zone, 55° to 65° North or South, geomagnetic c o o r d i n a t e s , between 1700 hours and 0100 hours l o c a l time, at the r a t e of a few per month.. T h e o r i e s of the g e n e r a t i o n mechanism of IPDPs have been proposed by; Gendrin et a l . (1967) and Heacock (1967) (Inward motion t h e o r y ) , F u k u n i s h i (1969, 1 973) (Azimuthal d r i f t t h e o r y ) , Eoxburgh (1970) (In c r e a s i n g f i e l d theory) , and L i n and Parks (1976) (Decreasing plasma d e n s i t y t h e o r y ) . Since an understanding of the IPDP ge n e r a t i o n mechanism could be very important i n understanding magnetospheric substorm processes, more work d i r e c t e d at determining the r e l e v a n c e and r e l a t i v e importance of these t h e o r i e s would be g u i t e u s e f u l . . T h i s t h e s i s w i l l t e s t these t h e o r i e s a g a i n s t data c o l l e c t e d from a l o n g i t u d i n a l l i n e (~291° East, magnetic coordinates) of magnetic s t a t i o n s . A review of the c u r r e n t t h e o r i e s w i l l be given i n chapter f o u r , and the experimental r e s u l t s w i l l be presented i n chapter f i v e . Chapter s i x w i l l o f f e r a d i s c u s s i o n of these r e s u l t s as they a f f e c t the t h e o r i e s i n g u e s t i o n , and o f f e r s u g g e s t i o n s f o r f u r t h e r work. 6 F i g . 2.. Waveform of a s e c t i o n of the IPDF event r e c o r d e d at F o r t S t . . J o h n , B.C., on August 8, 1979. 7 2:_ . DATA COLLECTION AND ANALYSIS T h i s c h a p t e r w i l l d i s c u s s t h e c o l l e c t i o n and p r o c e s s i n g of t h e m i c r o p u l s a t i o n d a t a , as w e l l as the s o u r c e s of the magnetic f i e l d d a t a and Kp i n d i c e s . 2-.1 Mi cr o p u I s a t i o n and Magnet i c F i e l d Data S o u r c e s F o r t h e purposes o f the r e s e a r c h p r e s e n t e d i n t h i s t h e s i s , i t was n e c e s s a r y t o c o l l e c t m i c r o p u l s a t i o n d a t a from a number of s t a t i o n s l o c a t e d a l o n g a l i n e o f geomagnetic l o n g i t u d e . . D a t a was o b t a i n e d from t h r e e such s t a t i o n s i n n o r t h - c e n t r a l B r i t i s h C o l u m b i a , r a n g i n g from F o r t S t . John t o t h e n o r t h , t o P r i n c e George, and W i l l i a m s Lake t o the s o u t h . . See Table 2 f o r t h e g e o g r a p h i c and geomagnetic c o o r d i n a t e s of t h e s e s t a t i o n s . Data from a more s o u t h e r l y s t a t i o n , l o c a t e d a t Pemberton, B.C., proved t o be unusable as a r e s u l t of a t a p e r e c o r d e r m a l f u n c t i o n . These s t a t i o n s were op e r a t e d c o n t i n u o u s l y t h r o u g h o u t most of t h e month of August, 1979. . T a b l e 2.. L o c a t i o n of M i c r o p u l s a t i o n S t a t i o n s S t a t i o n Geographic Geomagnetic L S h e l l Lat., JN]_ If2S.SLs.iIL LatiJNjL Long. (E) F o r t S t . John 56°14« 239° 05' 62. 3° 291.7° 4.6 P r i n c e George 53°55« 237° 11' 59.5" 290. 9° 3. 9 W i l l i a m s Lake 52°08' 237° 51• 57.9" 292. 5° 3. 5 8 Each m i c r o p u l s a t i o n s t a t i o n c o n s i s t e d of t h r e e i n d u c t i o n magnetometers (measuring d B / d t ) , t h e i r a s s o c i a t e d a m p l i f i e r s , and a slow speed t a p e r e c o r d e r . . C l o c k and WWVB t i m e code s i g n a l s were r e c o r d e d as w e l l as the magnetic s i g n a l s . The i n d u c t i o n magnetometers were high-/«. metal c o r e d s o l e n o i d s , a l i g n e d i n the H (magnetic north) , D (magnetic east) , and Z ( v e r t i c a l ) d i r e c t i o n s . S i n c e t h e response of each s e n s o r - a m p l i f i e r system was somewhat d i f f e r e n t , a l l were c a l i b r a t e d i n p l a c e w i t h a r t i f i c i a l magnetic s i g n a l s . . M a g n e t i c f i e l d data from p o i n t s near the l i n e o f m i c r o p u l s a t i o n s t a t i o n s , as w e l l as from p o i n t s t o i t s n o r t h and e a s t , and from e g u a t o r i a l s t a t i o n s , was a l s o r e g u i r e d f o r t h i s r e s e a r c h p r o j e c t . T h i s d a t a , i n t h e form of nor m a l - r u n magnetograms, was purchased from World Data C e n t r e A f o r S o l i d E a r t h G e o p h y s i c s i n B o u l d e r , C o l o r a d o . Data c o v e r a g e was o b t a i n e d f o r a l l o f August, 1979. The s t a t i o n s from which d a t a was a c g u i r e d a r e l i s t e d i n T a b l e 3. The Kp i n d i c e s , which p r o v i d e an e s t i m a t e o f high l a t i t u d e geomagnetic a c t i v i t y , were a l s o needed f o r t h i s r e p o r t . T h i s g u a s i - l o g a r i t h m i c s c a l e i s c a l c u l a t e d from 13 h i g h l a t i t u d e s t a t i o n s e v e r y t h r e e hours ( R o s t o k e r , 1972). The Kp i n d i c e s are p u b l i s h e d monthly i n t h e J o u r n a l o f G e o p h y s i c a l Research by J . V i r g i n i a L i n c o l n , E d i t o r . Those f o r August, 1979 are l i s t e d i n Appendix 1. 9 T a b l e 3.. L o c a t i o n of Magnetic O b s e r v a t o r i e s S t a t i o n G eographic Geomagnetic L9.ng.-iE! L a t i l N l L2ng._i.iEl Baker Lake 6 4 ° 1 0 ' 2 6 4 ° 3 0 « 7 3 . 9 ° 3 1 4 . 8 ° C o l l e g e 64°52» 2 1 2 ° 1 0 ' 6 4 . 6 ° 256.5" F o r t C h u r c h i l l 58°45« 2 6 6 ° 0 0 ' 6 8 . 8 ° 322.5" F r e d r i c k s b u r g 3 8 ° 1 2 ' 2 8 2 ° 3 8 « 49. 6° 349.8" Great Whale E i v e r 55°20« 2 8 2 ° 1 0 « 6 6 . 8 ° 3 4 7 . 2 ° Guam 13°35« 1 4 4 ° 5 2 ' 4. 0° 2 1 2 . 9 ° H o n o l u l u 21° 19' 2 0 2 ° 0 0 ' 21. r 2 6 6 . 5 ° Meanoo k 5 4 ° 3 6 « 246"42« 6 1 . 9 ° 3 0 0 . 7 ° Newport 48°16« 242"53' 55. 1° 300.0" Ottawa 45*25' 284"17' 57.0" 3 5 1 . 5 ° San Juan 18"07« 293° 51« 2 9 . 6 ° 3.1" S i t k a 5 7 ° 0 4 ' 224"40 • 60. 0" 275.4" S t . John's 47° 34' 3 0 7 ° 1 9 ' 58 .7" i 2 1 . 4 ° Tucson 3 2 ° 1 5 ' 2 4 9 ° 1 0 « 4 0 . 0 ° 3 1 2 . 2 ° V i c t o r i a 4 8 ° 2 6 ' 2 3 6 ° 4 0 ' 5 4 . 3 ° 292.7" Y e l l o w k n i f e 6 2 ° 3 0 ' 2 4 5 ° 3 1 • 69. 1° 2 9 2 . 6 ° 10 2^2 IPDP Event S e l e c t i o n The r i s i n g f r e g u e n c y s t r u c t u r e i s t h e dominant f e a t u r e of t h e IPDP c l a s s o f m i c r o p u l s a t i o n , s e p a r a t i n g i t from t h e o t h e r Pc1-type p u l s a t i o n s (see F i g . 3 ) . T h e r e f o r e , i t was t h i s f e a t u r e , i n c o n j u n c t i o n w i t h t h e known d i u r n a l v a r i a t i o n o f o c c u r r e n c e o f IPDPs, which was used t o i s o l a t e them from t h e wealth of m i c r o p u l s a t i o n data c o l l e c t e d . S i n c e v i r t u a l l y a l l IPDP e v e n t s occur between 1500 hours and 0100 hours l o c a l t i m e , dynamic s p e c t r a o f the F o r t S t . . John d a t a were t a k e n c o v e r i n g t h e p e r i o d between 1200 hours and 0200 hours l o c a l t i me f o r each day data was r e c o r d e d . . F o r t S t . . John was chosen due t o t h i s s t a t i o n ' s working c l o c k and more s e n s i t i v e i n s t r u m e n t s . I t was a l s o e x p e c t e d t h a t any IPDP e v e n t s would appear more s t r o n g l y t h e r e . . Any r i s i n g f r e g u e n c y s t r u c t u r e s found i n t h e s e s p e c t r a were then checked f o r t o t a l e l a p s e d t i m e , amount and r a t e of f r e g u e n c y r i s e , and r e p e t i t i o n o f the r i s i n g s t r u c t u r e s . . P e a r l p u l s a t i o n s ( a l s o i n t h e P e l group) a l s o e x h i b i t r i s i n g f r e g u e n c y s t r u c t u r e s , but t h e y can be d i s t i n g u i s h e d from IPDPs on s e v e r a l p o i n t s . They a r e s h o r t e r i n d u r a t i o n ( 5 minutes as opposed t o 20 minutes f o r I P D P s ) , they d i s p l a y a s m a l l e r change i n f r e g u e n c y , and t h e y r e p e a t at r e g u l a r i n t e r v a l s (see F i g . 3 ) . The IPDP e v e n t s i s o l a t e d above were compared t o slow speed c h a r t s (1 day = 1.08 metres) and t h e i r waveforms i d e n t i f i e d (see F i g . 4 ) . The slow speed c h a r t s from t h e o t h e r s t a t i o n s were th e n checked f o r s i m i l a r waveforms. No new e v e n t s were found. S i n c e t h e r e s e a r c h t o be done r e q u i r e d t h a t an IPDP event be c l e a r l y e v i d e n t i n t h e d a t a from at l e a s t two s t a t i o n s , 1 1 LT) IT) a ) 1 £ ° O a 0.0 10.0 —I ~T— 20.0 30.0 T I M E ( M I N ) 40.0 50.0 b ) COLLEGE E-C 0.5r • 0.0 18 SEPT, 1966 P 1 02UT 03 04 F i g . 3 D y n a m i c s p e c t r a o f a ) I P D P , b ) P P , a n d c ) C E . N o t e t h e d i f f e r e n c e s i n t h e r i s i n g f r e g u e n c y s t r u c t u r e s o f I P D P a n d P P ( p a r t s b ) a n d c ) f r o m H e a c o c k , 1 9 7 0 ) . 12 in iment Systems Division — I 1 1 1 1 1 1 1 1 1 H 1 1 1 1 1 1 1—I 1 1 1 1 f Printed in U.S.A. o.i~6 11; -U4J r.u r r n : : ii ii i i i i i m | i i i i i i i i i - i i i i 44-H iiii ;;ii i i i ti : : : : : ' : : : i i i ! 11 H ~fi SH iii 4TTJ ;ii : : : . : ;:; : ; : ; : • : • | j: : : : ' t r : : ! ; 17'.-'. : : : : . . . . : : . iii 1] i Hii i i i i \ffl : : ; : i n : s s '•::: Hii : :t *" : : ! : : ; n - : 31- : Si::HH- i i i Eg • ii | :: Hit im m S B I S p iiii ip • ; : ; i - J ta I : ii | -ii Sg ::: : i i : : : t j HH i i i i m i i i i ! 1 1 | i 1 iii : : : i fl ! m i i i i ::: . iiii : i|« i i i in: §J m i i i t mj iiii Hii i i i ' . . , . 1 i i + + iiii : : t : : : : : i f i U i m : : : . : ; i i i :pr ::: i i i i i in i i i m H i t l i f i B iiii ; i ;1 . : I iiii :::: SB = ii ii ii ±++ : t : r i i i : F i g . 4. Dynamic spectrum and slow speed c h a r t r e c o r d i n g o f the IPDP event r e c o r d e d a t F o r t S t . John on August 9. 1979. 13 dynamic s p e c t r a were taken a t a l l t h r e e s t a t i o n s a t t h e event t i m e s found from the F o r t S t . ..John d a t a . F i g u r e 5 shows t h r e e such s p e c t r a . A number of e v e n t s d e t e c t e d at F o r t S t . John were c o m p l e t e l y absent or o n l y weakly v i s i b l e at t h e o t h e r s t a t i o n s , and t h e r e f o r e were not u s a b l e . Only t h r e e events proved c l e a r l y v i s i b l e a t two or more s t a t i o n s . These e v e n t s , which were d e t e c t e d a t a l l t h r e e s t a t i o n s , a r e l i s t e d i n T a b l e 4. T a b l e 4.. IPDP Events Date Time 1. August 6, 1979 2100 - 2120 LT 2. August 8, 1979 2115 - 2145 LT 3. August 9,, 1979 2135 - 2215 LT 2.3 M i c r o p u l s a t i o n Data A n a l y s i s Methods D i g i t a l time s e r i e s a n a l y s i s was performed on t h e IPDP ev e n t s s e l e c t e d above t o det e r m i n e t h e power l e v e l s and f r e g u e n c i e s p r e s e n t at v a r i o u s p o i n t s t h r o u g h o u t each e v e n t . To do t h i s two d i f f e r e n t t e c h n i g u e s were employed, the periodogram approach and the maximum e n t r o p y method. The periodograms were used p r i m a r i l y t o check t h e r e s u l t s of the maximum e n t r o p y s p e c t r a . . B e f o r e a n a l y s i s w i t h t h e f a s t f o u r i e r t r a n s f o r m , t h e dat a was t a p e r e d w i t h a c o s i n e b e l l f u n c t i o n , and the mean was removed.. The r e s u l t i n g periodogram was smoothed w i t h a Hanning window. The r e s u l t s of the periodogram method were checked by comparison w i t h a s i m i l a r a n a l y s i s o f s y n t h e t i c s i g n a l s . The main problem i n c u r r e d by t h e use of t h e maximum e n t r o p y 14 ID r— o —i IT) O X t M o o o 0 .0 I 10.0 20.0 30.0 TIME (MIN) 40.0 50.0 i n 3 ~f— ' " T — — r — ^ 0.0 JO.O 20 . 0 30 . 0 40 . 0 5 0.0 TIME (MIN) a o "t •—r r h — i T j " i 1 — ] 0.0 JO.O 20.0 30.0 40.0 50.0 TIME (MIN) F i g . 