"Science, Faculty of"@en . "Earth, Ocean and Atmospheric Sciences, Department of"@en . "DSpace"@en . "UBCV"@en . "Koleszar, Thomas W."@en . "2010-10-13T16:39:22Z"@en . "1988"@en . "Doctor of Philosophy - PhD"@en . "University of British Columbia"@en . "Short period geomagnetic micropulsations termed IPDPs (Intervals of Pulsations of Diminishing Period) are investigated using ground station data, geosynchronous satellite magnetograms, and the Kp and Dst geomagnetic indices. A model for the generation of IPDPs is described, and consideration is given to three mechanisms which could be responsible for the IPDP frequency rise: the inward motion, azimuthal drift, and increasing background magnetic field mechanisms. A simplified IPDP generation model containing the first two of these mechanisms is tested by computer simulation. Results from this simulation indicate the possibility of significant source region inward motion without actual plasmapause displacement, and the possibility of eastward developing IPDPs. Using amplitude variations along a north-south line of ground stations, two methods, each applicable under different ionospheric propagation conditions, are developed for quantitatively determining the inward motion of the IPDP source region. A system for qualitatively determining the potential influence of the increasing background field mechanism on an IPDP using the Dst index and geosynchronous satellite magnetograms is also formulated. Lastly, a technique for the assessment of the effects of the azimuthal drift mechanism, in conjunction with the inward motion mechanism, is developed. This technique assumes that only these two mechanisms are operating. In addition to addressing the frequency shift mechanisms, it provides estimates of the injection boundary position and the magnitude of any (ring current created) magnetic field depression in the IPDP source region. The frequency rises of two IPDPs are analyzed in detail using these methods. In both cases, the inward motion effect is the dominant factor in producing the frequency rise, with the increasing background field mechanism having no significant effect. The azimuthal drift mechanism is a secondary factor in creating one event's frequency rise, and actually suppresses the frequency rise of the other event. The computer simulation calculations also generally show the inward motion mechanism to be the dominant effect in producing IPDP frequency rises. Longitudinal variations within an IPDP event are also examined. The results of this examination are consistent with the IPDP generation model used here, which includes showing significant variations between stations spaced comparatively closely in longitude."@en . "https://circle.library.ubc.ca/rest/handle/2429/29132?expand=metadata"@en . "THE GENERATION OF IPDF MICROPULSATIONS, WITH SPECIAL ATTENTION TO FREQUENCY SHIFT MECHANISMS by THOMAS W. ROLESZAR M . S c , The U n i v e r s i t y of B r i t i s h Columbia, 1980 B.Sc. (Honours), The U n i v e r s i t y of B r i t i s h C o lumbia, 1978 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES Geo p h y s i c s and Astronomy We ac c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA December 1988 \u00C2\u00A9 THOMAS W. KOLESZAR, 1988 In p resen t i ng this thesis in partial fu l f i lment of the requ i remen ts for an a d v a n c e d d e g r e e at the Un ivers i ty of Brit ish C o l u m b i a , I agree that t he Library shal l m a k e it f reely avai lable fo r re fe rence and s tudy. I fur ther agree that p e r m i s s i o n fo r ex tens ive c o p y i n g of this thes is fo r scho lar ly p u r p o s e s may b e g ran ted by the h e a d of m y d e p a r t m e n t o r by his o r her representa t ives . It is u n d e r s t o o d that c o p y i n g o r pub l i ca t i on of this thesis for f inancia l gain shal l no t b e a l l o w e d w i t hou t m y wr i t ten p e r m i s s i o n . D e p a r t m e n t of Q \u00E2\u0082\u00AC\u00E2\u0080\u00A2 0 A +~ A f~T/\u00C2\u00A3 T h e Un ivers i ty of Brit ish C o l u m b i a V a n c o u v e r , C a n a d a Da te Q e c If J -o z LU o m tr 0.5 P e r i o d i c HM Emission HM Emission Burst HM Whistler , 1 5 1 . 0 5 2 . 0 5 3 . 0 5 4 . 0 t ime (min . ) FIGURE 2 . Dynamic spectrum of the h o r i z o n t a l components ( t o p ) , and c h a r t r e c o r d (bottom) of the Y component f o r the Fe b r u a r y 15 IPDP event as obser v e d a t G i m l i , Manitoba ( c f . Tab l e I I I and f i g . 3 ) . The c h a r t r e c o r d c o v e r s o n l y 3 minutes (2151 - 2154 UT) near the b e g i n n i n g of the e v e n t . 7 a t t e n t i o n ; inward motion of the g e n e r a t i o n r e g i o n ( G e n d r i n et a l . , 1967; Heacock, 1967), westward d r i f t of hot p r o t o n s ( F u k u n i s h i , 1969), and i n c r e a s i n g background magnetic f i e l d s t r e n g t h (Roxburgh, 1970). I t has a l s o been observed t h a t more than one of t h e s e mechanisms may o p e r a t e a t once (Heacock, 1973; Kangas et a l . , 1974). U s i n g ground-based and s a t e l l i t e d a t a , t h i s t h e s i s w i l l p r e s e n t a q u a n t i t a t i v e assessment of the p o s s i b l e c o n t r i b u t i o n of each of t h e s e mechanisms t o the IPDP fr e q u e n c y r i s e i n the c o n t e x t of an o v e r a l l model f o r IPDP g e n e r a t i o n . Chapter Two w i l l d e s c r i b e the d a t a s o u r c e s and a n a l y s i s methods used h e r e , w h i l e Chapter Three i s an i n depth d e s c r i p t i o n of IPDPs and t h e i r r e l a t i o n s h i p s t o o t h e r geomagnetic phenomena. The g e n e r a t i o n p r o c e s s of IPDPs i s d i s c u s s e d i n Chapter Four, i n c l u d i n g the f r e q u e n c y s h i f t mechanisms, w h i l e Chapter F i v e p r e s e n t s the r e s u l t s of the e x p e r i m e n t a l t e s t s of these mechanisms, a l o n g w i t h a d i s c u s s i o n of t h e i r s i g n i f i c a n c e . CHAPTER 2 . DATA SOURCES AND ANALYSIS T h i s c h a p t e r o f f e r s a d e s c r i p t i o n of the dat a s e t s used i n t h i s t h e s i s , f o l l o w e d by a review of the t e c h n i q u e s used i n the a n a l y s i s of the IPDP d a t a . 2 . 1 . DATA SOURCES The r e s e a r c h work p r e s e n t e d i n C h a p t e r s Four and F i v e made use of i n f o r m a t i o n from f i v e s o u r c e s : the 1980 \"Aurora-ULF-VLF\" campaign m i c r o p u l s a t i o n r e c o r d s , GOES s a t e l l i t e magnetograms, magnetograms from a u r o r a l zone magnetic o b s e r v a t o r i e s , Rp i n d i c e s , and Dst i n d i c e s . The p r i m a r y d a t a s o u r c e , t h a t of the IPDP m i c r o p u l s a t i o n r e c o r d s , was the \"Aurora-ULF-VLF\" campaign (Oguti et a l . , 1982). As p a r t of t h i s p r o j e c t , t h i r t e e n ULF s t a t i o n s were o p e r a t e d i n western Canada a t a u r o r a l zone and plasmapause l a t i t u d e s d u r i n g J a nuary and F e b r u a r y of 1980. El e v e n of the t h i r t e e n s t a t i o n s were l o c a t e d at l a t i t u d e s s u i t a b l e f o r r e c o r d i n g IPDPs. These s t a t i o n s a r e l i s t e d , a l o n g w i t h t h e i r g e o g r a p h i c and c o r r e c t e d geomagnetic c o o r d i n a t e s ( G u s t a f s s o n , 1984), i n Tab l e I I I , and t h e i r l o c a t i o n s a r e p l o t t e d i n f i g u r e 3. The network they c o m p rised c o n s i s t e d e s s e n t i a l l y of t h r e e n o r t h - s o u t h l i n e s of s t a t i o n s ; one each i n B r i t i s h C olumbia, Saskatchewan, and Manitoba ( c f . f i g . 3 ) . Two eas t - w e s t l i n e s c o u l d a l s o be c o n s t r u c t e d from the network; a n o r t h e r n l i n e of SR, LR, and 8 9 Table III ULF Station Names and Coordinates Manitoba L i n e I s l a n d Lake ( I L ) G i m l i (GM) Geographic C o r r e c t e d Geomagnet i c Lat.(\u00C2\u00B0N) Long.(\u00C2\u00B0E) Lat.(\u00C2\u00B0N) Long.(\u00C2\u00B0E) 53.9 265.3 50.6 263.0 64.9 329.6 61.4 326.8 Saskatchewan L i n e R a b b i t Lake (RL) 58. 2 256. 3 67. 8 314.8 South End (SE) 56. 3 256. 5 66. 0 315.8 La Ronge (LR) 55. 2 254. 7 64. 6 313.7 Waskesiu (WS) 53. 9 253. 9 63. 1 313.1 Park S i t e (PS) 52. 2 252. 8 61 . 3 312.2 Lucky Lake (LL) 51 . 0 252. 9 60. 1 312.7 B.C. L i n e Steen R i v e r (SR) 59. 7 242. 8 66. 6 295.7 P r i n c e George (PG) 53. 9 237. 1 59. 6 292.4 V i c t o r i a (VC) 48. 3 236. 4 53. 8 294. 1 10 0) o C cn D E o Q> CD 72 70 68 66 64 62 60 58 56 54 . B.C. line OiSR -4-I J. \u00E2\u0080\u00A2 PGI 4V\u00E2\u0080\u0094-4~ Sask. line , RL, .4- - 4--V..4 4..... 1 <>\"SE ILR I I <>WS| J. L K>PS 1 I O L L I 4- I. I I I I Man. line 4\u00E2\u0080\u0094\u00E2\u0080\u0094-4- 4\u00E2\u0080\u0094 ---I. 4- I IL o \"IOGMI 4- l~. northern east-west line southern east-west line VC, 52 290 300 310 320 330 340 geomagnetic longitude (E) FIGURE 3. P l o t of ULF s t a t i o n l o c a t i o n s , i n geomagnetic c o o r d i n a t e s , f o r the \"Aurora-ULF-VLF\" campaign. The n o r t h - s o u t h and eas t - w e s t s t a t i o n l i n e s a r e a l s o shown. 11 I L , as w e l l as a s o u t h e r n l i n e of PG, PS and/or LL, and GM. The r e c o r d i n g systems a t these ground s t a t i o n s c o n s i s t e d of i n d u c t i o n magnetometers w i t h high-M m e t a l c o r e s , a m p l i f i e r s , and slow-speed FM analogue tape r e c o r d e r s . These systems were each c a p a b l e of r e c o r d i n g t h r e e o r t h o g o n a l components: X (magnetic n o r t h ) , Y (magnetic e a s t ) , and Z (downward). F u r t h e r i n f o r m a t i o n on the campaign, i n c l u d i n g the r e c o r d i n g systems used, can be o b t a i n e d from O g u t i et a l . (1982). The network of ULF s t a t i o n s was not w i t h o u t i t s problems. Depending on the r e c o r d i n g system, narrow band i n s t r u m e n t n o i s e was p r e s e n t w i t h i n the IPDP f r e q u e n c y band, at e i t h e r 0.5 or 0.7 Hz. Man-made i m p u l s i v e n o i s e a l s o i n t e r f e r e d w i t h some s t a t i o n s : t r a f f i c n o i s e a t GM, RL, PG, and SR; and r a d i o t r a n s m i s s i o n s a t I L and PG. In a d d i t i o n , WS r e c o r d e d broad band n o i s e below 0.2 Hz which was a t t r i b u t e d t o l a k e o s c i l l a t i o n s . A more s e r i o u s problem f o r the study of IPDPs proved t o be m i s s i n g d a t a i n t e r v a l s . For example, a t WS the X-component was not r e c o r d e d a t a l l , some of the t a p e s from PG and IL p r o v e d t o be u n r e a d a b l e , and almost a l l s t a t i o n s s u f f e r e d from i n c o m p l e t e coverage of the campaign p e r i o d . With t h e s e d i f f i c u l t i e s , i t was q u i t e r a r e t o have most of the s t a t i o n s o p e r a t i n g p r o p e r l y a t the time of an IPDP e v e n t , which l i m i t e d the c h o i c e of e v e n t s s u i t a b l e f o r d e t a i l e d a n a l y s i s . A l t o g e t h e r , t e n IPDPs were r e c o r d e d between J a n . 16 and 1 2 Feb. 24, 1980. These e v e n t s a re l i s t e d i n Ta b l e IV. A book of dynamic s p e c t r a from the Aurora-ULF-VLF campaign ( O g u t i et a l . , 1982) was used t o i d e n t i f y them. From th e s e t e n e v e n t s , t h r e e were s e l e c t e d f o r d e t a i l e d a n a l y s i s . These t h r e e , Feb. 14, Feb. 15, and Feb. 24c, w i l l be d i s c u s s e d e x t e n s i v e l y i n Chapter F i v e . The c r i t e r i a f o r s e l e c t i o n of the above e v e n t s i n c l u d e d t h a t they be r e c o r d e d a t more than one s i t e on a n o r t h - s o u t h l i n e and/or more than one s i t e on an e a s t - w e s t l i n e f o r a n a l y s i s purposes ( c f . Chapter F i v e ) , the q u a l i t y of the da t a o b t a i n e d , and the c l a r i t y of the IPDP, e n s u r i n g t h a t the event was unambiguously i d e n t i f i e d as an IPDP. Magnetograms from two geosynchronous s a t e l l i t e s , GOES 2 and GOES 3, were a l s o used. The magnetograms from both of these GOES s a t e l l i t e s c o n s i s t of 0000-2400 UT p l o t s of t h r e e o r t h o g o n a l components, H, D, and V, p l u s the t o t a l f i e l d s t r e n g t h , a l l b e i n g p l o t t e d i n gammas. The GOES 2 s a t e l l i t e o r b i t s near 251\u00C2\u00B0 E, and i s thus c l o s e t o the geomagnetic m e r i d i a n of the Saskatchewan n o r t h - s o u t h l i n e . D u r i n g the campaign p e r i o d , o n l y t w e l v e days of da t a a r e a v a i l a b l e from t h i s s a t e l l i t e , from Feb. 5 t o Feb. 16 i n c l u s i v e . The GOES 3 s a t e l l i t e o r b i t s near 225\u00C2\u00B0 E, c l o s e t o the geomagnetic m e r i d i a n of the B.C. n o r t h - s o u t h l i n e . Magnetograms from t h i s s a t e l l i t e a r e a v a i l a b l e f o r the e n t i r e campaign p e r i o d . The t h i r d d a ta s e t r e q u i r e d f o r the a n a l y s i s of IPDPs Table IV IPDP Events Event UT 1. J a n . 1 6 0255 - 031 5 2. J a n . 23 0535 - 0635 3. J a n . 27 2230 - 2320 4. J a n . 28 0000 - 0105 c J a n . 29 0150 - 0315 Feb. 1 4 0835 - 0940 Feb. 1 5 2145 - 2205 8. Feb. 24a 0000 - 01 30 9. Feb. 24b 0150 - 0300 10. Feb. 24c 0550 - 0650 (Events s e l e c t e d f o r d e t a i l e d a n a l y s i s u nder1ined.) 1 4 c o n s i s t s of magnetograms from an a r r a y of e i g h t a u r o r a l and s u b - a u r o r a l zone magnetic o b s e r v a t o r i e s (see T a b l e V ) . These magnetograms were o b t a i n e d from World Data Center A f o r s o l a r - t e r r e s t r i a l p h y s i c s i n B o u l d e r , C o l o r a d o (NOAA). The data a r e i n the form of one-minute v a l u e s g i v e n t o the ne a r e s t gamma f o r the magnetic n o r t h , magnetic e a s t , and v e r t i c a l components, as w e l l as f o r the t o t a l f i e l d s t r e n g t h . The l a s t two d a t a s e t s used here a r e the Kp and Dst i n d i c e s . Kp i n d i c e s were a v a i l a b l e from World Data Center A f o r s o l a r - t e r r e s t r i a l p h y s i c s , and Dst i n d i c e s from World Data C e n t e r A f o r r o c k e t s and s a t e l l i t e s i n G r e e n b e l t , M a r y l a n d (NASA). These two i n d i c e s a r e d e s c r i b e d i n d e t a i l i n Appendix C. 2 . 2 . DATA PROCESSING T h i s s e c t i o n p r o v i d e s a d e s c r i p t i o n of analogue and d i g i t a l p r o c e s s i n g t e c h n i q u e s employed d u r i n g the a n a l y s i s of the IPDP d a t a . The f i r s t s t e p i n the a n a l y s i s of an IPDP ev e n t , a f t e r i t s i d e n t i f i c a t i o n , i s s i m p l y t o look a t i t i n the form of a h i g h speed magnetogram or as a dynamic spectrum ( s p e c t r o g r a m ) . T h i s i s n e c e s s a r y both t o und e r s t a n d the gr o s s p r o p e r t i e s of the event and t o e s t a b l i s h the parameters f o r l a t e r d i g i t i z a t i o n and computer a n a l y s i s . Table V Magnetic Observatory Coordinates Geographic Lat.(\u00C2\u00B0N) Long.(\u00C2\u00B0E) S t . John's (STJ) 47. ,6 307. .4 Ottawa (OTT) 45. .4 284. .5 Great Whale R. (GWR) 55. .2 282, .3 W h i t e s h e l l (WHS) 40. .3 264. .8 F o r t C h u r c h i l l (FC) 58. ,8 265. .9 Meanook (ME) 54. .6 246. .7 Y e l l o w k n i f e (YEK) 62. ,4 245. ,6 V i c t o r i a (VC) 48. .5 236. .6 C o r r e c t e d Geomagnet i c Lat.(\u00C2\u00B0N) Long.(\u00C2\u00B0E 55.4 31.0 57.2 359.2 66.8 359.6 51.1 330.7 69.7 329.5 62.4 303.4 69.8 297.4 54.1 294.3 1 6 Each of t h e s e d i s p l a y s can be c r e a t e d from the analogue magnetic t a p e s ; d i r e c t l y i n the case of a magnetogram, and through a spectrum a n a l y s e r ( N i c o l e t 440B or S p e c t r a l Dynamics SD345) and f i b r e - o p t i c o s c i l l o g r a p h (Honeywell 1856A) f o r a dynamic spectrum. The IPDP events chosen f o r d e t a i l e d study r e q u i r e d d i g i t i z a t i o n p r i o r t o computer a n a l y s i s . The a n a l o g u e - t o - d i g i t a l c o n v e r s i o n system c o n s i s t e d of an analogue tape d r i v e , an analogue f i l t e r bank, and a Data T r a n s l a t i o n DT-2801-A A/D c a r d dumping the d i g i t i z e d d a t a d i r e c t l y onto an IBM PCAT computer. The s a m p l i n g f r e q u e n c y was set a t 3.75 Hz. P r i o r t o d i g i t i z a t i o n , 48 db/octave a n t i - a l i a s i n g f i l t e r s w i t h a c o r n e r f r e q u e n c y of 1.5 Hz were a p p l i e d . The d i g i t i z e d e v e n t s a r e then s u b j e c t e d t o d e t a i l e d a n a l y s i s i n o r d e r t o u n d e r s t a n d t h e i r f r e q u e n c y , a m p l i t u d e , and p o l a r i z a t i o n e v o l u t i o n . T h i s a n a l y s i s i s c a r r i e d out u s i n g programs f o r d i g i t a l f i l t e r i n g , f a s t F o u r i e r t r a n s f o r m s ( F F T s ) , and c r o s s - c o r r e l a t i o n s . The FFT r o u t i n e used f o r IPDP a n a l y s i s here i s a TM complex FFT r o u t i n e from the Microway 87FFT package. As p a r t of the pre-FFT p r o c e s s i n g , the d a t a were f i l t e r e d w i t h a B u t t e r w o r t h band-pass f i l t e r (Ranasewich, 1981) t o remove unwanted n o i s e , e s p e c i a l l y a t low f r e q u e n c i e s , o u t s i d e the IPDP's f r e q u e n c y range. The r o l l - o f f of t h i s f i l t e r i s 96 1 7 dB/octave. The FFT method f o r d e t a i l e d IPDP e v o l u t i o n a n a l y s i s r e q u i r e s t h a t the event be d i v i d e d i n t o a s e r i e s of r e l a t i v e l y s h o r t r e c o r d s , t y p i c a l l y of 512 or 1024 p o i n t s (2.27 or 4.55 minutes of d a t a ) , each of which i s then i n d i v i d u a l l y a n a l y s e d . W i t h i n t h e s e s h o r t d a t a segments the IPDP freq u e n c y i s assumed t o be c o n s t a n t f o r the purpose of a p p l y i n g an FFT. T h i s assumption has been t e s t e d by the a n a l y s i s of s y n t h e t i c s i g n a l s w i t h f r e q u e n c i e s i n c r e a s i n g a t r a t e s s i m i l a r t o those e n c o u n t e r e d i n IPDPs. For the segment l e n g t h s used, the FFT a n a l y s i s of these s i g n a l s reproduced t h e i r known a m p l i t u d e and f r e q u e n c y c h a r a c t e r i s t i c s v e r y w e l l , thus i n d i c a t i n g t h a t the assumption of c o n s t a n t f r e q u e n c y used here i s r e a s o n a b l e . The f r e q u e n c y and a m p l i t u d e e v o l u t i o n of an IPDP i s then found from the s p e c t r a computed from the FFTs of a s u c c e s s i o n of c o n s e c u t i v e d a t a segments c o m p r i s i n g the IPDP. The p o l a r i z a t i o n s p e c t r o g r a m s , from which the e v o l u t i o n of an e v e n t ' s p o l a r i z a t i o n i s found, a r e o b t a i n e d from the combined complex FFTs of c o i n c i d e n t X and Y component d a t a segments. P o l a r i z a t i o n s pectrograms appear as normal power s p e c t r a , except t h a t the d a t a p r e s e n t e d are f o r the g i v e n p o l a r i z a t i o n component o n l y . These spectrograms can be produced f o r r i g h t c i r c u l a r , l e f t c i r c u l a r , and l i n e a r p o l a r i z a t i o n s as shown below ( A r n o l d y et a l . , 1979). I f F 18 and fJ are the F o u r i e r t r a n s f o r m e d complex s e r i e s of the X and Y d a t a components F. = 2^=0 f e x p [ - i 2 7 r j k / N ] , then the r i g h t and l e f t c i r c u l a r p o l a r i z a t i o n components can be r e p r e s e n t e d a s : F r = ( Fx - i F^ )/v/2 (2.1a) J J J f o r the r i g h t component, and a s : Fl. = ( Fx + i F' )/v/2 (2.1b) J J J f o r the l e f t component. From th e s e c i r c u l a r components, the p o l a r i z a t i o n power s p e c t r a a r e c a l c u l a t e d as f o l l o w s : P c = I F r I 2 - I Fl. I 2 (2.2) J J J where p o s i t i v e r e p r e s e n t s power i n the r i g h t c i r c u l a r component, and n e g a t i v e P^ i n the l e f t component. L i n e a r p o l a r i z a t i o n spectrograms a r e c a l c u l a t e d from: 19 P L = [ ( | F r | 2 + | F / | 2 ) 2 - | P C | 2 ] 2 (2.3) . J ' J 1 1 ; 1 1 J ' F i n a l l y , c r o s s - c o r r e l a t i o n s a r e used t o compare r e c o r d i n g s of an event taken s i m u l t a n e o u s l y a t d i f f e r e n t s t a t i o n s . To f a c i l i t a t e t h i s , c r o s s - and a u t o - c o r r e l a t i o n TM r o u t i n e s from the Microway 87FFT package were used. In a d d i t i o n t o the above s i g n a l p r o c e s s i n g t e c h n i q u e s , some c u r v e - f i t t i n g i s a l s o r e q u i r e d f o r the IPDP a n a l y s e s . The c u r v e - f i t t i n g r o u t i n e employed h e r e , from the Laboratory Technol ogi es Inc. NOTEBOOK s o f t w a r e package, uses an i t e r a t i v e l e a s t - s q u a r e s r e g r e s s i o n t e c h n i q u e . CHAPTER 3. PROPERTIES OF IPDPS T h i s c h a p t e r w i l l r e v i ew the p h y s i c a l and o c c u r r e n c e c h a r a c t e r i s t i c s of IPDPs as observed by ground s t a t i o n s , and compare geosynchronous s a t e l l i t e o b s e r v a t i o n s t o ground o b s e r v a t i o n s . In a d d i t i o n , IPDP r e l a t i o n s h i p s w i t h o t h e r geomagnetic phenomena w i l l be d i s c u s s e d . 3.1. PHYSICAL CHARACTERISTICS IPDPs a re broad-band e v e n t s which e x h i b i t a p r o g r e s s i v e l y r i s i n g m id-frequency throughout t h e i r l i f e t i m e s . F i g u r e 4 shows a dynamic spectrum of a t y p i c a l IPDP e v e n t . Some of the b a s i c p h y s i c a l p r o p e r t i e s of IPDPs, as seen from ground s t a t i o n s , have been summarized i n Ta b l e V I . The parameters of most IPDPs w i l l f a l l w i t h i n the ranges g i v e n . However, i n extreme c o n d i t i o n s , some ev e n t s w i l l have some parameter v a l u e s o u t s i d e these ranges. I n i t i a l f r e q u e n c i e s as low as 0.05 Hz, which i s i n the Pc 3 fr e q u e n c y range, have been r e c o r d e d (Heacock, 1971). End f r e q u e n c i e s of up t o 2 Hz have a l s o been o b s e r v e d , e s p e c i a l l y a t lower l a t i t u d e s . The change i n frequ e n c y d u r i n g the c o u r s e of an event must be p o s i t i v e f o r the event t o be i d e n t i f i e d as an IPDP. A t y p i c a l i n c r e a s e i n f r e q u e n c y would be g r e a t e r than 1 o c t a v e , and sometimes as h i g h as 3 o c t a v e s ( S a i t o , 1969). Though the frequency s l o p e s which d i f f e r e n t IPDP e v e n t s can 20 21 PARK SITE \u00E2\u0080\u00A2 FIGURE 4 . Dynamic s p e c t r a of an IPDP r e c o r d e d on Feb. 14, 1980 a t Park S i t e and Lucky Lake, Saskatchewan. T h i s e v e n t , which o c c u r s near 0900UT, c l e a r l y shows the r i s i n g f r e q u e n c y t r e n d t y p i c a l of IPDPs. Table VI IPDP Physical C h a r a c t e r i s t i c s I n i t i a l f r e q u e n c y (F;. ) End fr e q u e n c y (F ) Change i n frequ e n c y ( F e - F / ) Average s l o p e ((F -F.)/T) D u r a t i o n (T) Amp l i t u d e 0.1 - 0.3 Hz 0.5 - 1.0 Hz 0.2 - 0.7 Hz 0.2 - 1.0 Hz/h 20 min - 2 h 0.0! - 1.0 7 23 e x h i b i t may be q u i t e d i f f e r e n t , w i t h i n an i n d i v i d u a l event they tend t o be f a i r l y c o n s t a n t . An average s l o p e of 0.73 Hz/h was o b t a i n e d by Heacock (1971) from 130 e v e n t s , w h i l e Roxburgh (1970) found a t y p i c a l s l o p e t o be 0.3 Hz/h. In extreme c a s e s , the s l o p e may be much l a r g e r than 1 Hz/h. For example, s l o p e s of up t o 5 Hz/h have been r e p o r t e d (Roxburgh, 1970). The w i d t h of the n o i s e band of IPDPs i s u s u a l l y i n the range of 0.1 - 0.3 Hz. From a sample of 66 e v e n t s , an average l e n g t h f o r IPDPs of 39 minutes was found by F u k u n i s h i et a l . (1981). Most IPDP event d u r a t i o n s exceed 20 mi n u t e s , though events l o n g e r than 2 hours a r e q u i t e r a r e . A mean a m p l i t u d e of 0.17 f o r IPDP e v e n t s was g i v e n by Ge n d r i n (1970). However, IPDPs o f t e n c o n t a i n s h o r t , h i g h e r a m p l i t u d e i n t e r v a l s as w e l l . The c h a r t r e c o r d i n g i n f i g u r e 5 shows an example of such an i n t e r v a l . These s t r u c t u r e d e l ements, as the h i g h a m p l i t u d e i n t e r v a l s a r e o f t e n c a l l e d , t end t o oc c u r a t randomly spaced i n t e r v a l s d u r i n g the c o u r s e of an IPDP e v e n t . The p o l a r i z a t i o n shown by IPDPs can be r i g h t - h a n d e d or l e f t - h a n d e d e l l i p t i c a l , or l i n e a r . A r n o l d y et a l . (1979) r e p o r t e d a p r o g r e s s i o n of f i r s t r i g h t - h a n d e d , then l i n e a r , then l e f t - h a n d e d , then l i n e a r a g a i n , and l a s t l y r i g h t - h a n d e d p o l a r i z a t i o n a g a i n d u r i n g the c o u r s e of an IPDP event. 24 (/(.) ap'n^idujD FIGURE 5. Y component magnetogram of a part of an IPDP event (0905 - 0909 UT) recorded at Park S i t e , Sask. on Feb. 14, 1980. A 0.4 - 1.0 Hz bandpass f i l t e r has been a p p l i e d to the data. Note the higher amplitude i n t e r v a l near 0908UT. 25 3.2. OCCURRENCE OF IPDPS T a b l e V I I p r e s e n t s a b r i e f summary of the o c c u r r e n c e c h a r a c t e r i s t i c s of e v e n i n g - s i d e IPDPs. M o r n i n g - s i d e IPDPs ( F u k u n i s h i and Toya, 1981; Dovbnya et a l . , 1984), which t y p i c a l l y appear near 0500 geomagnetic l o c a l time (GMLT), a r e p o s s i b l y a d i s t i n c t c l a s s of m i c r o p u l s a t i o n from e v e n i n g - s i d e IPDPs and are not c o n s i d e r e d i n t h i s t h e s i s . As w i t h Table V I , the v a l u e s g i v e n here w i l l be t y p i c a l of most, but not a l l , IPDP e v e n t s . IPDPs a r e s t r o n g l y c o n c e n t r a t e d i n the e v e n i n g l o c a l time s e c t o r , w i t h the peak i n o c c u r r e n c e near 2000 GMLT as shown i n f i g u r e 6. The h e a v i e s t c o n c e n t r a t i o n of ev e n t s a l s o o c c u r s i n the geomagnetic l a t i t u d e (GM L a t . ) range of 60\u00C2\u00B0 t o 65\u00C2\u00B0, the s u b - a u r o r a l zone. Very few have been o b s e r v e d a t l a t i t u d e s h i g h e r than 70\u00C2\u00B0. Below 50\u00C2\u00B0 GM L a t . , IPDPs a r e a l s o l e s s common, r e a c h i n g t h e s e l a t i t u d e s o n l y t h r o u g h i o n o s p h e r i c duct p r o p a g a t i o n ( c f . Appendix B) or on days of v e r y h i g h magnetospheric a c t i v i t y . Most IPDPs o c c u r on mo d e r a t e l y a c t i v e days (20 < ZKp < 30 ) , though some a r e o c c a s i o n a l l y seen on r e l a t i v e l y q u i e t days (10 < ZKp < 20). Heacock (1967) found a median v a l u e of 3- f o r the 3 - h o u r l y Kp index c o r r e s p o n d i n g t o an IPDP e v e n t ' s o c c u r r e n c e t i m e . F i g u r e 7 shows when IPDPs o c c u r r e d on a Kp v e r s u s time p l o t c o v e r i n g 2y months ( G e n d r i n , 1970). Heacock (1967) a l s o found t h a t IPDPs o c c u r r e d a t the r a t e of a p p r o x i m a t e l y 12 per q u a r t e r , Table VII IPDP Occurrence Characteristics L o c a l time L a t i t u d e 3 - h o u r l y Kp 1600 - 0100 GMLT 55\u00C2\u00B0 - 65\u00C2\u00B0 GM L a t . 20 - 35 1 - 5 27 F e b 1 9 6 5 - D e c 1966 6 12 18 0 6 Local Time (120\u00C2\u00B0W) FIGURE 6 . D i u r n a l d i s t r i b u t i o n of the o c c u r r e n c e of IPDPs, showing the peak i n o c c u r r e n c e i n the e v e n i n g h o u r s . These da t a were c o l l e c t e d a t S e a t t l e , Wash. (GM L a t . ^53\u00C2\u00B0) by K n a f l i c h and Kenney (1967). 28 Kp. 9 6 J 0 2 f 1 0 70 60 55 T r 1 1 1 1 1 1 1 r 1 1 1 1 ~i 1 1 \" .t. . . .tt. .i \u00E2\u0080\u009E t l . , ! \u00E2\u0080\u00A2 1 1 1 1 1 r 1 ; _ a ,t..t.t. .t. ,f. , 15 20 2S, , ,- , .JO, , 1 . . . . 5 10' 15 March - 10 April 1964 i r 1 1 1 1 r\u00E2\u0080\u0094 L . . \u00E2\u0080\u00A2 t. .f.t ~~I 1 1 1 1 1 1 T 1 J\u00E2\u0080\u0094 1 1 1 1 1 < 1 1 1 t . *_ . t t t. . . . . ,15. , . , ,20 25. . ' . , .30. \ , , , . 5 , 11 April \u00E2\u0080\u0094 07 May 1964 o 2 o 70 A C 6 S 60 55 , , 1 , , f.tl. ,t 25. \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 . ,30. \u00E2\u0080\u00A2' 08 May \u00E2\u0080\u0094 03 June 1964 FIGURE 7. Occurrence of IPDPs v e r s u s Kp index ( G e n d r i n , 1970). The v e r t i c a l arrows i n the c e n t r a l p a n e l s i n d i c a t e IPDPs, which tend t o occur i n more a c t i v e t i m e s ( h i g h e r K p ) . 29 i n c r e a s i n g t o s e v e r a l dozen per q u a r t e r i n the summer. F u k u n i s h i e t a l . (1981) o b t a i n e d the somewhat lower r a t e of 66 e v e n t s i n 25 months a t Syowa S t a t i o n , A n t a r c t i c a (GM L a t . = -65.9\u00C2\u00B0). As i n d i c a t e d above, on days of h i g h magnetospheric a c t i v i t y IPDPs are obs e r v e d a t lower l a t i t u d e s , w h i l e h i g h l a t i t u d e s t a t i o n s d e t e c t n o t h i n g . These lower l a t i t u d e e v e n t s t e n d t o e x h i b i t h i g h e r f r e q u e n c i e s than the h i g h l a t i t u d e IPDPs. A c c o r d i n g t o Soraas et a l . (1980), the low l a t i t u d e , h i g h Kp e v e n t s a l s o tend t o occur a t e a r l i e r l o c a l t i m e s , though, f o r c o n s t a n t Kp, the maximum o c c u r r e n c e r a t e i s a t an e a r l i e r GMLT f o r h i g h l a t i t u d e IPDPs. Heacock e t a l . (1976) found the d i u r n a l peak t o be near 1700 GMLT f o r C o l l e g e , A l a s k a (64.5\u00C2\u00B0 GM L a t . ) and near 2000 GMLT f o r P a l o A l t o , C a l i f o r n i a . (43.5\u00C2\u00B0 GM L a t . ) . Other l a t i t u d e e f f e c t s t h a t have been noted i n c l u d e 0.17 a m p l i t u d e s a t lower l a t i t u d e s v e r s u s 17 a m p l i t u d e s a t h i g h l a t i t u d e s (Heacock, 1967) as w e l l as lower f r e q u e n c y s l o p e s a t h i g h l a t i t u d e s ( P i k k a r a i n e n e t a l . , 1983). Heacock (1971) found t h a t IPDP s l o p e v a r i e s w i t h GMLT, d e t e r m i n i n g an average s l o p e of 0.55 Hz/h from a s e t of 63 IPDPs o c c u r r i n g i n the 1200 t o 1600 GMLT s e c t o r , and an average s l o p e of 0.91 Hz/h from 67 ev e n t s o c c u r r i n g i n the 1700 t o 2300 GMLT s e c t o r . However, Roxburgh (1970) c l a i m e d t o f i n d no c o r r e l a t i o n between s l o p e and GMLT. Heacock e t 30 a l . (1976) a l s o compared the s l o p e s of IPDPs t o the AE index f o r l a t e - e v e n i n g s e c t o r e v e n t s , f i n d i n g t h a t h i g h AE c o r r e l a t e d w i t h h i g h s l o p e s and low AE w i t h low s l o p e s . These c o r r e l a t i o n s were not e v i d e n t i n the a f t e r n o o n s e c t o r . Note t h a t both the Kp and AE i n d i c e s a r e d e s c r i b e d i n Appendix C. V a r i o u s s t u d i e s comparing IPDPs r e c o r d e d a t g e o m a g n e t i c a l l y c o n j u g a t e s t a t i o n s have been c o n d u c t e d . G e n d r i n et a l . (1966) r e p o r t e d t h a t IPDP s t r u c t u r e d e l e m e n t s , or h i g h a m p l i t u d e i n t e r v a l s , appeared s i m u l t a n e o u s l y a t c o n j u g a t e s t a t i o n s and w i t h the same p o l a r i z a t i o n , t h a t i s , both d i s p l a y i n g the same sense of magnetic v e c t o r r o t a t i o n a t one t i m e . Both th e s e c h a r a c t e r i s t i c s a r e o p p o s i t e t h o s e shown by s t r u c t u r e d Pc 1 ( p e a r l s ) , whose elements appear a l t e r n a t e l y and w i t h o p p o s i t e senses of v e c t o r r o t a t i o n a t c o n j u g a t e s t a t i o n s . A r n o l d y e t a l . (1979) found t h a t an IPDP r e c o r d e d a t S i p l e , A n t a r c t i c a , and R o b e r v a l , Quebec, showed n e i t h e r l e f t - h a n d p o l a r i z a t i o n nor cosmic n o i s e a b s o r p t i o n which accompanies l e f t - h a n d p o l a r i z a t i o n ( c f . s e c . 3.5) s i m u l t a n e o u s l y a t each s i t e even though R o b e r v a l i s o n l y 40km from S i p l e ' s c o n j u g a t e p o i n t . T h i s i n d i c a t e s t h a t c a r e must be taken i n i n t e r p r e t i n g \" c o n j u g a t e \" p o i n t p o l a r i z a t i o n o b s e r v a t i o n s . Heacock et a l . (1976) found t h a t i n v i r t u a l l y a l l c a s e s IPDPs r e c o r d e d a t one s i t e were a l s o seen a t the c o n j u g a t e 31 s i t e , and e x h i b i t e d the same frequ e n c y s l o p e a t both s i t e s . I t was a l s o found, however, t h a t the o c c u r r e n c e of s t r u c t u r e d elements w i t h i n an IPDP were u n c o r r e l a t e d between the c o n j u g a t e s i t e s , which i s i n c o n t r a s t t o the r e s u l t mentioned above. I t must be noted t h a t , w i t h r e s p e c t t o both p o l a r i z a t i o n and element o c c u r r e n c e , there- appears t o be some u n c e r t a i n t y i n IPDP p r o p e r t i e s . 3.3. NETWORK OBSERVATIONS Networks of ground s t a t i o n s have o f t e n been employed t o study IPDP e v e n t s . These networks have g e n e r a l l y c o n s i s t e d of n o r t h - south l i n e s of s t a t i o n s ( L u k k a r i et a l . , 1977; M a l t s e v a e t a l . , 1981; P i k k a r a i n e n e t a l . , 1983; M a l t s e v a et a l . , 1985; P i k k a r a i n e n e t a l . , 1986), and/or e a s t - west s t a t i o n a r r a y s ( M a l t s e v a e t a l . , 1970; Heacock, 1973; Soraas et a l . , 1980; P i k k a r a i n e n e t a l . , 1983). Magnetograms and spectrograms of an IPDP event r e c o r d e d a t s t a t i o n s i n a n o r t h - so u t h l i n e g e n e r a l l y have s i m i l a r appearances a t each s i t e . I o n o s p h e r i c d u c t i n g of IPDP s i g n a l s causes an event r e c o r d e d s i m u l t a n e o u s l y a t l a t i t u d i n a l l y s e p a r a t e d s t a t i o n s t o show the same f r e q u e n c y , s l o p e , d u r a t i o n , and s t r u c t u r e d elements a t each l o c a t i o n . The a m p l i t u d e of an IPDP, however, w i l l v a r y a l o n g a n o r t h -sou t h l i n e of s t a t i o n s , w i t h the l o c a t i o n of the peak a m p l i t u d e moving southward d u r i n g the event (among o t h e r s ; 32 L u k k a r i e t a l . , 1977, M a l t s e v a et a l . , 1981, P i k k a r a i n e n e t a l . , 1986). F i g u r e 8 shows s i m u l t a n e o u s c h a r t r e c o r d s of an IPDP o b t a i n e d from two of the s t a t i o n s of the Saskatchewan n o r t h - south c h a i n (PS and LL) s e p a r a t e d by 1.2\u00C2\u00B0 of l a t i t u d e , d e m o n s t r a t i n g the s i m i l a r i t y of s i g n a l s from c o - m e r i d i o n a l s t a t i o n s . Somewhat l e s s a t t e n t i o n has been p a i d t o s i m u l t a n e o u s o b s e r v a t i o n s of IPDPs at s t a t i o n s s e p a r a t e d i n l o n g i t u d e . The s t u d i e s t h a t have been done i n d i c a t e t h a t the l o n g i t u d i n a l range of IPDP e v e n t s can v a r y w i d e l y ; Soraas et a l . (1980) found e v e n t s c o v e r i n g more than 140\u00C2\u00B0 geomagnetic l o n g i t u d e (GM Long.) are r a r e , w h i l e 30% of the e v e n t s o b s e r v e d spanned l e s s than 60\u00C2\u00B0 GM L o n g i t u d e . Though P i k k a r a i n e n e t a l . (1983) commented t h a t no d r a s t i c changes i n IPDP f r e q u e n c y - time c h a r a c t e r i s t i c s a r e n e c e s s a r i l y o b s e r v e d over the 100\u00C2\u00B0 l o n g i t u d e range of an event and Soraas e t a l . (1980) found t h a t IPDPs can be q u i t e s i m i l a r over ranges of l e s s than 60\u00C2\u00B0 GM Long., i t i s n e v e r t h e l e s s c l e a r t h a t some l o n g i t u d i n a l d i f f e r e n c e s do e x i s t w i t h i n an IPDP event as seen on an e a s t - west c h a i n of s t a t i o n s . M a l t s e v a et a l . (1970) found t h a t both the f r e q u e n c y and s l o p e of IPDPs tends t o be h i g h e r towards the e a s t , t h a t i s , towards m i d n i g h t . W h i l e Heacock (1973) c o u l d not c o n f i r m the t r e n d f o r IPDP s l o p e s , i t was noted t h a t a d e l a y i n onset t i m e s t o the west of 15 minutes t o 1 hour was o f t e n seen 33 2.0 3.0 4.0 5.0 6.0 t ime (min ) 2.0 ' 3 . 0 4.0 5.0 6.0 t ime (min ) - FIGURE 8 . Comparison of Y component r e c o r d segments (0902 t o 0906 UT) from two s t a t i o n s on the same m e r i d i a n (Park S i t e , 312.2\u00C2\u00B0 E, and Lucky Lake, 312.7\u00C2\u00B0 E ) , Feb. 14 e v e n t . Each segment has been n o r m a l i z e d and a 0.4 - 1.0 Hz bandpass f i l t e r has been a p p l i e d . Note the s i m i l a r i t y i n the s i g n a l s between these two s t a t i o n s . 34 between Meanook and C o l l e g e , 44.5\u00C2\u00B0 west (towards dusk) of Meanook. P i k k a r a i n e n e t a l . (1983) o b t a i n e d a much f a s t e r onset d r i f t of 5\u00C2\u00B0 - 6\u00C2\u00B0/min t o the west from 23 e v e n t s . Three of t hese 23 ev e n t s were a l s o examined i n d e t a i l , w i t h a l l t h r e e showing l o n g e r d u r a t i o n s towards the west and l e s s i n t e n s e low f r e q u e n c i e s towards the e a s t . Two of the events d i s p l a y e d no change i n s l o p e w i t h l o n g i t u d e , w h i l e the t h i r d e x h i b i t e d lower s l o p e s towards the west. F i g u r e 9 shows s i m u l t a n e o u s c h a r t r e c o r d s of an IPDP from two s i t e s i n the sou t h e r n e a s t - west l i n e (PG and PS). Here, the s i g n a l s do not show the same degree of s i m i l a r i t y as those i n f i g u r e 8. The s t a t i o n s a r e s e p a r a t e d by 19.8\u00C2\u00B0 GM L o n g i t u d e . 3.4. SATELLITE OBSERVATIONS IPDPs have been s t u d i e d from geosynchronous s a t e l l i t e s by Bossen et a l . (1976), u s i n g ATS-1 d a t a , and McPherron (1981), u s i n g ATS-6 d a t a . Almost a l l e v e n t s seen a t geosynchronous o r b i t a r e a l s o seen a t a ground s t a t i o n near the f o o t of the s a t e l l i t e ' s f i e l d l i n e . For t h e s e IPDPs, the freque n c y spectrum seen a t the s a t e l l i t e i s narrower than t h a t on the ground, but i s c o n t a i n e d w i t h i n the same range. S a t e l l i t e s a l s o observe s m a l l e r changes i n fr e q u e n c y and s h o r t e r d u r a t i o n s than ground s t a t i o n s f o r IPDP events ( c f . f i g . 10). These d i f f e r e n c e s a r e l i k e l y due t o i o n o s p h e r i c d u c t i n g of the gro u n d - r e c o r d e d s i g n a l s ( c f . Appendix B ) . 35 40 41 42 43 44 45 time (min ) 40 41 42 43 44 45 time (min ) FIGURE 9. Comparison of Y component r e c o r d segments (0641 t o 0646 UT) from two s t a t i o n s near the same p a r a l l e l (Park S i t e , 61.3\u00C2\u00B0 N, and P r i n c e George, 59.6\u00C2\u00B0 N), Feb. 24c e v e n t . Each segment has been n o r m a l i z e d and a 0.2 - 0.6 Hz bandpass f i l t e r has been a p p l i e d . These l o n g i t u d i n a l y s e p a r a t e d s t a t i o n s e x h i b i t q u i t e d i f f e r e n t IPDP s i g n a l s . 36 FIGURE 1 0 . Comparison of s p e c t r a from an IPDP r e c o r d e d s i m u l t a n e o u s l y by s a t e l l i t e (ATS-1) and a t a ground s t a t i o n (Tungsten, NWT.) (Bossen e t a l . , 1976). Note the s h o r t e r event d u r a t i o n and s m a l l e r f r e q u e n c y r i s e seen by the s a t e l l i t e . 37 A m p l i t u d e s of about 57 have been r e c o r d e d i n o r b i t , which i s a p p r o x i m a t e l y 50 tim e s g r e a t e r than a t y p i c a l ground s t a t i o n a m p l i t u d e . The p o l a r i z a t i o n s o b s e r v e d a t thes e s a t e l l i t e s a r e l e f t - h a n d e d e l l i p t i c a l , and a t ATS-6, which i s 10\u00C2\u00B0 above the magnetic e q u a t o r , IPDP waves a r e always observed p r o p a g a t i n g away from the e q u a t o r . 3.5. RELATION TO GEOMAGNETIC PHENOMENA I t i s w e l l e s t a b l i s h e d t h a t IPDPs occur i n a c t i v e p e r i o d s f o l l o w i n g storm sudden commencements. In p a r t i c u l a r , t h ey are always a s s o c i a t e d w i t h magnetospheric substorms, o c c u r r i n g i n the e x p a n s i o n and r e c o v e r y phases (Heacock et a l . , 1976). The onset of the ex p a n s i o n phase i s seen on the ground as a sharp n e g a t i v e bay i n the X component a t h i g h l a t i t u d e s t a t i o n s near m i d n i g h t . In the dusk s e c t o r , the X component o f t e n e x h i b i t s h i g h l a t i t u d e p o s i t i v e bays d u r i n g a substorm e x p a n s i o n phase. IPDPs can occur i n the a f t e r n o o n or e v e n i n g s e c t o r s f o l l o w i n g , u s u a l l y w i t h i n an hour, the onset of a sharp n e g a t i v e bay near m i d n i g h t . The d e l a y time i s g e n e r a l l y l o n g e r f o r IPDPs o c c u r r i n g a t e a r l i e r l o c a l t i m e s , and i t has been found t h a t the s l o p e of an event tends t o dec r e a s e as t h i s d e l a y time i n c r e a s e s ( F u k u n i s h i , 1969). IPDPs a r e a l s o known t o occ u r i n c o n j u n c t i o n w i t h the dusk s e c t o r h i g h l a t i t u d e p o s i t i v e bays. D u r i n g a substorm e x p a n s i o n phase, s a t e l l i t e s i n geosynchronous o r b i t observe 38 a d e p r e s s i o n i n the magnetic f i e l d s t r e n g t h , f o l l o w e d by a r e c o v e r y . A l t h o u g h Roxburgh (1970) found t h a t IPDPs o c c u r r e d d u r i n g t h i s r e c o v e r y phase, the r e s u l t s of Bossen et a l . (1976) i n d i c a t e d t h a t 83% of the 33 e v e n t s s t u d i e d o c c u r r e d when the magnetic f i e l d a t geosynchronous o r b i t was e i t h e r d e c r e a s i n g or c o n s t a n t . P r o t o n p r e c i p i t a t i o n and a s s o c i a t e d p r o t o n a u r o r a have been o b s e r v e d w i t h IPDP e v e n t s ( F u k u n i s h i , 1973), as has cosmic n o i s e a b s o r p t i o n (CNA). Note, however, t h a t CNA i s most l i k e l y not caused by p r e c i p i t a t i n g p r o t o n s , but r a t h e r by i n c r e a s e d i o n i z a t i o n i n the i o n o s p h e r e caused by p r e c i p i t a t i n g p r o t o n s ( F u k u n i s h i , 1973), or by r e l a t i v i s t i c e l e c t r o n s p r e c i p i t a t e d by p a r a s i t i c i n t e r a c t i o n s between IPDP waves and these e l e c t r o n s (Thorne and K e n n e l , 1971; Thorne and L a r s e n , 1976). A r n o l d y et a l . (1979) found t h a t the l e f t - h a n d p o l a r i z e d phase of IPDPs was c o r r e l a t e d w i t h the o c c u r r e n c e of CNA, p a r t i c l e p r e c i p i t a t i o n , and a u r o r a l l i g h t . In a d d i t i o n t o v i s u a l a u r o r a , IPDPs have been a s s o c i a t e d w i t h the a u r o r a l s p o r a d i c E - l a y e r and a u r o r a l X-ray b u r s t s . IPDPs have a l s o been a s s o c i a t e d w i t h o t h e r t y p e s of m i c r o p u l s a t i o n s . Heacock (1967) r e p o r t e d t h a t 4-second band p u l s a t i o n s sometimes t e r m i n a t e i n IPDPs, and Roxburgh (1970) found t h a t o c c a s i o n a l l y hm e m i s s i o n s i m m e d i a t e l y f o l l o w IPDP e v e n t s . M a l t s e v a et a l . (1981) r e p o r t e d o b s e r v a t i o n s of Pc 39 4-5 p u l s a t i o n s a t geosynchronous o r b i t o n l y w h i l e IPDPs were seen on the ground. P i b u r s t s ( P i 1) were s t u d i e d i n c o n j u n c t i o n w i t h IPDPs by Heacock (1971). I t was noted t h a t P i b u r s t s o c c u r b e f o r e and towards m i d n i g h t of almost a l l IPDPs. They appear a t h i g h e r l a t i t u d e s than IPDPs, and are accompanied by l a r g e s c a l e p a r t i c l e p r e c i p i t a t i o n i n t o the i o n o s p h e r e . CHAPTER 4. MAGNETOSPHERIC MODEL OF IPDP GENERATION I t i s now g e n e r a l l y a c c e p t e d t h a t IPDP m i c r o p u l s a t i o n s a r e produced by an i o n - c y c l o t r o n i n s t a b i l i t y i n v o l v i n g l e f t - h a n d p o l a r i z e d waves and westward d r i f t i n g p a r t i c l e s i n j e c t e d i n t o the i n n e r magnetosphere from the m a g n e t o t a i l d u r i n g magnetospheric substorms ( H o r i t a et a l . , 1979; P i k k a r a i n e n e t a l . , 1983). However, not a l l the a s p e c t s of t h i s p r o c e s s a re c o m p l e t e l y u n d e r s t o o d , t h i s b e i n g e s p e c i a l l y t r u e of the mechanism(s) r e s p o n s i b l e f o r the r i s i n g f r e q u e n c y t r e n d e x h i b i t e d by IPDPs. In t h i s c h a p t e r , the magnetospheric p r o c e s s e s r e s p o n s i b l e f o r the appearance of IPDPs a r e d e s c r i b e d ( s e c t i o n 4.1), f o l l o w e d by a d e s c r i p t i o n and d i s c u s s i o n 'of the fre q u e n c y s h i f t mechanisms ( s e c t i o n s 4.2 and 4.3). L a s t l y , the p r o c e s s e s d e s c r i b e d i n s e c t i o n s 4.1 through 4.3 are examined u s i n g a s i m p l e computer s i m u l a t i o n of IPDP freq u e n c y b e h a v i o u r ( s e c t i o n 4.4) . 4 . 1 . IPDP - SUBSTORM MODEL At t he onset of a magnetospheric substorm, hot p a r t i c l e s , which may e v e n t u a l l y become i n v o l v e d i n IPDP g e n e r a t i o n , a r e i n j e c t e d from the plasma sheet i n towards the n i g h t s i d e of the E a r t h . T h i s i n j e c t i o n i s d r i v e n by the substorm a s s o c i a t e d i n t e n s i f i e d westward e l e c t r i c f i e l d . Though the plasma h e a t i n g mechanism r e s p o n s i b l e f o r the h i g h 40 41 p a r t i c l e e n e r g i e s i s not y e t w e l l u n d e r s t o o d , i t i s l i k e l y r e l a t e d t o the r e c o n n e c t i o n p r o c e s s o c c u r r i n g i n the m a g n e t o t a i l a t magnetospheric substorm onset ( N i s h i d a , 1978). Some of the p a r t i c l e s i n v o l v e d i n the i n j e c t i o n p r e c i p i t a t e d i r e c t l y i n t o the i o n o s p h e r e near m i d n i g h t a t h i g h l a t i t u d e s . T h i s i s most l i k e l y the p r e c i p i t a t i o n o b served i n c o n j u n c t i o n w i t h the P i b u r s t s , which a re o f t e n seen near m i d n i g h t p r e c e e d i n g IPDPs ( c f . s e c t i o n 3.5). A sh a r p i n n e r boundary of the i n j e c t e d p a r t i c l e s has been o b s e r v e d or i n f e r r e d by some a u t h o r s (Mauk and M c l l w a i n , 1974; M c l l w a i n , 1974; Mauk and Meng, 1983). I f d i r e c t o b s e r v a t i o n of t h i s boundary i s not p o s s i b l e , i t s o r i g i n a l p o s i t i o n can be c a l c u l a t e d by b a c k t r a c k i n g the d r i f t motions of the p a r t i c l e s from where they were d e t e c t e d by s a t e l l i t e . Such c a l c u l a t i o n s r e s u l t i n the i d e n t i f i c a t i o n of a s h a r p l y d e f i n e d s p i r a l or double s p i r a l shaped boundary, as shown i n f i g u r e 11 (double s p i r a l ) and f i g u r e 12 ( s i n g l e s p i r a l ) . These b o u n d a r i e s a r e c l o s e s t t o E a r t h j u s t a f t e r m i d n i g h t , w i t h the cusp of a double - s p i r a l boundary u s u a l l y f a l l i n g near 0100-0200 GMLT. S i n g l e s p i r a l b o u n d a r i e s , which almost always s p i r a l out westward towards dusk, can have t h e i r c l o s e s t p o i n t as f a r ea s t w a r d (towards morning) as 0300-0400 GMLT. Note t h a t b e f o r e d r i f t motions and p a r t i c l e p r e c i p i t a t i o n d i s t u r b the i n j e c t e d plasma, p a r t i c l e s of a l l e n e r g i e s and p i t c h a n g l e s a r e p r e s e n t 42 FIGURE 1 1 . Diagram of a d o u b l e - s p i r a l i n j e c t i o n boundary (Mauk and Meng, 1983). 43 00 FIGURE 1 2 . Westward s i n g l e - s p i r a l i n j e c t i o n boundary (Mauk and M c l l w a i n , 1974). Note the boundary p o s i t i o n v a r i a t i o n w i t h m agnetospheric a c t i v i t y ( K p ) : i n n e r boundary, Kp = 5; o u t e r boundary, Kp = 2. 44 t o g e t h e r . I t has been found t h a t the p o s i t i o n of the i n j e c t i o n boundary i s dependent on the l e v e l of magnetospheric a c t i v i t y ( K p ) , w i t h the boundary o c c u r r i n g f u r t h e r inward d u r i n g more a c t i v e t i m e s , as i l l u s t r a t e d i n f i g u r e 12. Mauk and M c l l w a i n (1974) have p r e s e n t e d a fo r m u l a r e l a t i n g boundary p o s i t i o n t o Kp and GMLT f o r a s i n g l e westward s p i r a l boundary: 122 - 1OKp / A . b = GMLT - 7.3 U ' } ) where L^ i s the L s h e l l of the boundary (L = [ d i s t a n c e from c e n t e r of E a r t h ] / [ r a d i u s of E a r t h ] ) and Kp i s the \" i n s t a n t a n e o u s \" Kp v a l u e . Note t h a t i n e q u a t i o n 4.1, GMLT, which i s e x p r e s s e d i n h o u r s , i s a c t u a l l y e q u a l t o GMLT + 2400 a f t e r m i d n i g h t ( i . e . 0100 becomes 2500). A r n o l d y and Moore (1983) have suggested a l s o t h a t the boundary forms f i r s t near m i d n i g h t , then expands c o n t i n u o u s l y t o the west f o r m i n g a s i n g l e s p i r a l , or both t o the e a s t and t o the west f o r m i n g a double s p i r a l . T h e i r s t u d i e s i n d i c a t e t h a t i t t a k e s a p p r o x i m a t e l y 10 t o 15 minutes f o r the e n t i r e i n j e c t i o n boundary t o form, w i t h the f o r m a t i o n p r o c e e d i n g more q u i c k l y near m i d n i g h t than t o the west or e a s t . 45 Immediately a f t e r the hot p r o t o n s a r e i n j e c t e d i n t o the i n n e r magnetosphere, they b e g i n t o d r i f t westward under the i n f l u e n c e of the g r a d i e n t and c u r v a t u r e of the geomagnetic f i e l d . The g r a d i e n t d r i f t v e l o c i t y i s g i v e n by ( J a c k s o n , 1975): v = g 2a 1 x Vj_B (4.2a) and the c u r v a t u r e d r i f t v e l o c i t y by: v c where v_^ and v\u00E2\u0080\u009E a r e the p a r t i c l e v e l o c i t i e s p e r p e n d i c u l a r and p a r a l l e l t o the magnetic f i e l d B. R\" i s the r a d i u s v e c t o r from the e f f e c t i v e c e n t e r of c u r v a t u r e t o the f i e l d l i n e and u> i s the p a r t i c l e g y r o f r e q u e n c y . From J a c k s o n (1975), and u s i n g u> = qB/mc, R = r E / 3 a t equator of a d i p o l e f i e l d ( r E i s d i s t a n c e from c e n t e r of E a r t h ) , and B = B / L 3 (B i s e q e q f i e l d s t r e n g t h on E a r t h ' s s u r f a c e a t the e q u a t o r ) , e q u a t i o n s 4.2a and 4.2b above can be combined t o g i v e a t o t a l d r i f t v e l o c i t y o f : v 2 w R R x B RB (4.2b) 46 3Wc (1 + c o s 2 a ) L 2 . . , . v , = \u00E2\u0080\u0094 \u00E2\u0080\u0094 (4.3) ^ E eg where W i s the t o t a l p a r t i c l e k i n e t i c energy, a i s t h e p i t c h a n g l e , R_ i s the r a d i u s of the E a r t h , and c i s the speed of l i g h t . Note t h a t s i n c e u> i s p o s i t i v e because q i s p o s i t i v e f o r p r o t o n s , the d r i f t v e l o c i t y i s d i r e c t e d westward. I t i s apparent from t h i s e q u a t i o n t h a t the d r i f t v e l o c i t y i n c r e a s e s w i t h p a r t i c l e energy and w i t h d i s t a n c e from E a r t h ( i n c r e a s i n g L ) . The energy dependence of v^ i n d i c a t e s t h a t a s a t e l l i t e i n the e v e n i n g s e c t o r s h o u l d see a s o f t e n i n g p r o t o n energy spectrum as p r o g r e s s i v e l y s l o w e r , lower energy p a r t i c l e s a re en c o u n t e r e d d u r i n g the westward d r i f t . T h i s e f f e c t , which i s more pronounced i n the dusk r e g i o n f u r t h e r from the i n j e c t i o n boundary i s w e l l s u p p o r t e d by o b s e r v a t i o n ( M c l l w a i n , 1974; H o r i t a et a l . , 1979; Mauk and Meng, 1983). The d u r a t i o n of IPDPs i s a l s o w e l l matched by the d u r a t i o n of the enhanced f l u x of westward d r i f t i n g p r o t o n s as measured by s a t e l l i t e (Soraas et a l . , 1980). Though the p i t c h a n g l e d i s t r i b u t i o n a t i n j e c t i o n i s v i r t u a l l y i s o t r o p i c , l e a d i n g t o l a r g e s c a l e p r e c i p i t a t i o n i n t o the io n o s p h e r e a t h i g h e r l a t i t u d e s , i n s i d e and towards dusk of the i n j e c t i o n boundary the westward d r i f t i n g p r o t o n s show an 47 h i g h l y a n i s o t r o p i c d i s t r i b u t i o n w i t h an almost empty l o s s cone ( W i l l i a m s and Lyons, 1974a,b) (see f i g . 13). Though t h e r e i s a s t r o n g dawn t o dusk e l e c t r i c f i e l d a c r o s s the m a g n e t o t a i l d u r i n g substorms, t h i s does not seem to a f f e c t the d r i f t motions of h i g h energy p a r t i c l e s i n s i d e the plasma sheet i n n e r edge. T h i s i s p r i m a r i l y due t o the f o r m a t i o n of the A l f v e n l a y e r , a l a y e r h a v i n g a net p o s i t i v e charge on the e v e n i n g s i d e and a net n e g a t i v e charge on the morning s i d e , which i s c r e a t e d by the d i f f e r e n t i a l d r i f t motions of p r o t o n s and e l e c t r o n s i n the i n n e r magnetosphere. The p o l a r i z a t i o n e l e c t r i c f i e l d produced by t h e s e charged l a y e r s i s d i r e c t e d dusk t o dawn, o p p o s i t e the t a i l f i e l d , and s i g n i f i c a n t l y reduces the net e l e c t r i c f i e l d i n s i d e the A l f v e n l a y e r ( N i s h i d a , 1978). Thus, f o r h i g h e r energy p r o t o n s above a few keV which a r e r e s p o n s i b l e f o r IPDP g e n e r a t i o n , the e l e c t r i c f i e l d e f f e c t s on d r i f t motion a r e n e g l i g i b l e and the d r i f t p a t h s a r e c i r c u l a r . Lower energy p a r t i c l e s w i l l undergo E x B* d r i f t as w e l l as g r a d i e n t and c u r v a t u r e d r i f t s , w i t h the e l e c t r i c f i e l d e f f e c t s becoming dominant a t e n e r g i e s of l e s s than one keV ( N i s h i d a , 1982). S a t e l l i t e o b s e r v a t i o n s of s p a t i a l p r o t o n energy d i s p e r s i o n p a t t e r n s a l s o show t h a t the e l e c t r i c f i e l d component of the d r i f t v e l o c i t y must be q u i t e s m a l l f o r h i g h energy p r o t o n s ( M c l l w a i n , 1974; Mauk and Meng, 1983). T h i s p o l a r i z a t i o n e l e c t r i c f i e l d i s a l s o b e l i e v e d t o be 48 westward H + drift (a anisotropic) (empty loss cone) Sun Earth Injection Boundary H + injection ( a isotropic) FIGURE 13. /Proton i n j e c t i o n and westward d r i f t t r a j e c t o r i e s d u r i n g a substorm. Note the., d i f f e r e n t p i t c h angle (a) d i s t r i b u t i o n s p r e s e n t d u r i n g the i n j e c t i o n and westward d r i f t phases. 49 r e s p o n s i b l e f o r d r i v i n g the ea s t w a r d e l e c t r o j e t which i s sometimes, though not a l w a y s , observed w i t h i o n o s p h e r i c substorms ( N i s h i d a , 1978; B o t e l e r , 1980). T h i s e l e c t r o j e t c r e a t e s the dusk s e c t o r p o s i t i v e bays seen w i t h IPDPs ( c f . s e c t i o n 3.5), and i s con n e c t e d t o the p a r t i a l r i n g c u r r e n t produced by the westward p r o t o n d r i f t by an inward f i e l d a l i g n e d c u r r e n t (see f i g . 14). I t i s noteworthy t h a t n e i t h e r IPDPs nor the eastward e l e c t r o j e t - p a r t i a l r i n g c u r r e n t system appear w i t h e v e r y substorm. T h i s may be due t o the f a c t t h a t weak substorms have weak i n j e c t i o n s t h a t do not p e n e t r a t e d e e p l y i n t o the i n n e r magnetosphere, thus d e p r i v i n g b o t h IPDPs and the p a r t i a l r i n g c u r r e n t of t h e i r s o u r c e s . As the hot p r o t o n s c o n t i n u e t h e i r westward d r i f t , t hose on lower L s h e l l s w i l l e v e n t u a l l y meet the plasmapause, which i s a r e g i o n of s t e e p g r a d i e n t s i n c o l d plasma d e n s i t y s e p a r a t i n g the h i g h d e n s i t y t r a p p e d c o l d plasma i n s i d e the plasmaspause from the much lower d e n s i t y plasmas o u t s i d e of i t . I t i s here t h a t the d r i f t i n g p r o t o n s undergo the i o n - c y c l o t r o n i n s t a b i l i t y which t r a n s f e r s p a r t i c l e energy t o wave energy, thus g e n e r a t i n g an IPDP ev e n t . The i n s t a b i l i t y o c c u r s when a wave w i t h IPDP f r e q u e n c i e s , whose p r o p a g a t i o n v e c t o r i s o p p o s i t e l y d i r e c t e d t o the p a r t i c l e v e l o c i t y p a r a l l e l t o the background magnetic f i e l d , has i t s f r e q u e n c y d o p p l e r s h i f t e d i n the p r o t o n r e s t frame t o match the 50 FIGURE 14. M a g n e t o s p h e r i c and i o n o s p h e r i c substorm c u r r e n t systems. The system f e a t u r e s r e l a t i n g t o IPDP o c c u r r e n c e a r e the p a r t i a l r i n g c u r r e n t and the downward f i e l d - a l i g n e d c u r r e n t s l a b e l l e d c' and d' which feed the e a s t w a r d e l e c t r o j e t (Kamide et a l . , 1976). 51 p r o t o n ' s g y r o f r e q u e n c y . The opposed d i r e c t i o n s of t r a v e l mean t h a t o n l y l e f t - h a n d p o l a r i z e d waves can i n t e r a c t w i t h the p r o t o n s s i n c e the d i r e c t i o n of r o t a t i o n of the wave f i e l d must c o i n c i d e w i t h the d i r e c t i o n of p r o t o n g y r a t i o n about the magnetic f i e l d l i n e s . The above i m p l i e s t h a t the wave f r e q u e n c y , w, must be l e s s than the p r o t o n g y r o f requency, J2^, which i s as o b s e r v e d ( t y p i c a l l y cj ~ 0 . 1 0 ) . P The i n s t a b i l i t y o c c u r s p r e f e r e n t i a l l y a t the plasmapause because of i t s s h a r p l y i n c r e a s i n g c o l d plasma d e n s i t y (n ). C o r n w a l l e t a l . (1970) and P e r r a u t et a l . * c (1976) c a l c u l a t e d t h a t the peak growth r a t e of i o n - c y c l o t r o n waves (ICW) i s j u s t i n s i d e the plasmapause, and Gomberoff and Cuperman (1982) have shown t h a t the growth of ICW i n c r e a s e s as n /n i n c r e a s e s , which o c c u r s as the c w ' plasmapause i s c r o s s e d , u n t i l n^/n^ r e a c h e s an optimum v a l u e , and then growth d e c r e a s e s a g a i n . The plasmapause as the IPDP g e n e r a t i o n l o c a t i o n i s a l s o s u p p o r t e d by o b s e r v a t i o n ( H o r i t a et a l . , 1979). The growth of ICW depends c r i t i c a l l y on the a n i s o t r o p y (A) i n the hot p r o t o n d i s t r i b u t i o n as w e l l as on n \u00C2\u00A3 . G e n d r i n et a l . (1971) have shown t h a t A > 1/[(A / u ) - 1 ] , where K P P p r o t o n g y r o f requency and A = [Tj_/T\u00C2\u00BB] - 1, f o r ICW t o grow. Here, T, and T\u00E2\u0080\u009E a r e d e f i n e d as T, = m < v 2 >/(2k) and T\u00E2\u0080\u009E m < v 2 >/K where m i s the p r o t o n mass, < v 2 > and < v 2 > P \" P j . \" 52 are the averag e s of the squares of the speeds p e r p e n d i c u l a r and p a r a l l e l t o the magnetic f i e l d , and K i s Boltzmann's c o n s t a n t . For fi^/w = 10, t h i s means A must be g r e a t e r than 0.11. The hot p r o t o n p i t c h a n g l e d i s t r i b u t i o n w i l l have become a n i s o t r o p i c ( i . e . A > 0) d u r i n g the westward d r i f t . However, g i v e n the v e r y low n c found o u t s i d e the plasmapause, A does not become l a r g e enough f o r the i o n - c y c l o t r o n i n s t a b i l i t y t o oc c u r i n t h i s r e g i o n . T h i s i s c o n f i r m e d by C o r n w a l l and S c h u l z (1971), who found t h a t , o u t s i d e the plasmapause, the storm-time r i n g c u r r e n t i s s t a b l e w i t h r e s p e c t t o the i o n - c y c l o t r o n i n s t a b i l i t y . I t i s not u n t i l the plasmapause i s reached t h a t both the a n i s o t r o p y and n c f a v o u r wave growth. Once i n s i d e the plasmapause, however, wave growth a g a i n d e c r e a s e s due t o e l e c t r o n - i o n c o l l i s i o n s ( C o r n w a l l et a l . , 1970) and an a l t e r e d hot p r o t o n p o p u l a t i o n . S i n c e the i n s t a b i l i t y p r o c e s s t a k e s the p a r t i c l e energy from Vj_, i t a l s o reduces A s i n c e T^/T,, i s reduced. T h i s has the e f f e c t of s c a t t e r i n g p r o t o n s i n t o the p r e v i o u s l y empty l o s s cone of t h e i r p i t c h a n g l e d i s t r i b u t i o n , r e s u l t i n g i n a l o s s of p a r t i c l e s t o the i o n o s p h e r e . The lowered A and n^ then r e s u l t i n a d e c r e a s e d wave growth i n s i d e the plasmapause. A f t e r a m p l i f i c a t i o n , the ICW propagate down f i e l d l i n e s towards E a r t h ' s s u r f a c e . S i m i l a r i t i e s i n o c c u r r e n c e times and dynamic s p e c t r a of IPDPs as r e c o r d e d a t c o n j u g a t e 53 s t a t i o n s i n the n o r t h e r n and s o u t h e r n hemispheres, and as o b s e r v e d by s a t e l l i t e s and ground s t a t i o n s near the same f i e l d l i n e s , p r o v i d e s t r o n g e v i d e n c e f o r such f i e l d l i n e g u i d i n g ( c f . s e c t i o n s 3.2 and 3.4). The c o r r e l a t i o n s of p r o t o n p r e c i p i t a t i o n and CNA w i t h the l e f t - h a n d p o l a r i z e d waves ( c f . s e c t i o n 3.5), which a r r i v e a t the i o n o s p h e r e d i r e c t l y overhead of a ground s t a t i o n , p r o v i d e f u r t h e r c o n f i r m a t i o n of f i e l d l i n e g u i d i n g of the waves. T h i s p r o t o n p r e c i p i t a t i o n r e p r e s e n t s a t l e a s t a p o r t i o n of the downward f i e l d a l i g n e d c u r r e n t c o n n e c t i n g the p a r t i a l r i n g c u r r e n t and the e a s t w a r d e l e c t r o j e t mentioned e a r l i e r . The o b s e r v a t i o n t h a t the waves always propagate away from the equator ( c f . s e c t i o n 3.4) a l s o i n d i c a t e s t h a t a m p l i f i c a t i o n of the ICW t a k e s p l a c e p r i m a r i l y i n the e q u a t o r i a l r e g i o n . The shape of the plasmapause e x e r t s s t r o n g c o n t r o l over where and when IPDPs appear. F i g u r e 15 shows t h r e e e s t i m a t e s of the averaged plasmapause c o n f i g u r a t i o n . The westward p r o t o n d r i f t from the m i d n i g h t r e g i o n and the dusk s e c t o r bulge i n the plasmapause account f o r the o b s e r v a t i o n t h a t IPDPs occur p r e d o m i n a n t l y i n the e v e n i n g s e c t o r ( c f . s e c t i o n 3.2). T h i s a l s o c o n t r o l s the l o n g i t u d i n a l e x t e n t of i n d i v i d u a l IPDPs ( c f . s e c t i o n 3.3). As w e l l , the e q u a t o r i a l plasmapause d i s t a n c e c o n t r o l s the l a t i t u d e s of peak IPDP o b s e r v a t i o n by ground s t a t i o n s . The plasmapause shape p r o v i d e s an o b v i o u s l a t i t u d e GMLT c o r r e l a t i o n i n IPDP 54 FIGURE 15. Three average plasmapause L v e r s u s LT p r o f i l e s as d e t e r m i n e d from w h i s t l e r o b s e r v a t i o n s ( C a r p e n t e r , 1966), Ogo 5 i o n mass s p e c t r o m e t e r d a t a ( C h a p p e l l e t a l . , 1971), and E x p l o r e r 45 dc probe d a t a ( h i s t o g r a m ) (Maynard and Grebowsky, 1977). Note the i n c r e a s e d plasmapasue r a d i u s near 1800 LT which i s termed the dusk s e c t o r b u l g e . 