5. Dynamic s p e c t r a of the August 9, 1979 IPDP event from a) F o r t S t . J o h n , b) P r i n c e George, and c) W i l l i a m s Lake. 15 method i s i n d e t e r m i n i n g the r e l i a b i l i t y of the r e s u l t i n g s p e c t r a . . T h i s n e c e s s i t a t e s c a r e f u l c o n s i d e r a t i o n i n c h o o s i n g t h e o r d e r of t h e p r e d i c t i o n e r r o r f i l t e r , s i n c e an attempt t o i n c r e a s e t h e r e s o l u t i o n t o o much by u s i n g a h i g h e r f i l t e r o r d e r w i l l r e s u l t i n s p l i t and s p u r i o u s peaks i n the s p e c t r a . The f i l t e r l e n g t h t h a t g i v e s the minimum f i n a l p r e d i c t i o n e r r o r (FPE) p r o v i d e s t h e b e s t compromise between r e s o l u t i o n and e r r o r . T h i s minimum FPE f i l t e r was used i n t h i s s t u d y , a f t e r h a v i n g s e a r c h e d f o r the minimum FPE w i t h f i l t e r o r d e r s of up t o h a l f t h e sample l e n g t h . T h i s r e s u l t e d i n s h o r t f i l t e r s , ~ 1 0 % of t h e sample l e n g t h , which i s i n a c c o r d a n c e w i t h t h e A k a i k e c r i t e r i o n f o r f i l t e r o r d e r s ( A k a i k e , 1969a,b, 1 970). Many s p e c t r a were computed w i t h f i l t e r o r d e r s both above and below t h e o r d e r which produced t h e minimum FPE, but i f the o r d e r was more than a few p o i n t s lower t h a n t h i s v a l u e the r e s o l u t i o n would be n o t i c e a b l y d e c r e a s e d , o r , i f t h e o r d e r was a few p o i n t s h i g h e r , t h e e x i s t i n g peaks would b e g i n t o s p l i t and s p u r i o u s peaks would appear.. E x t e n s i v e comparisons w i t h t h e maximum e n t r o p y s p e c t r a of s y n t h e t i c s i g n a l s and w i t h t h e p r e v i o u s l y mentioned periodograms were a l s o made. . These t e s t s tended t o c o n f i r m the c h o i c e o f f i l t e r l e n g t h s i n d i c a t e d above, and thus c o n f i r m e d t h e r e l i a b i l i t y of t h e r e s u l t i n g maximum e n t r o p y s p e c t r a . F i g u r e 6 shows a periodogram spectrum and a maximum e n t r o p y spectrum superimposed, i n d i c a t i n g t h e good agreement between the s e two methods. The lower power l e v e l s i n the periodogram spectrum a r e due t o the smoothing p r o c e s s . Each IPDP e v e n t t o be s t u d i e d was f i r s t d i v i d e d i n t o a number o f s h o r t segments, though t h e s e segments were chosen t o 16 F i g . 6. The periodogram and maximum entropy spectra of a segment of the August 9 event at Fort St. John. Note the good agreement between these two methods. 1 7 be o f s u f f i c i e n t l e n g t h t o a v o i d the problems i n h e r e n t i n computing the s p e c t r a of s h o r t r e c o r d s . The segments were then a n a l y z e d t o y i e l d a p r o f i l e of t h e changes t h a t took p l a c e d u r i n g each event. The n o i s e l e v e l s i n t h e data d i d c r e a t e o c c a s i o n a l problems i n computing the s p e c t r a . One v e r y weak event was r e n d e r e d unusable by n o i s e problems, s i n c e , u s i n g both of the s p e c t r a l a n a l y s i s methods a v a i l a b l e , i t proved i m p o s s i b l e t o o b t a i n r e l i a b l e s p e c t r a f o r enough of the segments t o g i v e an adeguate p i c t u r e o f the changes t a k i n g p l a c e d u r i n g the e v e n t . 18 3_. PROPERTIES OF IPDPS I n t h i s c h a p t e r , the g e n e r a l morphology o f IPDPs w i l l be examined..This w i l l i n c l u d e a d i s c u s s i o n o f t h e i r p h y s i c a l c h a r a c t e r i s t i c s , o c c u r r e n c e , and r e l a t i o n s h i p t o o t h e r geomagnetic phenomena. 3j___! P h y s i c a l C h a r a c t e r i s t i c s Though IPDPs are g e n e r a l l y c l a s s e d as P e l p u l s a t i o n s ( p e r i o d range: 5 s e c . - 0.2 s e c ) , t h e i r i n i t i a l p e r i o d s may be as l o n g as 20 seconds (Heacock, 1967), which i s i n t h e Pc3 range.. However, i n the case o f a more t y p i c a l e v ent the i n i t i a l p e r i o d o f p u l s a t i o n would be between 10 and f i v e seconds, and may be as s h o r t as t h r e e seconds. The s h o r t e s t p e r i o d s r e a c h e d a t the end of an IPDP event u s u a l l y f a l l between t h r e e seconds and one second, but can o c c a s i o n a l l y be as l o n g as f i v e s e c o n d s , o r as s h o r t as 0.3 seconds (Tepley and Amundsen, 1964). As i s e v i d e n t above, t h e r e are no s h a r p bounds l i m i t i n g the range of e i t h e r t h e minimum o r maximum f r e q u e n c i e s p r e s e n t i n IPDP e v e n t s . Those e v e n t s i d e n t i f i e d i n Chapter 2 had i n i t i a l p e r i o d s r a n g i n g from 5.6 seconds t o 4.2 seconds, and f i n a l p e r i o d s of between 2.8 and 1.9 seconds... The t o t a l amount of i n c r e a s e i n f r e g u e n c y can vary g u i t e w i d e l y between i n d i v i d u a l IPDP e v e n t s . T h i s i s a l s o t r u e of the r a t e of t h i s i n c r e a s e , which can range from a v e r y low v a l u e up to f i v e h e r t z / h o u r (Roxburgh, 1970), but w i l l more p r o b a b l y be between 0.2 h e r t z / h o u r and two h e r t z / h o u r . . R a t e s of i n c r e a s e 19 between about 0.35 and 0.65 h e r t z / h o u r were found f o r t h e e v e n t s mentioned above. The d u r a t i o n of an IPDP e v e n t i s t y p i c a l l y between 20 minutes and two h o u r s , though Roxburgh (1970) has suggested t h a t some may be as s h o r t as 10 m i n u t e s . The e v e n t s i d e n t i f i e d i n Chapter 2 were a l l between 20 and 40 minutes i n l e n g t h . O c c a s i o n a l l y two o r more IPDP e v e n t s w i l l o c c u r i n - s e g u e n c e (see F i g . 7 ) . . T h e r e i s no r e g u l a r p e r i o d of r e p e t i t i o n i n such c a s e s , and each event i s c o n s i d e r e d t o be a s e p a r a t e e n t i t y . G e n d r i n (1970) r e p o r t e d t h e mean a m p l i t u d e of IPDPs t o be ~0.1 gamma. .However, the s t r u c t u r a l elements, which appear a t i r r e g u l a r i n t e r v a l s i n many IPDP e v e n t s , are o f a s i g n i f i c a n t l y h i g h e r i n t e n s i t y . The f r e g u e n c y i n c r e a s e c o n t i n u e s s t e a d i l y t h r o u g h o u t both the n o i s e band and the s t r u c t u r a l e lements.. I t has a l s o been noted t h a t IPDPs have i d e n t i c a l s p e c t r a at c o n j u g a t e p o i n t s , and t h a t t h e r e i s e s s e n t i a l l y no phase s h i f t o b s e r v e d between t h e s e p o i n t s ( S a i t o , 1969). 3;_2 O c c u r r e n c e o f IPDPs The o c c u r r e n c e o f IPDP e v e n t s i s almost e n t i r e l y c o n c e n t r a t e d i n t h e e v e n i n g s e c t o r of t h e magnetosphere. The m a j o r i t y o f e v e n t s t a k e p l a c e between 1700 h o u r s and 2400 hours l o c a l t i m e , w i t h a s t r o n g peak of o c c u r r e n c e a t about 2000 hours l o c a l t i m e (see F i g . 8) . . F u k u n i s h i (1969) and Heacock (1971) r e p o r t e d t h a t IPDPs o c c u r r i n g e a r l i e r i n t h e day ( f u r t h e r from m i d n i g h t ) had lower r a t e s of f r e g u e n c y i n c r e a s e , though Roxburgh (1970) c o u l d not s u p p o r t t h i s c o n c l u s i o n . 20 F i g . 7. Two c o n s e c u t i v e IPDP events at Fo r t St. John on August 6, 1979. Only the second of these two events was e v i d e n t at s t a t i o n s f u r t h e r south, i n d i c a t i n g t h a t they are probably separate occurrences. 21 6 12 18 0 6 Local Time (120°W) F i g . 8. D i u r n a l v a r i a t i o n of o c c u r r e n c e of a t S e a t t l e , Wash., over an 11 month and Kenney, 1967). a l l IPDPs p e r i o d o b s e r v e d ( K n a f l i c h 22 G e n e r a l l y , IPDPs appear a t the r a t e of a few per month, w i t h a somewhat enhanced r a t e of o c c u r r e n c e d u r i n g t h e summer months (Heacock, 1967). They a l s o t e n d t o t a k e p l a c e on a c t i v e days (20 < IKp < 35; J a c o b s , 1970). . The e v e n t s s e l e c t e d i n Chapter 2 o c c u r r e d on days w i t h t o t a l Kp i n d i c e s (the sum o f t h e t h r e e - h o u r l y i n d i c e s ; Kp) of 14, 19*, and 26-. Most IPDPs o c c u r i n the h i g h s u b - a u r o r a l zone, between 55° and 65° geomagnetic l a t i t u d e , with the g r e a t e r c o n c e n t r a t i o n o f events i n the upper p a r t o f t h i s r a n g e . Events w i l l o c c a s i o n a l l y o c c u r o u t s i d e of t h i s r a n g e , i n middle or lower l a t i t u d e s , o r t h e y may be propagated t o lower l a t i t u d e s w i t h i n t h e i o n o s p h e r i c d u c t . The l o n g i t u d i n a l e x t e n t o f IPDPs i s u s u a l l y g u i t e l i m i t e d , though a t t i m e s one e v e n t can be r e c o r d e d a t two s t a t i o n s which ar e as much as 30° a p a r t . A l t h o u g h , as mentioned, most IPDPs appear a t h i g h e r l a t i t u d e s , t h o s e which do o c c u r f u r t h e r towards t h e e g u a t o r t e n d t o do so on very a c t i v e days w i t h h i g h TKp i n d i c e s (Roxburgh, 1970).. E v e n t s t a k i n g p l a c e at t h e s e lower l a t i t u d e s a r e a l s o i n c l i n e d t o e x h i b i t h i g h e r f r e g u e n c i e s than t h e i r h i g h e r l a t i t u d e c o u n t e r p a r t s . . The r e l a t i v e l y low £Kp i n d i c e s f o r the days o f t h e e v e n t s mentioned above seems t o i n d i c a t e t h a t t h e s e were h i g h e r l a t i t u d e e v e n t s . I i 3 R e l a t i o n t o o t h e r Geomagnetic Phenomena When IPDPs were f i r s t s t u d i e d ( T r o i t s k a y a , 1961) i t was noted t h a t t h e y o c c u r r e d on a c t i v e days, i n d i c a t i n g a p o s s i b l e r e l a t i o n s h i p w i t h p o l a r magnetic substorms.. S u b s e g u e n t l y , 23 F u k u n i s h i (1969), Roxburgh (1 970), and Heacock (1971) a l l found t h a t IPDP e v e n t s o c c u r r e d s h o r t l y a f t e r , w i t h i n one hour, of the i n i t i a t i o n o f t h e e x p a n s i o n phase of a substorm. F i g u r e 9 i l l u s t r a t e s t h e r e l a t i o n between IPDPs and substorms. The b e g i n n i n g o f the e x p a n s i o n phase i s marked by t h e onset of a s h a r p n e g a t i v e bay i n the a u r o r a l zone near l o c a l m i d n i g h t . The e x p a n s i o n phase i s t h a t p a r t o f a p o l a r magnetic substorm i n which energy p r e v i o u s l y b u i l t up i n the magnetosphere i s s u p p l i e d e x p l o s i v e l y t o t h e i o n o s p h e r e t h r o u g h the a c c e l e r a t i o n and i n j e c t i o n o f e n e r g e t i c p a r t i c l e s . . The dominant c u r r e n t f e a t u r e i n t h e i o n o s p h e r e a t t h i s time i s t h e a u r o r a l zone westward e l e c t r o j e t , which e x t e n d s from near l o c a l m i d n i g h t t h r o u g h the e a r l y morning h o u r s . T h i s e l e c t r o j e t i s r e s p o n s i b l e f o r the n i g h t s i d e n e g a t i v e bays r e c o r d e d a t h i g h l a t i t u d e ground s t a t i o n s . . The r e p e t i t i o n o f IPDP e v e n t s i s a r e s u l t of substorms r e c u r r i n g a t s h o r t i n t e r v a l s . Not a l l magnetic substorms r e s u l t i n IPDP a c t i v i t y . P i 2 m i c r o p u l s a t i o n s appear t o be generated i n c o n j u n c t i o n w i t h t h e o n s e t of t h e e x p a n s i o n phase of a substorm, and are t h e r e f o r e a l s o o f t e n observed i n a s s o c i a t i o n w i t h IPDP e v e n t s . Heacock (1971) noted t h a t P i b u r s t s ( P i 1 * Pi2) , o c c u r r i n g i n a s s o c i a t i o n w i t h substorms, were c e n t r e d near l o c a l m i d n i g h t a t a p p r o x i m a t e l y 70° l a t i t u d e . T h i s shows t h a t t h e s e m i c r o p u l s a t i o n s , as w e l l as t h e substorm produced n e g a t i v e bays, t a k e p l a c e t o the e a s t and n o r t h of t h e s u b s e g u e n t l y o c c u r r i n g IPDP e v e n t s . Other m i c r o p u l s a t i o n s have a l s o been r e p o r t e d i n c o n n e c t i o n w i t h IPDPs. Roxburgh (1970) showed t h a t o c c a s i o n a l l y IPDPs were 24 o to to ro ro m o 0.0 0.4 r 0.81 TIME 1 .2 (MRS) J . 6 2.0 a CT 3.0 .—I a LOCAL MIDNIGHT 4.0 5.0 \ j C O 7.0 3.0 4.D 5.0 6.0 UNIVERSAL TIME 7.0 a O.OCT . o 8.0 F i g . 9. Magnetic f i e l d H component from Great Whale R i v e r and IPDP dynamic spectrum from F o r t St. John. Note the sharp onset o f a n e g a t i v e bay s h o r t l y b e f o r e the IPDP event b e g i n s (August 8, 1979). 25 immediately f o l l o w e d by PP events, and Heacock (1967, 1971) found t h a t u n s t r u c t u r e d Pc1 - Pc2 a c t i v i t y o f t e n preceded the IPDPs recorded at C o l l e g e , Alaska (see F i g . 