55 o c c u r r e n c e , w i t h h i g h e r l a t i t u d e e v e n t s t e n d i n g t o occur a t e a r l i e r GMLT. S i n c e the plasmapause r a d i u s s h r i n k s w i t h h i g h e r magnetsopheric a c t i v i t y t h e r e i s a l s o a l a t i t u d e Kp c o r r e l a t i o n , w i t h h i g h e r l a t i t u d e e v e n t s o c c u r r i n g when Kp i s lower ( c f . s e c t i o n 3.2). Note t h a t t h e s e o b s e r v e d o c c u r r e n c e c h a r a c t e r i s t i c s and c o r r e l a t i o n s a l s o p r o v i d e c o n f i r m a t i o n t h a t IPDPs a r e g e n e r a t e d a t the plasmapause. 4.2. IPDP FREQUENCY SHIFT MECHANISMS The p r e c e d i n g s e c t i o n has d e s c r i b e d the g e n e r a l g e n e r a t i o n p r o c e s s e s which c r e a t e IPDPs, e x c e p t i n g those which produce the c h a r a c t e r i s t i c f r e q u e n c y r i s e . In t h i s s e c t i o n , t h r e e mechanisms which have been proposed t o account f o r the IPDP f r e q u e n c y s h i f t a r e r e v i e w e d . The p r i m a r y f a c t o r s c o n t r o l l i n g t he fre q u e n c y change of the i o n - c y c l o t r o n resonance g e n e r a t i n g IPDPs a r e the s t r e n g t h of the background magnetic f i e l d i n the g e n e r a t i o n r e g i o n and the energy of the hot r e s o n a t i n g p r o t o n s . In Appendix A ( e q u a t i o n A.4b), i t i s shown t h a t the fre q u e n c y ( f ) v a r i e s w i t h these parameters a s : The r i s i n g tone of IPDPs can t h e r e f o r e be caused by an 56 i n c r e a s i n g magnetic f i e l d B, or a d e c r e a s i n g p r o t o n energy W. Below, two p r o c e s s e s t h a t r e s u l t i n i n c r e a s i n g B, inward motion and i n c r e a s i n g background f i e l d , and one r e s u l t i n g i n d e c r e a s i n g W, a z i m u t h a l d r i f t , a r e d i s c u s s e d . 4.2.1. Inward Motion Inward motion of the IPDP g e n e r a t i o n r e g i o n from h i g h e r L s h e l l s i n towards the E a r t h , and thus t o r e g i o n s of h i g h e r magnetic f i e l d s t r e n g t h , was among the f i r s t mechanisms proposed t o account f o r the fr e q u e n c y r i s e of IPDPs (Gendrin et a l . , 1967; Heacock, 1967). T h i s inward motion was b e l i e v e d t o i n v o l v e the d i f f u s i o n inward a c r o s s f i e l d l i n e s i n the p r e m i d n i g h t - dusk s e c t o r of an hot p r o t o n c l o u d i n which the i o n - c y c l o t r o n i n s t a b i l i t y o c c u r r e d . The d i f f u s i o n was thought t o be d r i v e n by a westward e l e c t r i c f i e l d ( T r o i t s k a y a et a l . , 1968). r Roxburgh (1970) no t e d , however, t h a t the inward d i f f u s i o n v e l o c i t i e s (~6km/s) and e l e c t r i c f i e l d s (-6kV/R ) n e c e s s a r y f o r t h i s mechanism t o o p e r a t e a re not observed i n the IPDP g e n e r a t i o n r e g i o n . There i s , though, a way t o move the g e n e r a t i o n r e g i o n t o lower L s h e l l s w i t h o u t r e q u i r i n g a c r o s s L d r i f t of the hot p r o t o n s d u r i n g the ev e n t . As d i s c u s s e d i n s e c t i o n 4.1, IPDP g e n e r a t i o n o c c u r s a t the plasmapause a f t e r a westward d r i f t , i n c i r c u l a r o r b i t s , of the hot p r o t o n s . The r a d i a l p o s i t i o n of the g e n e r a t i o n 57 r e g i o n i s then c o n t r o l l e d by the plasmapause p o s i t i o n above, t h a t i s , i n the same m e r i d i a n a s , the ground s t a t i o n r e c o r d i n g the event. I f the plasmapause moves inw a r d , as i s observed t o happen d u r i n g magnetospheric s t o r m s , then the g e n e r a t i o n r e g i o n w i l l a l s o move inward, r e s u l t i n g i n the westward d r i f t i n g p r o t o n s meeting the plasmapause a t s u c c e s s i v e l y lower L s h e l l s i n the m e r i d i a n of the ground s t a t i o n , and c a u s i n g the IPDP e m i s s i o n f r e q u e n c y t o r i s e (Heacock, 1971; H o r i t a et a l . , 1979). I f i t i s assumed t h a t E a r t h ' s magnetic f i e l d i s a p p r o x i m a t e l y d i p o l a r (B L\" 3) a t the s e s m a l l r a d i a l d i s t a n c e s , and a l s o t h a t W i s assumed t o be c o n s t a n t i n or d e r t o i s o l a t e the e f f e c t s of the inward motion r e l a t e d magnetic f i e l d changes, then e q u a t i o n 4.4 becomes: L. i_ fl . 5 (4.5) where X^ . and Xy a r e , r e s p e c t i v e l y , the i n i t i a l and f i n a l v a l u e s f o r each q u a n t i t y . Note t h a t the s t r o n g dependence of f on L (power of 4.5) i n d i c a t e s t h a t a r e l a t i v e l y s m a l l change i n L can produce a s i g n i f i c a n t f r e q u e n c y r i s e . O b s e r v a t i o n s of inward source movement have been made i n t h r e e ways. L u k k a r i e t a l . (1977) and M a l t s e v a et a l . (1981) o b s e r v e d the l a t i t u d e of peak IPDP a m p l i t u d e moving 58 southward a l o n g a n o r t h - s o u t h c h a i n of s t a t i o n s as the freque n c y r o s e , i m p l y i n g inward source motion i n the e q u a t o r i a l p l a n e , M a l t s e v a et a l . (1985) and P i k k a r a i n e n e t a l . (1986) used r i o m e t e r a b s o r p t i o n e v e n t s t o t r a c e inward source movements, and A r n o l d y e t a l . (1979) observed the RH - LH - RH p o l a r i z a t i o n sequence over a ground s t a t i o n , a l s o i m p l y i n g source motion. Though i t i s now g e n e r a l l y a greed t h a t inward motion can p l a y a r o l e i n c r e a t i n g the IPDP fr e q u e n c y s h i f t , the s i g n i f i c a n c e of t h i s r o l e i s not ye t w e l l u n d e r s t o o d . I t has been v a r i o u s l y c l a i m e d t h a t the r o l e i s minor (Heacock, 1971) or major ( P i k k a r a i n e n et a l . , 1 983) . 4.2.2. Increasing Background F i e l d An a l t e r n a t i v e p r o c e s s f o r i n c r e a s i n g the magnetic f i e l d s t r e n g t h i n the IPDP g e n e r a t i o n r e g i o n i s t o have the r e g i o n remain a t a c o n s t a n t r a d i a l d i s t a n c e w h i l e the background f i e l d s t r e n g t h i n c r e a s e s w i t h t i m e . T h i s mechanism was f i r s t proposed by Roxburgh (1970). I t r e q u i r e s t h a t the IPDP event occur d u r i n g . the p a r t i a l r i n g c u r r e n t decay phase a f t e r a magnetospheric substorm, when the c u r r e n t ' s e q u a t o r i a l magnetic f i e l d d e p r e s s i o n i n the IPDP g e n e r a t i o n r e g i o n i s weakening. I f we assume t h a t L and W are c o n s t a n t , the i n c r e a s i n g f i e l d e f f e c t on fr e q u e n c y would be (from e q u a t i o n 4.4): 59 r B B. . 5 ( 4 . 6 ) . Though Roxburgh (1970) r e p o r t e d IPDP e v e n t s whose fr e q u e n c y r i s e c o u l d be q u a n t i t a t i v e l y e x p l a i n e d by t h i s i n c r e a s i n g f i e l d mechanism, the r e l a t i o n s h i p between the magnetic f i e l d a t geosynchronous o r b i t and t h a t i n an IPDP source r e g i o n a t lower L may not be as s i m p l e .as was supposed. The a c t u a l f i e l d b e h a v i o u r w i l l depend c r i t i c a l l y not o n l y on the growth and r e c o v e r y of the r i n g c u r r e n t , but i t s p o s i t i o n and movement as w e l l . T h i s c o u l d cause the magnetic f i e l d b e h a v i o u r at geosynchronous o r b i t and a t a lower IPDP source r e g i o n t o be q u i t e d i f f e r e n t . Bossen et a l . ( 1976), u s i n g a geosynchronous s a t e l l i t e and a c o n j u g a t e ground s t a t i o n , found t h a t the IPDP and magnetic f i e l d d a t a c o u l d not support the i n c r e a s i n g f i e l d mechanism ( c f . s e c t i o n 3.5). 4.2.3. Azimuthal D r i f t The a z i m u t h a l d r i f t mechanism f o r IPDP f r e q u e n c y s h i f t s was f i r s t a r t i c u l a t e d by F u k u n i s h i (1969). T h i s t h e o r y s t i p u l a t e s t h a t the IPDP freq u e n c y r i s e s as the energy of the p r o t o n s i n v o l v e d i n the i o n - c y c l o t r o n i n s t a b i l i t y f a l l s . 60 The g r a d u a l l y s o f t e n i n g p r o t o n energy spectrum i s c r e a t e d by the energy dependent westward a z i m u t h a l d r i f t v e l o c i t y of the p r o t o n s . A f t e r the substorm plasma i n j e c t i o n , h i g h e r energy p r o t o n s d r i f t westward f a s t e r , r e a c h i n g the g e n e r a t i o n r e g i o n ahead of the lower energy p r o t o n s on the same L s h e l l . T h i s e f f e c t would cause a st e a d y f r e q u e n c y r i s e t h roughout an IPDP e v e n t . I f B i s assumed c o n s t a n t , t h e n , from e q u a t i o n 4.4, the d e c r e a s i n g energy e f f e c t i s g i v e n by: f x . W. \"1 0 . 5 ( 4 . 7 ) . _i W Note t h a t the dependence of f on W i s r e l a t i v e l y weak (power of o n l y 0.5). The e x i s t e n c e of p r o t o n energy s o f t e n i n g as d e s c r i b e d above has been v e r i f i e d by c a l c u l a t i o n from ground o b s e r v a t i o n s , u s i n g the d e l a y time from substorm onset t o IPDP o c c u r r e n c e and p r o t o n d r i f t v e l o c i t i e s , by Kangas e t a l . (1974) and a l s o observed by s a t e l l i t e ( c f . s e c t i o n 4.1). D e s p i t e t h i s , t h e r e i s s t i l l c o n s i d e r a b l e u n c e r t a i n t y over the importance of the a z i m u t h a l d r i f t mechanism t o IPDP fre q u e n c y s h i f t s . Heacock (1971) a s c r i b e d t o i t the dominant r o l e , w h i l e P i k k a r a i n e n et a l . (1983) c o n c l u d e d t h a t i t s c o n t r i b u t i o n t o IPDPs must be minor and Soraas e t a l . (1980) 61 s t a t e d t h a t the observed energy d i s p e r s i o n was over too narrow a range t o p r o v i d e s i g n i f i c a n t f r e q u e n c y r i s e . Bossen et a l . (1976) noted t h a t the a z i m u t h a l d r i f t mechanism was a p l a u s i b l e mechanism t o e x p l a i n IPDPs. 4.3. DISCUSSION OF IPDP FREQUENCY SHIFT MECHANISMS I t i s c l e a r t h a t t he s t a t e of u n d e r s t a n d i n g of IPDP frequ e n c y s h i f t s i s f a r from complete s i n c e disagreement e x i s t s over the importance o f , and even the e x i s t e n c e o f , the mechanisms d e s c r i b e d i n s e c t i o n 4.2. I t s h o u l d a l s o be p o i n t e d out t h a t the r e l a t i v e importance of the r o l e s of the t h r e e mechanisms d i s c u s s e d here c o u l d p o s s i b l y change w i t h changing magnetospheric c o n d i t i o n s , and/or t h e i r s i g n i f i c a n c e c o u l d s i m p l y be d i f f e r e n t a t d i f f e r e n t GMLTs. The i n a d e q u a c i e s found i n each of the above mechanisms' a b i l i t y t o e x p l a i n the IPDP f r e q u e n c y s h i f t a l o n e has f o r c e d the c o n s i d e r a t i o n of the s u p e r p o s i t i o n of two or more of these mechanisms t o account f o r IPDP e v e n t s . Most of thes e h y b r i d models have i n v o l v e d the c o m b i n a t i o n of inward motion and a z i m u t h a l d r i f t e f f e c t s , w i t h the inward motion b e i n g due t o one of E x 1 d r i f t ( e . g . , F r a s e r and Wawryzniak, 1978), plasmapause motion ( e . g . , H o r i t a e t a l . , 1979), or s u c c e s s i v e i n j e c t i o n s p e n e t r a t i n g t o lower L b e f o r e t h e i r a z i m u t h a l d r i f t s t a r t s (Kangas et a l . , 1974). These h y b r i d models have not a c t u a l l y been q u a n t i t a t i v e l y t e s t e d a g a i n s t 62 IPDP d a t a , and r e p r e s e n t o n l y the g e n e r a l r e a l i z a t i o n t h a t some s o r t of s u p e r p o s i t i o n of mechanisms i s n e c e s s a r y t o e x p l a i n IPDPs. In t h i s t h e s i s , we w i l l t e s t an IPDP f r e q u e n c y s h i f t model i n v o l v i n g the a z i m u t h a l d r i f t and inward motion mechanisms which f o l l o w s l o g i c a l l y from the g e n e r a t i o n model d i s c u s s e d i n s e c t i o n 4.1. In t h i s model, the energy d i s p e r s i v e a z i m u t h a l d r i f t e f f e c t s o ccur d u r i n g the westward d r i f t of the hot p r o t o n s from the i n j e c t i o n boundary t o the plasmapause. The source r e g i o n inward motion r e s u l t s from the i n j e c t e d plasma c o v e r i n g a range i n L i n c o m b i n a t i o n w i t h plasmapause inward m o t i o n , w i t h the s l o w e r d r i f t i n g p r o t o n s a t lower L ( c f . e q u a t i o n 4.3) meeting a c o n t r a c t i n g plasmapause above a ground s t a t i o n a f t e r the f a s t e r d r i f t i n g p r o t o n s a t h i g h e r L i n t e r s e c t the plasmapause above the same ground s t a t i o n (see f i g . 16 ( t o p ) ) . In a d d i t i o n , the model a l s o i n c o r p o r a t e s a new inward motion p r o c e s s due t o plasmapause geometry. Even i f the plasmapause motion i s not s i g n i f i c a n t d u r i n g an e v e n t , the IPDP g e n e r a t i o n r e g i o n , as seen by a ground s t a t i o n , can s t i l l appear t o move t o lower L s h e l l s due t o the shape of the plasmasphere dusk s e c t o r b u l g e . As the E a r t h ' s r o t a t i o n c a r r i e s the ground s t a t i o n from dusk towards m i d n i g h t , the slowe r d r i f t i n g lower L p r o t o n s w i l l meet the plasmapause a t a s t e a d i l y d e c r e a s i n g r a d i a l d i s t a n c e overhead of the ground s t a t i o n (see f i g . 16 63 FIGURE 16. TOP: Diagram showing inward source motion due t o L-dependent a z i m u t h a l d r i f t v e l o c i t y v a r i a t i o n s and a c o n t r a c t i n g plasmapause. BOTTOM: Diagram showing t h a t inward motion of the IPDP so u r c e r e g i o n , due t o E a r t h ' s r o t a t i o n and the plasmapause bulge shape, s t i l l e x i s t s even when t h e r e i s no c o n t r a c t i o n of the plasmapause. The t i m e s t , and t 2 c o r r e s p o n d t o the tim e s of g e n e r a t i o n (plasmapause i n t e r s e c t i o n ) on the r e s p e c t i v e L s h e l l s . 64 ( b o t t o m ) ) . From e q u a t i o n 4.4, assuming a d i p o l a r f i e l d , and u s i n g e q u a t i o n 4.3 t o account f o r the v a r y i n g d r i f t v e l o c i t i e s a t d i f f e r e n t L, the fre q u e n c y s h i f t becomes: f . ALT ALT f 0 . 5 r L 7 (4.8) where ALT i s the a r c through which the p r o t o n s d r i f t , t h a t i s , the d i s t a n c e of d r i f t = ALT-L (ALT i n r a d i a n s ) , and t ^ i s the d r i f t time of the p r o t o n s from i n j e c t i o n t o plasmapause f o r each L s h e l l . The p r o t o n energy (W) has been r e p l a c e d i n t h i s e q u a t i o n by ALT and t ^ s i n c e we are no l o n g e r s a m p l i n g one stream of p r o t o n s on one L s h e l l w i t h i t s s i m p l e s o f t e n i n g spectrum, but c r o s s i n g L s h e l l s i n t o d i f f e r e n t p r o t o n streams which c o u l d r e s u l t i n a more c o m p l i c a t e d energy e v o l u t i o n . The d r i f t t i m e s and a r c s now c h a r a c t e r i z e the p r o t o n energy v a r i a t i o n seen at the plasmapause above a ground s t a t i o n as the s t a t i o n i s c a r r i e d eastward d u r i n g an IPDP e v e n t . E q u a t i o n 4.8 shows a s l i g h t l y reduced dependence on L compared t o e q u a t i o n 4.5, and a l s o t h a t i n c r e a s i n g d r i f t t i m e s and d e c r e a s i n g d r i f t a r c s w i l l r e s u l t i n f r e q u e n c y r i s e s . The f r e q u e n c y s h i f t model d e s c r i b e d here w i l l be t e s t e d by computer s i m u l a t i o n ( s e c t i o n 4.4), and the r e s u l t s of the 65 a n a l y s i s of data from a network of ground s t a t i o n s w i l l a l s o be i n t e r p r e t e d i n terms of t h i s model ( c f . Chapter F i v e ) . I f any t e m p o r a l changes, p o s i t i v e or n e g a t i v e , o c c u r i n the background magnetic f i e l d s t r e n g t h d u r i n g an IPDP e v e n t , the e f f e c t would be superimposed on the o t h e r mechanisms a l r e a d y o p e r a t i n g , enhancing or d e p r e s s i n g the fr e q u e n c y r i s e c r e a t e d by these o t h e r mechanisms. However, i n t h i s model, such f i e l d changes a re not e s s e n t i a l t o the development of an IPDP. 4.4. IPDP FREQUENCY BEHAVIOUR SIMULATION The magnetospheric p r o c e s s e s d e s c r i b e d i n s e c t i o n s 4.1 thr o u g h 4.3 can be s i m u l a t e d by computer. The purpose of t h i s s i m u l a t i o n i s t o q u a n t i t a t i v e l y t e s t the model t o see i f , s t a r t i n g from magnetospheric c o n d i t i o n s o b s e r v e d t o be a s s o c i a t e d w i t h IPDP o c c u r r e n c e , i t can reproduce IPDP f r e q u e n c y b e h a v i o u r as seen by ground s t a t i o n s . T h i s t e s t i s d i r e c t e d p r i m a r i l y a t IPDP f r e q u e n c y e v o l u t i o n s i n c e t h i s i s the o u t s t a n d i n g u n e x p l a i n e d f e a t u r e of IPDP-type m i c r o p u l s a t i o n s and the p r i n c i p a l f o c u s of t h i s t h e s i s . In a d d i t i o n t o f r e q u e n c i e s , however, the s i m u l a t i o n a l s o y i e l d s i n f o r m a t i o n on l o c a l t i m e s and l a t i t u d e s of IPDP o c c u r r e n c e , event d u r a t i o n s , and the e v o l u t i o n of the hot p r o t o n e n e r g i e s . 66 4.4.1. Computational Procedure The model c o n s i d e r e d here b e g i n s a t the f o r m a t i o n of the i n j e c t i o n boundary, f o l l o w s the d r i f t of the i n j e c t e d p r o t o n s from t h e r e t o the plasmapause where the IPDPs a r e g e n e r a t e d , and f i n a l l y d e t e r m i n e s what a ground s t a t i o n would see d u r i n g an e v e n t . The i n i t i a l s t e p of t h i s m o d e l l i n g p r o c e s s i n v o l v e s d e f i n i n g the s t a r t i n g c o n f i g u r a t i o n . T h i s r e q u i r e s s p e c i f y i n g the plasmapause and i n j e c t i o n boundary p o s i t i o n s . The l o c a t i o n of the i n j e c t i o n boundary i s c a l c u l a t e d as d i s c u s s e d i n s e c t i o n 4.1 ( c f . e q u a t i o n 4.1). Note t h a t the parameters i n t h i s e q u a t i o n can v a r y (Mauk and Meng, 1983), thus c h a n g i n g the form of the i n j e c t i o n boundary. The plasmapause p o s i t i o n i s d e t e r m i n e d from a s i m p l e t e a r d r o p model of the plasmapause shape, the f o r m u l a f o r which i s ( K i v e l s o n , 1976): L 2 R E E = C{[1 - (1 + s i n ( 0 ) ) * ] / s i n U ) } 2 (4.9) where E i s the magnetospheric e l e c t r i c f i e l d s t r e n g t h i n the e q u a t o r i a l p l a n e , C i s the c o r o t a t i o n p o t e n t i a l (- 90kV), and ^ ( r a d i a n s ) = 7r\u00C2\u00ABLT/l2 (LT = l o c a l time i n h o u r s ) . In e q u a t i o n 4.9, the r e f e r e n c e m e r i d i a n from which 4> i s measured i s the m e r i d i a n of the apex of the dusk s e c t o r b u l g e . 67 In the dusk s e c t o r , where most IPDPs o c c u r , the plasmapause shape produced by t h i s model i s q u i t e s i m i l a r t o the average plasmapause shape of Maynard and Grebowsky (1977) ( c f . f i g . 15). The o r i e n t a t i o n of the dusk s e c t o r b u l g e ( i . e . LT p o s i t i o n of the apex of the b u l g e ) and the a c t u a l r a d i u s of the plasmapause, i n the e q u a t o r i a l p l a n e , a r e known t o be v a r i a b l e . Here, these parameters are c a l c u l a t e d from s t a t i s t i c a l r e l a t i o n s found by H i g e l and L e i (1984). The o r i e n t a t i o n of the plasmapause bulge i s g i v e n by: LT = 23.45 - 0 . 6 i - L 9 h r K p ( 4 . 1 0 ) . The r a d i u s of the plasmapause i s c o n t r o l l e d by E ( c f . e q u a t i o n 4.9), which i s g i v e n by: E(kV/Rg) = 0.88 + 0.12Kp + 0.019Kp 2 ( 4 . 1 1 ) . The v a l i d i t y of t h i s r e l a t i o n i s l i m i t e d t o v a l u e s of E < 2kV/R E and Kp < 6. By u s i n g e q u a t i o n s 4.1 and 4.9 t o 4.11 f o r , r e s p e c t i v e l y , the plasmapause and i n j e c t i o n boundary, the model s t a r t i n g c o n f i g u r a t i o n can be produced by i n p u t t i n g o n l y the GMLT range of the i n j e c t i o n boundary and the Kp i n d i c e s f o r the p r e c e d i n g n i n e hours ( t h r e e 3 - h o u r l y 68 v a l u e s ) . At t h i s p o i n t , a p l o t of the model s t a r t i n g c o n f i g u r a t i o n can be produced, as shown i n the model f l o w c h a r t i n f i g u r e 17. The next s t e p of the m o d e l l i n g p r o c e s s i n v o l v e s c a l c u l a t i n g the i n j e c t e d p r o t o n d r i f t m o t i o n s . However, b e f o r e t h i s s t e p , both the energy range and increment ( i n keV) must be i n p u t i n t o the c o m p u t a t i o n ( c f . f i g . 17). For s i m p l i c i t y , i t i s assumed t h a t a l l the p r o t o n s , which a r e i n i t i a l l y a t r e s t , s t a r t d r i f t i n g from p o s i t i o n s on the i n j e c t i o n boundary. For co m p a r i s o n , however, some t e s t s have been c a r r i e d out under the assumption t h a t the i n j e c t e d plasma o c c u p i e s a l i m i t e d a r e a b e h i n d the boundary upon i n j e c t i o n (see s e c t i o n 4.4.3). At each (L,LT) p o i n t a l o n g the i n j e c t i o n boundary, t h e n , t h e r e e x i s t s a common range of energy v a l u e s . For each energy l e v e l (W) a t each (L,LT) p o i n t , the westward d r i f t motion of a p r o t o n of t h a t energy can now be c a l c u l a t e d . The p r o t o n d r i f t p a t h s a re assumed t o be c i r c u l a r ( c f . s e c t i o n 4.1), and the changing LT p o s i t i o n s of each p r o t o n a re f o l l o w e d u s i n g the westward d r i f t v e l o c i t y of e q u a t i o n 4.3. A new LT v a l u e i s c a l c u l a t e d f o r each p r o t o n a t each time s t e p of one minute d u r i n g the d r i f t phase of the model. Note t h a t the p i t c h a n g l e (a) used i n the v e l o c i t y c a l c u l a t i o n s was 60\u00C2\u00B0. T h i s would, assuming t h a t a l l p r o t o n s i n a d i s t r i b u t i o n had the same a, c o r r e s p o n d t o an a n i s o t r o p y of 69 INPUTS CALCULATIONS OUTPUTS activity (Kps) proton energy boundary type run.tiie plasiapause noveaent ground stations Initial \u00E2\u0080\u00A2odei configuration plasiapause Intersection points frequency and latitude calculations ground station assignment initial--\u00E2\u0080\u00A2odel plot-3 proton drift tables * frequency, latitude, tite, + energy tables ground observations FIGURE 17. Flow c h a r t f o r computer s i m u l a t i o n of m i c r o p u l s a t i o n s (see t e x t f o r d e t a i l e d d e s c r i p t i o n ) . IPDP 70 A = 2. G e n d r i n e t a l . (1971) found ( f o r Pc 1) t h a t A was g e n e r a l l y between 1 (a = 55\u00C2\u00B0) and 2 (a 60\u00C2\u00B0). Note a l s o t h a t the s t a r t of the d r i f t p r o c e s s i s d e l a y e d a t the western end of the i n j e c t i o n boundary i n accordance w i t h the f i n i t e boundary f o r m a t i o n time found by A r n o l d y and Moore (1983) ( c f . s e c t i o n 4.1). D u r i n g the d r i f t phase of the model, f o r each p r o t o n energy on each L s h e l l a t each time s t e p , the LT c o o r d i n a t e of the p r o t o n i s t e s t e d t o see i f i t i s l e s s than the plasmapause LT c o o r d i n a t e on the same L s h e l l a t t h a t time ( i e , LT (L,W,t) < LT ( L , t ) , where LT i s the d r i f t i n g P PP P p r o t o n ' s LT and L T ^ i s the plasmapause L T ) . For each c a s e , the f i r s t time s t e p a t which LT (L,W,t) < LT ( L , t ) d e f i n e s P PP when plasmapause i n t e r s e c t i o n i s s a i d t o have o c c u r r e d ( c f . f i g . 17). The p a r t i c l e d r i f t motions a re not f o l l o w e d a f t e r t h i s t i m e , s i n c e t h i s i s the p o i n t a t which IPDP g e n e r a t i o n i s s a i d t o take p l a c e . The i n t e r s e c t i o n p o i n t d e t e r m i n e s the LT and time ( t ) of IPDP g e n e r a t i o n f o r p r o t o n s of energy W d r i f t i n g a l o n g a p a t h of r a d i u s L. The model p r o v i d e s an o p t i o n f o r the inward movement of the plasmapause, due t o plasmasphere c o n t r a c t i o n , d u r i n g the d r i f t phase. I f t h i s o p t i o n i s s e l e c t e d , the plasmapause i s moved inward a t each time s t e p by d e c r e a s i n g the LT c o o r d i n a t e of each (L,LT) p a i r d e f i n i n g the plasmapause i n the a f t e r n o o n - e v e n i n g s e c t o r (see s e c t i o n 4.4.3). Because of the shape of the 71 plasmapause dusk s e c t o r bulge ( c f . f i g . 16 ( t o p ) ) , t h i s has the same e f f e c t as d e c r e a s i n g the r a d i a l d i s t a n c e L a t a f i x e d m e r i d i a n . Once the plasmapause i n t e r s e c t i o n p o i n t i s known, i t i s p o s s i b l e t o c a l c u l a t e the i o n - c y c l o t r o n wave fr e q u e n c y f o r t h a t p o i n t , r e l a t i v e t o a r e f e r e n c e f r e q u e n c y ^ r^> a s f o l l o w s (from e q u a t i o n 4.4 i n a d i p o l a r f i e l d ) : r L i H . 5 r w i r r L W (4.12) where i s the L v a l u e of the e a s t e r n ( l o w e r ) end of the i n j e c t i o n boundary and W i s the h i g h e s t p r o t o n energy v a l u e b e i n g c o n s i d e r e d . Assuming a d i p o l a r f i e l d , the geomagnetic l a t i t u d e can a l s o be found from the L v a l u e of the i n t e r s e c t i o n p o i n t as f o l l o w s : XGM = c o s \" 1 ( ]M L) (4.13). W i t h d a t a from each i n t e r s e c t i o n p o i n t , i t i s now p o s s i b l e t o produce a t a b l e of r e s u l t s which i n c l u d e s the l a t i t u d e , t i m e , energy, l o c a l t i m e , and r e l a t i v e f r e q u e n c y f o r each plasmapause i n t e r s e c t i o n p o i n t , the p o i n t a t which IPDP wave a m p l f i c a t i o n i s s a i d t o occur (see f i g . 17). T h i s , however, does not y e t r e p r e s e n t an IPDP event. In 72 o r d e r t o o b t a i n a r e p r e s e n t a t i o n of an IPDP event as seen by a ground s t a t i o n , we must f i r s t d e f i n e a s e t of ground s t a t i o n s , each of which \"sees\" o n l y a l i m i t e d LT s e c t o r of the plasmapause \"above\" i t , t h a t i s , near i t s own m e r i d i a n . The model a l l o w s s p e c i f i c a t i o n of an a r r a y of up t o ten ground s i t e s spaced by h a l f an hour i n LT (7.5\u00C2\u00B0 l o n g . ) . The s t a t i o n a r r a y can be p o s i t i o n e d over any l o c a l time range. Only the LT c o o r d i n a t e of a ground s i t e i s n e c e s s a r y s i n c e n o r t h - s o u t h i o n o s p h e r i c d u c t i n g i s c o n s i d e r e d t o be v e r y good, and a s i g n a l r e a c h i n g the io n o s p h e r e on one m e r i d i a n w i l l be d e t e c t e d a t any ground s t a t i o n i n the a u r o r a l and s u b - a u r o r a l zones a l o n g t h a t m e r i d i a n . The LT range of the plasmapause t h a t each ground s t a t i o n \" s e e s \" has been s e t a t \u00C2\u00B10.15h (or \u00C2\u00B12.25\u00C2\u00B0 Long.) f o r most r u n s . T h i s i s e q u i v a l e n t t o a 250km range a t 60\u00C2\u00B0 L a t . , and i s c o n s i s t e n t w i t h the Pc 1 source s i z e r e s u l t s of Hayashi e t a l . (1981). The LT c o o r d i n a t e of each i n t e r s e c t i o n p o i n t i s t e s t e d t o see i f i t f a l l s w i t h i n the LT range of a ground s t a t i o n . I f so, i t i s a s s i g n e d t o t h a t ground s t a t i o n and the r e l a t i v e f r e q u e n c y , l a t i t u d e , t i m e , and p r o t o n energy a s s o c i a t e d w i t h i t are s a i d t o be ob s e r v e d a t t h a t s t a t i o n . I t s h o u l d be noted t h a t the l o c a l time of each ground s i t e changes throughout the event as E a r t h ' s r o t a t i o n c a r r i e s the s t a t i o n e a s t w a r d . I t i s now p o s s i b l e t o w r i t e out a t a b l e f o r each s t a t i o n c o n t a i n i n g the 73 f r e q u e n c i e s , t i m e s , l a t i t u d e s , and e n e r g i e s \"observed\" a t each s t a t i o n (see f l o w c h a r t i n f i g . 17). These (f,t,X,W) d a t a s e t s a r e c h r o n o l o g i c a l l y a r r a n g e d , i n o r d e r of i n c r e a s i n g time ( t ) , and now r e p r e s e n t an IPDP event as observed by t h a t ground s t a t i o n . 