10).. T h i s a c t i v i t y i n c l u d e d CE p u l s a t i o n s (Pel) with p e r i o d s t y p i c a l l y near f o u r or f i v e seconds (also known as 4-second band p u l s a t i o n s ) . In a d d i t i o n , other geomagnetic phenomena, such as changes i n a u r o r a l l u m i n o s i t y , X-ray b u r s t s , and i n t e n s i t y changes i n the r a d i a t i o n b e l t s , have been reported i n a s s o c i a t i o n with IPDP eve n t s . F u k u n i s h i (1973) found proton aurorae o c c u r r i n g with IPDPs, and i n c r e a s e d cosmic noise a b s o r p t i o n (CNA) events have a l s o been detected i n connection with IPDPs ( F u k u n i s h i , 1973; L u k k a r i e t a l . , 1977) . 26 10. IPDP event from c o n j u g a t e s t a t i o n s a t Macguarie I s . and Kotzebue, A l a s k a . Note the Pc1 - Pc2 a c t i v i t y l e a d i n g up t o t h e event (Heacock et a l . , 1976). 27 Us. IRHR GENERATION MECHANISMS 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 IPDPs are produced by 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 p r o c e s s i n a r e g i o n o f t h e e g u a t o r i a l p l a n e of t h e a f t e r n o o n / e v e n i n g s e c t o r of the magnetosphere. I t i s a l s o apparent t h a t t h e i r g e n e r a t i o n i s r e l a t e d t o t h e p o l a r magnetic substorm p r o c e s s . T h i s c h a p t e r w i l l d e s c r i b e the g e n e r a l mechanism f o r t h e g e n e r a t i o n of IPDPs as w e l l as a number o f s p e c i f i c p r o p o s a l s f o r the f r e g u e n c y s h i f t mechanism. G e n e r a l G e n e r a t i o n P r o c e s s Hydromagnetic e m i s s i o n s i n t h e P e l range (PP, CE), which have been e x t e n s i v e l y s t u d i e d , a r e b e l i e v e d t o be ge n e r a t e d by 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 p r o c e s s . . Roxburgh (1970) and Heacock (1971) both noted t h a t t h e o c c u r r e n c e o f IPDPs i s sometimes c l o s e l y r e l a t e d t o t h e s e P e l p u l s a t i o n s (see s e c . . 3.3 and F i g . . 10).. The p e r i o d ranges and a m p l i t u d e s t r u c t u r e s of these p u l s a t i o n s a r e a l s o g u i t e s i m i l a r t o t h o s e of t h e IPDP e v e n t s when th e y o c c u r t o g e t h e r . T h e r e f o r e , t h e c o n c l u s i o n was drawn t h a t IPDPs may a l s o be ge n e r a t e d by 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 mechanism. Other e v i d e n c e , i n c l u d i n g t h e o b s e r v a t i o n of p r o t o n a u r o r a e o c c u r r i n g i n c o n n e c t i o n w i t h IPDPs ( F u k u n i s h i , 1973), and the s a t e l l i t e o b s e r v a t i o n 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 ( H o r i t a et a l . , 1979), has s u p p o r t e d t h i s c o n c l u s i o n . T h i s 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 p r o c e s s which produces 28 IPDP e v e n t s i n v o l v e s an i n t e r a c t i o n between e n e r g e t i c p r o t o n s and l e f t - h a n d e d c i r c u l a r l y p o l a r i z e d hydromagnetic waves. T h i s resonance c o n d i t i o n w i l l o c cur when t h e wave f r e g u e n c y , d o p p l e r s h i f t e d t o t h e p r o t o n s ' v e l o c i t y p a r a l l e l t o the magnetic f i e l d l i n e s , e g u a l s t h e g y r o f r e g u e n c y of the prot o n s about th e s e f i e l d l i n e s . The r e s u l t o f t h i s c y c l o t r o n i n s t a b i l i t y p r o c e s s i s a t r a n s f e r of some o f t h e k i n e t i c energy of the p r o t o n s t o the growing hydromagnetic waves. The p r o t o n s i n v o l v e d i n t h i s p r o c e s s a r e s u b s e q u e n t l y p r e c i p i t a t e d i n t o t h e i o n o s p h e r e , where they can r e s u l t i n pr o t o n a u r o r a e . A f u r t h e r d i s c u s s i o n of 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 p r o c e s s w i l l be p r e s e n t e d i n Appendix 2. The p r o t o n s i n v o l v e d i n t h e g e n e r a t i o n of IPDPs a r e a c c e l e r a t e d i n t h e m a g n e t o t a i l and i n j e c t e d i n towards t h e m i d n i g h t s e c t o r o f t h e i n n e r magnetosphere a t t h e b e g i n n i n g of t h e e x p a n s i o n phase of a p o l a r magnetic substorm.. They th e n become t r a p p e d on c l o s e d f i e l d l i n e s , and move westward towards the IPDP g e n e r a t i o n r e g i o n under t h e i n f l u e n c e o f the c u r v a t u r e and g r a d i e n t d r i f t mechanisms. The p i t c h angle a n i s o t r o p y needed f o r t h e 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 p r o c e s s t o o c c u r i s b e l i e v e d t o be c r e a t e d by t h e l o s s c f low p i t c h a n g l e p r o t o n s d u r i n g t h i s westward d r i f t . Some of t h e p a r t i c l e s a c c e l e r a t e d i n the t a i l a r e not t r a p p e d on c l o s e d f i e l d l i n e s , but are i n j e c t e d d i r e c t l y i n t o t h e i o n o s p h e r e a t h i g h l a t i t u d e s near m i d n i g h t , c r e a t i n g the westward e l e c t r o j e t and n e g a t i v e bays c h a r a c t e r i s t i c of substorms. T h i s p i c t u r e i s s u p p o r t e d by the observ e d d i u r n a l v a r i a t i o n of o c c u r r e n c e , and a s s o c i a t i o n w i t h substorms e x h i b i t e d by IPDPs, and Frank (1970) has d e t e c t e d a 29 F i g . 11. A model c u r r e n t system f o r a t y p i c a l p o l a r magnetic substorm, showing the p a r t i a l r i n g c u r r e n t on t h e e v e n i n g s i d e (Kamide and Fukushima, 1972). 30 p a r t i a l r i n g c u r r e n t c a r r i e d by westward d r i f t i n g p r o t o n s i n the e v e n i n g s e c t o r of t h e magnetosphere. F i g u r e 11 shows a model c u r r e n t system f o r p o l a r magnetic s u b s t o r m s , i l l u s t r a t i n g t h e o c c u r r e n c e o f t h i s p a r t i a l r i n g c u r r e n t . A s c h e m a t i c diagram o u t l i n i n g the p a r t i c l e a c c e l e r a t i o n i n the t a i l and t h e westward d r i f t o f the t r a p p e d p r o t o n s , f o l l o w e d by t h e c y c l o t r o n t u r b u l e n c e and p r e c i p i t a t i o n of t h e s e p r o t o n s , i s p r e s e n t e d i n F i g u r e 12. The i o n o s p h e r i c s e c t i o n c o m p l e t i n g t h e p a r t i a l r i n g c u r r e n t c i r c u i t i s b e l i e v e d t o be the eastward e l e c t r o j e t . . T h i s f e a t u r e , which appears on t h e ground as a h i g h l a t i t u d e p o s i t i v e bay i n the e v e n i n g s e c t o r , does not o c c u r w i t h a l l substorms ( B o t e l e r , 1980), i m p l y i n g t h a t t h e e n t i r e p a r t i a l r i n g c u r r e n t system may not appear w i t h e v e r y substorm. T h i s c o u l d account f o r t h e o b s e r v e d f a c t t h a t IPDP e v e n t s a l s o do not appear w i t h e v e r y substorm. F i g u r e 13 shows an IPDP event and t h e a s s o c i a t e d h i g h l a t i t u d e p o s i t i v e bay. As t h e p r o t o n s d r i f t westward frcm the i n j e c t i o n r e g i o n , t h e c y c l o t r o n t u r b u l e n c e i s b e l i e v e d t o occur i n or near t h e e q u a t o r i a l p l a n e . Such a g e n e r a t i o n r e g i o n l o c a t i o n i s r e g u i r e d t o produce t h e i d e n t i c a l s p e c t r a observed f o r IPDP e v e n t s a t c o n j u g a t e p o i n t s . The hydromagnetic waves t h u s g e n e r a t e d near the e q u a t o r t h e n p r o p a g a t e down the geomagnetic f i e l d l i n e s t o t h e s u b - a u r o r a l zones o f E a r t h . Ground based e s t i m a t e s of t h e energy o f t h e p r o t o n s i n v o l v e d i n t h e c y c l o t r o n i n s t a b i l i t y p r o c e s s range from 10 t o 100 KeV (Gendrin e t a l . , 1967; Heacock, 1973; Kangas et a l . , 1 9 7 4 ) . . S a t e l l i t e measurements of p r o t o n e n e r g i e s i n t h e IPDP 31 Schematic i l l u s t r a t i o n o f p a r t i c l e a c c e l e r a t i o n , d r i f t , and p r e c i p i t a t i o n d u r i n g a substorm ( B o t e l e r , 1980) . 32 3 . 0 . 4.0 5.0 6.C 7.0 8.0 UN IV E R S f l L TIME F i g . 13. Normal-run magnetogram frcm C o l l e g e , A l a s k a , and IPDP dynamic spectrum from F o r t S t . John. Note the p o s i t i v e bay o c c u r r i n g at C o l l e g e . There i s a s l i g h t time d i f f e r e n c e between the IPDP and t h e peak of t h i s bay. 33 g e n e r a t i o n r e g i o n y i e l d e d a range of one to 100 KeV ( H o r i t a et a l . # 1979), which i s i n good agreement w i t h the e a r l i e r e s t i m a t e s . . The r a d i a l p o s i t i o n i n the e g u a t o r i a l p l a n e o f t h e g e n e r a t i o n r e g i o n i s u n c e r t a i n , though most e s t i m a t e s put i t between L s h e l l s f i v e and e i g h t (Gendrin e t a l . , 1967; T r o i t s k a y a e t a l . , 1968; F u k u n i s h i , 1969; Heacock et a l . , 1976). H o r i t a e t a l . . (1 979) mentioned L v a l u e s of between 4.7 and 5.5 f o r t h e onset of IPDP g e n e r a t i o n . The s t e a d y r i s e i n f r e g u e n c y over the c o u r s e of each event i s the most prominent c h a r a c t e r i s t i c of IPDP p u l s a t i o n s . What p h y s i c a l mechanism i s b e h i n d t h i s f e a t u r e i s not c l e a r , though many have been proposed. G e n d r i n e t a l . (1967) put f o r w a r d t h e i d e a t h a t a c o n t i n u o u s l y i n c r e a s i n g background magnetic f i e l d i n t h e g e n e r a t i o n r e g i o n , due t o an earthward motion o f t h i s r e g i o n , r e s u l t e d i n a s t e a d i l y i n c r e a s i n g i o n g y r o f r e g u e n c y . T h i s r i s i n g g y r o f r e q u e n c y would t h e n produce a c o n s t a n t i n c r e a s e i n t h e f r e g u e n c y of the hydromagnetic waves g e n e r a t e d by t h e 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 mechanism. F u k u n i s h i (1969, 1973) proposed t h a t the f r e g u e n c y s h i f t was due t o t h e g r e a t e r a z i m u t h a l d r i f t v e l o c i t y of t h e h i g h e r energy p r o t o n s moving around from the i n j e c t i o n r e g i o n . S i n c e t h e f r e g u e n c y of t h e c y c l o t r o n i n s t a b i l i t y produced waves v a r i e s w i t h the p r o t o n energy as 1/E//Z, the h i g h e r energy p r o t o n s , which would a r r i v e i n t h e g e n e r a t i o n r e g i o n f i r s t , would r e s u l t i n lower f r e g u e n c y waves. As s l o w e r p r o t o n s of p r o g r e s s i v e l y lower e n e r g i e s a r r i v e d , t h e wave f r e q u e n c i e s would r i s e . Roxburgh (1970) a l s o a ttempted t o e x p l a i n the f r e g u e n c y s h i f t w i t h an i n c r e a s i n g 34 background magnetic f i e l d . U n l i k e p r e v i o u s work, however, t h e g e n e r a t i o n r e g i o n was s t a t i o n a r y and t h e i n c r e a s e i n the f i e l d was a t t r i b u t e d t o t h e decay o f the p a r t i a l r i n g c u r r e n t . I t has a l s o been p o i n t e d out ( L i n and P a r k s , 1976) t h a t a d e c r e a s i n g c o l d plasma d e n s i t y i n t h e g e n e r a t i o n r e g i o n c o u l d produce a r i s i n g f r e g u e n c y s t r u c t u r e . A l l of the t h e s e mechanisms w i l l be d i s c u s s e d i n g r e a t e r d e t a i l i n t h e next s e c t i o n . . 4^ .2 Freguency S h i f t Mechanisms I t can be shown (see Appendix 2) t h a t t h e f r e g u e n c y o f t h e waves g e n e r a t e d by 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 p r o c e s s i s g i v e n by; w ^ Bx (1) where B i s the E a r t h ' s d i p o l e f i e l d , i s t h e background plasma d e n s i t y , and W i s t h e p a r t i c l e (proton) k i n e t i c energy. Each of t h e f r e g u e n c y s h i f t t h e o r i e s d i s c u s s e d below p o s t u l a t e s a change i n one o f t h e parameters on the r i g h t h a n d s i d e o f (1) i n o r d e r to produce t h e r i s i n g t o n e of IPDPs. Inward Motion Theory., I n t h i s t h e o r y , t h e r i s i n g IPDP f r e g u e n c y i s a t t r i b u t e d to t h e inward d i f f u s i o n of e n e r g e t i c p r o t o n s a c r o s s geomagnetic f i e l d l i n e s . (Gendrin e t a l . , 1967, Heacock, 1967). As the p r o t o n s move in w a r d t oward r e g i o n s cf i n c r e a s i n g l y h i g h e r background magnetic f i e l d , t h e i r i n t e r a c t i o n w i t h hydromagnetic waves produces s t e a d i l y h i g h e r f r e g u e n c i e s . 35 I t i s e v i d e n t from (1) t h a t , assuming s t e a d y s t a t e m agnetospheric c o n d i t i o n s , under which N, c*. B, and no energy g a i n by the d i f f u s i n g p a r t i c l e s , t h e wave fregu e n c y would be: w B3/I (2) I f we r e p r e s e n t the E a r t h ' s d i p o l e f i e l d a s : B = JM. (3) R' where Be% i s t h e f i e l d s t r e n g t h on E a r t h ' s e q u a t o r and R i s the d i s t a n c e from t h e c e n t r e of the E a r t h measured i n E a r t h r a d i i , then (2) becomes: w <^  1 (4) R"* I t i s o b v i o u s from t h i s r e l a t i o n t h a t i n w a r d motion o f t h e g e n e r a t i o n r e g i o n ( d e c r e a s i n g R) w i l l produce a r i s i n g t o ne s t r u c t u r e . The t o t a l change i n f i e l d s t r e n g t h seen by a p a r t i c l e moving t h r o u g h a magnetic f i e l d i s g i v e n by: CB = ±B_ *• (v • V ) B (5) Dt bt However, f o r t h e inward d i f f u s i o n t h e o r y , the assumption t h a t i B / i t = Q (steady s t a t e c o n d i t i o n s ) i s made. T h e r e f o r e , the t o t a l f i e l d change seen by t h e d i f f u s i n g p r o t o n s i s : _DB_ = (v, • V) B (6) Dt Where vf i s t h e p r o t o n d i f f u s i o n v e l o c i t y ( d i r e c t e d inward) . . I f 36 t h e s t e a d y s t a t e c o n d i t i o n i s t o be m a i n t a i n e d , then i t must be assumed t h a t the d i f f u s i o n p r o c e s s does not a f f e c t the background p l a s m a . . I t i s e v i d e n t from the e g u a t i o n : J j 3 = vxv, xB ( 7 ) where vt i s t h e v e l o c i t y of the b u l k plasma, t h a t any such e f f e c t would produce a non-zero ^B/H term. S u b s t i t u t i n g e g u a t i o n (3) i n t o ( 6 ) , we g e t : DB = 3v, B (8) Dt R From (2) and (8) i t can then be shown (Roxburgh, 1 9 7 0 ) t h a t the i n w a r d motion r e q u i r e d t o produce the r i s i n g tone of IPDPs i s : v, = 2R Dw (9) 9w' Dt For a g e n e r a t i o n r e g i o n d i s t a n c e o f R= 6 , the d i f f u s i o n v e l o c i t y n e c e s s a r y would be ~ 6 km/sec. However, the u n c e r t a i n t y i n t h i s d i s t a n c e makes i t d i f f i c u l t t o o b t a i n r e l i a b l e v e l o c i t y e s t i m a t e s . I t has been suggested ( L a c o u r l y , 1 9 6 9 ) t h a t t h e i n w a r d d r i f t i s due to a westward e l e c t r i c f i e l d i n the e g u a t o r i a l p l a n e . The d i f f u s i o n v e l o c i t y would then be g i v e n by: v, = Ex B ( 1 0 ) B x The e l e c t r i c f i e l d s n e c e s s a r y t o produce the d r i f t v e l o c i t i e s g i v e n by ( 9 ) can now be e s t i m a t e d , a g a i n s u b j e c t t o the u n c e r t a i n t y i n the d i s t a n c e t o the g e n e r a t i o n r e g i o n . . L a c o u r l y 37 F i g . 14. Diagram showing the i n w a r d motion o f t h e g e n e r a t i o n r e g i o n due t o t h e i n w a r d motion of t h e plasmapause. The plasmapause i s r e p r e s e n t e d by t h e s o l i d and ( l a t e r ) dashed curved l i n e s . The ground s t a t i o n i s r e p r e s e n t e d by G, and L and T i n d i c a t e L - s h e l l and t i m e , r e s p e c t i v e l y ( H o r i t a e t a l . , 1979).. 38 - v-gave a v a l u e of —5x10 v o l t s / m f o r t h i s f i e l d , and, f o r a d i s t a n c e of R=6, Roxburgh found an average v a l u e of E=8.8x10"' v o l t s / m . . Another v e r s i o n of the inward motion t h e o r y i s d i s c u s s e d by H o r i t a e t a l . . ( 1 9 7 9 ) . I n t h i s c a s e , o n l y the area i n which the c o n d i t i o n s a re s u i t a b l e f o r i o n c y c l o t r o n t u r b u l e n c e moves i n w a r d . No inward d i f f u s i o n o f e n e r g e t i c p r o t o n s i s r e g u i r e d ; the p r o t o n s d r i f t i n g westward from the m i d n i g h t i n j e c t i o n r e g i o n c o n t i n u a l l y r e s u p p l y the g e n e r a t i o n r e g i o n as i t moves i n w a r d (see F i g . . 1 4 ) . The in w a r d motion i s b e l i e v e d t o be caused by an inward motion o f the plasmapause. . 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 i s tho u g h t t o be e x c i t e d when the d r i f t i n g p r o t o n s meet t h e ev e n i n g s i d e plasmasphere b u l g e . . E g u a t i o n (2) s t i l l c o n t r o l s the f r e g u e n c y of the ge n e r a t e d waves.. Azimutha 1 D r i f t Theory. . F u k u n i s h i (1969) a t t r i b u t e d the r i s i n g tone s t r u c t u r e of IEDPs t o a g r a d u a l l y s o f t e n i n g beam of p r o t o n s . . T h i s beam i s produced by the westward d r i f t of t h e p r o t o n s i n j e c t e d near l o c a l m i d n i g h t d u r i n g magnetic substorms. The g r a d i e n t and c u r v a t u r e o f t h e geomagnetic f i e l d produce a combined a z i m u t h a l d r i f t v e l o c i t y o f : v A = _ L_(1 tcosVc ) (11) eBRe where oc and R6 a r e , r e s p e c t i v e l y , the p i t c h a n g l e of t h e p r o t o n s , and the r a d i u s of c u r v a t u r e of the f i e l d l i n e s i n the r e g i o n where the d r i f t i s o c c u r r i n g . The magnetosphere i s assumed t o be i n a s t e a d y s t a t e c o n d i t i o n . I t i s o b v i o u s from (11) t h a t t h e a z i m u t h a l d r i f t v e l o c i t y 39 i s g r e a t e r f o r h i g h e r energy p r o t o n s and t h e y w i l l t h e r e f o r e a r r i v e i n the g e n e r a t i o n r e g i o n f i r s t . P r o t o n s o f lower e n e r g i e s w i l l a r r i v e l a t e r , p r o d u c i n g t h e s o f t e n i n g energy spectrum o f t h e beam r e q u i r e d f o r IPDP g e n e r a t i o n . Assuming dB/dt=0, and a c o n s t a n t background plasma d e n s i t y i n t h e g e n e r a t i o n r e g i o n , the g e n e r a t e d wave f r e q u e n c y from (1) would become: W o c J _ ( 1 2 ) T h e r e f o r e the e a r l i e r a r r i v i n g h i g h e r energy p r o t o n s would produce a lower f r e g u e n c y . As p r o g r e s s i v e l y l o w e r energy p r o t o n s a r r i v e d , t h e g e n e r a t e d f r e g u e n c y would go up, r e s u l t i n g i n the s t e a d i l y r i s i n g tone of IPDP p u l s a t i o n s . From e q u a t i o n s (11) and (12) i t can be shown t h a t t h e wave f r e g u e n c y r e s u l t i n g from t h e d i f f e r e n t i a l a z i m u t h a l d r i f t v e l o c i t i e s can be r e l a t e d t o t h e e l a p s e d time t s i n c e the substorm e x p a n s i o n phase onset ( p a r t i c l e i n j e c t i o n ) by: w t' / l (13) T h e r e f o r e , the r a t e of i n c r e a s e of w becomes: dw ^ J _ (14) dt f *• I t i s now e v i d e n t from (14) t h a t l o n g e r d e l a y s between t h e e x p a n s i o n phase onset and the g e n e r a t i o n of an IPDP event' w i l l produce l o w e r r a t e s of f r e g u e n c y r i s e . T h i s e f f e c t has been noted by some a u t h o r s (see s e c . 3. 2) . . F u k u n i s h i i n d i c a t e d t h a t t h e c y c l o t r o n t u r b u l e n c e g e n e r a t i n g IPDPs would occur when the p i t c h a n g l e a n i s o t r o p y 40 caused by t h e l o s s of s m a l l p i t c h a n g l e p a r t i c l e s d u r i n g t h e westward d r i f t became pronounced enough. I t has a l s o been su g g e s t e d t h e 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 s near t h e plasmapause as t h e westward d r i f t i n g p r o t o n s meet th e plasmasphere bulge (Heacock, 1973; H o r i t a e t a l . , 1979). lO-Creasing F i e l d Theory. . Roxburgh (1970) suggested t h a t the r i s i n g tone o f IPDPs was the r e s u l t of an i n c r e a s i n g 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 . The inward motion t h e o r y a l s o a c c o u n t s f o r the r i s i n g tone with an i n c r e a s i n g magnetic f i e l d , b u t a t t r i b u t e s t h i s i n c r e a s e t o the motion o f the g e n e r a t i o n r e g i o n i n w a r d toward areas o f h i g h e r f i e l d s t r e n g t h . . I n the i n c r e a s i n g f i e l d t h e o r y , the g e n e r a t i o n r e g i o n does not move, but t h e f i e l d s t r e n g t h changes w i t h t i m e . . S i n c e the g e n e r a t i o n r e g i o n i s s t a t i o n a r y , i t i s the second term on t h e r i g h t - h a n d s i d e of (5) which . i s s e t t o z e r o ([v y]B=0). T h e r e f o r e , t h e t o t a l change i n the magnetic f i e l d as seen by t h e p r o t o n s i n t h e g e n e r a t i o n r e g i o n i s g i v e n by: DB = _iB_ (1 5) Dt at In a c t u a l f a c t , t h e (v S J ) B term may be non-zero. E g u a t i o n (7) shows t h a t , i f iB/btfO, then v#0. T h i s e f f e c t would c r e a t e a non-zero (v n)B term i n ( 5 ) . However, i t i s b e l i e v e d t h a t t h i s term w i l l remain v e r y s m a l l ([v V]B < ^B/dt). Roxburgh ( 1970) showed t h a t , a t i t s extreme maximum, i t i s o n l y o f the same o r d e r of magnitude as t h e J B / H term. I f i t i s assumed t h a t both and W a r e c o n s t a n t , then (1) 4 1 shows t h a t , f o r the i n c r e a s i n g f i e l d t h e o r y , w w i l l be g i v e n by: w oc B * ( 1 6 ) Roxburgh o u t l i n e d the c o n d i t i o n s n e c e s s a r y t o produce the i n c r e a s i n g magnetic f i e l d and IPDP p u l s a t i o n s as f o l l o w s . . P r i o r t o the e x p a n s i o n phase o f a magnetic substorm, t h e f i e l d i n t h e IPDP g e n e r a t i o n area i s s l o w l y d e p r e s s e d by t h e f o r m a t i o n of the p a r t i a l r i n g c u r r e n t o u t s i d e t h i s a r e a . . T h i s c u r r e n t , which o c c u r s o n l y i n t h e e v e n i n g q u a d r a n t , i s b e l i e v e d t o be composed of westward d r i f t i n g p r o t o n s . . At t h e s t a r t of the e x p a n s i o n phase, t h e s o u r c e of these p r o t o n s , which i s near l o c a l m i d n i g h t , i s c u t o f f . The r i n g c u r r e n t then r a p i d l y decays, r e s u l t i n g i n t h e r e c o v e r y o f t h e 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 t o i t s normal s t r e n g t h . A s o u r c e o f e n e r g e t i c p r o t o n s w i t h an a n i s o t r o p i c p i t c h a n g l e d i s t r i b u t i o n i s needed f o r 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 t o o c c u r . I t i s thought t h a t such 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 s h o r t l y b e f o r e t h e onset of t h e substorm e x p a n s i o n phase. These p r o t o n s would then d r i f t westward, and be i n the IPDP g e n e r a t i o n r e g i o n when t h e magnetic f i e l d was r e c o v e r i n g . Any hydromagnetic waves then g e n e r a t e d by the s e p r o t o n s , v i a 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 mechanism, i n the presence o f the i n c r e a s i n g magnetic f i e l d would have t h e c h a r a c t e r i s t i c r i s i n g t o ne o f IPDPs. Though some a s p e c t s o f t h i s mechanism, such as the time of the p r o t o n i n j e c t i o n and the r o l e of t h e p a r t i a l r i n g c u r r e n t , are not i n p e r f e c t agreement w i t h the g e n e r a l mechanism 42 d i s c u s s e d i n s e c t i o n 4 . 