4.4.2. Model IPDPs versus Observed IPDPs The model d e s c r i b e d above has been run w i t h a l l v a r i a b l e s e x t e n d i n g t h r o u g h o u t , and sometimes beyond, t h e i r normal ranges a s s o c i a t e d w i t h IPDP a c t i v i t y . The Kp index a s s o c i a t e d w i t h the IPDP o c c u r r e n c e i n t e r v a l v a r i e d from 1 t o 7, w h i l e I ^ ^ K p v a r i e d from 1 t o 19. The p r o t o n energy ranges (W - W . ) used i n the runs extended from 10 t o 80 max mi n keV, and a l l the v a l u e s used f e l l w i t h i n the energy span of 10 t o 340 keV. Most runs used an i n j e c t i o n boundary c a l c u l a t e d from e q u a t i o n 4.1, however, some t e s t s were a l s o done w i t h d i f f e r e n t parameters s u b s t i t u t e d i n t o e q u a t i o n 4.1 ( c f . s e c t i o n 4.4.1) t o produce s t e e p e r or f l a t t e r boundary shapes. The r e s u l t s of these numerous runs can now be compared w i t h the p r o p e r t i e s of IPDPs d e s c r i b e d i n Chapter Three. However, the model produces o n l y r e l a t i v e f r e q u e n c y i n f o r m a t i o n ( f / f ^ . , c f . e q u a t i o n 4.12), which r e s t r i c t s the comparisons t h a t can be made. T h i s d i f f i c u l t y can be p a r t i a l l y c i r c u m v e n t e d by comparing the known IPDP 74 f r e q u e n c i e s t o f r e q u e n c i e s produced by models h a v i n g the most common Kps (near 3) and p r o t o n e n e r g i e s (40 t o 100 keV) a s s o c i a t e d w i t h o b s e r v e d IPDPs. The median f r e q u e n c y produced by thes e model runs i s assumed t o be the same as the median observed IPDP f r e q u e n c y , a l l o w i n g a v e r y rough adjustment t o be made t o t h e model f r e q u e n c i e s so t h a t they are comparable t o ob s e r v e d f r e q u e n c i e s . T h i s e n a b l e s the freq u e n c y ranges and s l o p e s d e r i v e d from th e s e a d j u s t e d model f r e q u e n c i e s t o be compared w i t h a c t u a l v a l u e s . I t must be emphasized, however, t h a t no comparison of a b s o l u t e f r e q u e n c i e s i s made h e r e , and t h a t a l l q u a n t i t a t i v e f r e q u e n c y - r e l a t e d i n f o r m a t i o n must be reg a r d e d as o n l y rough e s t i m a t e s when b e i n g compared t o ob s e r v e d v a l u e s . W i t h t h i s i n mind, we can then examine the r e s u l t s p r e s e n t e d i n Table V I I I . These r e s u l t s , which a re a summary of the p r o p e r t i e s of model IPDPs computed w i t h parameters most commonly a s s o c i a t e d w i t h r e a l e v e n t s , a re compared t o observe d IPDP c h a r a c t e r i s t i c s (from T a b l e s VI and V I I i n Chapter T h r e e ) . Though the ranges of the model r e s u l t s do not always e x a c t l y match the IPDP o b s e r v a t i o n s , i n g e n e r a l the agreement between the two i s q u i t e good. Note t h a t though no GMLT of peak o c c u r r e n c e can be a s s i g n e d from the model r e s u l t s s i n c e the a c t u a l r a t e s of IPDP o c c u r r e n c e v e r s u s the i n p u t parameters a r e not w e l l u n d e r s t o o d , the c e n t e r of the GMLT range of the model r e s u l t s l i e s a t 2030 Table VIII IPDP Characteristics Model R e s u l t s Observat i o n s I n i t i a l f r e q u e n c y 0.1 - 0.6 Hz (F. ) End f r e q u e n c y (F ) 0.2 - 1.1 Hz AF (Fe~F. ) 0.1 - 0.6 Hz S l o p e ( ( F -F )/T) 0.1 - 0.6 Hz/h D u r a t i o n (T) L o c a l time L a t i t u d e 0.25 - 1.75 h 1800 - 2300 GMLT 60\u00C2\u00B0 - 65.5\u00C2\u00B0 0.1 - 0.3 Hz 0.5 - 1.0 Hz 0.2 - 0.7 Hz 0.2 - 1.0 Hz/h 0.33 - 2.0 h 1600 - 0100 GMLT 55\u00C2\u00B0 - 65\u00C2\u00B0 76 GMLT, which compares w e l l w i t h the ob s e r v e d peak a t 2000 GMLT ( c f . s e c t i o n 3.2). The l a t i t u d e f r e q u e n c y and l a t i t u d e s l o p e c o r r e l a t i o n s mentioned i n s e c t i o n 3.2 (paragraph two) a r e a l s o produced by the model runs (see f i g . 18). I t i s i n t e r e s t i n g t o n o t e , however, t h a t a p o s s i b l e GMLT s l o p e r e l a t i o n s h i p about which c o n f l i c t i n g s t a t e m e n t s have appeared ( c f . s e c t i o n 3.2, par a g r a p h t h r e e ) , i s not c l e a r l y s u p p o r t e d by the model r e s u l t s . The Kp GMLT and Kp GM L a t . c o r r e l a t i o n s noted i n s e c t i o n 3.2 a r e a l s o r e p r o d u c e d by the model, though not i n p r e c i s e l y the same manner. P r e v i o u s comparisons have o n l y been concerned w i t h the s i n g l e Kp v a l u e a s s o c i a t e d w i t h the IPDP o c c u r r e n c e i n t e r v a l . W h i l e t h i s s i n g l e index can be used f o r the l a t i t u d e c o m p a r i s o n , s i n c e t h i s index c o n t r o l s the plasmapause r a d i a l d i s t a n c e ( c f . e q u a t i o n s 4.9 and 4.11) ( f i g . 19), i t i s by i t s e l f not e n t i r e l y a p p r o p r i a t e f o r the Kp GMLT r e l a t i o n . S i n c e L ^ ^ K p c o n t r o l s the GMLT o r i e n t a t i o n of the plasmapause ( c f . e q u a t i o n 4.10), i t i s t h i s parameter t h a t a c c o u n t s f o r the Kp GMLT r e l a t i o n t h a t i s both reproduced by the model and observ e d ( f i g . 19). Most of the m o d e l l e d IPDPs c o v e r e d 45\u00C2\u00B0-65\u00C2\u00B0 GM Long., though i t i s p o s s i b l e t o gen e r a t e e v e n t s spanning much g r e a t e r r a n g e s , such as 100\u00C2\u00B0 or more, examples of which have been r e p o r t e d ( c f . s e c t i o n 3.3). I t i s a l s o q u i t e c l e a r t h a t d i f f e r e n c e s can be seen w i t h i n m o d e l l e d IPDP e v e n t s 4.0 3.5 3.0 77 -P 2.5 cr 2.0 h N X 1.5 1.0 0.5 0.0 2.0 1.6 1.2 0) CL \" i 0.8 Q_ \u00C2\u00A3 0.4 0.0 52 52 56 . 60 64 GM lot. (deg.) 68 \u00E2\u0080\u00A2 + \u00E2\u0080\u00A2 + \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 J \u00E2\u0080\u0094 J 1 I I * 56 60 64 GM lot. (deg.) 68 FIGURE 18. S i m u l a t i o n r e s u l t s d e m o n s t r a t i n g the r e p r o d u c t i o n of the IPDP f r e q u e n c y - GM L a t . ( t o p ) and s l o p e - GM L a t . (bottom) c o r r e l a t i o n s . 78 0 4 Kp 7 8 24 4 23 _ \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 22 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2f \u00E2\u0080\u00A2 Kp = 3 21 \u00E2\u0080\u00A2 + t i 20 -+ \u00E2\u0080\u00A2 O 19 \u00E2\u0080\u00A2 18 17 16 1 1 1 8 10 *9hrKp 12 14 16 FIGURE 19. S i m u l a t i o n r e s u l t s showing the GM L a t . - Kp ( Z p ^ K p c o n s t a n t ) (top) and GMLT - Zp/^Kp (Kp = c o n s t a n t ) (bottom) c o r r e l a t i o n s produced. 79 \"observed\" a t ground s i t e s spaced q u i t e c l o s e l y i n l o n g i t u d e (AGMLT = 0.5h). These d i f f e r e n c e s can become v e r y o b v i o u s over spans of 60\u00C2\u00B0 GM Long., a range over which l o n g i t u d i n a l v a r i a t i o n s have been r e p o r t e d i n observed IPDPs ( c f . s e c t i o n 3.3). The model r e s u l t s agree w i t h the r e p o r t e d l a t e r GMLT h i g h e r f r e q u e n c y c o r r e l a t i o n ( f i g . 20, top) and a l s o show a l a t e r GMLT s t e e p e r s l o p e c o r r e l a t i o n ( f i g . 20, bottom), though not always i n a c l e a r f a s h i o n . Most model event d u r a t i o n s a r e e i t h e r l o n g e r t o the west or a p p r o x i m a t e l y the same a t a l l s t a t i o n s s e e i n g the event, though o n l y c a s e s of lo n g e r d u r a t i o n s t o the west have been r e p o r t e d i n the l i t e r a t u r e ( c f . s e c t i o n 3.3). The event onset d r i f t r a t e s from the model can d i f f e r s i g n i f i c a n t l y from those d i s c u s s e d i n s e c t i o n 3.3. For model IPDPs on l e s s a c t i v e days ( I ^ ^ K p < 10), onset d r i f t s g e n e r a l l y agree w i t h r e p o r t e d o b s e r v a t i o n s , f a l l i n g i n the 2-5\u00C2\u00B0/min. range. However, on more a c t i v e days ( I p ^ K p > 10), the onset d r i f t s tend t o be n e g a t i v e , as shown i n f i g u r e 21, r e p r e s e n t i n g events d e v e l o p i n g from the west r a t h e r than the e a s t . Such eastward development i s c o n t r a r y t o what has p r e v i o u s l y been thought t o be the c a s e . T h i s problem w i l l be d i s c u s s e d i n more d e t a i l i n a subsequent s e c t i o n . > 2.0 \u00E2\u0080\u00A2P 1.5 o cr 65 \u00C2\u00A3 ~ 60 v> 55 r \u00C2\u00B0 50 89 6 - 8-station-ano. 6 8 station no. \u00C2\u00A3 a> \u00E2\u0080\u00A2o 0.0 -0.2 -0.4 -0.6 6 8 station no. 10-10 - WEST EAST ^ ^ \" ** \u00E2\u0080\u0094r* \u00E2\u0080\u0094 I I I I 10 FIGURE 24. S i m u l a t i o n r e s u l t s : westward v e r s u s e a s t w a r d d e v e l o p i n g IPDPs. Onset t i m e s ( t o p ) , d u r a t i o n s ( m i d d l e ) , and p r o t o n e n e r g i e s (bottom) a re compared f o r an e a s t - west l i n e of s t a t i o n s (models as i n f i g . 2 3 ) . The s t a t i o n s a r e s e p a r a t e d by 7j\u00C2\u00B0 l o n g . ( y h ) . The s o l i d l i n e s a r e f o r the westward d e v e l o p i n g event and the dashed l i n e s f o r the eastward d e v e l o p i n g e v e n t . 90 event. Due t o the n a t u r e of the model and t h e r e a l event a n a l y s i s r e q u i r e m e n t s , however, o n l y the GMLT range of o c c u r r e n c e can be compared f o r a l l t e n IPDPs i n the da t a s e t under c o n s i d e r a t i o n . For the ten events a v a i l a b l e , the GMLT span over which each o c c u r r e d has been d e t e r m i n e d . - The GMLT range of p o s s i b l e IPDP o c c u r r e n c e a l l o w e d by the model was found, f o r each e v e n t , by a s i m u l a t i o n run u s i n g the Kp i n d i c e s a s s o c i a t e d w i t h t h a t e v e n t . Such a run d e t e r m i n e s the plasmapause p o s i t i o n and, assuming an i n j e c t i o n boundary easternmost end of 0200 GMLT, the lo w e s t L s h e l l of hot pr o t o n d r i f t . The L range c o v e r e d by the westward d r i f t i s determined by t h i s lower l i m i t and an upper l i m i t g i v e n by the plasmapause bulge apex L. T h i s L range combined w i t h the plasmapause p o s i t i o n then g i v e s the GMLT range of p o s s i b l e IPDP g e n e r a t i o n . For seven of the ten IPDPs s t u d i e d , the observed GMLT span f a l l s w i t h i n the range a l l o w e d by the model, and one o t h e r e v e n t s ' s GMLT span l i e s m a i n l y (more than 50%) w i t h i n the p e r m i t t e d range. In the case of o n l y two e v e n t s does the observ e d GMLT range not c o r r e s p o n d t o the model r e s u l t s at a l l . F i g u r e 25 shows a s u c c e s s f u l match, the Feb. 15 e v e n t , and a f a i l e d match, the Feb. 14 event. These model r e s u l t s i n d i c a t e t h a t the model i s r e a s o n a b l y s u c c e s s f u l i n p r e d i c t i n g the p o t e n t i a l GMLT IPDPX Plasmapause t Sun 91 Feb. 15 event X \ Earth U FIGURE 25. M o d e l l e d v e r s u s observed IPDP GMLT co m p a r i s o n s . The plasmapause s e c t i o n p l o t t e d i n d i c a t e s where the model p r e d i c t e d an IPDP c o u l d o c c u r , and the ob s e r v e d IPDP GMLTs are marked by the dashed l i n e s . Here, a s u c c e s s f u l p r e d i c t i o n i s shown (Feb. 15 e v e n t , t o p ) , a l o n g w i t h an u n s u c c e s s f u l one (Feb. 14 e v e n t , bottom). 92 p o s i t i o n s of IPDPs. The s t a t i s t i c a l n a t u r e of the r e l a t i o n s d e t e r m i n i n g the plasmapause s i z e and o r i e n t a t i o n and the i n j e c t i o n boundary p o s i t i o n may be the cause of the two f a i l e d GMLT p r e d i c t i o n s , though a l a r g e r IPDP d a t a s e t would be n e c e s s a r y f o r a prop e r e v a l u a t i o n of the performance of these r e l a t i o n s as combined i n the c o n t e x t of t h i s IPDP model. 4.4.5. Discussion of IPDP Simulation Model As mentioned a t the o u t s e t of the d e s c r i p t i o n of t h i s IPDP model, the model i s q u i t e s i m p l e and of l i m i t e d purpose. I t c a l c u l a t e s o n l y r e l a t i v e f r e q u e n c i e s , and the plasmapause and i n j e c t i o n boundary p o s i t i o n s a r e d e t e r m i n e d from s t a t i s t i c a l r e l a t i o n s which w i l l not always be a p p l i c a b l e t o i n d i v i d u a l e v e n t s . Furthermore t h e s e r e l a t i o n s ar e not v a l i d f o r a l l Kps ( c f . s e c t i o n 4.4.1). Another l i m i t a t i o n of the model i s i t s l a c k of f a c i l i t y t o a l l o w f o r the e f f e c t s of tempor a l changes i n the geomagnetic f i e l d s t r e n g t h , a t a f i x e d L, on IPDP f r e q u e n c y e v o l u t i o n . T h i s was not i n c l u d e d s i n c e the i n c r e a s i n g background f i e l d mechanism i s not b e l i e v e d t o be n e c e s s a r y f o r p r o d u c i n g IPDP frequ e n c y b e h a v i o u r ( c f . s e c t i o n 4.3). The assumption of good i o n o s p h e r i c d u c t i n g a p p l i e s o n l y a l o n g the geomagnetic m e r i d i a n , and not t o d u c t i n g i n the east-west d i r e c t i o n , p e r p e n d i c u l a r t o the geomagnetic 93 m e r i d i a n . That good n o r t h - s o u t h d u c t i n g of IPDP s i g n a l s i n the s u b - a u r o r a l zone i o n o s p h e r e o c c u r s i s w e l l known, but the r o l e of e a s t - w e s t d u c t i n g i s l e s s w e l l u n d e r s t o o d ( c f . Appendix B ) . I f e a s t - w e s t d u c t i n g does e x i s t , i t s p r i m a r y e f f e c t would be t o i n c r e a s e the f r e q u e n c y band-width of an IPDP as observed a t the l a t i t u d e of the source f i e l d l i n e s by a d d i n g , a t g e n e r a l l y lower a m p l i t u d e s , lower or h i g h e r f r e q u e n c i e s d u cted from the west or e a s t r e s p e c t i v e l y , t o the g e n e r a l l y h i g h e r a m p l i t u d e s i g n a l s o b s e r v e d from i t s own m e r i d i a n by a ground s t a t i o n . An a d d i t i o n a l a ssumption used t o f a c i l i t a t e the c a l c u l a t i o n of the change i n IPDP fr e q u e n c y due t o a change i n L, and a l s o the geomagnetic l a t i t u d e from L, i s t h a t of a d i p o l a r geomagnetic f i e l d . W i t h i t s framework of l i m i t a t i o n s and assumptions d i s c u s s e d above, t h i s model may be c o n s i d e r e d t o be a \" f i r s t a p p r o x i m a t i o n \" a t t e m p t . To d e v e l o p i t f u r t h e r would r e q u i r e the i n c l u s i o n of a more s o p h i s t i c a t e d geomagnetic f i e l d model, i n c l u d i n g r i n g c u r r e n t and t e m p o r a l e f f e c t s , b e t t e r i n f o r m a t i o n on the f o r m a t i o n and p o s i t i o n of the i n j e c t i o n boundary and the n a t u r e of the plasma b e h i n d i t , improved knowledge of the shape and movement of the plasmapause, and a more d e t a i l e d t r e a t m e n t of the i o n - c y c l o t r o n i n s t a b i l i t y g e n e r a t i n g the IPDP and the subsequent p r o p a g a t i o n of the HM waves th r o u g h the magnetcsphere and i o n o s p h e r e t o the ground s t a t i o n s . 94 Where i t was p o s s i b l e t o make com p a r i s o n s , the model r e s u l t s a greed q u i t e w e l l w i t h 'the known IPDP o b s e r v a t i o n s ( c f . s e c t i o n 4.4.2). A check of mo d e l l e d IPDP GMLTs v e r s u s o b s e r v e d IPDP GMLTs f o r t e n events a l s o r e v e a l e d a good match (75%, c f . s e c t i o n 4.4.4). These r e s u l t s , w h i l e not p r o v i n g the c o r r e c t n e s s of the model, r a i s e c o n f i d e n c e i n i t s u s e f u l n e s s and i n d i c a t e t h a t the new r e s u l t s produced by i t m e r i t c o n s i d e r a t i o n and i n v e s t i g a t i o n . In summary, the s e new r e s u l t s i n c l u d e the s i g n i f i c a n t a pparent inward motion p o s s i b l e w i t h o u t a c t u a l plasmapause inward motion and the p o s s i b i l i t y of eastward d e v e l o p i n g IPDP e v e n t s . CHAPTER 5. EXPERIMENTAL RESULTS Three IPDPs, the Feb. 14, Feb. 15, and Feb. 24c ev e n t s ( c f . s e c . 2.1), have been a n a l y s e d i n d e t a i l ( c f . s e c . 2.2). The r e s u l t s of t h e s e a n a l y s e s a r e used here t o study the causes of the IPDP freq u e n c y r i s e and the l o n g i t u d i n a l development of IPDPs. The p r i m a r y aim of t h i s work i s t o p r o v i d e some e x p e r i m e n t a l i n d i c a t i o n of the r e l a t i v e i m p o r t a n c e , or even e x i s t e n c e , of the v a r i o u s f r e q u e n c y s h i f t mechanisms d i s c u s s e d i n s e c t i o n s 4.2 and 4.3. S e c t i o n 5.1 examines the inward motion mechanism's e f f e c t on the Feb. 14 and Feb. 15 IPDPs ( c f . s e c t i o n 4.2.1), w h i l e s e c t i o n 5.2 p r e s e n t s a study of the i n c r e a s i n g background magnetic f i e l d mechanism ( c f . s e c t i o n 4.2.2). In s e c t i o n 5.3, the c o n t r i b u t i o n s of the a z i m u t h a l d r i f t mechanism ( c f . s e c t i o n 4.2.3) t o the fre q u e n c y s h i f t s of the two ev e n t s s t u d i e d i n s e c t i o n 5.1 a r e examined. The l o n g i t u d i n a l development r e s u l t s a r e p r e s e n t e d i n s e c t i o n 5.4, and s e c t i o n 5.5 c o n t a i n s a d i s c u s s i o n of a l l the e x p e r i m e n t a l r e s u l t s w i t h r e f e r e n c e t o the IPDP model d e s c r i b e d i n Chapter F o u r . 5.1. INWARD MOTION OF IPDP SOURCE REGION In o r d e r t o u n d e r s t a n d the fre q u e n c y e f f e c t s of the inward motion mechanism, the inward motion of the IPDP sour c e r e g i o n must be d e t e r m i n e d . T h i s can be a c h i e v e d t h r o u g h the a n a l y s i s of the e v o l u t i o n of a m p l i t u d e 95 96 v a r i a t i o n s as observed a l o n g a n o r t h - s o u t h l i n e of s t a t i o n s d u r i n g an IPDP event. Such a n a l y s e s have been c a r r i e d out f o r the Feb. 14 and Feb. 15 IPDPs, and a r e d e s c r i b e d below. The Feb. 24c event i s not s u i t a b l e f o r such a n a l y s i s s i n c e o n l y one of the s t a t i o n s s i t u a t e d t o r e c o r d the event on each n o r t h - s o u t h l i n e was o p e r a t i n g . 5.1.1. Feb. 14 Event The IPDP event of Feb. 14 was ob s e r v e d by the t h r e e s t a t i o n s a t the s o u t h e r n end of the Saskatchewan l i n e ; WS, PS, and LL ( c f . s e c t i o n 2.1, f i g . 3 ) . From each of these t h r e e s t a t i o n s , d a t a b l o c k s c e n t e r e d e v e r y f i v e minutes from 0835 t o 0940 UT, are a n a l y z e d ( c f . s e c t i o n 2.2) i n o r d e r t o f o l l o w the f r e q u e n c y , a m p l i t u d e , and p o l a r i z a t i o n e v o l u t i o n of the e v e n t . The p o l a r i z a t i o n s pectrograms from PS and LL p r o v i d e i n f o r m a t i o n on the p r o p a g a t i o n c h a r a c t e r i s t i c s of the IPDP waves i n the ionos p h e r e n e c e s s a r y f o r the u n d e r s t a n d i n g of t h e i r a m p l i t u d e v a r i a t i o n s a l o n g a n o r t h - s o u t h s t a t i o n l i n e . The l e f t - h a n d (LH) p o l a r i z e d f i e l d - l i n e g u i d e d waves from the magnetospheric IPDP sou r c e r e g i o n e n t e r the io n o s p h e r e and p e n e t r a t e through the F - l a y e r . Some of the wave energy may become t r a p p e d i n the i o n o s p h e r i c F - l a y e r waveguide i f the wave fr e q u e n c y i s above a lower c u t - o f f f r e q u e n c y d e t e r m i n e d by the i o n o s p h e r i c plasma c h a r a c t e r i s t i c s . The 97 waveguide i s formed i n the A l f v e n v e l o c i t y minimum c r e a t e d by the peak i n i o n i z a t i o n i n the F 2 - l a y e r ( c f . Appendix B ) . The t r a p p e d wave energy, which i s c o n v e r t e d from LH t o RH ( r i g h t - h a n d p o l a r i z a t i o n ) , can then propagate h o r i z o n t a l l y a l o n g the geomagnetic m e r i d i a n f o r l o n g d i s t a n c e s . T h e r e f o r e , IPDPs s u b j e c t t o i o n o s p h e r i c p r o p a g a t i o n w i l l show LH p o l a r i z a t i o n i f the f i e l d l i n e s g u i d i n g the waves from the magnetospheric source r e g i o n e n t e r the i o n o s p h e r e overhead of the ground s i t e and RH p o l a r i z a t i o n i f they a r e t o the n o r t h or s o u t h of the ground s t a t i o n ( G r e i f i n g e r , 1972; A r n o l d y e t a l . , 1979). I f no such i o n o s p h e r i c p r o p a g a t i o n i s o c c u r r i n g , then o n l y LH p o l a r i z a t i o n s h o u l d be o b s e r v e d . A study of the appearance of RH p o l a r i z a t i o n then t e l l s us whether i o n o s p h e r i c p r o p a g a t i o n i s o c c u r r i n g and below which f r e q u e n c y t h i s e f f e c t i s c u t o f f , and thus i n d i c a t e s whether or not wave a m p l i t u d e v a r i a t i o n w i t h d i s t a n c e from the wave e n t r y p o i n t i n t o the i o n o s p h e r e i s a f f e c t e d by i o n o s p h e r i c p r o p a g a t i o n . Note t h a t the p o i n t , or a r e a , on each m e r i d i a n a t which the IPDP waves e n t e r the i o n o s p h e r e i s o f t e n termed the \"secondary s o u r c e \" . In the p o l a r i z a t i o n s pectrograms from the Feb. 14 e v e n t , RH p o l a r i z a t i o n appears o n l y above ^0.5Hz, thus i n d i c a t i n g the lower c u t - o f f f r e q u e n c y of i o n o s p h e r i c p r o p a g a t i o n e f f e c t s d u r i n g t h i s IPDP ( f o r example, see f i g . 26 and 27). The p a t t e r n of appearance of RH p o l a r i z a t i o n 98 ^ \u00C2\u00B0 - 8 0.4 a \u00C2\u00A3 o 0.0 c \u00C2\u00AB - 0 . 4 o CL \u00E2\u0080\u00940.8 RH power 0840UT LH power 0.2 0.4 0.6 0.8 frequency (Hz) 1.0 0.4 0.6 0.8 frequency (Hz) FIGURE 26. P o l a r i z a t i o n s p e c t r o g r a m ( t o p ) and power spectrum ( t o t a l h o r i z o n t a l component) (bottom) from PS f o r 0840UT, Feb. 14. The p o l a r i z a t i o n spec txojg ram i s a c t u a l l y p r e s e n t e d as [ p o l a r i z e d power ]/[ h o r i z o n t a l . : component power]. The change- from LH p o l a r i z a t i o n at lower f r e q u e n c i e s t o RH p o l a r i z a t i o n j u s t above ^0. 5Hz\"In'ajtS'ates the p o s i t i o n of the lower c u t - o f f f r e q u e n c y of i o n o s p h e r i c p r o p a g a t i o n . 99 d u r i n g t h i s IPDP i s a l s o c o n s i s t e n t w i t h waves t r a v e l l i n g w i t h i n the io n o s p h e r e from a southward moving secondary s o u r c e . At PS, f i r s t RH p o l a r i z a t i o n appears a t 0840UT, i n the band above 0.5Hz ( c f . f i g . 2 6 ) , then LH i s dominant i n the c e n t e r of the freq u e n c y band a t 0900UT ( f i g . 2 7 ) , and l a s t l y we see o n l y RH a g a i n a t 0940UT ( f i g . 27). The p o l a r i z a t i o n spectrograms from LL i n f i g u r e 28 a l s o support t h i s p i c t u r e , w i t h the s i g n a l showing RH p o l a r i z a t i o n a t 0900UT when the secondary source i s t o the n o r t h , near PS, and LH p o l a r i z a t i o n i n the upper p a r t of the f r e q u e n c y band a t 0940UT as the secondary s o u r c e approaches LL. S i n c e v i r t u a l l y a l l of t h i s event i s a t f r e q u e n c i e s >0.5Hz, p r o p a g a t i o n i n the i o n o s p h e r i c waveguide i s t a k i n g p l a c e . Thus, when comparing IPDP power l e v e l s o b s e r v e d a t the t h r e e s t a t i o n s f o r the purpose of d e t e r m i n i n g the secondary source p o s i t i o n , the energy a t t e n u a t i o n between s i t e s can be t r e a t e d as a d u c t e d wave problem. I t s h o u l d be p o i n t e d out t h a t the s i m u l t a n e o u s appearance of both LH and RH bands i n the IPDP s p e c t r a ( c f . f i g . 26, 27) i n d i c a t e s t h a t the magnetospheric s o u r c e r e g i o n i s not a o n e - d i m e n s i o n a l l i n e a l o n g the plasmapause, but o c c u p i e s a more extended t w o - d i m e n s i o n a l a r e a i n the v i c i n i t y of the plasmapause (Hayashi et a l . , 1988). I f the g e n e r a t i o n r e g i o n were p u r e l y o n e - d i m e n s i o n a l , then we s h o u l d see o n l y one p o l a r i z a t i o n , LH or RH, a t a t i m e . 100 N o o c o 0.8 0.4 0.0 \u00E2\u0080\u00A20.4 - 0 . 8 h 0.0 ^ 0.8 X> N \"6 E t_ o c o CL 0) N o c =: o CL 0.8 0.4 0.0 -0.4 -0.8 h 0.0 0.8 0.4 0.0 0.0 RH power 0900UT LH power 0.4 0.8 frequency (Hz) 1.2 RH power w 0940UT ' V\" LH power i i i i i 0.4 0.8 frequency (Hz) 1.2 FIGURE 28. P o l a r i z a t i o n s p e c t r o g r a m s ' f r o m LL f o r 0900UT and 0940UT ( p r e s e n t e d as i n f i g . 2 7 ) . Here, the p o l a r i z a t i o n i s RH a t 0900UT s i n c e the secondary source i s near PS ( c f . f i g . 27) and i s p r e d o m i n a n t l y LH i n the---upper p a r t of the IPDP f r e q u e n c y band a t 0940UT, i n d i c a t i n g t h a t the secondary source has moved southward and i s a p p r o a c h i n g LL. 1 02 Due t o r e c o r d i n g system problems i n the X component a t WS, IPDP s i g n a l power i n o n l y the Y da t a component can be compared between a l l t h r e e s t a t i o n s . These d i f f i c u l t i e s a l s o e l i m i n a t e the p o s s i b i l i t y of s t u d y i n g p o l a r i z a t i o n s pectrograms from WS. However, as p a r t of a study of IPDP s i g n a l power v a r i a t i o n s a l o n g a n o r t h - s o u t h l i n e of s t a t i o n s , the problem of d i f f e r i n g power v a r i a t i o n s between the X and Y components a l o n g the l i n e was examined by K o l e s z a r (1980). The r e s u l t was t h a t the X and Y component v a r i a t i o n s were s u f f i c i e n t l y s i m i l a r t o j u s t i f y t he use of one component o n l y , though the d i s t a n c e s from the secondary s o u r c e concerned were l e s s than 1.6\u00C2\u00B0 of l a t i t u d e . T h i s i s c o n f i r m e d by the s i m i l a r i t y of the X and Y component power v a r i a t i o n s a t LL d u r i n g the Feb. 14 IPDP, as shown i n f i g u r e 29. The l i k e n e s s of the X and Y component power v a r i a t i o n s may, however, break down a t l a r g e r d i s t a n c e s from the secondary source s i n c e the p o l a r i z a t i o n below the duct becomes l i n e a r a l o n g the m e r i d i a n , or i n the X - d i r e c t i o n , w i t h the Y component t h e r e f o r e becoming v e r y s m a l l . Note t h a t LL and WS are s e p a r a t e d by ^3\u00C2\u00B0 of l a t i t u d e . A l t h o u s e and D a v i s (1978) showed t h a t the Y component i s much weaker r e l a t i v e t o the X component a t a low l a t i t u d e s i t e than i t i s a t s i t e s =*l000km t o the n o r t h which a r e c l o s e r t o the secondary s o u r c e . In o r d e r t o q u a n t i t a t i v e l y d etermine the l a t i t u d i n a l 1 03 FIGURE 29. P l o t s of t h e X and Y component peak power v a r i a t i o n s f o r the Feb. 14 IPDP. For ease of comp a r i s o n , each component i s n o r m a l i z e d t o i t s 0940UT-- l e v i l v \" T h e p l o t s a r e g e n e r a l l y q u i t e s i m i l a r , though the s t r o n g e r . X component b e f o r e 0845UT may be i n d i c a t i n g the b e g i n n i n g of _the presence of l i n e a r p o l a r i z a t i o n below the duct (see t e x t ) . 1 04 p o s i t i o n of the secondary s o u r c e , we must know the a t t e n u a t i o n f a c t o r f o r the d u c t e d waves. T h i s can be d e t e r m i n e d e x p e r i m e n t a l l y from the power r a t i o s between ground s t a t i o n s and the known i n t e r - s t a t i o n d i s t a n c e s i f the secondary s o u r c e i s known not t o be between the two s i t e s i n q u e s t i o n . T h i s r e l a t i v e secondary s o u r c e p o s i t i o n c an, i n t u r n , be e s t a b l i s h e d from the p o l a r i z a t i o n s pectrograms and a q u a l i t a t i v e e x a m i n a t i o n of i n t e r - s t a t i o n power r a t i o s . For the Feb. 14 IPDP, the p o l a r i z a t i o n spectrograms from PS e x h i b i t the c h a r a c t e r i s t i c RH - LH - RH time p r o f i l e of a southward moving secondary source w i t h t h i s s o u r c e b e i n g n o r t h o f , or i n the v i c i n i t y o f , PS u n t i l =* 0910UT, and south of PS t h e r e a f t e r . An e x a m i n a t i o n of the i n t e r - s t a t i o n power r a t i o s can, under \u00E2\u0080\u00A2 some c i r c u m s t a n c e s , p r o v i d e c o n f i r m a t i o n as t o whether or not the secondary source i s a c t u a l l y between any two s i t e s . For example, i f the power r a t i o LL/WS = 1, then the secondary source would be a p p r o x i m a t e l y h a l f way between WS and LL. T h i s would be c o n f i r m e d by h a v i n g the r a t i o s PS/WS and PS/LL both s i g n i f i c a n t l y g r e a t e r than one (see f i g . 35 f o r s t a t i o n l o c a t i o n s ) , and would p l a c e the secondary source somewhere between PS and WS. T h i s type of c o n f i r m a t i o n can be i m p o r t a n t , s i n c e near the secondary s o u r c e , the p o l a r i z a t i o n p a t t e r n can sometimes be more complex than the s i m p l e s i t u a t i o n d e s c r i b e d above ( c f . Appendix B ) . 