1 , Roxburgh's work must s t i l l be c o n s i d e r e d . D e c r e a s i n g Plasma D e n s i t y Theory^ L i n and Parks ( 1 9 7 6 ) i n v e s t i g a t e d i n d e t a i l the r o l e of 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 p r o c e s s i n c l o u d s of p a r t i c l e s a l l o w e d t o d r i f t i n t h e magnetosphere. The p a r t i c l e s c o n s i d e r e d were i n j e c t e d near m i d n i g h t onto c l o s e d f i e l d l i n e s a t L=7, t h e n a l l o w e d t o d r i f t westward,around t o the IPDP g e n e r a t i o n r e g i o n . . C a l c u l a t i o n s of t h e growth r a t e of hydromagnetic waves g e n e r a t e d by t h e 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 p r o c e s s i n t h e s e d r i f t i n g p a r t i c l e s i n d i c a t e d t h a t b o t h the a z i m u t h a l d r i f t e f f e c t s d i s c u s s e d e a r l i e r , and t h e e f f e c t o f a changing c o l d plasma d e n s i t y must be a c c o u n t e d f o r i n o r d e r t o understand the f r e q u e n c y c h a r a c t e r i s t i c s of t h e s e waves. I t was shown t h a t e i t h e r the energy dependent a z i m u t h a l d r i f t or a d e c r e a s i n g c o l d plasma d e n s i t y c o u l d e a c h , i n d e p e n d e n t l y , r e s u l t i n a r i s i n g t o ne f r e g u e n c y s t r u c t u r e . I n a c o n s t a n t magnetic f i e l d , t h e f r e g u e n c i e s generated by d r i f t i n g p a r t i c l e s w i t h a c o n s t a n t background c o l d plasma d e n s i t y i s d e s c r i b e d by ( 1 2 ) . However, i f N i s a l l o w e d t o v a r y , w i t h t h e d r i f t e f f e c t s not i n c l u d e d , the f r e g u e n c y o f the g e n e r a t e d waves i s g i v e n by: w o * J _ ( 1 7 ) which shows t h a t i t i s a l s o p o s s i b l e t o have r i s i n g t ones when i s d e c r e a s i n g . The e f f e c t s o f each of t h e s e two c o n d i t i o n s 43 Tl ME (minutes) TIME (minutes) • F i g . 15.. Growth r a t e c o n t o u r s f o r s t a t i c c o l d plasma d e n s i t y w i t h d r i f t e f f e c t s i n c l u d e d ( t o p ) , and d e c r e a s i n g c o l d plasma d e n s i t y w i t h no d r i f t (bottom) ( L i n and P a r k s , 1976). . 44 F i g . 16. Growth r a t e c o n t o u r s f o r v a r i o u s c o l d plasma d e n s i t y p r o f i l e s , a l l w i t h d r i f t e f f e c t s i n c l u d e d . Note the r i s i n g t o n e s f o r the c o n s t a n t and d e c r e a s i n g c o l d plasma d e n s i t y p l o t s ( L i n and P a r k s , 1 976). 45 ar e i l l u s t r a t r e d s e p a r a t e l y i n F i g u r e 15. I t i s t h e n c l e a r from the work of L i n and P a r k s t h a t a z i m u t h a l d r i f t o r d e c r e a s i n g d e n s i t y e f f e c t s can produce IPDP-type s p e c t r a . . I t i s a l s o p o i n t e d out t h a t i t i s g u i t e p o s s i b l e t h a t b o t h t h e s e e f f e c t s may o p e r a t e t o g e t h e r t o produce r i s i n g tone s t r u c t u r e s . T h i s s i t u a t i o n i s i l l u s t r a t e d i n F i g u r e 16. 4;_3 P i sc us s i on of Freguency S h i f t Mechanisms At p r e s e n t , t h e r e l a t i v e i m p o r t a n c e o f each of t h e above mechanisms proposed t o acco u n t f o r the f r e g u e n c y s h i f t of IPDPs i s n o t c l e a r . , I t i s g u i t e p r o b a b l e t h a t more t h a n one of the s e p r o c e s s e s may be i n v o l v e d i n t h e g e n e r a t i o n of an IPDP e v e n t , though what c o m b i n a t i o n s a r e p o s s i b l e , and the r e l a t i v e c o n t r i b u t i o n s t o the f r e g u e n c y r i s e of each mechanism i n a c o m b i n a t i o n , remains t o be d e t e r m i n e d . Many of t h e assumptions made f o r each o f t h e t h e o r i e s , such as the time c o n s t a n t magnetic f i e l d s r e g u i r e d by t h e i n w a r d motion and a z i m u t h a l t h e o r i e s and t h e s t a t i c p a r t i c l e d e n s i t y of t h e i n c r e a s i n g f i e l d t h e o r y , can be broken w i t h o u t i n v a l i d a t i n g t h e t h e o r y . . These assu m p t i o n s are made p r i m a r i l y t o f a c i l i t a t e t he e v a l u a t i o n and comparison of t h e v a r i o u s t h e o r i e s . I f they a r e found t o be i n v a l i d i t would, i n most c a s e s , merely mean t h a t two or more mechanisms were o p e r a t i n g s i m u l t a n e o u s l y . An example o f t h i s t y p e o f s i t u a t i o n i s the s u p e r p o s i t i o n o f t h e a z i m u t h a l d r i f t and d e c r e a s i n g plasma d e n s i t y mechanisms proposed by L i n and P a r k s (1976). For t h e v e r s i o n of t h e inward motion t h e o r y proposed by 46 G e n d r i n e t a l . (1967) t h e assumption was made t h a t the d i f f u s i o n p r o c e s s a f f e c t e d o n l y the p r o t o n s i n v o l v e d i n the c y c l o t r o n t u r b u l e n c e , and d i d not d i s t u r b t h e background plasma. . I t i s d i f f i c u l t t o see how t h i s background plasma c o u l d remain c o m p l e t e l y u n a f f e c t e d , e s p e c i a l l y i f the i n w a r d d i f f u s i o n i s caused by an ExB d r i f t . However, i f a b u l k motion o f the plasma does c r e a t e a non-zero ) B / H term (from ( 7 ) ) , the f r e g u e n c y r i s e due t o t h e inward motion w i l l be a f f e c t e d • (from ( 5 ) ) . The e x t e n t of t h i s e f f e c t i s hot known, s i n c e i t i s v e r y d i f f i c u l t t o c a l c u l a t e t h e iB/bt term c r e a t e d by t h e background plasma motion. . Another example of the p o s s i b l e o v e r l a p of f r e g u e n c y s h i f t mechanisms would be t h e c o m b i n a t i o n of t h e i n w a r d motion and a z i m u t h a l d r i f t e f f e c t s . I f t h e g e n e r a t i o n r e g i o n i s moving i n w a r d due t o the Earthward d i s p l a c e m e n t of t h e plasmapause, and t h e 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 t u r b u l e n c e i n t h i s r e g i o n a r e b e i n g c o n t i n u o u s l y r e s u p p l i e d by p r o t o n s d r i f t i n g a z i m u t h a l l y on p r o g r e s s i v e l y lower L s h e l l s , t h e n both these e f f e c t s would c o n t r i b u t e t o t h e r i s i n g t o ne of hydromagnetic waves g e n e r a t e d . However, i n t h i s c a s e , the e f f e c t s on t h e a z i m u t h a l d r i f t p r o c e s s of t h e changing d r i f t v e l o c i t y due t o t h e h i g h e r magnetic f i e l d s t r e n g t h a t lower L s h e l l s and d e c r e a s i n g d r i f t path l e n g t h on l o w e r L s h e l l s must be taken i n t o a c c o u n t . Under t h e s e c o n d i t i o n s , and assuming t h a t t h e E a r t h ' s magnetic f i e l d i s t h e d i p o l e f i e l d r e p r e s e n t e d by ( 3 ) , e g u a t i o n (13) d e s c r i b i n g t h e a z i m u t h a l d r i f t e f f e c t s becomes: w oc ( R t ) V l (18) 47 Note t h a t t h i s r e s u l t s i n a d e c r e a s e d f r e g u e n c y s h i f t e f f e c t from t h e a z i m u t h a l d r i f t mechanism. On the o t h e r hand, i f G e n d r i n ' s p i c t u r e of the inward motion t h e o r y i s c o r r e c t ( p r o t o n s d i f f u s i n g i n w a r d a c r o s s f i e l d l i n e s ) , then the two mechanisms c o u l d be superimposed w i t h o u t a f f e c t i n g each o t h e r . Here, t h e p r o t o n s would d r i f t westward on one L s h e l l , then d i f f u s e inward i n the g e n e r a t i o n r e g i o n under the i n f l u e n c e o f an e l e c t r i c f i e l d . An i n c r e a s i n g magnetic f i e l d i n a s t a t i o n a r y g e n e r a t i o n r e g i o n would a l s o i n f l u e n c e the a z i m u t h a l d r i f t mechanism..From (11) i t i s apparent t h a t t h e i n c r e a s i n g f i e l d would cause a r e d u c t i o n i n t h e d r i f t v e l o c i t y . I f the i n c r e a s i n g f i e l d o c c u r s , as Roxburgh p o s t u l a t e s , t h r o u g h o u t the e v e n i n g s e c t o r , t h e r e s u l t would be t o slow the s o f t e n i n g of the p r o t o n beam, and t h e r e f o r e slow t h e f r e g u e n c y r i s e due t o the a z i m u t h a l d r i f t . . I t a p p e a r s , however, t h a t most of the p o t e n t i a l c o m b i n a t i o n s i n v o l v e o n l y t h e s i m p l e s u p e r p o s i t i o n of the mechanisms on one a n o t h e r w i t h o u t a f f e c t i n g the p r o c e s s e s i n v o l v e d i n each mechanism. There i s e v i d e n c e t o s u p p o r t each o f the t h e o r i e s examined i n s e c t i o n 4.2 and t h e i r p o s s i b l e s u p e r p o s i t i o n . The s a t e l l i t e ( E x p l o r e r 45) o b s e r v a t i o n s of t h e r e s o n a n t p r o t o n s ( H o r i t a e t a l . , 1979) seem t o support the a z i m u t h a l d r i f t t h e o r y , but t h e p o s s i b i l i t y of i n w ard motion o f t h e g e n e r a t i o n r e g i o n i n c o n j u n c t i o n w i t h t h i s d r i f t i s l e f t open. Other a u t h o r s , n o t a b l y Heacock (1973) and Kangas e t a l . (1974), have found t h a t t h e a z i m u t h a l d r i f t e f f e c t s a l one are i n s u f f i c i e n t t o produce the observed f r e g u e n c y s h i f t . They su g g e s t t h a t inward m o t i o n , and 48 p o s s i b l y c o l d plasma d e n s i t y d e c r e a s e s , must a l s o be i n v o l v e d . . Heacock et a l . [1976) i n d i c a t e d t h a t the inward d r i f t mechanism c o u l d be q u i t e i m p o r t a n t , e s p e c i a l l y f o r IPDPs g e n e r a t e d c l o s e r t o m i d n i g h t . G u l ' e l m i (1974) p o i n t s out e v i d e n c e f o r t h e s u p e r p o s i t i o n of the i n w a r d motion and a z i m u t h a l d r i f t t h e o r i e s i n t h e g e n e r a t i o n of IPDPs, and a l s o s u g g e s t s t h a t t h e e f f e c t of an i n c r e a s i n g background magnetic f i e l d s h o u l d be t a k e n i n t o a c c o u n t . The r e s u l t s from the F i n n i s h n o r t h - s o u t h c h a i n p r e s e n t e d by L u k k a r i e t a l . . (1977) i n d i c a t e an i n w a r d motion of the g e n e r a t i o n r e g i o n . I t i s a l s o s u g g e s t e d t h a t c h a n g i n g c o l d plasma d e n s i t i e s c o u l d have a s t r o n g e f f e c t . Roxburgh (1970), u s i n g magnetic f i e l d d a t a from s a t e l l i t e ATS-1, p r e s e n t e d s t r o n g e v i d e n c e f o r the e x i s t e n c e of an i n c r e a s i n g 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 d u r i n g IPDP e v e n t s . 49 5_i -EXPERIMENTAL RESULTS The e x p e r i m e n t a l work r e p o r t e d on i n t h i s c h a p t e r d e a l s w i t h t h e IPDP f r e g 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 o f t h e p r e c e d i n g c h a p t e r . In C h a p t e r 2 t h r e e IPDP e v e n t s were i d e n t i f i e d and t h e a n a l y s i s of t h e i r power s p e c t r a was r e v i e w e d . U s i n g the i n f o r m a t i o n o b t a i n e d from t h i s a n a l y s i s , and the normal-run magnetograms a l s o d i s c u s s e d i n Chapter 2, an attempt i s made here t o determine which mechanism or mechanisms a r e r e s p o n s i b l e f o r the f r e q u e n c y r i s e o b s e r v e d i n t h e IPDP e v e n t s under c o n s i d e r a t i o n . 