1 05 U s i n g the PS/LL power r a t i o s b e f o r e 091 OUT (see a b o v e ) , we can then c a l c u l a t e the a t t e n u a t i o n as f o l l o w s : A = 1000 1 39 10 Log PS LL (5.1) where A i s the a t t e n u a t i o n i n dB/1000km, which i s the form commonly used t o e x p r e s s duct a t t e n u a t i o n (Manchester, 1966; G r e i f i n g e r and G r e i f i n g e r , 1973; A l t h o u s e and D a v i s , 1978), and 139 i s the PS - LL s e p a r a t i o n d i s t a n c e i n k i l o m e t e r s . The r e s u l t i n g a t t e n u a t i o n f a c t o r i s 21.5 \u00C2\u00B1 2.4 dB/l000km. Due t o v e r y weak s i g n a l s t r e n g t h s at WS a f t e r 091 OUT, no a t t e n u a t i o n c a l c u l a t i o n s were p o s s i b l e u s i n g the PS/WS power r a t i o s . There was no n o t i c e a b l e f r e q u e n c y dependence of the a t t e n u a t i o n , though the f r e q u e n c y range c o v e r e d i n the above c a l c u l a t i o n s was q u i t e narrow (0.15Hz) as compared t o some duct model c a l c u l a t i o n s ( c f . Appendix B ) . T h i s a t t e n u a t i o n f a c t o r may now be used t o c a l c u l a t e the p o s i t i o n , a l o n g the m e r i d i a n , of the secondary source when t h i s source i s between two s t a t i o n s . To f a c i l i t a t e t h i s , t h e o r e t i c a l power r a t i o v e r s u s n o r t h - s o u t h p o s i t i o n p r o f i l e s were c a l c u l a t e d f o r each of the t h r e e s t a t i o n p a i r s of the Saskatchewan c h a i n (PS/WS, PS/LL, and LL/WS) u s i n g A f o r the Feb. 14 event as c a l c u l a t e d above. These p r o f i l e s a r e shown i n f i g u r e 30. For c o m p a r i s o n , the e x p e r i m e n t a l south north 0 I i i i i i i i i - 2 0 0 - 1 0 0 0 100 2 0 0 position (km) FIGURE 30. T h e o r e t i c a l power r a t i o v e r s u s p o s i t i o n c u r v e s f o r the PS/WS, PS/LL, and LL/WS s t a t i o n p a i r s . The A v a l u e used here i s t h a t c a l c u l a t e d from the Y component of the Feb. 14 event. The l e t t e r s (a-h) i n d i c a t e the e x p e r i m e n t a l p o i n t s w i t h t i m e s (UT) and fr e q u e n c y (Hz) as f o l l o w s : a-0835,0.50; b-0840,0.56; c-0850,0.59; d-0915,0.75; e-0920,0.84; f-0930,0.87; g-0935,0.89; h-0940,0.89. The p o i n t s i n d i c a t e d by x, *, and + are a l s o from 0840UT, but d i f f e r e n t from the p o i n t s l a b e l l e d b above by b e i n g from a lower f r e q u e n c y band (< 0.5Hz) (see t e x t ) . The p o s i t i o n s f o r the p o i n t s on the h o r i z o n t a l branch a re d e t e r m i n e d from the o t h e r power r a t i o ( s ) f o r t h a t t i m e . P o s i t i o n i n t h i s p l o t i s c e n t e r e d a t PS. 1 07 power r a t i o s a r e a l s o marked i n f i g u r e 30. Note t h a t the t h e o r e t i c a l p l o t shows t h a t the PS/LL power r a t i o i s c o n s t a n t w h i l e the secondary source i s n o r t h of PS, and t h a t the e x p e r i m e n t a l PS/LL r a t i o s are a l s o r e l a t i v e l y c o n s t a n t u n t i l =*091 OUT, thus c o n f i r m i n g the p o l a r i z a t i o n s p e ctrogram r e s u l t t h a t the secondary source i s n o r t h o f , or i n the v i c i n i t y o f , PS u n t i l =0910UT. That th e s e power r a t i o s l i e on or near the h o r i z o n t a l branch of the t h e o r e t i c a l c u r v e a l s o demonstrates t h a t the e x p o n e n t i a l s i g n a l decay model ( c f . e q u a t i o n 5.1) i s a p p r o p r i a t e f o r the . a n a l y s i s of t h i s e v e n t , or a t l e a s t f o r the m a j o r i t y of i t which has f r e q u e n c i e s above 0.5Hz. I f s i g n a l decay were due t o g e o m e t r i c a l s p r e a d i n g as e x p r e s s e d i n e q u a t i o n 5.2, no such h o r i z o n t a l branch would e x i s t and the PS/LL power, r a t i o s s h o u l d d e c r e a s e w i t h i n c r e a s i n g secondary source d i s t a n c e n o r t h of PS. F i g u r e 30 a l s o i n c l u d e s power r a t i o s c a l c u l a t e d from the s i g n a l band below 0.5Hz at 0840UT and i n d i c a t e d by x (PS/WS), * ( P S / L L ) , and + (LL/WS). S i n c e t h e s e s i g n a l s are below 0.5Hz, they s h o u l d not be a f f e c t e d by i o n o s p h e r i c p r o p a g a t i o n . Thus, as e x p e c t e d , they do not l i e on the t h e o r e t i c a l c u r v e s , e x c e p t f o r the LL/WS r a t i o p o i n t . In the case of t h i s LL/WS p o i n t , the secondary so u r c e p o s i t i o n happens t o be almost e x a c t l y h a l f way between LL and WS r e s u l t i n g i n a power r a t i o near 1 and a r a t i o p o s i t i o n near the t h e o r e t i c a l c u r v e . The p o s i t i o n e s t i m a t e from t h i s low 108 f r e q u e n c y p o i n t i s 27km n o r t h of PS f o r 0840UT, j u s t s l i g h t l y d i f f e r e n t than the 23km n o r t h e s t i m a t e made from the s i g n a l band above 0.5Hz. The method used f o r e s t i m a t i n g secondary source p o s i t i o n s when IPDP s i g n a l decay i s due t o g e o m e t r i c a l s p r e a d i n g i s d e s c r i b e d i n d e t a i l i n the d i s c u s s i o n of the Feb. 15 event below ( c f . s e c t i o n 5.1.2). I t s h o u l d a l s o be noted here t h a t the power and frequency v a l u e s used i n the secondary s o u r c e p o s i t i o n a n a l y s i s a re taken from the peaks i n the s p e c t r a , the f r e q u e n c i e s of which a r e g e n e r a l l y near the IPDP m i d - f r e q u e n c y . The secondary source p o s i t i o n can now be d e t e r m i n e d by matching the t h r e e s t a t i o n p a i r power r a t i o s , when each i s a v a i l a b l e , t o the t h e o r e t i c a l c u r v e s , and r e a d i n g the p o s i t i o n a s s o c i a t e d w i t h t h a t r a t i o from these c u r v e s . T h i s method assumes t h a t , on each m e r i d i a n , the secondary source can be ap p r o x i m a t e d by a p o i n t s o u r c e . T h i s i s r e a s o n a b l e s i n c e the plasmapause, the p r i m a r y source r e g i o n ( c f . s e c t i o n 4.1), i s p r o b a b l y l e s s than 0.15R\u00E2\u0080\u009E a c r o s s , w i t h the plasma d e n s i t y i n c r e a s i n g from 1 t o 100 cm\" 3 over t h i s d i s t a n c e ( J a c o b s , 1970). The main r e g i o n of IPDP wave growth, ( i . e . t h a t p a r t r e s p o n s i b l e f o r the s p e c t r a l p e a k ) , l i k e l y c o v e r s o n l y a s m a l l p o r t i o n of t h i s 0.15R E range. I f i t c o v e r e d o n l y \u00E2\u0080\u0094 of t h i s range, the r a d i a l d i m e n s i o n of t h i s p a r t of the magnetospheric g e n e r a t i o n r e g i o n would be ^lOOkm. When t h i s range i s mapped down the c o n v e r g i n g f i e l d 109 l i n e s t o E a r t h ' s s u r f a c e , the range a l o n g the m e r i d i a n becomes o n l y -6km, or 0.05\u00C2\u00B0, a t the l a t i t u d e of PS. For the Feb. 14 IPDP, secondary s o u r c e p o s i t i o n s have been d e t e r m i n e d b e f o r e 0900UT u s i n g both the PS/WS and LL/WS power r a t i o s . Reasonable agreement was o b t a i n e d between the p o s i t i o n s found from each of thes e two r a t i o s a t each p o i n t (see f i g . 3 0 ) . A f t e r 0910UT, however, o n l y the PS/LL r a t i o was a v a i l a b l e , s i n c e the s i g n a l s t r e n g t h a t WS was too weak to produce r e l i a b l e r e s u l t s . Though s p e c t r a l e s t i m a t e s were made from d a t a b l o c k s c e n t e r e d every f i v e minutes thr o u g h o u t the e v e n t , source l o c a t i o n p o i n t s do not appear a t each of these t i m e s . T h i s i s due t o i n t e r v a l s of v e r y low s i g n a l / n o i s e r a t i o , and a l s o t o p e r i o d s of mismatched, or d i s s i m i l a r s p e c t r a a t the v a r i o u s s t a t i o n s . These p e r i o d s a r e p o s s i b l y i n d i c a t i v e of temporary poor s i g n a l p r o p a g a t i o n , s l i g h t s i g n a l d i f f e r e n c e s caused by the s m a l l l o n g i t u d i n a l d i f f e r e n c e s between the s t a t i o n s ( c f . s e c . 5.4), or the L-s p r e a d of the IPDP sou r c e r e g i o n mentioned e a r l i e r . The p o s i t i o n s of the IPDP secondary s o u r c e , as deter m i n e d by the above method, f o r the Feb. 14 IPDP a r e p r e s e n t e d i n f i g u r e 31 i n terms of c o r r e c t e d geomagnetic l a t i t u d e ( G u s t a f s s o n , 1984). A l s o shown a r e the e q u i v a l e n t e q u a t o r i a l r a d i a l p o s i t i o n s , i n L, of the magnetospheric source r e g i o n . In a d d i t i o n t o thes e d a t a p o i n t s , a p o i n t a t 1 10 CM CD LO 63.0 1 \u00E2\u0080\u0094 US u s -CO \ r LflT. 62.0 1 GM L a t . / / / CD CD \" o CD - P S / / ^ / \u00E2\u0080\u00A2 -\u00E2\u0080\u0094 \ / \ \ / w ' w * w P S - cn O O - L L ^ L L - CD CD 1 ' 1 :' 1 ' 8.0 8 .5 9 .0 UT (H) 9 .5 10.0 FIGURE 31. Geomagnetic l a t i t u d e and e q u a t o r i a l r a d i a l p o s i t i o n ( L ) , r e s p e c t i v e l y f o r the secondary and magnetospheric s o u r c e s ; Feb. 14 IPDP. S t a t i o n l o c a t i o n s a r e a l s o shown. The source r e g i o n inward motion i s c l e a r l y e v i d e n t . 111 0900UT has been added d i r e c t l y over PS. The PS p o l a r i z a t i o n s p ectrograms show LH p o l a r i z a t i o n i n the c e n t e r of the IPDP fr e q u e n c y band a t t h i s t i m e , which i n d i c a t e s t h a t the secondary s o u r c e i s overhead of the s i t e . These r e s u l t s show a c l e a r inward motion t r e n d f o r the magnetospheric source r e g i o n of t h i s IPDP e v e n t . The e f f e c t of t h i s inward motion on the IPDP e v e n t ' s f r e q u e n c y e v o l u t i o n can be e s t i m a t e d u s i n g e q u a t i o n 4.5 ( c f . s e c t i o n 4.2.1). The f r e q u e n c y r i s e due t o d e c r e a s i n g L p r e d i c t e d by t h i s i s shown i n f i g u r e 32, a l o n g w i t h the a c t u a l f r e q u e n c y r i s e o b s e r v e d d u r i n g the Feb. 14 e v e n t . In t h i s f i g u r e , and i n a l l the f o l l o w i n g f r e q u e n c y s h i f t a n a l y s e s , we use freq u e n c y n o r m a l i z e d t o the i n i t i a l v a l u e of the event under s t u d y ( f / f ). I t i s e v i d e n t t h a t the inward motion e f f e c t produces ' a s i g n i f i c a n t amount, a p p r o x i m a t e l y \u00E2\u0080\u00A2\u00C2\u00A7-, of the freq u e n c y r i s e of t h i s IPDP, but c e r t a i n l y cannot be s a i d t o account f o r i t a l l . 5.1.2. Feb. 15 Event The second event s t u d i e d , t h a t of Feb. 15, was a l s o o bserved on the t h r e e southernmost s t a t i o n s of the Saskatchewan l i n e . The a n a l y s i s p r o c e d u r e f o r t h i s IPDP i s g e n e r a l l y t h e same as t h a t f o r the Feb. 14 e v e n t , i n c l u d i n g the n e c e s s i t y of u s i n g the Y component d a t a o n l y . However, some p r o c e d u r a l adjustment i s r e q u i r e d by the d i f f e r e n t 1 1 2 2.0 1.8 > / * 6.6 \ / / (geosynchronous orbit) F. ring current forming I. moving inward (early stage) II. moving inward (later stage) III. static IV. ring current decaying FIGURE 4 1 . R i n g c u r r e n t r e l a t e d magnetic f i e l d b e h a v i o u r i n the IPDP g e n e r a t i o n r e g i o n . The s l o p e of the arrows i n d i c a t e s whether the f i e l d i s d e c r e a s i n g , c o n s t a n t , or i n c r e a s i n g a t each L s h e l l f o r each c a s e . Case F i s the r i n g c u r r e n t f o r m a t i o n a l phase, and ca s e s I through IV c o r r e s p o n d t o th o s e d i s c u s s e d i n the t e x t . 1 34 a c t u a l l y r i s i n g as w e l l , t h e r e b y c o n t r i b u t i n g t o the e v e n t ' s f r e q u e n c y r i s e . T h i s c l e a r l y d emonstrates the u n r e l i a b i l i t y of u s i n g geosynchronous s a t e l l i t e magnetograms a l o n e f o r a s s e s s i n g the i n c r e a s i n g f i e l d mechanism f o r IPDP freq u e n c y s h i f t s , as has p r e v i o u s l y been done, u n l e s s the secondary s o u r c e s of the events c o n s i d e r e d a r e a t v e r y h i g h l a t i t u d e , t h a t i s , near 67\u00C2\u00B0 GM L a t . or L = 6.6 (geosynchronous o r b i t ) . F i g u r e 42 i s a p l o t of Dst v e r s u s IPDP o c c u r r e n c e f o r the p e r i o d of January 15 t o F e b r u a r y 25, 1980. Ten IPDPs o c c u r r e d d u r i n g t h i s p e r i o d , i n c l u d i n g examples of a l l of the f o u r c a s e s d e s c r i b e d above. F i g u r e 43 shows a sample of each of t h e s e cases w i t h an expanded s c a l e . Even w i t h o u t f u r t h e r a n a l y s i s i t i s o b v i o u s t h a t an i n c r e a s i n g magnetic f i e l d cannot be c o n s i d e r e d a n e c e s s a r y c o n d i t i o n f o r IPDP frequ e n c y s h i f t s t o o c c u r , because of the e x i s t e n c e of case I and I I I e v e n t s . The case IV e v e n t s make i t e q u a l l y o b v i o u s , however, t h a t t h e r e a r e s i t u a t i o n s where the i n c r e a s i n g f i e l d mechanism can c o n t r i b u t e t o the IPDP frequ e n c y r i s e . 5.2.2. Individual IPDP Event Assessments U s i n g the f o u r e v e n t s from f i g u r e 43, a more d e t a i l e d d i s c u s s i o n of i n d i v i d u a l IPDP e v e n t s , which e x e m p l i f y each of the f o u r IPDP v e r s u s Dst c a s e s d e s c r i b e d above, f o l l o w s . Feb. 14 Event. The IPDP of Feb. 14 (event no. 6, 135 O'Sfr O'O O'St?- 0 '06- 0 ' 9 G l -(UNNdO) i s a FIGURE 42. IPDP o c c u r r e n c e v e r s u s the Dst index f o r the p e r i o d January 15.to F e b r u a r y 25, 1980. IPDPs occur i n a l l phases of the r i n g c u r r e n t development and decay c y c l e . The IPDP events a r e numbered as l i s t e d i n T a b l e IV (Chapter Two). 1 36 UT (h) UT (h) FIGURE 43. Examples of each of the f o u r IPDP v e r s u s Dst cases i n l a r g e r s c a l e ; a ) c a s e I ; Feb. 14 e v e n t , b) case I I ; Feb. 15 ev e n t , c) case I I I ; J a n . 29 e v e n t , and d) case IV; Feb. 24c event. The IPDP events o c c u r r e d i n the i n t e r v a l s marked by the boxes. 1 37 f i g . 42) i s an example of a case I e v e n t , as are two o t h e r e v e n t s , J a n . 28 and Feb. 24b. In f i g u r e 44, i t can be seen t h a t the Dst index i s above z e r o f o r most of the IPDP e v e n t , b e g i n n i n g t o f a l l i n t o i t s l a r g e r i n g c u r r e n t c r e a t e d n e g a t i v e d e p r e s s i o n o n l y near the e v e n t ' s end (see Appendix C f o r a d i s c u s s i o n of the Dst z e r o l e v e l ) . Meanwhile, the f i e l d ( t o t a l f i e l d s t r e n g t h ) a t geosynchronous o r b i t i s r i s i n g t h roughout the IPDP e v e n t . T h i s c o m b i n a t i o n , a c c o r d i n g t o f i g u r e 41, i n d i c a t e s a case I event w i t h the r i n g c u r r e n t l o c a t e d j u s t e a r t h w a r d of L = 6.6 and not y e t w e l l d e v e l o p e d a t lower L s h e l l s . Ground based o b s e r v a t i o n s of t h i s event i n d i c a t e t h a t i t was g e n e r a t e d w i t h i n the L range of 4 t o 4y ( c f . s e c t i o n 5.1), which i s most l i k e l y w i t h i n the d e c r e a s i n g f i e l d regime f o r a case I event ( c f . f i g . 41). For an event a t t h i s low L t o see a r i s i n g magnetic f i e l d , the r i n g c u r r e n t would have t o be a t v e r y low L, such as L < 4y, and moving inw a r d , which would c r e a t e a l a r g e Dst d e p r e s s i o n . R e c a l l t h a t f i g u r e 40b, w i t h the r i n g c u r r e n t moving i n t o L ^ 5, showed AB t o be s t i l l n e g a t i v e a t L = 4 - 4y w h i l e a l s o i n d i c a t i n g a s i g n i f i c a n t f i e l d d e p r e s s i o n a t ground l e v e l ( D s t ) . S i n c e such a d e p r e s s i o n i s not p r e s e n t d u r i n g t h i s IPDP, i t i s e v i d e n t t h a t the i n c r e a s i n g f i e l d mechanism does not c o n t r i b u t e t o the f r e q u e n c y r i s e of t h i s e v e n t . I t i s even p o s s i b l e t h a t the background magnetic f i e l d i s 1 38 FIGURE 44. D s t p r o f i l e a n d G O E S 2 m a g n e t b g r a m ( \" t o t a l f i e l d s t r e n g t h , B T ) f o r t h e F e b . 14 I P D P , w i t h t h e ' I P D P o c c u r r e n c e t i m e i n d i c a t e d b y t h e b o x . T h i s i s a c a s e I e v e n t . 1 39 d e c r e a s i n g a l i t t l e i n the IPDP source r e g i o n , a c t u a l l y s u p r e s s i n g the f r e q u e n c y r i s e s l i g h t l y , though due t o the low L t h i s i s u n l i k e l y t o be a s i g n i f i c a n t e f f e c t f o r t h i s e v e n t. Feb. 15 Event. Case I I i s a l s o seen i n t h r e e e v e n t s ; J a n . 16, J a n . 23, and Feb. 15 (event no. 7, f i g . 42). F i g u r e 45 shows the Dst index and geosynchronous s a t e l l i t e magnetograms f o r the Feb. 15 e v e n t . Here, both the Dst and magnetogram a r e s t r o n g l y d e p r e s s e d , though the magnetogram shows the b e g i n n i n g of a f i e l d r e c o v e r y a t L = 6.6 w h i l e the Dst c o n t i n u e s t o d r o p . T h i s s i t u a t i o n i m p l i e s a case I I e v e n t , w i t h the r i n g c u r r e n t f u r t h e r i n than the case I event d i s c u s s e d above. Note t h a t the magnetogram i s c o m p l i c a t e d by the onset of a second substorm d u r i n g the IPDP as shown by the Great Whale R i v e r X-component magnetogram i n f i g u r e 46. T h i s second substorm causes the magnetic f i e l d a t L = 6.6 t o b e g i n d r o p p i n g a g a i n a f t e r o n l y a s l i g h t r e c o v e r y s i n c e the r i n g c u r r e n t i s s t r e n g t h e n e d o u t s i d e L = 6.6 i n the e a r l y phase of the substorm ( N i s h i d a , 1978). I t s h o u l d be noted t h a t the o c c u r r e n c e of the second substorm makes the p r o p e r case assignment l e s s o b v i o u s f o r t h i s e v e n t , though s i n c e the s i t u a t i o n began as a t y p i c a l case I I type b e f o r e the c o m p l i c a t i o n s o c c u r r e d , t h i s (case I I ) assignment has been made. 1 40 FIGURE 45. Dst p r o f i l e and GOES 2 magnetogram f o r the Feb. 15 IPDP, w i t h the IPDP o c c u r r e n c e time i n d i c a t e d by the box. T h i s i s a case I I event. 141 10400 9800 ' 1 1 1 '\u00E2\u0080\u0094 1 1 1 1 16 18 20 22 24 UT (h) FIGURE 46. X component magnetogram from Great Whale R i v e r , 1600 -2400 UT, F e b r u a r y 1 5 , 1980. Note the onset of a second substorm d u r i n g the IPDP e v e n t . 1 42 The Feb. 15 IPDP was g e n e r a t e d w i t h i n the L range of 4.1 t o 4.8 ( c f . sec. 5.1). In t h i s s i t u a t i o n , however, w i t h the r i n g c u r r e n t a t lower L (case I I e v e n t , c f . f i g . 40, 41) , i t i s v e r y d i f f i c u l t t o e s t i m a t e the magnetic f i e l d b e h a v i o u r i n the IPDP g e n e r a t i o n r e g i o n , and t h e r e f o r e the e f f e c t i v e n e s s of the i n c r e a s i n g f i e l d mechanism, w i t h o u t h a v i n g f u r t h e r d a t a on the r i n g c u r r e n t d i s t r i b u t i o n . I f the r i n g c u r r e n t i s a t v e r y low L, i t i s p o s s i b l e t h a t the magnetic f i e l d i s i n c r e a s i n g i n the IPDP sou r c e r e g i o n , though i t i s more p r o b a b l e ( c f . f i g . 41) t h a t the magnetic f i e l d i s d e c r e a s i n g or c o n s t a n t d u r i n g t h i s IPDP. In any c a s e , the Feb. 15 IPDP i s v e r y s h o r t , w i t h o n l y a 16 minute i n t e r v a l s t u d i e d i n d e t a i l , and any magnetic f i e l d changes i n t h i s b r i e f time are l i k e l y t o be q u i t e s m a l l , m i n i m i z i n g the e f f e c t of the i n c r e a s i n g f i e l d mechanism. J a n . 29 Event. The o n l y event observed t h a t q u a l i f i e d as a case I I I IPDP o c c u r r e d on J a n . 29 (event no. 5, f i g . 42) . Both the Dst and geosynchronous s a t e l l i t e magnetograms were s t r o n g l y d e p r e s s e d and had not y e t begun t h e i r g e n e r a l r e c o v e r y phases. S i n c e they were each r e l a t i v e l y s t a b l e (see f i g . 4 7 ) , the f i e l d i n the IPDP g e n e r a t i o n r e g i o n s h o u l d have been s i m i l a r l y s t a b l e . T h e r e f o r e the i n c r e a s i n g f i e l d mechanism c o u l d not be r e s p o n s i b l e f o r t h i s IPDP's f r e q u e n c y r i s e . Feb. 24c Event. Three e v e n t s , J a n . 27, Feb. 24a, and 143 FIGURE 47. Dst p r o f i l e and GOES 3 magnetogram f o r the J a n . 29 IPDP, w i t h the IPDP o c c u r r e n c e time i n d i c a t e d by the box. T h i s i s a case I I I e v e n t . 1 44 Feb. 24c (event no. 10, f i g . 4 2 ) , o c c u r r e d when Dst i s r i s i n g back towards z e r o . The t h i r d of the t h r e e IPDPs r e c o r d e d on Feb. 24, event Feb. 24c, i s shown i n f i g u r e 48, a l o n g w i t h i t s c o r r e s p o n d i n g Dst i n d i c e s and geosynchronous s a t e l l i t e magnetogram. The r e c o v e r i n g Dst and geosynchronous magnetic f i e l d i n d i c a t e a case IV e v e n t . The magnetic f i e l d s h o u l d then a l s o be i n c r e a s i n g i n the IPDP g e n e r a t i o n r e g i o n . T h e r e f o r e , f o r t h i s e v ent, the i n c r e a s i n g f i e l d mechanism s h o u l d c o n t r i b u t e t o the IPDP f r e q u e n c y s h i f t . Of the i n d i v i d u a l e v e n t s d i s c u s s e d above, o n l y the Feb. 24c event shows good i n d i c a t i o n t h a t the i n c r e a s i n g f i e l d mechanism c o n t r i b u t e s t o i t s f r e q u e n c y r i s e . The q u e s t i o n i s how much of t h i s e v e n t ' s f r e q u e n c y r i s e i s a t t r i b u t a b l e t o t h i s mechanism? In o r d e r t o a s c e r t a i n t h i s , we must know the L s h e l l of both the IPDP g e n e r a t i o n r e g i o n and the r i n g c u r r e n t . The secondary source p o s i t i o n c o u l d not be de t e r m i n e d f o r t h i s event ( c f . s e c t i o n 5.1), however, the p o l a r i z a t i o n spectrograms from PG (L - 3.9), f i r s t r i g h t - h a n d and then l e f t - h a n d at the v e r y end of the e v e n t , i n d i c a t e t h a t most of the event o c c u r r e d t o the n o r t h of the s t a t i o n (L 4 + ? ) . Though the p r e c i s e d i s t r i b u t i o n of the r i n g c u r r e n t d u r i n g t h i s IPDP i s unknown, models such as t h a t of Kawasaki and A k a s o f u (1971), and measurements (Berko et a l . , 1975), show t h a t t h i s p o s i t i o n i s near the p o i n t of the g r e a t e s t magnetic f i e l d d e p r e s s i o n of a t y p i c a l r i n g 145 FIGURE 48. Dst p r o f i l e and GOES 3 magnetogram f o r the Feb. 24c IPDP, w i t h the IPDP o c c u r r e n c e time i n d i c a t e d by the box. T h i s i s a case IV event. 1 46 c u r r e n t . T h i s demonstrates t h a t the f i e l d r e c o v e r y i n the IPDP g e n e r a t i o n r e g i o n has the p o t e n t i a l t o be q u i t e l a r g e . For t h i s e v e n t , though, the s m a l l Dst d e p r e s s i o n i n d i c a t e s t h a t the r i n g c u r r e n t may have been weaker and/or f u r t h e r out than normal. Note t h a t W i l l i a m s (1985) showed t h a t the amount of Dst d e p r e s s i o n i s r e l a t e d t o r i n g c u r r e n t p a r t i c l e f l u x , and Lyons and W i l l i a m s (1980) i n d i c a t e d t h a t o n l y l a r g e storms have s i g n i f i c a n t r i n g c u r r e n t f l u x e s a t lower L's. T h i s s i t u a t i o n i n d i c a t e s a c o r r e s p o n d i n g l y s m a l l e r f i e l d r e c o v e r y i n the IPDP g e n e r a t i o n r e g i o n . I f a v a l u e f o r the f i e l d d e p r e s s i o n a t L = 4 of - I O O 7 were chosen f o r t h i s e v e n t , then the f i e l d r e c o v e r y i n the IPDP g e n e r a t i o n r e g i o n c o u l d be c r u d e l y e s t i m a t e d . Note t h a t t h i s f i e l d d e p r e s s i o n v a l u e i s p r o b a b l y an o v e r e s t i m a t e f o r t h i s weak D s t ; Berko et a l . , (1975) obse r v e d v a l u e s of - 1 2 O 7 near L = 3 T and - I O O 7 near L = 4 f o r a Dst of - 8 O 7 . The magnetic f i e l d r e c o v e r y d u r i n g the IPDP can be gauged from the degree of r e c o v e r y back towards t h e i r q u i e t time l e v e l s of the f i e l d a t geosynchronous o r b i t , r o u g h l y - 6 5 7 t o - 4 5 7 , or =30%, and of the Dst i n d e x , r o u g h l y - 2 O 7 t o - 1 6 7 , or =20%. The f i e l d a t L = 4 would most l i k e l y r e c o v e r by a s i m i l a r p r o p o r t i o n d u r i n g t h i s t i m e , assuming t h a t the r i n g c u r r e n t changes o n l y i n s t r e n g t h and not i n s p a t i a l d i s t r i b u t i o n . Assuming E a r t h ' s magnetic f i e l d t o be d i p o l a r , i t s s t r e n g t h i n q u i e t t i m e s a t L = 4 s h o u l d be: 1 47 B B 0 = - 4 8 4 7 ( 5 . 4 ) . U s i n g the - I O O 7 d e p r e s s i o n d i s c u s s e d above and a 30% r e c o v e r y e s t i m a t e , the magnetic f i e l d i n the g e n e r a t i o n r e g i o n s h o u l d then r i s e from 3847 t o 4147 d u r i n g the IPDP. U s i n g e q u a t i o n 4.6 from s e c t i o n 4.2.2, the f r e q u e n c y s h i f t can then be e s t i m a t e d a s : For t h i s e v e n t , however, the a c t u a l v a l u e i s f y / f j = 2.62. Thus, i n t h i s crude e s t i m a t e , the i n c r e a s i n g f i e l d mechanism acco u n t e d f o r o n l y -7% of the t o t a l f r e q u e n c y r i s e f o r t h i s IPDP. Though the f i e l d r e c o v e r y f i g u r e s used f o r t h i s e s t i m a t e a r e o n l y v e r y rough e s t i m a t e s , i t i s v e r y u n l i k e l y t h a t they c o u l d be a l t e r e d enough t o account f o r a l a r g e p r o p o r t i o n of the f r e q u e n c y s h i f t o bserved h e r e . I n c r e a s i n g the i n i t i a l d e p r e s s i o n t o -1507 and the r e c o v e r y f a c t o r t o 50% would s t i l l o n l y y i e l d 22% of the o b s e r v e d f r e q u e n c y r i s e . Note t h a t here the f r e q u e n c y r i s e r e f e r e d t o i s a r e l a t i v e f r e q u e n c y r i s e from 1 ( i . e . i./i.) t o f , / f .. f. L 3847 . 5 = 1.12 ( 5 . 5 ) . 1 48 5.2.3. Ring Current and Inward Motion Mechanism The c a l c u l a t i o n s p r e s e n t e d above f o r the i n c r e a s i n g magnetic f i e l d e f f e c t on the Feb. 24c event assume t h a t the IPDP sou r c e r e g i o n i s a t c o n s t a n t L ( c f . s e c t i o n 4.2.2). However, the p a t t e r n of p o l a r i z a t i o n v a r i a t i o n s (see above) i n d i c a t e s t h a t t h i s i s not the t r u e s i t u a t i o n . T h e r e f o r e , i n a d d i t i o n t o the i n c r e a s i n g f i e l d mechanism, i t i s a l s o n e c e s s a r y t o c o n s i d e r the e f f e c t of the d e p r e s s e d magnetic f i e l d environment i n the IPDP sou r c e r e g i o n on the inward motion f r e q u e n c y s h i f t mechanism. The e x a m i n a t i o n of the f r e q u e n c y e f f e c t of the inward motion mechanism under these c o n d i t i o n s shows t h a t t h e r e i s another manner i n which the r i n g c u r r e n t magnetic f i e l d can a f f e c t an IPDP's f r e q u e n c y r i s e independent of t e m p o r a l changes i n the r i n g c u r r e n t . I f the r i n g c u r r e n t i s i n a s t a t e such t h a t i t s magnetic f i e l d d e p r e s s e s the background magnetic f i e l d , t h i s f i e l d d e p r e s s i o n w i l l c r e a t e a h i g h e r magnetic f i e l d s t r e n g t h r a t i o B y / B j - than normal f o r a d i p o l a r c o n f i g u r a t i o n . T h i s then s e r v e s t o i n c r e a s e the f r e q u e n c y s h i f t e f f e c t due t o the inward motion mechanism, as i s i l l u s t r a t e d below. For the purpose of d i s c u s s i o n o n l y , we can assume r e a s o n a b l e c h o i c e s f o r the amount of source inward movement, from, say, L = 4.5 t o 3.9 d u r i n g the Feb. 24c IPDP. In the absence of any r i n g c u r r e n t e f f e c t s ( f i e l d d e p r e s s i o n s ) , t h i s motion would y i e l d , from e q u a t i o n 4.5, f f / i . = 1.90. 1 49 F u r t h e r , we can assume a f i e l d d e p r e s s i o n of -8O7 a t L = 4.5 and -IOO7 a t L = 3.9 and a r e c o v e r y f a c t o r of 25% d u r i n g the IPDP. A g a i n , t h e s e a re r e a s o n a b l e c h o i c e s made f o r the sake of d i s c u s s i o n o n l y . U s i n g t h e s e v a l u e s , the inward motion mechanism, i n the dep r e s s e d f i e l d environment (but w i t h no f i e l d r e c o v e r y ) , would produce a fre q u e n c y r i s e as f o l l o w s (from e q u a t i o n 4.6): Ll. f . 1 where 5237 and 34O7 are the d i p o l a r f i e l d s t r e n g t h s (from e q u a t i o n 5.4) a t 3.9L and 4.5L, r e s p e c t i v e l y , and 1OO7 and 8O7 are the f i e l d d e p r e s s i o n s d i s c u s s e d above. T h i s i s an i n c r e a s e of 20% over the case w i t h no r i n g c u r r e n t e f f e c t s , d e m o n s t r a t i n g t h a t , even w i t h no te m p o r a l changes i n the r i n g c u r r e n t f i e l d d u r i n g an IPDP, i t i s s t i l l p o s s i b l e f o r the r i n g c u r r e n t t o have an im p o r t a n t e f f e c t on an IPDP's f r e q u e n c y r i s e , and i t t h e r e f o r e cannot be i g n o r e d . F i n a l l y , t he combined e f f e c t of the i n c r e a s i n g magnetic f i e l d mechanism, u s i n g the 25% r e c o v e r y f a c t o r , and the inward motion mechanism would y i e l d t he f o l l o w i n g f r e q u e n c y r i s e : (523-100)7 (340-80)7 1 . 5 = 2.08 (5.6a) 1 50 \" (523-75)7 \" (340-80)7 . . 5 = 2.26 ( 5 . 6 b ) . T h i s i s o n l y a 17% i n c r e a s e i n the f r e q u e n c y r i s e over the inward motion o n l y case d i s c u s s e d above ( e q u a t i o n 5.6a). W h i l e some of the numbers used here r e p r e s e n t assumptions o n l y and may bear l i t t l e r e l a t i o n t o the a c t u a l parameters c o n c e r n i n g t h i s IPDP, parameters f o r which we have i n s u f f i c i e n t i n f o r m a t i o n t o p r o p e r l y d e t e r m i n e , they cannot be r e a s o n a b l y a l t e r e d t o produce a s i g n i f i c a n t l y l a r g e r i n c r e a s i n g f i e l d mechanism c o n t r i b u t i o n . T h e r e f o r e , whether the IPDP g e n e r a t i o n r e g i o n i s ' assumed t o be s t a t i o n a r y or no t , the i n c r e a s i n g f i e l d mechanism makes o n l y a r e l a t i v e l y minor c o n t r i b u t i o n t o the f r e q u e n c y r i s e of the Feb. 24c IPDP. In s e c t i o n 5.1 i t was shown t h a t , f o r both the Feb. 14 and Feb. 15 IPDPs, the inward motion mechanism was i n s u f f i c i e n t t o account f o r the obse r v e d f r e q u e n c y r i s e of the IPDPs. Here, i t has a l s o been demonstrated t h a t the i n c r e a s i n g f i e l d mechanism makes o n l y a minor, i f any, c o n t r i b u t i o n t o the f r e q u e n c y s h i f t s of t h e s e e v e n t s ( c f . s e c t i o n 5.2.2). However, the p o s s i b l e e f f e c t s of the r i n g c u r r e n t c r e a t e d magnetic f i e l d d e p r e s s i o n on the inward motion mechanism's f r e q u e n c y s h i f t c o n t r i b u t i o n t o these 151 events must s t i l l be c o n s i d e r e d . For the Feb. 14 event t h i s r i n g c u r r e n t e f f e c t i s l i k e l y t o be s m a l l s i n c e the r i n g c u r r e n t i s p r o b a b l y not yet w e l l d e v e l o p e d i n the source r e g i o n L s h e l l s . The c u r r e n t i s r e l a t i v e l y weak i n any c a s e , as i s demonstrated by the f a c t t h a t the maximum f i e l d d e p r e s s i o n s o b s e r v e d d u r i n g the e n t i r e magnetospheric storm p e r i o d a r e o n l y - 5 O 7 a t L = 6.6 and o n l y - 3 5 t a t L = 1 ( D s t ) . C a l c u l a t i o n s s i m i l a r t o t h a t of e q u a t i o n 5.6a show t h a t a u n i f o r m f i e l d d e p r e s s i o n of \u00E2\u0080\u0094115-y would be n e c e s s a r y i n o r d e r t o enhance the inward motion produced f r e q u e n c y s h i f t s u f f i c i e n t l y t o account f o r the e n t i r e f r e q u e n c y r i s e of t h i s e v e nt. Such d e p r e s s i o n s a r e v e r y u n l i k e l y t o be p r e s e n t i n such a case I event g e n e r a t e d a t low L ( c f . s e c t i o n 5.2.1). Even w i t h a c o n s t a n t f i e l d d e p r e s s i o n of - 5 O 7 i n the g e n e r a t i o n r e g i o n , p r o b a b l y s t i l l much l a r g e r than would be r e a l i s t i c , the inward motion mechanism c o u l d account f o r o n l y ^77% of the IPDP's o v e r a l l f r e q u e n c y r i s e , as opposed t o =*66% w i t h no r i n g c u r r e n t induced magnetic f i e l d d e p r e s s i o n . I t has a l r e a d y been noted t h a t d u r i n g the Feb. 15 event the magnetic f i e l d s t r e n g t h i s u n l i k e l y t o change much a t c o n s t a n t L. I t w i l l , however, be s t r o n g l y d e p r e s s e d i n the IPDP sou r c e r e g i o n , as i n d i c a t e d by the s t r o n g Dst d e p r e s s i o n ( c f . f i g . 45) and the form of t y p i c a l r i n g c u r r e n t f i e l d p r o f i l e s ( c f . f i g . 40, a l s o Kawasaki and 152 A k a s o f u , 1971; Berko e t a l . , 1975). I t has been found t h a t a s o u r c e r e g i o n f i e l d d e p r e s s i o n of -1057 would be n e c e s s a r y t o enhance the inward motion produced f r e q u e n c y r i s e so t h a t i t would best match the observed r i s e of t h i s IPDP. A f i e l d d e p r e s s i o n of t h i s magnitude i s q u i t e p o s s i b l e f o r t h i s event (see above), though i t cannot be d i r e c t l y c o n f i r m e d by o b s e r v a t i o n . However, the d e p r e s s i o n s h o u l d be g r e a t e r than the Dst d e p r e s s i o n of = - 5 5 7 . U s i n g t h i s - 5 5 7 v a l u e as a lower l i m i t on the source r e g i o n f i e l d d e p r e s s i o n , the enhanced inward motion mechanism f r e q u e n c y s h i f t can account f o r >75% of the IPDP's o v e r a l l f r e q u e n c y r i s e , compared t o =60% w i t h no r i n g c u r r e n t f i e l d i n f l u e n c e . F i g u r e 49 compares the r e a l f r e q u e n c y r i s e t o those enhanced inward motion c r e a t e d f r e q u e n c y s h i f t s c a l c u l a t e d f o r source r e g i o n magnetic f i e l d d e p r e s s i o n s of -1057 and - 5 5 7 . 