5^ _1 Inward M o t i o n of G e n e r a t i o n Region A n o r t h - south l i n e of m i c r o p u l s a t i o n s t a t i o n s , such as the B.C.. c h a i n , i s i d e a l f o r t h e d e t e c t i o n and a n a l y s i s o f a p o s s i b l e inward movement of the IPDP g e n e r a t i o n r e g i o n . . I f t h e g e n e r a t i o n r e g i o n moved inward i n the e g u a t o r i a l p l a n e , t h e hydromagnetic waves produced would t r a v e l a l o n g s u c c e s s i v e l y l o w e r f i e l d l i n e s t o lower l a t i t u d e s on E a r t h . . T h i s would c r e a t e a s h i f t towards t h e eguator of t h e IPDP event as observed on a n o r t h - s o u t h l i n e of s t a t i o n s . However, a f t e r p r o p a g a t i n g down t o the i o n o s p h e r e , t h e hydromagnetic waves o f IPDPs may t r a v e l 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 . They c o u l d t h e r e f o r e appear s i m u l t a n e o u s l y a t a l l t he s t a t i o n s of a s h o r t c h a i n , such as t h e one i n B.C. p r o v i d i n g d a t a f o r t h i s s t u d y . Even i n such c a s e s , though, an e g u a t o r i a l d i s p l a c e m e n t of t h e peak a m p l i t u d e of the IPDP event 50 s h o u l d be d i s c e r n i b l e on a n o r t h - south c h a i n i f an in w a r d motion o f the g e n e r a t i o n r e g i o n i 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 of t h e e v e n t . I f i o n o s p h e r i c d u c t i n g i s t a k i n g p l a c e d u r i n g the IPDP events r e c o r d e d on the B.C. c h a i n , t h e n t h e s e e v e nts s h o u l d appear a t a l l t h r e e s t a t i o n s s i m u l t a n e o u s l y w i t h each event e x h i b i t i n g v e r y s i m i l a r f r e g u e n c y and power p r o f i l e s a l o n g the whole c h a i n . F i g u r e 17 shows the peak f r e g u e n c y and peak power p r o f i l e s of one IPDP ev e n t . I t i s e v i d e n t t h a t t h e f r e q u e n c y e v o l u t i o n o f t h i s IPDP i s almost i d e n t i c a l a t a l l t h r e e s t a t i o n s . The shape of the power p r o f i l e s o b t a i n e d from each o f the s t a t i o n s are a l s o very s i m i l a r , though t h e a b s o l u t e power l e v e l s a r e g u i t e d i f f e r e n t , and t h e r e l a t i v e power l e v e l s between the s t a t i o n s vary somewhat as t h e event p r o g r e s s e s . I t i s then c o n s i s t e n t w i t h t h i s e v i d e n c e t h a t t h e hydromagnetic waves were 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 duct d u r i n g t h i s IPDP ev e n t . The c h a r a c t e r i s t i c s d e s c r i b e d above which l e a d t o t h i s c o n c l u s i o n were a l s o observed i n each of t h e o t h e r two e v e n t s s e l e c t e d from the B.C. c h a i n d a t a . The a n a l y s i s p r o d u c i n g t h e f r e g u e n c y and power i n f o r m a t i o n d i s c u s s e d above was conducted o n l y on the H component of the m i c r o p u l s a t i o n r e c o r d s . The power p r e s e n t i n the Z component was ve r y much l e s s t h a n t h a t i n the H component, and t h e r e f o r e i t need not be c o n s i d e r e d . However, t h e power i n t h e D component was o f the same o r d e r of magnitude as t h a t i n t h e H component, hence i t would have a s t r o n g e f f e c t on the shape of the t o t a l power p r o f i l e s of the IPDP e v e n t s . On a h i g h speed c h a r t r e c o r d i n g , t h e a m p l i t u d e p r o f i l e s of the H and D components 51 F i g . 17. The f r e g u e n c y (top) and power (bottom) p r o f i l e s of an IPDP event r e c o r d e d on the B.C. n o r t h - south c h a i n . 52 appeared t o be q u i t e s i m i l a r a t a l l t h r e e s t a t i o n s . To v e r i f y t h i s , a combined H - D component power p r o f i l e was compared t o t h e c o r r e s p o n d i n g H component p r o f i l e f o r one e v e n t . The r e s u l t s showed good agreement between the two (see F i g . 18), d e m o n s t r a t i n g t h e v a l i d i t y of t h e use of t h e H component a l o n e . . The i o n o s p h e r i c duct i s a n a t u r a l waveguide formed by t h e s h a r p l y v a r y i n g i o n c o n c e n t r a t i o n s i n t h e upper atmosphere.. The h i g h l e v e l of i o n i z a t i o n a t the peak of t h e i o n o s p h e r i c F2 l a y e r produces a minimum i n t h e A l f v e n wave v e l o c i t y t h e r e , c r e a t i n g the p o s s i b i l i t y of hydromagnetic wave energy becoming t r a p p e d i n t h i s l a y e r and t r a v e l l i n g h o r i z o n t a l l y as i n a waveguide.. The l o c a l t i m e , s e a s o n , and l e v e l o f magnetic a c t i v i t y a l l e f f e c t the a b i l i t y of t h i s waveguide t o propagate hydromagnetic waves, s i n c e t h e s e f a c t o r s a l l a f f e c t the l e v e l and l o c a t i o n o f the i o n i z a t i o n peaks i n t h e i o n o s p h e r e . D u r i n g the day, f o r i n s t a n c e , the r e f l e c t i v i t y o f the waveguide's l o w e r w a l l (the E r e g i o n ) d e c r e a s e s , r e s u l t i n g i n a g r e a t e r a t t e n u a t i o n f o r waves p r o p a g a t i n g i n the duct. The lower c u t - o f f f r e g u e n c y f o r p r o p a g a t i o n i n t h e i o n o s p h e r i c duct i s b e l i e v e d t o be ~ 0 . 5 h e r t z ( N i s h i d a , 1 978). T h i s means t h a t m i c r o p u l s a t i o n s below t h i s f r e g u e n c y , i n c l u d i n g t h e m a j o r i t y o f IPDPs, w i l l n o t be e f f e c t i v e l y c o n t a i n e d w i t h i n t h i s waveguide. The wave energy w i l l l e a k a c r o s s both t h e upper and l o w e r w a l l s of t h e waveguide as i t t r a v e l s h o r i z o n t a l l y , s p r e a d i n g upward throughout the magnetosphere and p e n e t r a t i n g down t o the E a r t h ' s s u r f a c e where the waves can be d e t e c t e d as m i c r o p u l s a t i o n s . T h i s r a p i d a t t e n u a t i o n may account f o r the r e l a t i v e l y s m a l l a r e a over which most IPDPs a r e observed. 53 F i g . . 1 8 . F o r t S t . John power p r o f i l e s f o r t h e H component ( s o l i d l i n e ) and t h e t o t a l h o r i z o n t a l component (H>D) (dashed l i n e ) . S i n c e t h i s r e l a t i v e r e l a t i o n s h i p between H and H>D appeared t o be the same at a l l t h r e e s t a t i o n s , i t i s f e a s i b l e t o use the H component a l o n e . 54 S i n c e t h e i o n o s p h e r i c d u c t i s o b v i o u s l y a f f e c t i n g t h e IPDP wave p r o p a g a t i o n d u r i n g t h e e v e n t s s t u d i e d , an e g u a t o r i a l d i s p l a c e m e n t of t h e peak IPDP a m p l i t u d e must, as mentioned, be l o o k e d f o r i n o r d e r t o d e t e c t an inward motion o f the g e n e r a t i o n r e g i o n . Such a s h i f t c o u l d be d e t e c t e d by s e a r c h i n g f o r any c o n t i n u o u s changes i n the r e l a t i v e a m p l i t u d e s between s t a t i o n p a i r s . I n p a r t i c u l a r , i f the IPDP g e n e r a t i o n r e g i o n were on an L s h e l l such t h a t t h e waves t r a v e l l i n g down t h e f i e l d l i n e s a r r i v e d i n t h e i o n o s p h e r i c duct above F o r t S t . John, t h e n t h e a m p l i t u d e seen on t h e ground a t F o r t S t . John s h o u l d be much g r e a t e r t h a n t h a t seen a t P r i n c e George or W i l l i a m s Lake. I f the g e n e r a t i o n r e g i o n then began moving inward to lower L s h e l l s , the waves would a r r i v e i n the duct a t lower l a t i t u d e s c l o s e r t o P r i n c e George. T h e r e f o r e , t h e a m p l i t u d e a t P r i n c e George, r e l a t i v e t o F o r t S t . John, would i n c r e a s e . I f t h e g e n e r a t i o n r e g i o n were s t a t i o n a r y , then the r e l a t i v e a m p l i t u d e s would not change. F o r each e v e n t , p l o t s were made of the peak power (at t h e IPDP midfreguency) r e c o r d e d at each ground s t a t i o n r e l a t i v e t o t h a t r e c o r d e d a t each o f the o t h e r s t a t i o n s . . I n every c a s e , c o n s i s t e n t r e g u l a r changes i n t h e r e l a t i v e power l e v e l s were found which i n d i c a t e d an i n w a r d motion o f the IPDP g e n e r a t i o n r e g i o n (see F i g , 19). By examining t h e form o f t h e s e power r a t i o p l o t s i t i s p o s s i b l e t o e s t i m a t e r o u g h l y where t h e g e n e r a t i o n r e g i o n i s , and t o what e x t e n t i t i s moving. However, i f rough m o d e l l i n g c a l c u l a t i o n s can be c a r r i e d out t o d e t e r m i n e t h e s t r e n g t h on the ground o f the IPDP s i g n a l a f t e r i t has t r a v e l l e d a l o n g t h e i o n o s p h e r i c d u c t , t h e n more g u a n t i t a t i v e r e s u l t s can 5 5 I 1 | , |- a 0-0 5.0 10.0 15.0 20.0 25.0 T I M E (MIN) F i g . 19. The power r a t i o p r o f i l e s f o r each p o s s i b l e s t a t i o n p a i r i n g f o r an IPDP observed on the B.C. c h a i n . Note the r e g u l a r changes i n d i c a t i n g a n o n - s t a t i o n a r y g e n e r a t i o n r e g i o n . 56 be o b t a i n e d f o r t h e l o c a t i o n and movement o f t h e g e n e r a t i o n r e g i o n . Such c a l c u l a t i o n s can be performed i f the a t t e n u a t i o n i n and t h e h e i g h t o f t h e i o n o s p h e r i c duct are known. The p o s i t i o n s o f t h e ground s t a t i o n s and the power r a t i o s found from t h e s e s t a t i o n s can then be used t o determine the geomagnetic l a t i t u d e a t which t h e IPDP s i g n a l e n t e r e d t h e i o n o s p h e r i c d u c t . Each p o w e r . r a t i o would y i e l d two p o s s i b l e l a t i t u d e s ; however, as d e s c r i b e d above, the* shape of t h e power r a t i o c u r v e s would be s u f f i c i e n t t o determine which was t h e c o r r e c t r e s u l t . To a c h i e v e the r e s u l t s d e s c r i b e d above rough assumptions must be made c o n c e r n i n g the degree of a t t e n u a t i o n s u f f e r e d i n t h e i o n o s p h e r i c duct and t h e h e i g h t o f the lower boundary of the d u c t . These assumptions a r e n e c e s s a r y to determine where t h e IPDP s i g n a l must have e n t e r e d t h e duct t o produce t h e observed s i g n a l s t r e n g t h s a t the ground s t a t i o n s . Due t o t h e f a c t t h a t the IPDPs o b s e r v e d were below t h e duct c u t - o f f f r e g u e n c y , t h e s i g n a l s t r e n g t h was assumed t o f a l l o f f i n p r o p o r t i o n t o the sguare of the d i s t a n c e as the waves t r a v e l l e d through t h e duct and then through t h e l o w e r atmosphere t o the ground.. T h i s a s s u m p t i o n i s c o n s i d e r e d t o be very rough, and may w e l l over e s t i m a t e the a t t e n u a t i o n undergone, though i t i s s u p p o r t e d by the l a t i t u d i n a l a m p l i t u d e p r o f i l e of P i 2 m i c r o p u l s a t i o n s g i v e n by J a c o b s (1970)., Using t h i s a ssumption, c a l c u l a t i o n s t o d e t e r m i n e t h e l a t i t u d e of the incoming waves were attempted u s i n g a number of h e i g h t s f o r t h e lower duct boundary. An a p p r o x i m a t e i d e a o f the lower boundary h e i g h t can be g a i n e d from a study of t h e i o n o s p h e r i c l a y e r s , a l t h o u g h , as mentioned, t h e 57 p o s i t i o n s and s t r e n g t h s of t h e s e l a y e r s are not c o n s t a n t . For t h e e v e n t s s t u d i e d , an a l t i t u d e of 150 k i l o m e t r e s seemed t o p r o v i d e t h e b e s t r e s u l t s . Once t h e geomagnetic l a t i t u d e c f t h e area i n which th e IPDP hydromagnetic waves are a r r i v i n g i n t h e i o n o s p h e r e i s known, the L v a l u e can be e a s i l y c a l c u l a t e d . T h i s v a l u e g i v e s t h e r a d i a l p o s i t i o n o f t h e g e n e r a t i o n r e g i o n i n the e g u a t o r i a l p l a n e , i n u n i t s of E a r t h r a d i i . For each e v e n t , L v a l u e s were c a l c u l a t e d from a l l t h r e e p o s s i b l e power r a t i o s . The r e s u l t s o b t a i n e d from the P r i n c e George/Fort S t . John and W i l l i a m s L a k e / F o r t S t . John r a t i o s were q u i t e c o n s i s t e n t (<5% a p a r t ) . However, the W i l l i a m s L a k e / P r i n c e George L v a l u e s were not c l o s e to t h o s e o f t h e o t h e r two s t a t i o n p a i r s . . T h e much weaker s i g n a l s r e c o r d e d a t the P r i n c e George and W i l l i a m s Lake s t a t i o n s may have i n c r e a s e d t h e e r r o r s n o t i c e a b l y . . A l s o , t h e s e two s t a t i o n s have e s s e n t i a l l y t h e same s e p a r a t i o n i n l o n g i t u d e as t h e y do i n l a t i t u d e . . S i n c e a l l changes i n t h e power r a t i o s a r e assumed t o be due t o l a t i t u d i n a l e f f e c t s , any unknown l o n g i t u d i n a l e f f e c t s c o u l d s t r o n g l y i n f l u e n c e t h e W i l l i a m s L a k e / P r i n c e George r e s u l t s . S i n c e t h e l a t i t u d i n a l s e p a r a t i o n s between F o r t S t . John and t h e o t h e r two s t a t i o n s a r e much g r e a t e r than t h e i r c o r r e s p o n d i n g l o n g i t u d i n a l s e p a r a t i o n s (see Table 2 ) , such l o n g i t u d i n a l e f f e c t s would be much l e s s e v i d e n t i n t h e r e s u l t s from these s t a t i o n p a i r s . A c c o r d i n g l y , t h e r e s u l t s o f o n l y t h e P r i n c e G eorge/Fort S t . John and W i l l i a m s L a k e / F o r t S t . John c a l c u l a t i o n s were c o n s i d e r e d t o produce t h e L v a l u e p r o f i l e s f o r each event. These r e s u l t s , which demonstrate the i n w a r d motion of the IPDP g e n e r a t i o n r e g i o n , a r e shown i n F i g u r e 20 f o r a l l t h r e e e v e n t s . 58 U s i n g e g u a t i o n (4) from Chapter 4, and s u b s t i t u t i n g i n the L v a l u e s found above f o r R, the r e l a t i v e freguency r i s e due t o t h e i n w a r d motion can be c a l c u l a t e d . From (4) we have: where w0 and L 0 are the i n i t i a l wave f r e g u e n c y and i n i t i a l L v a l u e of t h e g e n e r a t i o n r e g i o n , r e s p e c t i v e l y . The r e l a t i v e f r e q u e n c y i n c r e a s e s found from (19) a r e a l s o i n c l u d e d i n F i g u r e 2 0 , a l o n g w i t h t h e a c t u a l r e l a t i v e f r e g u e n c y i n c r e a s e s f o r t h e s e events as o b t a i n e d from the e x p e r i m e n t a l d a t a . On comparing t h e s e measured and c a l c u l a t e d f r e g u e n c y s h i f t s , i t must be noted t h a t t h e c a l c u l a t e d s h i f t s a r e g e n e r a l l y below the measured ones when e v e r y p o i n t t h r o u g h o u t a l l t h r e e o f t h e e v e n t s i s c o n s i d e r e d . A l t h o u g h , i n t h e case of one of t h e s e IPDPs, the f i n a l t o t a l measured and c a l c u l a t e d f r e g u e n c y i n c r e a s e s a r e very c l o s e , i t i s thought t h a t t h e 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 measured from the e x p e r i m e n t a l d a t a d u r i n g t h i s event a r e more s i g n i f i c a n t . On t h e b a s i s o f t h e above c o n c l u s i o n , i t i s b e l i e v e d t h a t , f o r t h e t h r e e e v e n t s s t u d i e d h e r e , the freguency r i s e due t o the i n w a r d motion of the IPDP g e n e r a t i o n r e g i o n i s i n s u f f i c i e n t t o a c c o u n t f o r the t o t a l i n c r e a s e observed. The remainder o f t h i s i n c r e a s e must then be g e n e r a t e d by one (or more) of t h e o t h e r mechanisms d i s c u s s e d i n the l a s t c h a p t e r . T h i s p o i n t w i l l be f u r t h e r examined i n t h e f o l l o w i n g s e c t i o n s . . ( 1 9 ) 59 m 0 .0 CM 0.0 0 .0 8.0 16.0 24.0 32.0 _ J L SHELL V Ac / icr\t_ r-R.e Qix.£/vcy 8.0 16.0 24.0 TIME (MIN) 32.0 15.0 24.0 TIME (MIN) 32.0 4? •& r o ro ro ro t n d c : a 40.0 40.0 .20.. The i n w a r d motion o f t h e IPDP g e n e r a t i o n r e g i o n i n terms of L v a l u e s , and the f r e g u e n c y s h i f t p r e d i c t e d from t h e s e v a l u e s . The a c t u a l f r e g u e n c y s h i f t i s i n c l u d e d f o r comparison. P a r t ( a ) , August 6 e v e n t ; p a r t (b) , August 8 eve n t ; and p a r t (c) , August 9 event ( f o l l o w i n g page) . . 61 5;_2 Frequency S h i f t from A z i m u t h a l D r i f t E f f e c t s There has been a g r e a t d e a l o f e v i d e n c e p u b l i s h e d i n s u p p o r t o f t h e a z i m u t h a l d r i f t f r e g u e n c y s h i f t mechanism, and i t would seem t o be a l i k e l y c a n d i d a t e t o produce t h e r e m a i n i n g p a r t of the f r e g u e n c y r i s e not accounted f o r by the i n w a r d motion mechanism. I f t h e i n w a r d motion of t h e g e n e r a t i o n r e g i o n i s due t o t h e inward d i f f u s i o n of the r e s o n a n t p r o t o n s , then t h e a z i m u t h a l d r i f t and i n w a r d motion mechanisms can be s i m p l y superimposed (see s e c . 4.3). I n t h i s c a s e , t h e f r e g u e n c y s h i f t from t h e a z i m u t h a l d r i f t w i l l be g i v e n by ( 1 3 ) , and w i t h t h e i n w a r d motion e f f e c t from ( 4 ) , the t o t a l r e l a t i v e f r e g u e n c y s h i f t becomes: (20) where t„ i s t h e s t a r t time of t h e IPDP event. The d e l a y t i m e t i s s e t t o ze r o a t t h e t i m e of t h e sharp onset o f the n e g a t i v e bay r e c o r d e d near l o c a l m i d n i g h t at Great Whale E i v e r s h o r t l y b e f o r e each IPDP e v e n t . I n g e n e r a l , t h e freg u e n c y i n c r e a s e g i v e n by (20) i s s l i g h t l y c l o s e r t o t h e a c t u a l i n c r e a s e observed t h a n t h a t p r e d i c t e d by t h e inward motion a l o n e (from ( 1 9 ) ) . . However, t h e combined i n c r e a s e from . t h e s e two mechanisms i n s i m p l e s u p e r p o s i t i o n c o n s i s t e n t l y o v e r e s t i m a t e s the a c t u a l i n c r e a s e , as opposed t o the u n d e r e s t i m a t i o n of the inward motion mechanism. In an e f f o r t t o a c h i e v e an even c l o s e r match between the r e a l and p r e d i c t e d f r e g u e n c y s h i f t s , t h e a z i m u t h a l d r i f t mechanism 62 w i l l now be examined i n a s s o c i a t i o n w i t h t h e inward motion mechanism where t h i s motion i s now caused by t h e Ea r t h w a r d d i s p l a c e m e n t of t h e plasmapause, w i t h t h e r e s o n a n t p r o t o n s c o n t i n u o u s l y d r i f t i n g i n t o the g e n e r a t i o n r e g i o n from the e a s t . As p o i n t e d o ut i n s e c t i o n 4.3, t h e d r i f t mechanism i s now a f f e c t e d by t h e i n w a r d m o t i o n , and i t s wave e m i s s i o n f r e g u e n c y i s now c o n t r o l l e d by (18). I n t h i s c a s e , t h e t o t a l r e l a t i v e f r e g u e n c y r i s e due t o the a z i m u t h a l d r i f t and i n w a r d motion mechanisms i s now not g i v e n by (20), but by: which produces a s l i g h t l y s l o w e r r a t e of i n c r e a s e . F i g u r e 21 shows t h e f r e g u e n c y i n c r e a s e due t o the westward d r i f t e f f e c t s (from (18)) as w e l l as the t o t a l i n c r e a s e due t o t h e c o m b i n a t i o n of mechanisms under c o n s i d e r a t i o n as g i v e n by (21). I t can be seen t h a t t h e t o t a l p r e d i c t e d f r e g u e n c y s h i f t matches t h e r e a l s h i f t r e a s o n a b l y w e l l t h r o u g h o u t a l l t h r e e e v e n t s . I t appears then t h a t t h i s combined p r o c e s s of plasmapause a s s o c i a t e d i n w a r d motion o f t h e IPDP g e n e r a t i o n r e g i o n , t o g e t h e r w i t h t h e energy dependent a z i m u t h a l d r i f t o f t h e r e s o n a n t p r o t o n s i n t o t h i s r e g i o n d u r i n g i t s movement, can account f o r t h e observed s p e c t r a of t h e s e IPDPs. F u r t h e r e v i d e n c e f o r the i n v o l v e m e n t o f t h e a z i m u t h a l d r i f t mechanism can be found by s t u d y i n g the r e l a t i o n between t h e r a t e of the fr e g u e n c y r i s e and t h e d e l a y t i m e between the substorm o n s e t and the IPDP e v e n t . For the IPDPs c o n s i d e r e d h e r e , i t was c l e a r t h a t t h e l o n g e r d e l a y t i m e s were a s s o c i a t e d w i t h lower r a t e s of f r e g u e n c y i n c r e a s e as produced by the a z i m u t h a l d r i f t (21) 63 a) b) a ro 0.0 J — 8.0 ro ro ro 3°cV 0 r ~ C £ t o L i - -CD 0.0 0.0 0.0 16.0 _J 24.0 32.0 _ J f T O T A L PUBOICTEO FK.E QU.B N c V A i m t t T M rti. Oftip — I 16.0 24.0 TIME (MIN) 16.0 24.0 32.0 32.0 8.0 16.0 24.0 TINE (MINJ 32.0 ro ro ro ro 40.0 4 0 . 0 a 40.0 F i g . 2 1 . The f r e q u e n c y s h i f t due t o the a z i m u t h a l d r i f t mechanism as c o r r e c t e d f o r t h e inward motion of t h e g e n e r a t i o n r e g i o n , and the t o t a l s h i f t due t o t h e c o m b i n a t i o n o f thes e two mechanisms (as g i v e n by ( 2 1 ) ) . . The r e a l f r e g u e n c y s h i f t i s i n c l u d e d f o r comparison. P a r t (a) , August 6 e v e n t ; p a r t (b) , August 8 e v e n t ; and p a r t (c) , August 9 ev e n t ( f o l l o w i n q page) . ; 65 mechanism a l o n e (from e q u a t i o n ( 1 8 ) ) . T h i s e f f e c t has been observed by o t h e r a u t h o r s (Chapter 3) and, from (14), i s a p r e d i c t e d consequence o f t h e a z i m u t h a l d r i f t mechanism. 5j_3 I n c r e a s i n g F i e l d and D e c r e a s i n g Plasma D e n s i t y P r o c e s s e s S i n c e i t i s e v i d e n t t h a t t h e f r e q u e n c y s h i f t of t h e IPDP e v e n t s under s t u d y can be a t t r i b u t e d e n t i r e l y t o the inward motion - a z i m u t h a l d r i f t mechanism as d e s c r i b e d above, no c o n t r i b u t i o n i s needed from t h e o t h e r two mechanisms d i s c u s s e d i n C h a p t e r 4; t h e i n c r e a s i n q f i e l d t h e o r y and t h e d e c r e a s i n q plasma d e n s i t y t h e o r y . Though the i n c r e a s i n q f i e l d t h e o r y cannot be e v a l u a t e d by a c h a i n o f m i c r o p u l s a t i o n s t a t i o n s , normal-run magnetograms o b t a i n e d from o b s e r v a t o r i e s near the c h a i n and from e g u a t o r i a l r e g i o n s a t a p p r o x i m a t e l y t h e same l o n g i t u d e as t h e c h a i n can be used t o de t e r m i n e whether or not t h i s p r o c e s s i s c o n t r i b u t i n g t o the f r e g u e n c y r i s e of an IPDP. A c c o r d i n g t o t h e i n c r e a s i n g f i e l d t h e o r y , the IPDP p u l s a t i o n s a r e g e n e r a t e d as the p a r t i a l r i n g c u r r e n t decays, and t h e r e b y produces a r i s i n g background 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 . The decay o f t h e p a r t i a l r i n g c u r r e n t , and t h e r e f o r e of the e n t i r e a s s o c i a t e d c u r r e n t system i n c l u d i n g the eas t w a r d e l e c t r o j e t , can be seen on the ground w i t h the a i d of the normal-run magnetograms. . The decay of t h e p a r t i a l r i n g c u r r e n t can be seen d i r e c t l y as t h e r e c o v e r y of the substorm a s s o c i a t e d e q u a t o r i a l r e g i o n H component n e g a t i v e bay 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 . . I f an IPDP ev e n t i s observed a t t h e same time and at t h e same 66 l o n g i t u d e as t h i s f i e l d r e c o v e r y , then t h e i n c r e a s i n g magnetic f i e l d r e s u l t i n g from the p a r t i a l r i n g c u r r e n t decay may be c o n t r i b u t i n g t o the f r e g u e n c y r i s e o f the IPDP. The decay o f the p a r t i a l r i n g c u r r e n t system can a l s o be observed as t h e r e c o v e r y of an H component p o s i t i v e bay a t high l a t i t u d e s as the e a s t w a r d e l e c t r o j e t a b a t e s . . A g a i n , i f an IPDP appears d u r i n g t h i s p o s i t i v e bay r e c o v e r y , t h e n t h e i n c r e a s i n g f i e l d mechanism c o u l d be a t l e a s t i n p a r t r e s p o n s i b l e f o r the f r e g u e n c y i n c r e a s e . . I f an IPDP event does not o c c u r a t t h e same ti m e as t h e s e bay r e c o v e r i e s , then t h e i n c r e a s i n g f i e l d t h e o r y cannot be i n v o l v e d i n t h e g e n e r a t i o n c f t h e event s i n c e t h e p a r t i a l r i n g c u r r e n t decay n e c e s s a r y to produce t h e i n c r e a s i n g f i e l d w i l l not be o c c u r r i n g . The H component magnetograms from H o n o l u l u show no s i g n i f i c a n t f i e l d r e c o v e r i e s near the t i m e s a t which the IPDPs were recorded..Even though t h e H o n o l u l u o b s e r v a t o r y i s somewhat n o r t h of t h e e g u a t o r and west of t h e B.C. m i c r o p u l s a t i o n c h a i n , t h i s must be c o n s i d e r e d t o be v i a b l e e v i d e n c e a g a i n s t t h e p o s s i b i l i t y of the i n c r e a s i n g f i e l d p r o c e s s b e i n g i n v o l v e d i n t h e g e n e r a t i o n of t h e s e e v e n t s . As w e l l , the c o r r e l a t i o n o f t h e IPDPs s t u d i e d here w i t h h i g h l a t i t u d e H component p o s i t i v e bays g e n e r a l l y d i d not s u p p o r t the i n v o l v e m e n t of the i n c r e a s i n g f i e l d mechanism. The IPDP e v e n t s r e c o r d e d on August 8 and August 9 d i d not occur d u r i n g a p o s i t i v e bay r e c o v e r y .(see F i g . 22) . However, the s i t u a t i o n on August 6 was somewhat more c o n f u s e d . Higher l a t i t u d e s t a t i o n s , such as C o l l e g e and Meanook, d i d r e c o r d a p o s i t i v e bay r e c o v e r y d u r i n g t h e IPDP event (see F i g . 1 3 , C h a p t e r 4 ), a l t h o u g h magnetograms from lower l a t i t u d e 67 4.0 5.0 6.0 7.0 3.0 9.0 U N I V E R S A L T I M E F i g . 