5.2.4. Discussion of Ring Current Ef f e c t s on IPDPs A much l a r g e r number of IPDPs must be s t u d i e d i n o r d e r t o g a i n a c l e a r e r p i c t u r e of the p r o p o r t i o n of e v e n t s t o which the i n c r e a s i n g f i e l d mechanism i s i m p o r t a n t . Here, based on the IPDP - r i n g c u r r e n t c l a s s i f i c a t i o n scheme d i s c u s s e d i n s e c t i o n 5.2.1, t h i s mechanism may have c o n t r i b u t e d t o the f r e q u e n c y r i s e of between t h r e e , the c l a s s IV e v e n t s , and s i x , the c l a s s I I and IV e v e n t s , of the te n IPDPs s t u d i e d , w i t h the c o n t r i b u t i o n b e i n g e i t h e r s m a l l 153 2.4 ^ 2 - 2 s 1.6 o \u00E2\u0080\u00A2c 3 1 4 75%, and p o s s i b l y up t o 100%, of the f r e q u e n c y r i s e . W i t h r e s p e c t t o these two IPDPs, however, the c o n c l u s i o n i s t h a t we must l o o k s t i l l f u r t h e r than the inward motion and i n c r e a s i n g f i e l d mechanisms i n o r d e r t o f u l l y u n d e r s t a n d the e n t i r e f r e q u e n c y s h i f t s of these e v e n t s . 1 55 5.3. AZIMUTHAL DRIFT EFFECTS ON IPDP FREQUENCY EVOLUTION The t h i r d of the t h r e e IPDP f r e q u e n c y s h i f t mechanisms c o n s i d e r e d i n t h i s t h e s i s i s the a z i m u t h a l d r i f t e f f e c t ( c f . s e c t i o n 4.2.3). From s e c t i o n 5.2, i t i s e v i d e n t t h a t c o n t r i b u t i o n s from t h i s mechanism are r e q u i r e d by a t l e a s t one, and p o s s i b l y b o t h , of the IPDPs s t u d i e d i n o r d e r t o f u l l y account f o r t h e i r f r e q u e n c y s h i f t s . T h i s s e c t i o n w i l l then examine the e f f e c t s of the a z i m u t h a l d r i f t mechanism on the Feb. 14 and Feb. 15 IPDPs. A n a l y s i s of the a z i m u t h a l d r i f t mechanism's e f f e c t r e q u i r e s a knowledge of the e v o l u t i o n of the e n e r g i e s of the p r o t o n s i n v o l v e d i n the i o n - c y c l o t r o n i n s t a b i l i t y i n the IPDP magnetospheric source r e g i o n above a ground s t a t i o n ' s m e r i d i a n . E q u a t i o n 4.3 ( s e c t i o n 4.1) shows t h a t i n o r d e r t o deter m i n e the energy (W) of the i n t e r a c t i n g p r o t o n s , both L and the p r o t o n d r i f t v e l o c i t y ( v^) must be known. Though the L v a l u e s were d e t e r m i n e d i n s e c t i o n 5.1, v^ i s unknown, and cannot be c a l c u l a t e d w i t h o u t the time and p o s i t i o n of the i n j e c t i o n boundary f o r m a t i o n b e i n g known. The time of f o r m a t i o n can be e s t i m a t e d from a u r o r a l - z o n e ground s t a t i o n magnetograms (see b e l o w ) , but the boundary shape remains unknown. Note t h a t the s t a t i s t i c a l r e l a t i o n d e s c r i b i n g i n j e c t i o n boundary shape p r e s e n t e d i n s e c t i o n 4.1 ( e q u a t i o n 4.1) c a n n o t , i n the form g i v e n , be f i t s a t i s f a c t o r a l l y i n t o the d e s c r i p t i o n of the IPDP e v e n t s c o n s i d e r e d h e r e . T h i s i s 156 e s p e c i a l l y t r u e i n the case of the Feb. 14 ev e n t , s i n c e the boundary shape produced would not rea c h t o low enough L t o form the event as observ e d ( f o r example, see f i g . 55 ( b o t t o m ) ) . C o n s e q u e n t l y , a method by which the boundary p o s i t i o n and t h e r e f o r e the p r o t o n energy can be e s t i m a t e d f o r each IPDP i s r e q u i r e d . Such a method i s d e s c r i b e d - b e l o w . S i n c e i t was shown i n s e c t i o n 5.2 t h a t a r i n g c u r r e n t magnetic f i e l d d e p r e s s i o n i n the IPDP g e n e r a t i o n r e g i o n can have an im p o r t a n t i n f l u e n c e on an IPDP's f r e q u e n c y r i s e , t h i s method a l l o w s f o r the e f f e c t of such a d e p r e s s i o n and y i e l d s an e s t i m a t e of i t s magnitude. In o r d e r t o e s t i m a t e the i n j e c t i o n boundary p o s i t i o n from IPDP d a t a , the p o s i t i o n of the source r e g i o n (L,GMLT) and the westward d r i f t a r c of the p r o t o n s between the i n j e c t i o n boundary and the plasmapause (ALT) must be known. The source r e g i o n GMLT i s e q u i v a l e n t t o the GMLT of the o b s e r v i n g ground s t a t i o n , and L i s found as i n s e c t i o n 5.1. The r e l a t i v e d r i f t a r c s ALT/ALT ^. can be found from a m o d i f i e d form of e q u a t i o n 4.8 ( c f . s e c t i o n 4.3) as f o l l o w s : ALT ALT. i f . i f 2 r L. / L ODS (5.7a) where f ^ r e p r e s e n t s the observ e d IPDP fr e q u e n c y and L i s as found i n s e c t i o n 5.1. T h i s e q u a t i o n y i e l d s t he ALT/ALT^. 157 n e c e s s a r y f o r the f r e q u e n c y r i s e p r e d i c t i o n s of the combined a z i m u t h a l d r i f t and inward motion mechanisms t o match the observed f r e q u e n c y s h i f t of an IPDP. Note t h a t e q u a t i o n 5.7a assumes a d i p o l a r magnetic f i e l d c o n f i g u r a t i o n . The p r o t o n d r i f t t i m e s ( t ^ ) r e q u i r e d by e q u a t i o n 5.7a are e s t i m a t e d from a u r o r a l - z o n e s t a t i o n magnetograms and the i n j e c t i o n e x p a n s i o n t i m e s of A r n o l d y and Moore (1983) ( c f . s e c t i o n 4.1). The substorm*s onset time i s d e t e r m i n e d from the magnetograms of the a u r o r a l - z o n e s t a t i o n which f i r s t sees a l a r g e n e g a t i v e bay i n i t s X-component, a s i g n of the s t a r t of a new substorm, p r e c e d i n g the IPDP e v e n t , and i s a l s o c o n f i r m e d by the o c c u r r e n c e of P i 2 p u l s a t i o n s . The time of the b e g i n n i n g of the bay a t t h i s f i r s t s t a t i o n g i v e s the onset of the substorm, and t h e r e f o r e the b e g i n n i n g of i n j e c t i o n boundary f o r m a t i o n ( A r n o l d y and Moore, 1983), near the s t a t i o n ' s m e r i d i a n . T h i s p r o c e d u r e then a l s o p r o v i d e s a t e n t a t i v e e s t i m a t e of the m e r i d i a n of the i n i t i a l i n j e c t i o n a t substorm o n s e t . S i n c e the boundary t a k e s 10 t o 15 minutes a f t e r substorm onset t o complete i t s e x p a n s i o n t o the west ( c f . s e c t i o n 4.1), p r o t o n d r i f t from the boundary s h o u l d begin w i t h i n 15 minutes a f t e r substorm o n s e t . The a c t u a l time of d r i f t onset f o r an IPDP's p r o t o n s depends on how f a r t o the west of the m e r i d i a n of i n i t i a l i n j e c t i o n the s e c t i o n of the i n j e c t i o n boundary forms from which t h e s e p r o t o n s d r i f t . The c o n c l u s i o n of the westward d r i f t phase of the 1 58 p r o t o n s concerned i s marked by t h e i r i n v o l v m e n t i n the i o n - c y c l o t r o n i n s t a b i l i t y a t the plasmapause g e n e r a t i n g the IPDP. The d r i f t t i m e s t o be used i n e q u a t i o n 5.7a can then be found from the d i f f e r e n c e between the e s t i m a t e d i n j e c t i o n time and the measured g e n e r a t i o n t i m e . E q u a t i o n 5.7a can a c t u a l l y be r e p l a c e d by a more v e r s a t i l e form by r e p l a c i n g L w i t h the magnetic f i e l d s t r e n g t h (B) i n the inward motion f a c t o r o n l y . Thus, e q u a t i o n 5.7a then becomes: ALT ALT. di L L~ r f - i 2 ' B \" f obs B. L i J (5.7b) where B can now be c a l c u l a t e d from L as B = (B / L 3 ) . + AB. eq' The replacement of L by B i n the inward motion f a c t o r and the i n c l u s i o n of the AB term i n c a l c u l a t i n g B now p e r m i t s the e f f e c t of magnetic f i e l d d e p r e s s i o n s , which a l t e r the p u r e l y d i p o l e f i e l d p r o f i l e g i v e n by B / L 3 by an assumed e q c o n s t a n t amount AB, on the inward motion mechanism t o be ta k e n i n t o a c c o u n t . The s i m p l i f y i n g assumption of c o n s t a n t AB i n the IPDP g e n e r a t i o n r e g i o n d u r i n g the event i s made h e r e . I t must a l s o be noted t h a t t h i s form of e q u a t i o n 5.7 assumes t h a t the f i e l d d e p r e s s i o n a f f e c t s o n l y the inward 159 motion mechanism, and does not i n f l u e n c e the a z i m u t h a l d r i f t p r o c e s s ( i . e . AB = 0 d u r i n g the d r i f t p h a s e ) . At the b e g i n n i n g of the d r i f t phase, AB can g e n e r a l l y be assumed s m a l l s i n c e the r i n g c u r r e n t i s o f t e n not w e l l d e v e l o p e d a t t h i s t i m e . However, as the r i n g c u r r e n t d e v e l o p s ( c f . s e c t i o n 5.2), the AB l a t e r i n the d r i f t phase may become l a r g e r . D e t e r m i n i n g d r i f t v e l o c i t i e s f o r t h i s type of s i t u a t i o n i s q u i t e d i f f i c u l t , e s p e c i a l l y s i n c e the i n f o r m a t i o n needed t o e s t i m a t e the AB's a f f e c t i n g the p r o t o n d r i f t i s l a c k i n g . T h e r e f o r e , the p r o c e s s has been i d e a l i z e d by s e t t i n g AB = 0 d u r i n g the d r i f t phase, then a l l o w i n g AB to be non-zero (but u n i f o r m ) d u r i n g IPDP g e n e r a t i o n a t the plasmapause. I f non-zero AB i s p r e s e n t d u r i n g the d r i f t phase, a reduced magnetic f i e l d s t r e n g t h (B) w i l l i n c r e a s e d r i f t v e l o c i t e s somewhat ( c f . e q u a t i o n 4.2a), though t h i s c o u l d be p a r t i a l l y o f f s e t by an i n c r e a s e d f i e l d l i n e r a d i u s of c u r v a t u r e near the e q u a t o r ( c f . e q u a t i o n 4.2b). A v e r y l a r g e AB would have t o e x i s t over most of the westward d r i f t range i n o r d e r t o s i g n i f i c a n t l y a f f e c t the e n e r g i e s of the p r o t o n s i n v o l v e d i n IPDP g e n e r a t i o n , i n which case the IPDP p r o t o n e n e r g i e s s h o u l d be somewhat lo w e r . E q u a t i o n 5.7b now produces the n e c e s s a r y ALT/ALT^. f o r the combined fre q u e n c y s h i f t s from a z i m u t h a l d r i f t and A B - a d j u s t e d inward motion mechanisms t o match the o b s e r v e d f r e q u e n c y r i s e . However, s i n c e AB i s not known w i t h any 1 60 p r e c i s i o n , a number of c a l c u l a t i o n s must be c a r r i e d out f o r a range of AB v a l u e s , g i v i n g many p o s s i b l e ALT/ALTV s e t s f o r a s i n g l e IPDP. The next s t e p r e q u i r e d i s the s e l e c t i o n of the energy of the i n i t i a l p r o t o n s i n v o l v e d i n the IPDP g e n e r a t i o n (VI.), a l l o w i n g the c a l c u l a t i o n of ALT. (ALT. t,.W.L.). Here 3 i i di i i a g a i n , the a c t u a l i n i t i a l energy i s unknown, so we must repeat the c a l c u l a t i o n over a range of v a l u e s . Once ALT^. i s known, a l l the ALTs can be de t e r m i n e d from the r a t i o s found from e q u a t i o n 5.7b above. These ALTs p l u s the source r e g i o n GMLTs then y i e l d the i n j e c t i o n boundary l o c a l t i m e s at the L v a l u e s of the IPDP sou r c e r e g i o n . The net r e s u l t of a l l t h e s e c a l c u l a t i o n s i s t h a t , f o r each p a i r of (W;. ,AB) v a l u e s s e l e c t e d , we have a s e r i e s . of (L,LT) p o i n t s which d e f i n e a segment of an i n j e c t i o n boundary which g i v e s , f o r t h a t and AB, an e x a c t match of the combined a z i m u t h a l d r i f t and A B - a d j u s t e d inward motion p r e d i c t e d f r e q u e n c i e s , h e n c e f o r t h termed the \"combined mechanisms\" p r e d i c t e d f r e q u e n c i e s , t o the observed IPDP f r e q u e n c i e s . I t must now be d e t e r m i n e d which of the s e (VI. ,AB) p a i r s and c o r r e s p o n d i n g i n j e c t i o n boundary segments best r e p r e s e n t s the a c t u a l magnetospheric s i t u a t i o n i n v o l v i n g the IPDP event i n o r d e r t o e s t i m a t e the prop e r i n j e c t i o n boundary p o s i t i o n . The boundary segments c a l c u l a t e d by the above method 161 co v e r l i m i t e d spans i n L and LT compared t o an e n t i r e i n j e c t i o n boundary. C o n s i d e r : i f t h e s e p r o s p e c t i v e b o u n d a r i e s a r e extended t o co v e r the f u l l LT range t y p i c a l of an i n j e c t i o n boundary, do they resemble the d e s c r i p t i o n s p r o v i d e d by Mauk and Meng (1983) ( c f . s e c . 4.1)? T h i s can be t e s t e d by f i t t i n g the boundary p o i n t s t o the e x p r e s s i o n f o r a s i n g l e , duskward s p i r a l i n j e c t i o n boundary (Mauk and Meng, 1983): LT = \u00C2\u00A3l + K 2 (5.8) L where K , and K2 a r e c o n s t a n t s t o be d e t e r m i n e d by the c u r v e - f i t t i n g p r o c e s s . Note t h a t t h i s r e l a t i o n i s e s s e n t i a l l y the same as t h a t of e q u a t i o n 4.1, except t h a t the c o n s t a n t s remain t o be d e t e r m i n e d . I t i s now p o s s i b l e t o p l o t a f u l l i n j e c t i o n boundary f o r each (VI. ,AB) p a i r f o r which boundary p o i n t s were d e t e r m i n e d . The new c u r v e - f i t i n j e c t i o n b o u n d a r i e s a l l o w us to r e c a l c u l a t e the p r e d i c t e d f r e q u e n c y r i s e u s i n g t h e s e new boundary shapes from each (VI. ,AB) p a i r , and t o p r e s e n t some c r i t e r i a f o r s e l e c t i n g the (W^ . ,AB) p a i r which b e s t c h a r a c t e r i z e s each IPDP e v e n t . These c r i t e r i a , a l o n g w i t h a few o t h e r s , a r e : Boundary shape. Does the i n j e c t i o n boundary, i n terms of 162 the v a l u e s of K , and ic2 i n e q u a t i o n 5.8, approximate the d e s c r i p t i o n s d e r i v e d from o b s e r v a t i o n , and does i t s eastward end c o r r e s p o n d t o the i n j e c t i o n onset GMLT observed by a u r o r a l - z o n e s t a t i o n s ? Frequency match. How w e l l do the combined mechanisms p r e d i c t i o n s , u s i n g the new c u r v e - f i t boundary shape, match the o b s e r v e d f r e q u e n c y r i s e ? Boundary match. How w e l l does the new i n j e c t i o n boundary f i t the o r i g i n a l boundary p o i n t s , t h a t i s , what i s the e r r o r between the o r i g i n a l p o i n t s and the new boundary as c a l c u l a t e d i n the c u r v e - f i t t i n g p r o c e s s ? Note t h a t t h i s i s s e p a r a t e from the boundary shape c r i t e r i o n s i n c e a good f i t of the d a t a t o e q u a t i o n 5.8 does not n e c e s s a r i l y imply t h a t the shape of the boundary produced i s r e a s o n a b l e . AB range. Does the AB f o r t h i s boundary f a l l w i t h i n a r e a s o n a b l e range? T h i s range i s d e t e r m i n e d by c o n s i d e r i n g t y p i c a l r i n g c u r r e n t AB p r o f i l e s a l o n g w i t h the d e p r e s s i o n s of the Dst index and the geosynchronous s a t e l l i t e magnetograms a s s o c i a t e d w i t h an IPDP, and can be d i f f e r e n t f o r each IPDP. W range. Do the p r o t o n e n e r g i e s f o r the whole event l i e w i t h i n the broad range of =10 t o =300 keV w i t h i n which IPDPs a r e thought t o o c c u r ? These s e l e c t i o n c r i t e r i a can now be a p p l i e d t o the 163 r e s u l t s of the i n j e c t i o n boundary c a l c u l a t i o n s f o r each (VI.,&B) p a i r i n o r d e r t o choose the b e s t p a i r . The f i r s t s e r i e s of c a l c u l a t i o n s performed f o r t h i s purpose used a l a r g e ,AB g r i d s p a c i n g , w i t h v a r y i n g by 20-30 keV and AB by 10-20 7, i n o r d e r t o i s o l a t e the range of i n t e r e s t f o r each of the pa r a m e t e r s . Then p r o g r e s s i v e l y f i n e r g r i d s , down t o a g r i d s p a c i n g of 2keV by 27, are used u n t i l the best p a i r i s o b t a i n e d . The s e l e c t i o n c r i t e r i a d i s c u s s e d above a r e used t o determine the b e s t (VI. ,AB) p a i r as f o l l o w s . F i r s t , they a r e employed i n a g e n e r a l manner t o det e r m i n e where t o make c a l c u l a t i o n s over f i n e r g r i d s , then i n a more d e t a i l e d manner on the r e s u l t s of the c a l c u l a t i o n s from the f i n e s t g r i d s p a c i n g i n o r d e r t o s e l e c t the b e s t (W;. ,AB) p a i r . T h i s d e t a i l e d e v a l u a t i o n of the s e l e c t i o n c r i t e r i a i s performed i n a q u a n t i t a t i v e manner u s i n g the boundary shape, f r e q u e n c y match, and boundary match c r i t e r i a o n l y . For the AB and W range c r i t e r i a , the AB and W ranges f o r each IPDP a r e s i m p l y judged e i t h e r a c c e p t a b l e or u n a c c e p t a b l e , w i t h the u n a c c e p t a b l e p a i r s b e i n g r e j e c t e d . For the q u a n t i t a t i v e e v a l u t i o n , each of the t h r e e c r i t e r i a f o r a p a r t i c u l a r (vr ,AB) p a i r a r e r a t e d r e l a t i v e t o t h a t c r i t e r i a from the o t h e r p a i r c a l c u l a t i o n s . For example, the (W^ . ,AB) p a i r w i t h the b e s t f r e q u e n c y match would be a s s i g n e d t e n r a t i n g p o i n t s , w h i l e t h a t w i t h the worst match, c o n s i d e r i n g o n l y the p a i r s f o r which d e t a i l e d e v a l u a t i o n s a r e b e i n g done, 1 64 would be g i v e n z e r o p o i n t s . The o t h e r (W. ,AB) p a i r s c o n s i d e r e d would be a s s i g n e d i n t e r m e d i a t e v a l u e s w i t h i n t h i s range depending on the q u a l i t y of t h e i r f r e q u e n c y matches. The same scheme i s a p p l i e d t o the o t h e r two c r i t e r i a . F i n a l l y , the r a t i n g p o i n t s from each c r i t e r i o n f o r each (W;. ,AB) p a i r a r e summed, and t h a t p a i r w i t h the l a r g e s t sum i s deemed t o be the p a i r b e s t d e s c r i b i n g the IPDP e v e n t ' s s i t u a t i o n i n t h a t i t has the b e s t c o m b i n a t i o n of i n j e c t i o n boundary and f r e q u e n c y match. Note t h a t the boundary shape and f r e q u e n c y match c r i t e r i a a r e g i v e n double weight i n the summing p r o c e s s . F i g u r e 50 c o n t a i n s a f l o w c h a r t which summarizes the e n t i r e p r o c e s s , as d e s c r i b e d above, f o r d e t e r m i n i n g the e f f e c t s the a z i m u t h a l d r i f t and A B - a d j u s t e d inward motion mechanisms have on an IPDP's f r e q u e n c y s h i f t . T h i s p r o c e s s r e p r e s e n t s an i n t u i t i v e , p r a c t i c a l approach t o the problem of u n d e r s t a n d i n g IPDP f r e q u e n c y s h i f t s , and, though s t i l l q u i t e s i m p l e , i s the b e s t a v a i l a b l e and does g i v e r e a s o n a b l e f r e q u e n c y s h i f t e s t i m a t e s . 5.3.1. Feb. 14 Event The above boundary s e l e c t i o n p r o c e s s can now be a p p l i e d t o the two e v e n t s s t u d i e d i n d e t a i l i n s e c t i o n s 5.1 and 5.2. F i r s t , we w i l l l o o k a t the Feb. 14 IPDP. B e f o r e the boundary c a l c u l a t i o n can be made, however, 165 f r e q u e n c i e s (observed) s o u r c e L.LT (sec. 5.1) d r i f t time i n i t i a l U i . e s t i m a t e s ? i n j e c t i o n boundary ( \u00E2\u0080\u00A2 d e l t a - B p a i r s p o i n t s e s t i m a t e new d r i f t t imes T I I no A. f i t p o i n t s t o boundary e q u a t i o n i i n j e c t i o n boundary e s t i m a t e I c a l c u l a t e delta-ni.M.+delta-B) a n d d e l T a - f l f i . D . ) i i a p p l y s e l e c t i o n c r i t e r i a a r e o r i g i n a l b e s t i n j e c t i o n d r i f t time boundary e s t i m a t e s O K ? yes -~A f i n a l i n j e c t i o n boundary e s t i m a t e - a z i m u t h a l d r i f t f r e q u e n c y e f f e c t - delta-B a d j u s t e d inward motion e f f e c t FIGURE 50. Flow c h a r t f o r the e s t i m a t i o n of i n j e c t i o n boundary p o s i t i o n and the a z i m u t h a l d r i f t and A B - a d j u s t e d inward motion f r e q u e n c y s h i f t e f f e c t s (see t e x t f o r d e t a i l e d d e s c r i p t i o n ) . 166 the d r i f t t i m e s ( t ^ ) must be e s t i m a t e d . For t h i s e v e n t , the Great Whale R i v e r (GWR) magnetogram showed the substorm onset e a r l i e r than s t a t i o n s t o the e a s t or west, and t h e r e f o r e i n d i c a t e s t h a t t h i s substorm, and thus the plasma i n j e c t i o n , s t a r t near 0807UT (see f i g . 5 1 ) , a t 27.35 GMLT. The onset time i s a l s o c o n f i r m e d by P i 2 o b s e r v a t i o n s . For t h i s IPDP t h e n , the p r o t o n d r i f t must s t a r t w e l l a f t e r m i d n i g h t , s i n c e the IPDP o c c u r s a f t e r m i d n i g h t . The d r i f t i s e s t i m a t e d t o be g i n a p p r o x i m a t e l y 1\u00C2\u00B11 minutes a f t e r t he i n j e c t i o n s t a r t s . T h i s e s t i m a t e i s based on an i n j e c t i o n boundary f o r m a t i o n time of 12 m i n u t e s , s t a r t i n g from 27.35 GMLT and then expanding t o the west t h r o u g h 10 hours of GMLT, w i t h the IPDP d r i f t onset time e s t i m a t e b e i n g made by i n t e r p o l a t i o n w i t h i n t h i s i n t e r v a l u s i n g a f o r m a t i o n r a t e which i s t e n times f a s t e r a t the e a s t e r n end than a t the western end ( c f . s e c t i o n 4.1). The u n c e r t a i n t y i n d r i f t s t a r t t i m e s i s q u i t e s m a l l when compared t o the a c t u a l d r i f t t imes of 27 t o 92 mi n u t e s . The AB f o r t h i s event i s l i k e l y t o be f a i r l y s m a l l ( c f . s e c t i o n 5.2), and t h e r e f o r e boundary c a l c u l a t i o n s w i l l be c a r r i e d out over the range 0 < AB < - 6 O 7 . The W;. range used f o r the s e c a l c u l a t i o n s i s 10 < W.' < 140 keV. With t h e s e p a r a m e t e r s , the b e s t - f i t i n j e c t i o n boundary f o r the Feb. 14 IPDP was t h a t c a l c u l a t e d from the s t a r t i n g p o i n t of W. = 14keV and AB = -14-y. T h i s (W^ . ,AB) p a i r 1 67 10100 9 2 0 0 ' 1 1 1 1 1 1 0 2 4 6 8 10 12 UT (h) FIGURE 51. X-component magnetogram from Great Whale R i v e r , 0000-1200UT, Feb. 14, 1980. Note the l a r g e n e g a t i v e bay b e g i n n i n g a t 0807UT, s h o r t l y b e f o r e the IPDP event s t a r t s . produced the best c o m b i n a t i o n of boundary shape and fre q u e n c y match compared t o the r e s u l t s f o r these c r i t e r i o n f o r the o t h e r (VI. ,AB) p a i r c a l c u l a t i o n s . The W and AB range c r i t e r i a a r e a l s o s a t i s f i e d , w i t h the W v a l u e s b e i n g w i t h i n the range n o r m a l l y a s s o c i a t e d w i t h IPDPs and the AB v a l u e b e i n g q u i t e a c c e p t a b l e when compared t o the Dst index and geosynchronous s a t e l l i t e magnetogram f o r Feb. 14 ( c f . s e c t i o n 5.2). In a d d i t i o n , the boundary match (LT e r r o r between d a t a p o i n t s and c u r v e : 0.l63h) i s a l s o a c c e p t a b l e , f a l l i n g a p p r o x i m a t e l y i n the mi d d l e of the range of boundary c u r v e - f i t e r r o r s of 0.161 t o 0.166 h produced by b o u n d a r i e s f o r which r a t i n g s sums were c a l c u l a t e d . T h i s i n j e c t i o n boundary and the c a l c u l a t e d plasmapause p o i n t s a s s o c i a t e d w i t h the IPDP are shown i n f i g u r e 52. F i g u r e 53 i l l u s t r a t e s the change i n p r o t o n energy d u r i n g the IPDP. T h i s energy p r o f i l e i s found u s i n g the new boundary, as shown i n f i g u r e 52, thus W^. = 16keV, not 14keV, due t o the d i f f e r e n c e between the new c u r v e - f i t boundary and the o r i g i n a l boundary p o i n t s . Note t h a t VI. , and not t^., i s a l t e r e d t o accomodate the new c u r v e - f i t boundary shape s i n c e t^. as e s t i m a t e d from the boundary f o r m a t i o n time cannot change. The obser v e d f r e q u e n c y r i s e and t h a t p r e d i c t e d by the p r o t o n energy change (or a z i m u t h a l d r i f t ) e f f e c t , b oth n o r m a l i z e d , a r e a l s o shown i n f i g u r e 53. The f r e q u e n c y s h i f t s due t o the hot p r o t o n energy changes are c a l c u l a t e d 169 H 1 1 1 1 1 1-Earth i 1 H - 8 . - 6 . - 4 . - 2 . 2.--plasmapause segment injection boundary \u00E2\u0080\u00A26.-L FIGURE 52. Model p l o t f o r Feb. 14 e v e n t , showing the i n j e c t i o n boundary s e l e c t e d and the plasmapause segment d e f i n e d by the IPDP g e n e r a t i o n r e g i o n (L,GMLT) c o o r d i n a t e s . The r e g i o n t h r o u g h which the p r o t o n s d r i f t e d f o r t h i s IPDP (as observed on the Saskatchewan l i n e ) i s e n c l o s e d by the dashed l i n e s . The sun i s towards the t o p of the page, and the d i s t a n c e l a b e l s on the axes a r e i n L ( E a r t h r a d i i ) . Note t h a t the source r e g i o n GMLTs of =0100-0200 a r e q u i t e l a t e compared t o t y p i c a l IPDPs. 1 70 UT -(H) FIGURE 53. Top: p r o t o n energy p r o f i l e p l u s the obse r v e d ( s o l i d l i n e ) and a z i m u t h a l d r i f t mechanism p r e d i c t e d (dashed l i n e ) f r e q u e n c y p r o f i l e s ( n o r m a l i z e d ) f o r the Feb. 14 IPDP. Bottom: magnetic f i e l d s t r e n g t h p r o f i l e p l u s the o b s e r v e d ( s o l i d l i n e ) and A B - a d j u s t e d inward motion mechanism p r e d i c t e d (dashed l i n e ) f requency p r o f i l e s f o r the Feb. \" 14 IPDP. 171 from e q u a t i o n 4.7. I t s h o u l d be p o i n t e d out here t h a t the f r e q u e n c y e f f e c t s of c h a n g i n g p r o t o n e n e r g i e s and inward s o u r c e motion cannot r e a l l y be i s o l a t e d i n t h i s manner, s i n c e inward motion o c c u r s s i m u l t a n e o u s l y w i t h the p r o t o n energy changes. The c a l c u l a t i o n u s i n g e q u a t i o n 4.7 f o r the energy change f r e q u e n c y s h i f t i s then an h y p o t h e t i c a l case o n l y i n which, f o r the purpose of d i s c u s s i o n , inward motion i s assumed t o be z e r o . In t h i s d i s c u s s i o n we have a l s o used the terms \" a z i m u t h a l d r i f t e f f e c t \" and \"hot p r o t o n energy change e f f e c t \" i n t e r c h a n g a b l y . Though the a z i m u t h a l d r i f t e f f e c t c r e a t e s hot p r o t o n energy changes ( c f . s e c t i o n 4.2), i t i s not the o n l y e f f e c t c a u s i n g t h e s e changes s i n c e IPDP g e n e r a t i o n , as seen from a ground s t a t i o n , i n v o l v e s p r o t o n s d r i f t i n g on d i f f e r e n t L - s h e l l s a t d i f f e r e n t t i m e s . The p r o t o n streams on t h e s e d i f f e r e n t L - s h e l l s have d i f f e r e n t v e l o c i t i e s and d i f f e r e n t d r i f t s t a r t and end t i m e s , and can t h e r e f o r e have d i f f e r e n t p r o t o n e n e r g i e s a t any one t i m e , d e m o n s t r a t i n g t h a t c r o s s i n g L - s h e l l s i n t o t h e s e d i f f e r e n t streams can a l s o cause p r o t o n energy changes. Thus, h e n c e f o r t h we w i l l use terms such as \"hot p r o t o n energy change e f f e c t \" i n s t e a d of \" a z i m u t h a l d r i f t e f f e c t \" when d i s c u s s i n g energy change f r e q u e n c y s h i f t s . D u r i n g the Feb. 14 IPDP, as shown i n f i g u r e 53, the p r o t o n energy drops r a p i d l y and the hot p r o t o n energy change 1 72 e f f e c t f r e q u e n c y s h i f t i n c r e a s e s s i g n i f i c a n t l y a t the b e g i n n i n g of the e v e n t , and then they have l i t t l e net change over the f i n a l -| of the IPDP. T h i s r e d u c t i o n , and temporary r e v e r s a l , of the r a t e of change of t h e s e p r o f i l e s c o u l d be a t t r i b u t e d t o r a p i d inward motion of the plasmapause d u r i n g the c e n t r a l p a r t of the IPDP, r e q u i r i n g the p r o t o n s t o be more e n e r g e t i c i n o r d e r t o r e a c h i t w i t h i n the d r i f t time a v a i l a b l e . F i g u r e 53 a l s o shows the magnetic f i e l d p r o f i l e a l o n g w i t h i t s p r e d i c t e d f r e q u e n c y r i s e and the obse r v e d r i s e f o r the Feb. 14 IPDP. The f r e q u e n c y r i s e due t o the i n c r e a s i n g magnetic f i e l d i s d e t e r m i n e d by e q u a t i o n 4.6. The f r e q u e n c y r i s e p r e d i c t e d here i s v e r y s i m i l a r t o t h a t shown i n f i g u r e 32 f o r inward motion w i t h o u t a AB a d j u s t m e n t , though the i n c r e a s e i s s l i g h t l y l a r g e r i n t h i s c a s e ; 68% of the observed end f r e q u e n c y , up from 66%. The combined e f f e c t s of the i n c r e a s i n g B and g e n e r a l l y d e c r e a s i n g W can be c a l c u l a t e d from a r e a r r a n g e d v e r s i o n of e q u a t i o n 5.7b: f_ f . r ALT. L_ L. o . 5 B_ B. . 5 ALT ( 5 . 9 ) . T h i s combined frequency r i s e i s compared t o the obse r v e d frequency i n f i g u r e 54. The r e l a t i v e l y good match between the two i s , of c o u r s e , a r e s u l t of the (W ,AB) p a i r 1 73 2.0 1.8 l k. 1.0 8.0 predicted frequency observed frequency 8.4 8.8 9.2 UT (h) 9.6 10.0 injection boundary Earth -6 i FIGURE 55. Top: P r e d i c t e d f r e q u e n c y r i s e f o r W/ = lOkeV and AB -IO7 f o r the Feb. 14 ev e n t . Bottom: I n j e c t i o n boundary f o r Wz- = 22keV and AB = -3O7. These parameters produce r e s u l t s much worse than t h o s e f o r the b e s t c a s e . 176 f u r t h e r enhanced somewhat by a d e p r e s s e d (-147) magnetic f i e l d i n the IPDP g e n e r a t i o n r e g i o n . T h i s cannot account f o r the e n t i r e f r e q u e n c y r i s e , though, and a secondary r o l e i s p l a y e d by hot p r o t o n energy changes. However, f o r the f i r s t \u00E2\u0080\u00A2j of the e v e n t , t h i s hot p r o t o n energy change e f f e c t i s a c t u a l l y the dominant f a c t o r i n p r o d u c i n g the f r e q u e n c y s h i f t , w i t h the inward motion mechanism o c c u p y i n g a secondary r o l e . R e c a l l t h a t i t was shown i n s e c t i o n 5.2 t h a t the i n c r e a s i n g f i e l d mechanism i s not i m p o r t a n t h e r e . 5.3.2. Feb. 15 Event As w i t h the Feb. 14 e v e n t , b e f o r e the i n j e c t i o n boundary p o s i t i o n i s c a l c u l a t e d the p r o t o n d r i f t t i m e s must be e s t i m a t e d . For t h i s e v e n t , the substorm and i n j e c t i o n onset o c c u r r e d e a s t of the a u r o r a l - z o n e s t a t i o n s a v a i l a b l e t o us. However, the substorm e f f e c t s were obse r v e d t o b e g i n i n the a f t e r n o o n s e c t o r a t GWR (GMLT = 1533) a t 2036UT ( f i g . 