22. A p o s i t i v e bay recorded a t C o l l e g e simultaneously with the o b s e r v a t i o n of an IPDP event on the B.C..chain. The time of occurrence of the IPDP i s marked on the magnetogram by the v e r t i c a l l i n e s . . N o t e that the IPDP does not occur on the recovery side of the bay. 68 stations (Victoria, Sitka, Newport) could not confirm t h i s observation.. The p o s s i b i l i t y remains, though, that for at least t h i s event, the increasing f i e l d mechanism could have contributed to the IPDP freguency r i s e , although t h i s i s not considered l i k e l y , since the entire s h i f t has already been accounted for (see sec. 5.2). In general, then, the magnetograms from both the eguatorial and northern regions can be seen as confirming that the increasing f i e l d freguency s h i f t process does not contribute to the freguency r i s e of the IPDP events studied here. No data was obtained for the evaluation of the decreasing plasma density theory.. However, since the inward motion and azimuthal d r i f t theories can account f o r the entire freguency r i s e , there i s no evidence to support the inclu s i o n of t h i s e f f e c t i n the generation process of the IPDPs under consideration. 5:4 Discussion I t has been shown that, using rough calculations to determine the L s h e l l of the IPDP generation region and using the onset of the midnight sector negative bay as the start time of the westward d r i f t , the combination of the inward motion and azimuthal d r i f t freguency s h i f t mechanisms described by (21) can account for the observed freguency r i s e of the IPDPs analyzed, Eguation (21) can be regarded as describing the freguency r i s e of the IPDPs as produced by the inward motion process corrected for the ef f e c t s of the energy dependent azimuthal d r i f t of the 69 p r o t o n s t o t h e g e n e r a t i o n r e g i o n a l o n g d i f f e r e n t paths t h r o u g h d i f f e r e n t background magnetic f i e l d s t r e n g t h s . . As p o i n t e d out i n s e c t i o n 5 . 3 , t h e c o n d i t i o n s may have been r i g h t f o r Roxburgh's i n c r e a s i n g f i e l d mechanism t o c o n t r i b u t e t o the f r e g u e n c y s h i f t of one of the IPDP e v e n t s s t u d i e d , even though t h e t o t a l f r e g u e n c y i n c r e a s e f o r t h i s event can be accounted f o r i n o t h e r ways. I t i s g u i t e p o s s i b l e , however, t h a t e r r o r s i n d u c e d by t h e approximate n a t u r e of t h e c a l c u l a t i o n s (say from the assumptions c o n c e r n i n g the pure d i p o l e n a t u r e of t h e background magnetic f i e l d c r the c o n d i t i o n s o f t h e i o n o s p h e r i c duct) used t o p r e d i c t t h i s f r e g u e n c y s h i f t c o u l d l e a v e room f o r the p o s s i b l e c o n t r i b u t i o n t o t h e i n c r e a s e by the i n c r e a s i n g f i e l d p r o c e s s . The same argument a l s o h o l d s t r u e f o r t h e d e c r e a s i n g plasma d e n s i t y t h e o r y , though i t i s b e l i e v e d t h a t t h e c o n t r i b u t i o n s from these two p r o c e s s e s would be s m a l l i f they a r e p r e s e n t a t a l l . I t was mentioned i n Chapter 2 t h a t a number o f IPDP e v e n t s were r e c o r d e d o n l y a t t h e F o r t S t . John s t a t i o n . S i n c e t h e r e l a t i v e a m p l i t u d e s found from at l e a s t one p a i r of s t a t i o n s are r e q u i r e d t o f i n d the L v a l u e of the g e n e r a t i o n r e g i o n , any p o s s i b l e motion of t h e g e n e r a t i o n r e g i o n f o r t h e s e events c o u l d not be a n a l y z e d . These r e c o r d i n g s c o u l d r e p r e s e n t the s o u t h e r n -most e x t e n t of IPDPs moving southward frcm h i g h e r l a t i t u d e s , or they c o u l d be e v e n t s w i t h s t a t i o n a r y g e n e r a t i o n r e g i o n s l o c a t e d near t h e L s h e l l of F o r t S t . John. P o o r e r 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 duct c o u l d account f o r t h e s e IPDPs not b e i n g d e t e c t a b l e f u r t h e r t o the s o u t h , a t P r i n c e George or W i l l i a m s Lake. 70 6 •. - CONCLUSIONS AND FUTURE EXPERIMENTS With t h e a i d of the m i c r o p u l s a t i o n data from the B.C. n o r t h - s o u t h c h a i n and the norma l - r u n magnetograms from Great Whale R i v e r i t has been e s t a b l i s h e d t h a t t h e freg u e n c y s h i f t o f a l l t h r e e o f t h e IPDP e v e n t s s t u d i e d c o u l d . b e accounted f o r by an i n w a r d motion o f the g e n e r a t i o n r e g i o n combined w i t h the energy dependent westward d r i f t e f f e c t s on the r e s o n a n t p r o t o n s . The f r e g u e n c y o f the IPDP hydromagnetic waves produced by t h e pro t o n c y c l o t r o n i n s t a b i l i t y p r o c e s s r i s e s due t o t h e i n c r e a s i n g magnetic f i e l d which r e s u l t s from the inward motion t o a r e a s o f h i g h e r f i e l d s t r e n g t h of t h e plasmapause, near which the i n s t a b i l i t y p r o c e s s o c c u r s . The s t e a d i l y s o f t e n i n g n a t u r e of the beam of p r o t o n s a r r i v i n g i n t h e g e n e r a t i o n r e g i o n d u r i n g i t s E a r t h w a r d movement a l s o c o n t r i b u t e s t o the f r e g u e n c y s h i f t . . I t must be p o i n t e d out, however, t h a t t h e r e a r e l i m i t a t i o n s on t h e c o n c l u s i o n s which can be drawn from the s t u d y of o n l y t h r e e e v e n t s . . While i t i s now apparent t h a t IPDPs can be ge n e r a t e d by the mechanism d e s c r i b e d above, i t i s not n e c e s s a r y t h a t a l l e v e n t s be produced i n t h i s manner..IPDPs which appear at d i f f e r e n t l a t i t u d e s and/or d i f f e r e n t l o n g i t u d e s , or under d i f f e r e n t substorm c o n d i t i o n s , may i n v o l v e d i f f e r e n t f r e g u e n c y s h i f t mechanisms, e i t h e r s i n g l y or i n c o m b i n a t i o n . The f a c t t h a t a l l t h e e v e n t s s t u d i e d here o c c u r r e d a t a p p r o x i m a t e l y t h e same l a t i t u d e and l o c a l t i m e may e x p l a i n why the same g e n e r a t i o n mechanism was observed i n each c a s e . The d e t a i l e d s t u d y of many more IPDP events w i l l be n e c e s s a r y b e f o r e t h e i r g e n e r a t i o n i s w e l l u n d e r s t o o d . An extended l o n g i t u d i n a l ( n o r t h - south) c h a i n would be n e c e s s a r y 71 t o d e t e r m i n e the l o c a t i o n and motion of the g e n e r a t i o n r e g i o n of a wide range of e v e n t s . . I n a d d i t i o n , a c h a i n of m i c r o p u l s a t i o n s t a t i o n s a l o n g a l i n e of c o n s t a n t l a t i t u d e c o u l d p r o v i d e u s e f u l i n f o r m a t i o n on t h e l o n g i t u d i n a l e x t e n t and v a r i a t i o n of i n d i v i d u a l IPDPs. Such data c o u l d be i n s t r u m e n t a l i n c o n f i r m i n g t h e r o l e of the a z i m u t h a l d r i f t mechanism, as w e l l as a i d i n g i n t h e r e m o v a l of the e f f e c t s of any l o n g i t u d i n a l v a r i a t i o n s i n an IPDP event from th e r e s u l t s produced by a n o r t h - s o u t h c h a i n w i t h s t a t i o n s a t s l i g h t l y d i f f e r e n t l o n g i t u d e s . Both ground based a n d . s a t e l l i t e based o b s e r v a t i o n s , c a r r i e d out i n c o n j u n c t i o n w i t h m i c r o p u l s a t i o n o b s e r v a t i o n s , on t h e p o l a r magnetic substorm c u r r e n t system i n g e n e r a l , and on the p a r t i a l r i n g c u r r e n t system i n p a r t i c u l a r , c o u l d be very i m p o r t a n t t o the e v e n t u a l u n d e r s t a n d i n g o f IPDPs and t h e i r r e l a t i o n t o t h e magnetospheric substorm p r o c e s s . Such d a t a would be u s e f u l e s p e c i a l l y f o r the e v a l u a t i o n of t h e i n c r e a s i n g f i e l d t h e o r y . S a t e l l i t e p a r t i c l e o b s e r v a t i o n s would a l s o be r e g u i r e d f o r t h e d i r e c t e v a l u a t i o n o f t h e d e c r e a s i n g plasma d e n s i t y t h e o r y . A s p e c i f i c experiment aimed a t c o n f i r m i n g t h e o c c u r r e n c e of t h e g e n e r a t i o n mechanism p r e s e n t e d i n t h i s t h e s i s t o account f o r t h e f r e g u e n c y s h i f t of the t h r e e e v e n t s s t u d i e d c o u l d be c a r r i e d out w i t h t h e a i d of an e a s t - west ( l a t i t u d i n a l ) c h a i n of m i c r o p u l s a t i o n s t a t i o n s . Due t o t h e shape of the e v e n i n g s i d e plasmasphere bulge (see F i g . 14, Chapter 4) IPDPs o c c u r r i n g c l o s e r t o m i d n i g h t s h o u l d tend t o appear a t lower l a t i t u d e s s i n c e t h e westward d r i f t would have t o occur on lower L s h e l l s i n o r d e r t o i n t e r s e c t t h e plasmapause, which approaches c l o s e r 72 t o E a r t h towards t h e midnight s e c t o r (away from the b u l g e ) . Though t h e assumptions c o n c e r n i n g the a t t e n u a t i o n i n and the h e i g h t of t h e i o n o s p h e r i c duct seemed t o produce r e a s o n a b l e r e s u l t s f o r t h e inward motion of t h e IPDP g e n e r a t i o n r e g i o n , t h e degree of c o n f i d e n c e i n the o v e r a l l mechanism proposed f o r t h e f r e g u e n c y s h i f t of t h e events s t u d i e d i n t h i s t h e s i s c o u l d a l s o be i n c r e a s e d s i g n i f i c a n t l y by a much more d e t a i l e d and i n depth s t u d y of t h e p r o p a g a t i o n of IPDP-type waves i n t h e duct. Such a s t u d y , however, would become g u i t e i n v o l v e d , and must t h e r e f o r e be l e f t f o r f u t u r e work. 73 REFERENCES A k a i k e , H., F i t t i n g auto r e g r e s s i v e models f o r p r e d i c t i o n , Ann.. I n s t . 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KJO I N D I C E S F O R AUGUST J979 Th r e e - H o u r l y 2 3 4 0 + 1- 4-3 3 + 3 3 3 3 + 3+ 3+ 3-3- 2 1 + 3 + 4 4 2 3 2 2 2- 2-2 2- 2 1 + 1 2-2- 1 + 2 2 2 + 4 1 3 + 7-2- 1 + 1 1 + 1 1-1 + 2 + 1 + 1 + 2 1-1- 1 1 5 4 + 5 3- 4- 3-4 4- 3 + 3- 3- 2 + 1 2- 1 + 1- 1 + 2-2- 3 4 + 3 3 + 3-3 3 + 3 3- 2 + 3 5- 5+ 5 + 4 3 + 3-1 + 2 3 I n d i c e s (Kp) 5 6 7 5- 4- 3 1 + 2+ 2 2 2- 1 3+ 3- 4 1- 2 + 3-4 3 + 2 2 2* 3 + 2 2 2-2 2+ 1 + 2 2 3 2+ 2- 3+ 2- 2- 4-7+ 7- 7 2 - 2 2 1 1+ 1 + 2- 1- 1-1- 3 3+ 2* 2+ 2+ 4+ 4- 3-3+ 7 6 + 3+ 3- 4-3 3 3-2 1 2-2+ 5- 4 4- 4 5-3 2+ 4-2 3+ 3-2+ 2 1-6 8- 7-2- 2- 2-4 3- 3-Sum (IKp) 8 4- 20 1- 19-2 + 18+ 3- 24 + 2* 15 2 26-3- 19 + 2 16 0 + 14 3- 14 + 3 + 18 5 + 24-6- 41-2- 15-2 9 + 1 + 11-1 14 5 16 4- 34 + 4 + 33 + 2 + 28 2 21 + 1 10 3- 18 4 + 27 + 1 + 23 1 * 20 + 3- 19-6 45-1 + 21 3 20-78 APPENDIX 2 PROTON CYCLOTRON INSTABILITY FREQUENCY 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 plasma c o n s i s t i n g o f p r o t o n s and e l e c t r o n s i s (Jacobs, 1970): w1 - c 1 kl - .n-l w -w+w. -n.^w = 0 w-w„ U) where -nt (plasma freguency) i s : _ r L l = 47TNt e* , m. 1 = p, e ( i i ) and OJL ( c y c l o t r o n frequency) i s : eB c mt c 1 = p, e ( i i i ) S i n c e , f o r resonance t o o c c u r , the wave f r e g u e n c y must be d o p p l e r s h i f t e d t o t h e p r o t o n 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 , the resonance c o n d i t i o n can be e x p r e s s e d a s : w - kv, - up = 0 (i v ) where Vs i s t h e p r o t o n s t r e a m i n g v e l o c i t y . U s i n g t h e a p p r o x i m a t i o n s me << mp and w << we , and assuming t h a t Ne = N^, , ( i ) can be w r i t t e n a s : w* - c* k 1 - 4TTN, ecw* = 0 B 0 (w-w,) (v) 79 Now, u s i n g ( i v ) t o s u b s t i t u t e i n t o (v) f o r k, and the a p p r o x i m a t i o n VS « c, we have: 4TTN/, ecw* = -c"1 (w - w, )* ( v i ) B0 («-»,) v; which, on a l g e b r a i c m a n i p u l a t i o n , becomes: w1 = B? e* / l -_w_V ( v i i ) N, W„ ' a/Fiffc* ' I w J where W/; i s the p a r a l l e l energy of the p r o t o n s . I t i s t h e n o b v i o u s t h a t , u s i n g the assumption t h a t w << w,, , ( v i i ) y i e l d s : w Bl ( v i i i ) (N, B„ )'" S i n c e Sfy i s r e l a t e d t o the t o t a l energy W by t h e p i t c h a n g l e (W = Wcos 1^) ( v i i i ) becomes: w ex. B] ( i x ) (N, W)'/2 which i s e g u a t i o n ( 1 ) of Cha p t e r 4,. 

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