56). From the onset of P i 2 p u l s a t i o n s , though, the a c t u a l substorm onset o c c u r r e d near 2028UT. The westward d r i f t of the p r o t o n s i n v o l v e d i n the IPDP would then have s t a r t e d sometime a f t e r t h i s t i m e . In a d d i t i o n , the d r i f t of the IPDP p r o t o n s s t a r t e d from a boundary segment a t lower L - s h e l l s , and t h e r e f o r e l a t e r GMLTs, than GWR, l i k e l y from the dusk s e c t o r . Based on a boundary f o r m a t i o n time of a p p r o x i m a t e l y 8 minutes t o the m e r i d i a n of GWR and u s i n g a s i m i l a r 1 77 10400 9800 L ' ' \u00C2\u00BB L _ 1 I 12 14 16 18 20 22 24 UT (h) FIGURE 56. X-component magnetogram from Great Whale R i v e r , 1200-2400UT, Feb. 15, 1980. Note the l a r g e n e g a t i v e bay b e g i n n i n g a t 2036UT, when the s t a t i o n i s a t 1533GMLT. 178 i n t e r p o l a t i o n p r o c e s s as f o r the Feb. 14 ev e n t , the d r i f t s t a r t time i s e s t i m a t e d a t =3\u00C2\u00B11 minutes a f t e r substorm o n s e t . Note t h a t i n the absence of an e s t i m a t e of the substorm onset m e r i d i a n , a t y p i c a l onset GMLT of 0130 ( c f . s e c t i o n 4.1) has been used. The one minute u n c e r t a i n t y i s s t i l l q u i t e s m a l l when compared t o the d r i f t t i m e s f o r t h i s event of 78 t o 94 m i n u t e s , and t e s t s have a l s o shown t h a t the c a l c u l a t e d boundary shapes a r e not s e n s i t i v e t o s m a l l (<5 min) changes i n the d r i f t time e s t i m a t e s . S i n c e the Dst index and the geosynchronous s a t e l l i t e r e c o r d s i n d i c a t e a much deeper AB f o r t h i s event than f o r the Feb. 14 IPDP, a range of 0 ^ AB < -I6O7 i s used i n the boundary e s t i m a t i o n c a l c u l a t i o n s . The VI. range c o v e r e d i s 10 < VI. < 300 keV, v i r t u a l l y the e n t i r e range of e n e r g i e s p o s s i b l y r e l a t e d t o IPDPs. From a l l the c a l c u l a t i o n s over t h e s e parameter ranges, the optimum c u r v e - f i t boundary emerges as t h a t c a l c u l a t e d u s i n g W;. = 30KeV and AB = -13O7. T h i s i n j e c t i o n boundary produced the best r a t i n g s sum; 38 out of a maximum of 50. The boundary c a l c u l a t e d from t h i s p a i r had each of the boundary shape, f r e q u e n c y match, and boundary match c r i t e r i a r a t e d as among the b e s t , r e s u l t i n g i n the h i g h e s t r a t i n g s sum. The AB and W v a l u e s a s s o c i a t e d w i t h the b e s t case boundary a r e w i t h i n the a c c e p t a b l e ranges f o r t h i s IPDP. The model p l o t of the s e l e c t e d boundary i s shown i n f i g u r e 57. 1 79 5.T injection boundary -5.-L FIGURE 5 7 . Model p l o t f o r Feb. 15 e v e n t , showing the i n j e c t i o n boundary s e l e c t e d and the plasmapause segment d e f i n e d by the IPDP g e n e r a t i o n r e g i o n (L,GMLT) c o o r d i n a t e s . The r e g i o n t h r ough which the p r o t o n s d r i f t e d f o r t h i s IPDP (as obser v e d on the Saskatchewan l i n e ) i s e n c l o s e d by the dashed l i n e s . The sun i s towards the t o p of the page, and the d i s t a n c e l a b e l s on the axes a r e i n L ( E a r t h r a d i i ) . Note t h a t the source r e g i o n GMLTs (near 1400) a r e q u i t e e a r l y compared t o t y p i c a l IPDPs. 180 Note t h a t the IPDP p r o t o n s b e g i n t h e i r d r i f t from a boundary segment i n the l a t t e r p a r t of the dusk s e c t o r , c o n f i r m i n g the d r i f t s t a r t time e s t i m a t e s d i s c u s s e d above. The p r o t o n energy e v o l u t i o n f o r the Feb. 15 IPDP i s shown i n f i g u r e 58. For t h i s IPDP, the energy i s i n c r e a s i n g w i t h t i m e , r a t h e r than d e c r e a s i n g as would have p r e v i o u s l y been e x p e c t e d ( c f . s e c t i o n 4.2.3). As w i t h the Feb. 14 e v e n t , a r a p i d inward movement of the plasmapause d u r i n g the IPDP may be r e s p o n s i b l e f o r t h i s u nusual b e h a v i o u r . C o r r e s p o n d i n g l y , the f r e q u e n c y s h i f t due t o the hot p r o t o n energy change e f f e c t , a l s o p l o t t e d i n f i g u r e 58, must show a s l i g h t decreasing f r e q u e n c y t r e n d . The magnetic f i e l d s t r e n g t h p r o f i l e and i t s c o r r e s p o n d i n g f r e q u e n c y s h i f t a r e a l s o i l l u s t r a t e d i n f i g u r e 58, a l o n g w i t h the o b s e r v e d f r e q u e n c y r i s e f o r c o m p a r i s o n . In t h i s c a s e , the AB adjustment t o the inward motion mechanism makes t h i s f r e q u e n c y r i s e much l a r g e r than t h a t f o r the u n a l t e r e d , or AB = 0, inward motion mechanism ( c f . f i g . 3 9 ) ; here i t a c t u a l l y reaches 116% of the t o t a l o b s e r v e d IPDP f r e q u e n c y s h i f t , as opposed t o o n l y 60% w i t h o u t the AB a d j u s t m e n t . The combined f r e q u e n c y e f f e c t s of p r o t o n energy and magnetic f i e l d v a r i a t i o n s i n the IPDP source r e g i o n a r e p l o t t e d i n f i g u r e 59, showing t h a t the n e g a t i v e a z i m u t h a l d r i f t e f f e c t b r i n g s the A B - a d j u s t e d inward motion f r e q u e n c y r i s e down i n t o l i n e w i t h the eg 21.6 21.8 22.0 22.2 22.4 UT (H) FIGURE 58. Top: p r o t o n energy p r o f i l e p l u s the obse r v e d ( s o l i d l i n e ) and a z i m u t h a l d r i f t mechanism p r e d i c t e d (dashed l i n e ) f r e q u e n c y p r o f i l e s ( n o r m a l i z e d ) f o r the Feb. 15 IPDP. Bottom: magnetic f i e l d s t r e n g t h p r o f i l e p l u s the o b s e r v e d ( s o l i d l i n e ) and A B - a d j u s t e d inward motion mechanism p r e d i c t e d (dashed l i n e ) f r e q u e n c y p r o f i l e s f o r the Feb. 15 IPDP. 182 o b s e r v e d f r e q u e n c y s h i f t of t h i s e v e n t . I t can be c o n c l u d e d , t h e n , t h a t the Feb. 15 IPDP's fr e q u e n c y r i s e i s produced s o l e l y by the inward motion mechanism o p e r a t i n g i n a de p r e s s e d (-13O7) magnetic f i e l d e n vironment. The hot p r o t o n energy change e f f e c t does not c o n t r i b u t e a t a l l ; i n s t e a d , i t a c t u a l l y d e p r e s s e s the fre q u e n c y r i s e somewhat. A g a i n , r e c a l l t h a t the i n c r e a s i n g f i e l d mechanism i s l i k e l y a v e r y minor p l a y e r i n t h i s event ( c f . s e c t i o n 5.2). In summary, t h i s s e c t i o n has p r e s e n t e d a method f o r e s t i m a t i n g the i n j e c t i o n boundary p o s i t i o n u s i n g ground based IPDP d a t a , and then used i t t o a s s e s s the fr e q u e n c y e f f e c t s of p r o t o n energy changes f o r two IPDPs. The r e s u l t s show t h a t p r o t o n energy changes have a c o m p a r a t i v e l y minor e f f e c t on the fr e q u e n c y r i s e s of th e s e e v e n t s . 5 . 4 . LONGITUDINAL IPDP DEVELOPMENT In the p r e v i o u s s e c t i o n s of t h i s c h a p t e r , IPDPs have been s t u d i e d u s i n g a n o r t h - s o u t h l i n e of s t a t i o n s . In t h i s s e c t i o n , d a t a from the s o u t h e r n e a s t - w e s t l i n e ( c f . s e c t i o n 2.1, f i g . 3) i s a n a l y s e d i n o r d e r t o g a i n f u r t h e r i n s i g h t i n t o the l o n g i t u d i n a l c h a r a c t e r i s t i c s of the IPDP g e n e r a t i o n r e g i o n . In a d d i t i o n t o the two eve n t s s t u d i e d i n s e c t i o n s 5.1 and 5.3, a t h i r d IPDP i s a l s o a n a l y s e d h e r e ; the Feb. 24c e v e n t . W h i l e d a t a f o r the o r i g i n a l two IPDPs a re 183 2.4 21.6 21.8 22.0 22.2 22.4 UT (h) FIGURE 59. The f r e q u e n c y r i s e s as o b s e r v e d and as c a l c u l a t e d f o r the combined a z i m u t h a l d r i f t - A B - a d j u s t e d inward motion mechanisms f o r the Feb. 15 e v e n t , showing the e x c e l l e n t agreement between the two c u r v e s . 184 a v a i l a b l e o n l y from GM and PS, the e a s t e r n and c e n t r a l s i t e s i n the s o u t h e r n e a s t - w e s t l i n e , the Feb. 24c event has d a t a a v a i l a b l e from a l l t h r e e s i t e s i n t h i s l i n e . Note t h a t the l o n g i t u d i n a l d i f f e r e n c e between GM and PS i s o n l y 14.6\u00C2\u00B0, but t h a t the l o n g i t u d i n a l span of the l i n e expands t o 34.6\u00C2\u00B0 when PG, the westernmost s t a t i o n , i s i n c l u d e d . The d e t a i l e d l o n g i t u d i n a l a n a l y s e s a r e p r e s e n t e d below f o r each e v e n t . They a r e f o l l o w e d by a d i s c u s s i o n of the r e s u l t s of t h e s e a n a l y s e s . 5.4.1. Feb. 14 Event The f i r s t IPDP d i s c u s s e d i s the Feb. 14 e v e n t . F i g u r e 60 demonstrates the f r e q u e n c y e v o l u t i o n of t h i s event at b o t h GM and PS. Note t h a t the f r e q u e n c y i s g e n e r a l l y h i g h e r t o the e a s t , a t GM, a v e r a g i n g =0.06Hz above PS. The f r e q u e n c y s l o p e s are s i m i l a r , w i t h t h a t f o r GM, 0.43Hz/h, b e i n g s l i g h t l y h i g h e r than the 0.36Hz/h s l o p e a t PS. However, as can be seen i n f i g u r e 60, t h e r e are some s h o r t e r term v a r i a t i o n s i n f r e q u e n c y s l o p e which a r e not s h a r e d by b o t h s t a t i o n s . The event was o b s e r v e d t o b e g i n a t a p p r o x i m a t e l y the same time a t GM and PS, =0835UT, but i t l a s t e d =10 minutes l o n g e r , u n t i l 0950UT, a t GM, the e a s t e r n s t a t i o n . Comparisons between the IPDP s i g n a l s as o b s e r v e d a t GM and PS a r e made u s i n g c r o s s - c o r r e l a t i o n s . A s e r i e s of 2048 185 FIGURE 60. Frequency e v o l u t i o n a t both GM and PS f o r the Feb. 14 event. Note the h i g h e r f r e q u e n c i e s a t GM and the d i f f e r e n t l o c a l v a r i a t i o n s i n s l o p e a t the two s t a t i o n s . 186 p o i n t (9.1 min) d a t a windows, s t a r t i n g e v e r y f i v e m i n u t e s , from GM were c o r r e l a t e d w i t h a 8192 p o i n t (36.4 min) d a t a window, s t a r t i n g a t 0845UT, from PS. The r e s u l t s show c o r r e l a t i o n c o e f f i c i e n t s t o be <0.2 a t a l l time s h i f t s f o r each window, i n d i c a t i n g no s i g n i f i c a n t c o r r e l a t i o n between t h e s e s t a t i o n s . For c o m p a r i s o n , s t a t i o n s on the same m e r i d i a n , PS and LL, have r e c o r d s which appear t o be v e r y s i m i l a r , w i t h a c o r r e l a t i o n c o e f f i c i e n t of 0.36 f o r a l e a d of o n l y 1.3 seconds a t LL u s i n g the same d a t a window as above f o r PS c o r r e l a t e d w i t h a 9.1 minute window s t a r t i n g a t 0855UT from LL. Note, however, t h a t PS and LL a r e s e p a r a t e d o n l y by 1.2\u00C2\u00B0 of l a t i t u d e ( c f . s e c t i o n 2.1). An e x a m i n a t i o n of power s p e c t r a computed from the same time i n t e r v a l s a t GM and PS shows the d i f f e r e n c e s i n the IPDP s i g n a l as observed by these two s t a t i o n s (see f i g . 6 1 ) ; t h e s p e c t r a not o n l y c o v e r somewhat d i f f e r e n t bands, but the d i s t r i b u t i o n of power w i t h i n the bands i s a l s o d i s s i m i l a r . 5.4.2. Feb. 15 Event The f r e q u e n c y e v o l u t i o n of the Feb. 15 event i s shown i n f i g u r e 62, d e m o n s t r a t i n g t h a t the f r e q u e n c y i s a g a i n h i g h e r t o the e a s t , a t GM, though by o n l y an average of -0.02Hz. As w e l l , the s l o p e s a r e v e r y s i m i l a r h e r e , though the average s l o p e i s s l i g h t l y h i g h e r a t PS, 1.06Hz/h, than a t GM, 1.0!Hz/h. As f o r the Feb. 14 IPDP, the event onset 187 250 0.0 0.2 0.4 0.6 0.8 frequency (Hz) 250 0.0 0.2 0.4 0.6 0.8 frequency (Hz) FIGURE 61. Top: Power s p e c t r a from PS f o r 0910UT, F e b r u a r y 14. Bottom: Power s p e c t r a from GM f o r same time p e r i o d . Both s p e c t r a a r e of the t o t a l h o r i z o n t a l component from a\"\"*4.6 minute d a t a window. Note the d i f f e r e n t s i g n a l bands and the d i f f e r e n t power d i s t r i b u t i o n s i n the s e two s p e c t r a . 188 FIGURE 62. Frequency e v o l u t i o n f o r GM and PS, Feb. 15 event. GM has the h i g h e r f r e q u e n c i e s , but the s l o p e i s s l i g h t l y lower than a t PS. 189 t i m e s a r e e s s e n t i a l l y the same; 2147UT a t GM and 2148UT a t PS. However, i n t h i s c a s e , the d u r a t i o n was l o n g e r a t the western s t a t i o n , PS, a t 25 m i n u t e s , as compared t o 20 minutes a t GM. Note t h a t the d e t a i l e d a n a l y s i s of t h i s IPDP i n the p r e v i o u s s e c t i o n s was o n l y c a r r i e d out t o 2205UT, s i n c e a v e r y weak s i g n a l , and c o n s e q u e n t l y poor s i g n a l / n o i s e r a t i o , made the a n a l y s i s r e s u l t s of the l a s t s e c t i o n v e r y d i f f i c u l t t o i n t e r p r e t and t h e r e f o r e u n r e l i a b l e . A comparison of the appearance of the IPDP s i g n a l as seen a t GM and PS a l s o y i e l d s a r e s u l t u n l i k e t h a t f o r the Feb. 14 e v e n t . Here, each s t a t i o n e x h i b i t s s i m i l a r h i g h a m p l i t u d e i n t e r v a l s on the magnetograms, though these i n t e r v a l s do not n e c e s s a r i l y occur p r e c i s e l y s i m u l t a n e o u s l y . C r o s s - c o r r e l a t i o n a l a n a l y s i s shows t h a t each i n t e r v a l a t GM l e a d s the c o r r e s p o n d i n g one a t PS by between 54 and 4 seconds, w i t h the l a r g e s t l e a d s b e i n g e a r l i e r i n the e v e n t . In c o n t r a s t t o t h i s , t h e s e h i g h a m p l i t u d e i n t e r v a l s appear n e a r l y s i m u l t a n e o u s l y , the time s h i f t always b e i n g <5 seconds, at PS and LL, which a r e s e p a r a t e d o n l y i n l a t i t u d e . The c o r r e l a t i o n c o e f f i c i e n t s of up t o 0.60 a r e a l s o much h i g h e r between PS and LL than between PS and GM, which show c o e f f i c i e n t s of up t o o n l y 0.39. For t h i s e v e n t , the c o r r e l a t i o n s are done u s i n g 1024 p o i n t (4.6 min) d a t a windows from a l l s t a t i o n s . Note t h a t the h i g h a m p l i t u d e i n t e r v a l s a r e s h o r t compared t o the 4.6 minute d a t a windows. 190 C o r r e l a t i o n s were performed on f o u r windows w i t h s t a r t t i m e s of 2150, 2154, 2158, and 2203 UT. F i g u r e 63 shows sample c o r r e l a t i o n s between PS and GM and between PS and LL from the 2154UT window. D i f f e r e n t background n o i s e c o n d i t i o n s a t each s i t e and low a m p l i t u d e s a r e b e l i e v e d t o be r e s p o n s i b l e f o r the r e l a t i v e l y low l e v e l s of the c o r r e l a t i o n c o e f f i c i e n t s . The i n d i v i d u a l power s p e c t r a e x h i b i t the same k i n d s of d i f f e r e n c e s between GM and PS as they d i d f o r the Feb. 14 IPDP, even though the magnetograms from t h e s e two s t a t i o n s appear, a t l e a s t a t f i r s t g l a n c e , t o be q u i t e s i m i l a r i n t h i s c a s e . 5.4.3. Feb. 24c Event T h i s event was o b s e r v e d a t a l l t h r e e s t a t i o n s i n the s o u t h e r n e a s t - w e s t l i n e (GM, PS, and PG). The f r e q u e n c y p r o f i l e s from th e s e s t a t i o n s are shown i n f i g u r e 64. Though the PS and GM f r e q u e n c i e s appear t o be q u i t e s i m i l a r , t o the west the PG s t a t i o n o b s e r v e d f r e q u e n c i e s a v e r a g i n g 0.07Hz lower than the o t h e r s t a t i o n s . The average f r e q u e n c y s l o p e s a t each s i t e a r e s i m i l a r , l y i n g near 0.3Hz/h, w i t h PG b e i n g s l i g h t l y h i g h e r and GM somewhat lower than t h i s v a l u e . However, as f i g u r e 64 shows, t h e r e a r e d i f f e r e n t s h o r t e r term v a r i a t i o n s i n s l o p e w i t h i n the event a t each s i t e which can make the s l o p e s q u i t e d i f f e r e n t between s t a t i o n s f o r -100 - 5 0 0 50 100 time shift (s) 1.01 \u00E2\u0080\u0094 \u00E2\u0080\u0094 -100 - 5 0 0 50 100 time shift (s) FIGURE 63. Top: Sample c r o s s - c o r r e l a t i o n between LL and PS from the Feb. 15 e v e n t , showing t h a t the good c o r r e l a t i o n between the s e two s i t e s , which a r e on the same m e r i d i a n , i s near z e r o l a g . Bottom: C r o s s - c o r r e l a t i o n between GM and PS from the same time i n t e r v a l . Both c o r r e l a t i o n s use the Y component o n l y ( w i t h a 0.2-0.6 Hz bandpass f i l t e r ) . Note the s i g n i f i c a n t l y p o o r e r c o r r e l a t i o n t h e s e two l o n g i t u d i n a l l y s e p a r a t e d s i t e s . Here, GM l e a d s PS by 22 seconds. 1 92 FIGURE 64. Frequency e v o l u t i o n f o r a l l t h r e e s t a t i o n s o b s e r v i n g the Feb. 24c IPDP. PG, i n .the west, has the l o w e s t f r e q u e n c i e s . Note a l s o t h a t t h e r e are s i g n i f i c a n t l o c a l v a r i a t i o n s i n s l o p e between the s t a t i o n s . 193 some i n t e r v a l s d u r i n g the IPDP. The event i n t e r v a l s o b s e r v e d a t each s i t e a r e : GM, 0550 t o 0630 UT; PS, 0554 t o 0650 UT; and PG, 0558 t o 0700 UT. Note t h a t the GM d a t a were v e r y n o i s y and d i f f i c u l t t o i n t e r p r e t , making c o n c l u s i o n s based on i t l e s s r e l i a b l e . As w i t h the Feb. 14 e v e n t , but u n l i k e the Feb. 15 IPDP, t h e r e does not appear t o be any s i g n i f i c a n t c o r r e l a t i o n of the s i g n a l s between any of the t h r e e s t a t i o n s i n the e a s t - w e s t l i n e , s i n c e a l l c o r r e l a t i o n c o e f f i c i e n t s were a g a i n <0.2. No o t h e r r e c o r d i n g s i t e s on any of the n o r t h - s o u t h l i n e s are a v a i l a b l e f o r comparison f o r t h i s e v e n t . The power s p e c t r a f o r t h i s event behave much as has been d e s c r i b e d f o r the p r e v i o u s two c a s e s , w i t h the f r e q u e n c y bands c o v e r e d and the power d i s t r i b u t i o n w i t h i n the bands b e i n g n o t a b l y d i f f e r e n t a t each s i t e f o r the same time i n t e r v a l s . 5.4.4. Discussion A l l t h r e e e v e n t s d i s c u s s e d here e x h i b i t g e n e r a l l y h i g h e r f r e q u e n c i e s t o the e a s t . T h i s i m p l i e s g e n e r a t i o n on lower L - s h e l l s t o the e a s t , and thus i n d i c a t e s t h a t the g e n e r a t i o n r e g i o n f o l l o w s the plasmapause shape which i s a t lower L a t l a t e r , or more e a s t e r l y GMLTs. Two of the t h r e e IPDPs, Feb. 15 and Feb. 24c, show l o n g e r d u r a t i o n s t o the 1 94 west and e a r l i e r onset t i m e s t o the e a s t . T h i s i s c o n s i s t e n t w i t h the model d i s c u s s e d i n s e c t i o n 4.1, i n which the l a t e r o n s e t s imply l o n g e r d r i f t t i m e s which c r e a t e a l a r g e r GMLT spread i n the d r i f t i n g p r o t o n c l o u d , g i v i n g l o n g e r event d u r a t i o n s . Note t h a t v e r y low a m p l i t u d e s a t the s t a r t or end of an event can make i t v e r y d i f f i c u l t t o c o r r e c t l y p i c k the s t a r t or end t i m e s , which may be why the d u r a t i o n and/or onset time of the Feb. 14 IPDP does not f i t the above p a t t e r n . For a l l t h r e e e v e n t s , i n d i v i d u a l power s p e c t r a c a l c u l a t e d from i d e n t i c a l time i n t e r v a l s show major d i f f e r e n c e s between s i t e s on the e a s t - w e s t l i n e , but not f o r n o r t h - s o u t h l i n e s t a t i o n s . Each event a l s o shows temporary d i f f e r e n c e s i n s l o p e e x h i b i t e d by the s t a t i o n s on the east-west l i n e . Two of the t h r e e IPDPs s t u d i e d , Feb. 14 and Feb. 24c, show no s i g n i f i c a n t c o r r e l a t i o n between s t a t i o n s on the e a s t - w e s t l i n e , though the t h i r d e v e n t , the Feb. 15 IPDP, does show a weak ea s t - w e s t c o r r e l a t i o n . These r e s u l t s imply t h a t each s t a t i o n r e c e i v e s the IPDP s i g n a l s from a d i f f e r e n t p a r t of the magnetospheric s o u r c e r e g i o n . The e a s t - w e s t c o r r e l a t i o n s e x h i b i t e d by the Feb. 15 event c o u l d be caused by the magnetospheric s o u r c e r e g i o n s \"above\" each s t a t i o n r e c e i v i n g s i m i l a r \" p a c k e t s \" of d r i f t i n g p r o t o n s n e a r l y s i m u l t a n e o u s l y , thus c r e a t i n g s i m i l a r h i g h a m p l i t u d e i n t e r v a l s a t each s t a t i o n w i t h time s e p a r a t i o n s of 195 l e s s than one minute. Note t h a t good c o r r e l a t i o n s a r e o b s e r v e d between s t a t i o n s s e p a r a t e d i n l a t i t u d e o n l y , i l l u s t r a t i n g good n o r t h - s o u t h d u c t i n g from a common secondary s o u r c e . In summary, the p r i m a r y p o i n t of t h i s a n a l y s i s i s t o show t h a t t h e r e are s i g n i f i c a n t d i f f e r e n c e s w i t h i n an IPDP as ob s e r v e d on an e a s t - w e s t l i n e of s t a t i o n s . These d i f f e r e n c e s , which i n c l u d e v a r i a t i o n s i n magnetograms, f r e q u e n c y , s l o p e , and s p e c t r a , can be seen over as l i t t l e as 15\u00C2\u00B0 GM Long., and i m p l y t h a t each s i t e i s s e e i n g a s e p a r a t e magnetospheric s o u r c e . The e a s t - w e s t p a t t e r n of these d i f f e r e n c e s , which a l s o i n c l u d e onset times and d u r a t i o n s , i s c o n s i s t e n t w i t h the model d i s c u s s e d i n s e c t i o n 4.1, w i t h s i m u l t a n e o u s IPDP g e n e r a t i o n over a l o n g i t u d i n a l l y extended a r e a of the plasmapause a f t e r westward d r i f t of the p r o t o n s on d i f f e r e n t L - s h e l l s . Each ground s t a t i o n on the east-west l i n e i s then s e e i n g the IPDP as g e n e r a t e d on a d i f f e r e n t s e c t i o n of the plasmapause c l o s e t o t h a t s t a t i o n ' s m e r i d i a n , r e s u l t i n g i n the i n t e r - s t a t i o n v a r i a t i o n s i n the IPDP s i g n a l d e s c r i b e d above. Good n o r t h - s o u t h p r o p a g a t i o n w i t h i n the i o n o s p h e r e ensures t h a t a l l s i t e s on one m e r i d i a n see the same s i g n a l s from the same s o u r c e , w i t h o n l y the p o l a r i z a t i o n c h a r a c t e r i s t i c s and a m p l i t u d e s a l t e r e d by t h i s i o n o s p h e r i c p r o p a g a t i o n . 196 5.5. DISCUSSION OF EXPERIMENTAL RESULTS In s t u d y i n g the f r e q u e n c y r i s e of IPDPs, we have t e s t e d t h r e e mechanisms c a p a b l e of p r o d u c i n g t h i s e f f e c t ; the inward motion of the magnetospheric s o u r c e r e g i o n , an i n c r e a s i n g background magnetic f i e l d s t r e n g t h i n the s o u r c e r e g i o n , and the p r o t o n energy v a r i a t i o n s produced d u r i n g the a z i m u t h a l d r i f t of the hot p r o t o n s . The assessment of t h e s e mechanisms has been c a r r i e d out i n the c o n t e x t of the model d e s c r i b e d i n Chapter Four. In s e c t i o n s 5.1 t h r o u g h 5.3, i t was shown t h a t the inward motion was, f o r the e v e n t s a n a l y z e d , the p r i m a r y , though not always the e n t i r e , cause of the IPDPs' f r e q u e n c y r i s e . I t i s i m p o r t a n t t o note t h a t , f o r a p r o p e r assessment of t h i s mechanism, the e f f e c t of the r i n g c u r r e n t magnetic f i e l d on the r a d i a l geomagnetic f i e l d p r o f i l e must be t a k e n i n t o a c c o u n t , s i n c e i t can, i f the r i n g c u r r e n t i s w e l l d e v e l o p e d , s i g n i f i c a n t l y enhance the magnitude of the f r e q u e n c y r i s e a t t r i b u t a b l e t o inward motion of the IPDP g e n e r a t i o n r e g i o n . T h i s r e p r e s e n t s a f i r s t , i f s i m p l e , s t e p beyond the p u r e l y d i p o l e f i e l d model d i s c u s s e d i n Chapter Four. The inward motion of the source r e g i o n has e a r l i e r been d e s c r i b e d as b e i n g due t o the shape of the plasmapause, w i t h the p o s s i b l e a d d i t i o n of inward motion of the plasmapause i t s e l f ( c f . Chapter F o u r ) . The inward motion d e t e r m i n e d here 1 97 would be the sum of the s e two e f f e c t s , i f both a r e p r e s e n t . The i r r e g u l a r r a t e of inward motion demonstrated by both IPDPs s t u d i e d c o u l d then be i n t e r p r e t e d t o mean t h a t the plasmapause shape i t s e l f i s somewhat i r r e g u l a r w i t h the plasmapause moving e i t h e r v e r y l i t t l e or a t a c o n s t a n t r a t e d u r i n g t h e s e e v e n t s . A l t e r n a t e l y , d u r i n g the p e r i o d s of f a s t e r motion e x h i b i t e d d u r i n g t h e i r c e n t r a l time spans by bot h IPDPs ( c f . f i g . 31, 3 8 ) , a d d i t i o n a l plasmapause inward d i s p l a c e m e n t c o u l d be superimposed on a r e l a t i v e l y smooth inward motion due t o a smoother plasmapause shape. That the plasmapause would move most d u r i n g the m i d d l e of an IPDP event may not be unexpected, s i n c e the e l e c t r i c and magnetic f i e l d s which c o n t r o l the plasmapause p o s i t i o n may a l s o be chan g i n g a t t h i s time due t o magnetospheric substorm e f f e c t s . These' e f f e c t s , which i n c l u d e the ch a n g i n g plasma and f i e l d e nvironments a s s o c i a t e d w i t h the p r o t o n westward d r i f t p r o c e s s , c o u l d have an e f f e c t on the plasmapause p o s i t i o n , and i f so then may a f f e c t the plasmapause most when the p r o t o n s g e n e r a t i n g the IPDP are a r r i v i n g t h e r e . The r i n g c u r r e n t - IPDP model d i s c u s s e d i n s e c t i o n 5.2, though s i g n i f i c a n t l y improved over p r e v i o u s models, i s s t i l l q u i t e s i m p l e . N e v e r t h e l e s s , the c o n c l u s i o n can be drawn from i t t h a t the i n c r e a s i n g magnetic f i e l d mechanism f o r the IPDP f r e q u e n c y r i s e i s not a n e c e s s a r y c o n d i t i o n f o r IPDPs t o o c c u r , s i n c e case I and I I I e v e n t s do occur ( c f . s e c t i o n 198 5.2). I t can, however, under c e r t a i n c i r c u m s t a n c e s , s t i l l c o n t r i b u t e t o the f r e q u e n c y s h i f t of seme IPDPs, such as case I I and IV e v e n t s . I t i s a l s o shown t h a t the geosynchronous s a t e l l i t e magnetograms a l o n e cannot be used as a method of d e t e r m i n i n g IPDP sou r c e r e g i o n f i e l d b e h a v i o u r u n l e s s the IPDP i s b e i n g g e n e r a t e d i n the v i c i n i t y of L = 6.6. The i n c r e a s i n g f i e l d mechanism does not appear t o have c o n t r i b u t e d s i g n i f i c a n t l y t o the IPDPs examined h e r e . For t h i s mechanism, however, the assessment remains o n l y a q u a l i t a t i v e one due t o the d i f f i c u l t y i n q u a n t i t a t i v e l y d e t e r m i n i n g any changes i n magnetic f i e l d s t r e n g t h i n the IPDP s o u r c e r e g i o n from the i n f o r m a t i o n a v a i l a b l e . Lower a l t i t u d e , t h a t i s , L < 6.6, s a t e l l i t e magnetic f i e l d measurements i n the g e n e r a t i o n r e g i o n d u r i n g an IPDP would be n e c e s s a r y t o e v a l u a t e q u a n t i t a t i v e l y the i n c r e a s i n g f i e l d mechanism e f f e c t on IPDP f r e q u e n c y s h i f t s . The hot p r o t o n energy change e f f e c t p l a y e d a secondary r o l e i n c r e a t i n g the IPDP f r e q u e n c y s h i f t s o b s e r v e d h e r e . In one e v e n t , i t a c t u a l l y had the unusual e f f e c t of s u p p r e s s i n g the f r e q u e n c y r i s e . S e c t i o n 5.3 showed t h a t both the r i n g c u r r e n t i n d u c e d magnetic f i e l d d e p r e s s i o n and the i n j e c t i o n boundary p o s i t i o n must be e s t i m a t e d i n o r d e r t o f i n d the e n e r g i e s of the p r o t o n s g e n e r a t i n g the IPDP. T h i s e s t i m a t i o n p r o c e s s r e q u i r e s the assumption t h a t o n l y the p r o t o n energy 199 e f f e c t and the A B - a d j u s t e d inward motion mechanism a r e o p e r a t i n g , and would be i n a p p r o p r i a t e i f a p p l i e d t o an IPDP t o which the i n c r e a s i n g f i e l d mechanism was b e l i e v e d t o be making a s i g n i f i c a n t c o n t r i b u t i o n . I t s h o u l d a l s o be p o i n t e d out t h a t the s e l e c t i o n p r o c e s s by which the b e s t f i e l d d e p r e s s i o n v a l u e and i n j e c t i o n boundary p o s i t i o n a r e chosen i s p a r t i a l l y s u b j e c t i v e , e s p e c i a l l y w i t h r e g a r d s t o the w e i g h t s a s s i g n e d t o each of the s e l e c t i o n c r i t e r i a . The a n a l y s i s of the l o n g i t u d i n a l s t r u c t u r e and development of IPDPs p r e s e n t e d i n s e c t i o n 5.4 i n d i r e c t l y s u p p o r t s the f r e q u e n c y r i s e r e s u l t s d i s c u s s e d above by s u p p o r t i n g the model from which they are produced. In a d d i t i o n , the d e t a i l e d a n a l y s e s of the IPDPs showed t h a t l o n g i t u d i n a l v a r i a t i o n s w i t h i n IPDP e v e n t s e x i s t over much s m a l l e r l o n g i t u d i n a l s e p a r a t i o n s than p r e v i o u s l y r e p o r t e d ( c f . s e c t i o n 3.3). In c o n s i d e r i n g the o v e r a l l s i g n i f i c a n c e of the r e s u l t s d i s c u s s e d above, i t must be remembered t h a t o n l y two IPDP ev e n t s have been s t u d i e d i n d e t a i l . From j u s t two e v e n t s , s t r o n g c o n c l u s i o n s \u00E2\u0080\u00A2 r e g a r d i n g the r e l a t i v e importance of the d i f f e r e n t f r e q u e n c y s h i f t mechanisms cannot be extended t o r e l i a b l y a p p l y t o a l l IPDP e v e n t s . For example, the degree of i n f l u e n c e of each mechanism may change w i t h v a r y i n g m agnetospheric c o n d i t i o n s and/or IPDP source r e g i o n 200 l o c a t i o n s . I t i s i n t e r e s t i n g t o note t h a t the two IPDPs s t u d i e d here d i d occur a t d i s p a r a t e GMLT l o c a t i o n s and under d i v e r s e l e v e l s of magnetospheric a c t i v i t y . W h i l e both e x h i b i t e d s t r o n g inward motion mechanism c o n t r i b u t i o n s , t h e i r hot p r o t o n energy change e f f e c t s were of o p p o s i t e s i g n , i n d i c a t i n g t h a t such s y s t e m a t i c v a r i a t i o n s i n the f r e q u e n c y s h i f t mechanisms' c o n t r i b u t i o n s a r e a t l e a s t a p o s s i b i l i t y . To study p o t e n t i a l t r a i t s such as t h e s e , the a n a l y s i s of many more e v e n t s would be r e q u i r e d . The n e g a t i v e f r e q u e n c y s h i f t from the hot p r o t o n energy change e f f e c t d i s p l a y e d by one IPDP here ( c f . f i g . 58) has not been p r e v i o u s l y r e p o r t e d and was termed u n u s u a l above, y e t , w i t h o u t an extended s t u d y c o v e r i n g many e v e n t s , i t i s not r e a l l y known how r a r e such b e h a v i o u r a c t u a l l y i s . I t i s a l s o n e c e s s a r y t o be somewhat c a u t i o u s when c o n s i d e r i n g the d e t a i l s of the i n d i v i d u a l r e s u l t s . We must bear i n mind such t h i n g s as the i n c o m p l e t e d a t a s e t on which the a n a l y s e s were performed, the somewhat s i m p l i s t i c a p p l i c a t i o n of i o n o s p h e r i c duct t h e o r y n e c e s s a r y , and the s i m p l i f y i n g assumptions i n v o l v e d i n the IPDP g e n e r a t i o n model. These a s p e c t s can a f f e c t not o n l y the a c c u r a c y of the IPDP s o u r c e p o s i t i o n d e t e r m i n a t i o n and inward motion f r e q u e n c y s h i f t e s t i m a t e , but a l s o the a z i m u t h a l d r i f t f r e q u e n c y s h i f t e s t i m a t e , s i n c e t h i s depends, i n p a r t , on the s o u r c e inward motion r e s u l t s . The a z i m u t h a l d r i f t 201 e s t i m a t e a l s o depends on the assumption t h a t a l l i n j e c t i o n b o u n d a r i e s t a k e the form e x p r e s s e d by e q u a t i o n 5.8. However, b a r r i n g any major s h i f t s i n our g e n e r a l u n d e r s t a n d i n g of such p r o c e s s e s as i n j e c t i o n boundary f o r m a t i o n , r i n g c u r r e n t development, or i o n o s p h e r i c duct p r o p a g a t i o n , the g e n e r a l c o n c l u s i o n s r e g a r d i n g the r e l a t i v e importance of each of the f r e q u e n c y s h i f t mechanisms t o the e v e n t s s t u d i e d here s h o u l d be v a l i d . CHAPTER 6 . CONCLUSION We have made a q u a n t i t a t i v e study of two IPDP f r e q u e n c y s h i f t mechanisms, s u p p o r t e d by a q u a l i t a t i v e assessment of the r o l e of a p o t e n t i a l t h i r d mechanism. W i t h i n the framework of a magnetospheric IPDP g e n e r a t i o n model, i t has become e v i d e n t t h a t the inward motion of the magnetospheric source r e g i o n i s the dominant cause of the IPDP f r e q u e n c y r i s e , w i t h the hot p r o t o n energy v a r i a t i o n s c o n t r i b u t i n g t o a l e s s e r degree. The model c o n s i d e r e d c o n s i s t s of a westward d r i f t of e n e r g e t i c p r o t o n s from a substorm i n j e c t i o n boundary and subsequent wave a m p l i f i c a t i o n by t h e s e p r o t o n s at the plasmapause t h r o u g h the p r o t o n - c y c l o t r o n i n s t a b i l i t y . These c o n c l u s i o n s a r e the outcome of the d e t a i l e d a n a l y s e s of the two e v e n t s s t u d i e d h e r e . These r e s u l t s a r e s u p p o r t e d by model c a l c u l a t i o n s ( s e c t i o n 4.4), which a l s o show the inward motion mechanism g e n e r a l l y c o n t r i b u t i n g s i g n i f i c a n t l y more than the hot p r o t o n energy change e f f e c t . In a d d i t i o n , model c a l c u l a t i o n s show t h a t the inward motion can be l a r g e l y due t o the shape of the plasmapause, as opposed t o inward d i s p l a c e m e n t of the plasmapause. These model c a l c u l a t i o n s a l s o show t h a t the p o s s i b i l i t y e x i s t s t h a t e a stward d e v e l o p i n g IPDPs, o p p o s i t e to what i s now c o n s i d e r e d the normal t r e n d , may o c c u r . We have shown t h a t p r e v i o u s methods of i n t e r p r e t i n g the i n c r e a s i n g magnetic f i e l d mechanism's e f f e c t on IPDPs gave 202 203 i n s u f f i c i e n t a t t e n t i o n t o the d i f f e r e n c e s i n t e m p o r a l f i e l d b e h a v i o u r between geosynchronous o r b i t and the somewhat lower IPDP source r e g i o n s as caused by the dynamic n a t u r e of the storm time r i n g c u r r e n t . When even a s i m p l e d e s c r i p t i o n of r i n g c u r r e n t dynamics i s used, i n c l u d i n g the r i n g c u r r e n t ' s growth, inward d i s p l a c e m e n t , and decay d u r i n g the c o u r s e of a magnetic storm, i t becomes e v i d e n t t h a t the i n c r e a s i n g f i e l d mechanism may enhance, s u p p r e s s , or have no e f f e c t on an IPDP's f r e q u e n c y r i s e depending on the e v e n t ' s source r e g i o n l o c a t i o n and the storm phase d u r i n g which i t o c c u r s . However, t h i s mechanism i s never a r e q u i r e d p r o c e s s upon which an IPDP's e x i s t e n c e depends. In c o n t r a s t t o t h i s , due t o plasmapause geometry, some inward motion of the IPDP so u r c e r e g i o n w i l l always e x i s t . However, a c t u a l plasmapause inward d i s p l a c e m e n t w i l l not n e c e s s a r i l y always t a k e p l a c e . T h i s inward motion mechanism i s , though, the o n l y mechanism which w i l l always be p r e s e n t , as shown by the f a c t t h a t one of the two e v e n t s s t u d i e d d i s p l a y e d hot p r o t o n energy v a r i a t i o n s which r e s u l t e d i n a s l i g h t s u p p r e s s i o n of the f r e q u e n c y r i s e . In s p i t e of the f a c t t h a t a z i m u t h a l d r i f t v e l o c i t e s w i l l always produce a s o f t e n i n g p r o t o n energy spectrum as observed a t c o n s t a n t L, r a p i d c r o s s - L motion of the s o u r c e can r e v e r s e t h i s t r e n d , as \"seen\" by a ground s t a t i o n , y i e l d i n g an i n c r e a s i n g energy t r e n d whose e f f e c t a c t s t o d e p r e s s an IPDP's f r e q u e n c y r i s e . 204 Due t o l i m i t a t i o n s of the 1980 IPDP d a t a s e t used here ( c f . s e c . 2.1), o n l y two events were s t u d i e d i n d e t a i l and even t h e s e s u f f e r e d from i n c o m p l e t e s t a t i o n c o v e r a g e . D e s p i t e t h i s , i t has s t i l l been p o s s i b l e t o g a i n new i n s i g h t s i n t o the g e n e r a t i o n p r o c e s s e s of IPDPs. In a d d i t i o n , new methods f o r the stu d y of IPDPs have a l s o been d e v e l o p e d , as d e s c r i b e d i n s e c t i o n s 4.4 th r o u g h 5.4, which p r o v i d e a good b a s i s f o r f u t u r e work u s i n g more complete d a t a s e t s . As noted i n Chapter One, IPDPs have o f t e n been t o u t e d as a p o t e n t i a l l y u s e f u l t o o l f o r the d i a g n o s i s of magnetospheric c o n d i t i o n s . U n f o r t u n a t e l y , t h i s has not been r e a l i z e d t o any l a r g e e x t e n t as y e t . Now, however, w i t h a b e t t e r u n d e r s t a n d i n g of the f r e q u e n c y s h i f t mechanisms, we can b e g i n t o r e a l i z e some of the p o t e n t i a l of the stu d y of IPDPs. I t has been demonstrated here t h a t the d e t a i l e d s t u d y of i n d i v i d u a l IPDP events can y i e l d i n f o r m a t i o n on plasmapause p o s i t i o n and movement, d r i f t i n g p r o t o n e n e r g i e s , i n j e c t i o n boundary shapes, and r i n g - c u r r e n t c r e a t e d magnetic f i e l d d e p r e s s i o n s i n the IPDP g e n e r a t i o n r e g i o n . T h i s i s o n l y a b e g i n n i n g , however. The q u a l i t y and r e l i a b i l i t y of such i n f o r m a t i o n c o u l d be improved and o t h e r uses of IPDPs made i f our u n d e r s t a n d i n g of t h e s e m i c r o p u l s a t i o n s were t o be s o l i d i f i e d and extended. To do t h i s would r e q u i r e the a n a l y s i s of many w e l l r e c o r d e d e v e n t s from s t a t i o n networks 205 which i n c l u d e two or more a d j a c e n t n o r t h - s o u t h c h a i n s of s i t e s , a l l o w i n g the development of a t w o - d i m e n s i o n a l p i c t u r e of IPDP g e n e r a t i o n founded on e x p e r i m e n t . I t would a l s o be n e c e s s a r y t o i n c l u d e s a t e l l i t e magnetograms from L < 6.6 and/or a much more s o p h i s t i c a t e d r i n g c u r r e n t model t o q u a n t i t a t i v e l y u n d e r s t a n d the r o l e of t e m p o r a l magnetic f i e l d v a r i a t i o n s i n IPDP g e n e r a t i o n . I f such c o n c e r n s can be s a t i s f i e d by f u t u r e work, IPDPs may f i n a l l y t a k e t h e i r p l a c e as a u s e f u l type of m i c r o p u l s a t i o n i n magnetospheric p h y s i c s . REFERENCES A l t h o u s e , E.L., and J.R. 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Res. 81, 5501-5506. T r o i t s k a y a , V.A., 1961, P u l s a t i o n of the e a r t h ' s e l e c t r o m a g n e t i c f i e l d w i t h p e r i o d s of 1 t o 15 seconds and t h e i r c o n n e c t i o n w i t h phenomena i n the h i g h atmosphere: J . Geophys. Res. 66, 5-18. T r o i t s k a y a , V., and M. M e l n i k o v a , 1959, About c h a r a c t e r i s t i c 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 s : D o k l . Acad. Nauk CCCP 128, 917. T r o i t s k a y a , V.A., R.V. Shchepetnov, and A.V. G u l ' y e l m i , 1968, E s t i m a t e of e l e c t r i c f i e l d s i n the magnetosphere from the frequency d r i f t of m i c r o p u l s a t i o n s : Geomag. Aeron. 8, 634. W i l l i a m s , D.J., and L.R. Lyons, 1974a, The p r o t o n r i n g c u r r e n t and i t s i n t e r a c t i o n w i t h the plasmapause: storm r e c o v e r y phase: J . Geophys. Res. 79, 4195-4207. W i l l i a m s , D.J., and L.R. Lyons, 1974b, F u r t h e r a s p e c t s of the p r o t o n r i n g c u r r e n t i n t e r a c t i o n w i t h the plasmapause: main and r e c o v e r y phases: J . Geophys. Res. 79, 4791-4798. W i l l i a m s , D.J., 1985, Dynamics of E a r t h ' s r i n g c u r r e n t : t h e o r y and o b s e r v a t i o n : Space S c i . Rev. 42, 375-396. APPENDIX A. THE ION-CYCLOTRON INSTABILITY AND IPDP FREQUENCY In o r d e r t o comprehend how the IPDP f r e q u e n c y r i s e i s produced, we must u n d e r s t a n d which p h y s i c a l f a c t o r s a f f e c t the f r e q u e n c y of waves a m p l i f i e d by the i o n - c y c l o t r o n i n s t a b i l i t y mechanism as w e l l as the magnitude of the e f f e c t of each of th e s e f a c t o r s . The d i s p e r s i o n r e l a t i o n f o r a l e f t hand p o l a r i z e d i o n - c y c l o t r o n wave p r o p a g a t i n g p a r a l l e l t o the background magnetic f i e l d i n a two component, p r o t o n and e l e c t r o n , plasma i s ( J a c o b s , 1 9 7 0 ) : ( k / c ) 2 c 2 = 1 - \"P* - \"PP ( A . 1 ) u>(u>+ S2 ) o n c o - f l ; 1 e 1 p where u>^ i s the plasma f r e q u e n c y , fl i s the g y r o f r e q u e n c y , and the s u b s c r i p t s { g) and ( ) r e f e r , r e s p e c t i v e l y , t o the e l e c t r o n and p r o t o n components. For a c o l d plasma, the p r o t o n - c y c l o t r o n resonance o c c u r s when the phase v e l o c i t y v ^ = cj/k = 0 . From e q u a t i o n A . 1 , t h i s happens when (w - fl ) = 0 , or OJ = 0 . For the IPDP P P c a s e , however, i n which the i n t e r a c t i o n i s between waves and warm p r o t o n s w i t h a ,non-zero s t r e a m i n g v e l o c i t y v\u00E2\u0080\u009E, the resonance c o n d i t i o n can be e x p r e s s e d as ( J a c o b s , 1 9 7 0 ) : 2 1 4 215 a) , - kv\u00E2\u0080\u009E - co = 0 or CJ - kv\u00C2\u00BB - U = 0 (A. 2) obs em p where w , i s the o b s e r v e d f r e q u e n c y and w i s the e m i t t e d obs ^ * em frequency i n the p r o t o n \" r e s t frame\", s i n c e the wave frequency (\" 0^ 5 \u00C2\u00B0 r must be d o p p l e r s h i f t e d , i n the p r o t o n \" r e s t frame\", t o match the p r o t o n g y r o f r e q u e n c y i^em or 0 ^ ) . The p r o t o n r e s t frame mentioned above i s t h a t r e f e r e n c e frame moving w i t h v e l o c i t y v\u00C2\u00AB a l o n g the background magnetic f i e l d l i n e i n such a way t h a t the p r o t o n p a r a l l e l v e l o c i t y i s z e r o w i t h i n the r e f e r e n c e frame. By s u b s t i t u t i n g the above IPDP resonance c o n d i t i o n i n t o e q u a t i o n A.1, we can e l i m i n a t e the k dependence, and t h e r e f o r e study the e f f e c t s on the resonance f r e q u e n c y (w) of p arameters such as background magnetic f i e l d s t r e n g t h ( B 0 ) , and hot p r o t o n d e n s i t y ^ n p ^ a n < ^ energy (W) . In o r d e r to do t h i s , we c o n s i d e r the f o l l o w i n g : m^ i s n e g l i g i b l e as compared t o m^ , u> i s n e g l i g i b l e as compared t o u p e i the plasma i s n e u t r a l ( n ^ = n ), and the p r o t o n \" p a r a l l e l energy\" i s g i v e n by W\u00C2\u00BB = m^v 2/2. The r e s u l t i s : * - - i 3 2 B \u00C2\u00B0 q 2 n W\u00C2\u00AB 87T m2 c 2 P P 1 \" (2 P (A.3) where q r e p r e s e n t s the e l e c t r i c charge of the r e s o n a t i n g 216 p a r t i c l e s . S i n c e co < fl^, e q u a t i o n A.3 can be f u r t h e r s i m p l i f i e d t o (Roxburgh, 1970): Bo C J = * K* j (A.4a) (n W \u00E2\u0080\u009E ) 2 P i where K = ( q 2 / ( 8 7 r m^ c 2 ) ) 2 . Another common s i m p l i f y i n g assumption i s t h a t n^ B 0 (Roxburgh, 1970; G e n d r i n e t a l . , 1971; P e r r a u t e t a l . , 1984). In a d d i t i o n , the t o t a l p r o t o n energy W can be r e l a t e d t o W\u00C2\u00AB by W\u00E2\u0080\u009E = Wcos 2a, where a i s the p r o t o n p i t c h a n g l e . Then, s u b s t i t u t i n g f o r n^ and VI,,, e q u a t i o n A.4a becomes: 3. ( B 0 ) 2 w X (A.4b) W2 E q u a t i o n A.4b c l e a r l y shows the e f f e c t s of background magnetic f i e l d s t r e n g t h and hot p r o t o n energy on IPDP f r e q u e n c y , and thus a l l o w s us t o examine the problem of IPDP frequency s h i f t s i n terms of changes i n t h e s e p a r a m e t e r s . T h i s r e s u l t i s used i n the study of IPDPs i n C h a p t e r s Four and F i v e . APPENDIX B. THE IONOSPHERIC WAVEGUIDE M i c r o p u l s a t i o n s w i t h f r e q u e n c i e s i n the upper p a r t of the Pc 1 range, which i n c l u d e s many IPDPs, a re commonly ob s e r v e d a t low l a t i t u d e s even though t h e i r s o u r c e f i e l d l i n e s a r e u s u a l l y a t L > 4, i n d i c a t i n g t h a t they r e a c h the s u r f a c e a t ^60\u00C2\u00B0 GM l a t i t u d e . S i n c e t h e s e waves propagate down t o the io n o s p h e r e as f i e l d - g u i d e d l e f t - h a n d (LH) p o l a r i z e d hydromagnetic waves, a l s o termed slow mode hm waves, they must r e a c h t h e s e lower l a t i t u d e s t h r ough h o r i z o n t a l p r o p a g a t i o n from h i g h e r l a t i t u d e s i n the i o n o s p h e r i c waveguide. C o n s i d e r a b l e e x p e r i m e n t a l e v i d e n c e e x i s t s f o r p r o p a g a t i o n i n such a waveguide a l o n g the geomagnetic m e r i d i a n , though the presence of d u c t i n g i n o f f - m e r i d i a n d i r e c t i o n s i s l e s s c l e a r . ( T e p l e y and L a n d s h o f f , 1966; Campbell and T h o r n b e r r y , 1972; F r a s e r , 1975a,b; A l t h o u s e and D a v i s , 1978; Hayashi e t a l . , 1981). The a b i l i t y of the io n o s p h e r e t o t r a p and guide hm waves i s due t o i t s height-dependent i o n i z a t i o n s t r u c t u r e (see f i g . 6 5 ) . The pronounced peak i n i o n i z a t i o n c r e a t e s an A l f v e n v e l o c i t y minimum t h e r e , and i t i s w i t h i n t h i s l a y e r t h a t d u c t i n g can ta k e p l a c e . Note t h a t f i g u r e 65 a l s o shows t h a t the i o n i z a t i o n peak i s s h a r p e r a t n i g h t , r e s u l t i n g i n lower duct a t t e n u a t i o n than d u r i n g the day. As mentioned above, slow, or o r d i n a r y , mode waves a r e f i e l d g u i d e d , and so cannot c r o s s the magnetic f i e l d l i n e s . 217 218 6 7 8 9 10 11 12 13 electron density (log c m \" 3 ) FIGURE 65. E l e c t r o n d e n s i t y p r o f i l e s f o r both day and n i g h t sunspot maximum c o n d i t i o n s ( P r i n c e and B o s t i c k , 1964). Note t h a t a t n i g h t , the F2 l a y e r i o n i z a t i o n i s , r e l a t i v e t o the daytime p r o f i l e , much s t r o n g e r than the l a y e r s beneath i t . 219 T h i s , t h e r e f o r e , cannot be the mode p r o p a g a t i n g h o r i z o n t a l l y i n the i o n o s p h e r i c d u c t , s i n c e , except near the e q u a t o r , the geomagnetic f i e l d l i n e s c u t o b l i q u e l y a c r o s s the d u c t . The mode b e l i e v e d t o c a r r y the energy h o r i z o n t a l l y i n the duct i s t he f a s t , or e x t r a o r d i n a r y , mode. P r o p a g a t i o n of t h i s f a s t mode i s i s o t r o p i c , and s i n c e i t i s not g u i d e d by the ambient magnetic f i e l d , i t can t r a v e l h o r i z o n t a l l y w i t h i n the d u c t . The c o u p l i n g between th e s e two modes, which i s n e c e s s a r y f o r energy i n j e c t i o n i n t o the d u c t , has been a t t r i b u t e d t o the f i n i t e e x t e n t of the a r e a of i o n o s p h e r i c i n c i d e n c e , a l s o termed the secondary s o u r c e , by Jacobs and Watanabe (1962). I t i s a l s o s a i d t o be a consequence of a l t i t u d e - d e p e n d e n t v a r i a t i o n s i n p o l a r i z a t i o n of the incoming slow mode wave as i t t r a v e r s e s the F - l a y e r (Altman and F i j a l k o w , 1980). N u m e r i c a l a n a l y s i s p r e s e n t e d i n the l a t t e r work a l s o s u g g e s t s t h a t energy i n j e c t i o n i n t o the duct i s most e f f i c i e n t a t h i g h e r l a t i t u d e s (>45\u00C2\u00B0), and t h a t i t t a k e s p l a c e over the e n t i r e a l t i t u d e range of the F 2 - l a y e r d u c t . Other i o n o s p h e r i c waveguide models (such as Manchester, 1966,1968; G r e i f i n g e r and G r e i f i n g e r , 1968) have not s p e c i f i c a l l y t r e a t e d the problem of i n j e c t i o n i n t o the duct o t h e r than t o say t h a t mode c o u p l i n g t a k e s p l a c e i n the lower i o n o s p h e r e . Once i n the i o n o s p h e r i c d u c t , the t r a p p e d wave 220 p r o p a g a t e s h o r i z o n t a l l y i n a s e r i e s of r e f l e c t i o n s from the upper and lower duct w a l l s , as i l l u s t r a t e d i n f i g u r e 66. T h i s f i g u r e shows t h a t most of the energy i s r e f l e c t e d from narrow a l t i t u d e ranges a t both the t o p and bottom of the d u c t , g i v i n g a w e l l d e f i n e d duct r e g i o n . The r e f l e c t i o n c o e f f i c i e n t s a t thes e w a l l s f o r the t r a p p e d f a s t mode wave a r e t y p i c a l l y 0.5 - 0.85 (Altman and F i j a k o w , 1980) (see f i g . 6 6 ) . E s t i m a t e s of a t t e n u a t i o n i n the duct v a r y somehat depending on the i o n o s p h e r i c waveguide model c o n s i d e r e d ; Manchester (1968), a t t r i b u t i n g a t t e n u a t i o n p r i m a r i l y t o a b s o r p t i o n , e s t i m a t e d ^4 db/1000km, w h i l e Altman and F i j a l k o w (1980) found a r a t e of 6-9 db/l000km due t o f a s t - t o - s l o w mode c o u p l i n g i n the d u c t . A d i u r n a l v a r i a t i o n i n duct a t t e n u a t i o n i s a l s o produced by thos e models c o n s i d e r i n g the d a i l y v a r i a t i o n s i n i o n o s p h e r i c s t r u c t u r e . The appearance of the E r e g i o n i n the daytime i o n o s p h e r e s t r o n g l y a f f e c t s the i o n i z a t i o n p r o f i l e ( c f . f i g . 6 5 ) , r e s u l t i n g i n i n c r e a s e d duct a t t e n u a t i o n d u r i n g the day. T h i s i n c r e a s e , r e l a t i v e t o n i g h t i m e a t t e n u a t i o n , has been c a l c u l a t e d t o be of r o u g h l y an o r d e r of magnitude ( G r e i f i n g e r and G r e i f i n g e r , 1968) or more (Manchester, 1966). The e x p e r i m e n t a l r e s u l t s of A l t h o u s e and D a v i s (1978) y i e l d e d a t y p i c a l a t t e n u a t i o n of =*6.5 db/1000km d u r i n g the e a r l y morning h o u r s , though the v a l u e s were q u i t e v a r i a b l e from day t o day and reached as n i g h as 13 db/1000km. I I I f = 1Hz NIGHT SUNSPOT MAX. 0.2 0.4 0.6 0.8 REFLECTION COEFFICIENTS FIGURE 66. Top: T y p i c a l p r o p a g a t i o n p a t h s f o r t r a p p e d f a s t mode ( l a b e l l e d E ( e x t r a o r d i n a r y ) mode i n the diagram) waves i n the F2 r e g i o n duct ( a f t e r Manchester, 1966). Bottom: H e i g h t p r o f i l e of R-mode r e f l e c t i o n c o e f f i c i e n t s f o r d i f f e r e n t v a l u e s of S n e l l ' s c o n s t a n t S (=n\u00C2\u00ABsin0) ( a f t e r Altman and F i j a l k o w , 1980). 222 F i n a l l y , i t s h o u l d be p o i n t e d out t h a t the a t t e n u a t i o n v e r s u s f r e q u e n c y p r o f i l e s produced by the d i f f e r e n t waveguide models d i f f e r s i g n i f i c a n t l y . The i o n o s p h e r i c waveguide a l s o appears t o e x h i b i t a lower c u t - o f f f r e q u e n c y near 0.5Hz. T h i s c u t - o f f f r e q u e n c y v a r i e s w i t h duct c o n d i t i o n s and has been v a r i o u s l y c a l c u l a t e d a t 0.45Hz by Manchester (1968), w i t h the c u t - o f f b e i n g due t o a t t e n u a t i o n , and depending on the i o n i z a t i o n c o n d i t i o n s between 0.10 and 0.36 Hz by G r e i f i n g e r and G r e i f i n g e r (1968), w i t h the c u t - o f f b e i n g due t o boundary c o n d i t i o n s . One a s p e c t on which the d i f f e r e n t models agree f a i r l y w e l l , b o th among themselves and w i t h o b s e r v a t i o n s , i s the group v e l o c i t y of f a s t mode p r o p a g a t i o n w i t h i n the d u c t , which i s t y p i c a l l y 300-800 km/sec, depending on i o n o s p h e r i c c o n d i t i o n s ( T e p l e y and L a n d s h o f f , 1966; Manchester, 1966, 1968; G r e i f i n g e r and G r e i f i n g e r , 1968; Altman and F i j a l k o w , 1980). Note t h a t two of the most i m p o r t a n t f a c t o r s c o n t r o l l i n g i o n i z a t i o n c o n d i t i o n s i n the i o n o s p h e r i c waveguide a r e the l o c a l time and the sunspot number. The events s t u d i e d i n t h i s t h e s i s were r e c o r d e d near sunspot maximum. The waveguide r e s u l t s d i s c u s s e d so f a r have been f o r m e r i d i o n a l p r o p a g a t i o n o n l y , s i n c e a common s i m p l i f y i n g assumption i n duct models, j u s t i f i e d by some e x p e r i m e n t a l r e s u l t s , has been t o c o n s i d e r o n l y p r o p a g a t i o n i n t h i s 223 d i r e c t i o n . G r e i f i n g e r and G r e i f i n g e r (1973) showed t h a t , f o r o f f - m e r i d i a n d i r e c t i o n s , c o u p l i n g between the d u c t e d f a s t mode wave and the f i e l d g u i d e d slow mode wave produces g e n e r a l l y two t o f o u r l a r g e peaks i n a t t e n u a t i o n w i t h i n the IPDP f r e q u e n c y band. The f r e q u e n c y ranges c o v e r e d by t h e s e peaks, each of which i s = 0.1 t o 0.3 Hz wide, a r e dependent on geomagnetic l a t i t u d e . Thus, f o r any o f f - m e r i d i a n d i r e c t i o n e x cept p u r e l y e a s t - w e s t , each f r e q u e n c y component of a wave w i l l e ncounter a r e g i o n of h i g h a t t e n u a t i o n as the l a t i t u d e v a r i e s a l o n g the wave's p a t h , e f f e c t i v e l y e l i m i n a t i n g o f f - m e r i d i o n a l d u c t i n g ( G r e i f i n g e r and G r e i f i n g e r , 1973). The t r e a t m e n t of Altman and F i j a l k o w (1980) i n c l u d e d d u c t i n g i n both the n o r t h - s o u t h and e a s t - w e s t d i r e c t i o n s , and found t h a t a t t e n u a t i o n of waves t r a v e l l i n g i n the e a s t - w e s t d i r e c t i o n t o be g e n e r a l l y o n l y s l i g h t l y l a r g e r than f o r those t r a v e l l i n g a l o n g the m e r i d i a n . E x p e r i m e n t a l l y , the Pc 1 o b s e r v a t i o n s of Hayashi et a l . (1981) a l s o i n d i c a t e t h a t d u c t i n g o c c u r s p r e f e r e n t i a l l y i n the e a s t - w e s t and n o r t h - s o u t h d i r e c t i o n s . The p o l a r i z a t i o n c h a r a c t e r i s t i c s of some Pc 1 band m i c r o p u l s a t i o n s , i n c l u d i n g IPDPs, can be v e r y u s e f u l i n u n d e r s t a n d i n g these e v e n t s . As s t a t e d above, the i n i t i a l i ncoming slow mode wave has LH p o l a r i z a t i o n . However, the d u c t e d mode i n t o which i t i s c o n v e r t e d , the f a s t mode, has RH p o l a r i z a t i o n . T h i s c o u l d be e x p e c t e d t o l e a d t o 224 o b s e r v a t i o n s of LH p o l a r i z a t i o n a t ground s t a t i o n s below the incoming f i e l d g uided wave, and RH p o l a r i z a t i o n a t s t a t i o n s beneath the d u c t e d wave. However, i t has been shown t h a t the h o r i z o n t a l component p e r p e n d i c u l a r t o the d i r e c t i o n of p r o p a g a t i o n i s not t r a n s m i t t e d t o the s u r f a c e , so t h a t , a t l a r g e d i s t a n c e s from the source f i e l d l i n e s , the p o l a r i z a t i o n s h o u l d be n e a r l y l i n e a r w i t h the e l l i p s e a x i s a l i g n e d w i t h the d i r e c t i o n of p r o p a g a t i o n ( G r e i f i n g e r and G r e i f i n g e r , 1968; Rudenko et a l . , 1985). The v e r t i c a l component of the wave f i e l d w i l l v a n i s h a t the s u r f a c e , assuming i n f i n i t e ground c o n d u c t i v i t y ( G r e i f i n g e r , 1972). In r e g i o n s near but not under the incoming wave, the p o l a r i z a t i o n s can be complex, w i t h the d i r e c t wave, here a p p e a r i n g as RH ( G r e i f i n g e r , 1972), superimposed on the l i n e a r appearance of the d u c t e d wave. E x p e r i m e n t a l l y , A l t h o u s e and D a v i s (1978) and Hayashi et a l . (1981) o b t a i n e d mixed r e s u l t s from Pc 1 p o l a r i z a t i o n s t u d i e s , though i n the former case s t a t i o n s f a r from the source d i d show m a i n l y l i n e a r p o l a r i z a t i o n . These r e s u l t s may be due t o the near source complex r e g i o n noted above and/or t o the s u p e r p o s i t i o n of two or more waves a r r i v i n g a t the same s i t e from d i f f e r e n t d i r e c t i o n s as a r e s u l t of h o r i z o n t a l g r a d i e n t s i n i o n o s p h e r i c d e n s i t i e s a f f e c t i n g wave p r o p a g a t i o n p a t h s (Altman and F i j a l k o w , 1980). In g e n e r a l t h e r e i s a r e a s o n a b l y good q u a l i t a t i v e match 225 between most model c a l c u l a t i o n r e s u l t s and duct p r o p a g a t i o n o b s e r v a t i o n s . Examples of t h i s i n c l u d e the e x i s t e n c e of a c u t - o f f f r e q u e n c y , g e n e r a l p o l a r i z a t i o n p a t t e r n s , d i u r n a l v a r i a t i o n s i n duct a t t e n u a t i o n , and l a c k of a s i g n i f i c a n t v e r t i c a l wave component. However, on a more d e t a i l e d l e v e l , i n c l u d i n g q u a n t i t a t i v e a s p e c t s , the models' p r e d i c t i o n s do not always agree w e l l w i t h each o t h e r or w i t h e x p e r i m e n t a l r e s u l t s . T h i s i s q u i t e l i k e l y due t o the d i f f e r e n t approaches taken by some a u t h o r s , and, perhaps more i m p o r t a n t l y , the v a r i a n t assumptions used i n t h e i r d i f f e r e n t works. These assumptions i n c l u d e , among o t h e r a s p e c t s ; v e r t i c a l s t r a t i f i c a t i o n s of the i o n o s p h e r e , wave i n c i d e n c e a n g l e s , h o r i z o n t a l homogeneity i n the i o n o s p h e r e , c o l l i s i o n s , mode c o u p l i n g , background magnetic f i e l d s , and ground c o n d u c t i v i t y . Such d i s a g r e e m e n t s make i t i m p r a c t i c a l t o use any s p e c i f i c r e s u l t s as an a i d t o IPDP i n t e r p r e t a t i o n . T h e r e f o r e , the c h a r a c t e r i s t i c s of i o n o s p h e r i c p r o p a g a t i o n r e q u i r e d i n t h i s t h e s i s have been o b t a i n e d from the d a t a a n a l y s e d f o r the Feb. 14 and Feb. 15 IPDPs. A t t e n u a t i o n has been c a l c u l a t e d from the measured s i g n a l l e v e l s from s t a t i o n s on a n o r t h - s o u t h l i n e , and proved t o be g r e a t e r than most model r e s u l t s . W h i l e the a t t e n u a t i o n found from the daytime e v e n t , the Feb. 15 e v e n t , was l a r g e r than t h a t f o r the n i g h t e v e n t , the Feb. 14 IPDP, the d i f f e r e n c e was 226 not as extreme as p r e d i c t e d . The p o l a r i z a t i o n p a t t e r n seen i n t h e s e IPDPs of LH below the secondary source and RH elsewhere was as e x p e c t e d . In a d d i t i o n , t h e r e were i n t e r v a l s of LH p o l a r i z a t i o n c o v e r i n g the low f r e q u e n c y b e g i n n i n g s of the e v e n t s , i n d i c a t i n g the presence of non-ducted waves a t f r e q u e n c i e s below the duct c u t - o f f f r e q u e n c y . These c u t - o f f f r e q u e n c i e s were g e n e r a l l y s i m i l a r t o , though somewhat h i g h e r t h a n , the e x p e c t e d v a l u e s . The p a t t e r n of t h e i r d i u r n a l v a r i a t i o n , lower d u r i n g the day, was as p r e d i c t e d . APPENDIX C. GEOMAGNETIC INDICES A geomagnetic index i s a system which a t t e m p t s t o p r o v i d e summarized i n f o r m a t i o n c o n c e r n i n g the b e h a v i o u r of a s p e c i f i c geomagnetic v a r i a t i o n . I n d i c e s a re g e n e r a l l y p r e s e n t e d as d i s c r e t e v a l u e s c a l c u l a t e d from a c e r t a i n time i n t e r v a l u s i n g d a t a from one or more geomagnetic o b s e r v a t o r i e s . There a r e a number of d i f f e r e n t k i n d s of geomagnetic i n d i c e s r e l a t e d t o v a r i o u s geomagnetic phenomena of both l o c a l and p l a n e t a r y s c a l e . An index i s not o n l y u s e f u l f o r s t u d y i n g the s p e c i f i c geomagnetic v a r i a t i o n from which i t i s c a l c u l a t e d , but can a l s o be h e l p f u l i n u n d e r s t a n d i n g r e l a t e d geomagnetic phenomena. In t h i s t h e s i s , we have used or mentioned t h r e e i n d i c e s i n the l a t t e r manner. These a r e the Dst index ( r i n g c u r r e n t ) , the Kp index (magnetospheric a c t i v i t y ) , and the AE index ( a u r o r a l e l e c t r o j e t s ) . A d e s c r i p t i o n of each of the s e i s p r e s e n t e d below. I f more i n f o r m a t i o n on t h e s e , or o t h e r , i n d i c e s i s d e s i r e d , the re a d e r s h o u l d r e f e r t o the monograph of Mayaud (1980). Dst Index The magnetic f i e l d of the, r i n g c u r r e n t , which f l o w s westward around E a r t h i n the e q u a t o r i a l p l a n e , has the e f f e c t of d e p r e s s i n g the d i p o l e f i e l d a t E a r t h ' s magnetic e q u a t o r . The Dst index i s i n t e n d e d t o mon i t o r t h i s e f f e c t , and t h e r e f o r e a l s o monitor the i n t e n s i t y of the r i n g c u r r e n t 227 228 i t s e l f . I t does t h i s q u i t e w e l l , and i s p r o b a b l y the most a c c u r a t e of a l l the geomagnetic i n d i c e s i n r e p r e s e n t i n g the phenomenon f o r which i t i s d e r i v e d . There a r e , however, some d i f f i c u l t i e s i n d e t e r m i n i n g the Dst i n d e x ; most i m p o r t a n t l y , s e p a r a t i n g r i n g c u r r e n t v a r i a t i o n s from o t h e r t r a n s i e n t v a r i a t i o n s and from s e c u l a r v a r i a t i o n s . Some t r a n s i e n t v a r i a t i o n s a r e averaged out by the one hour i n t e r v a l over which each v a l u e of the Dst index i s c a l c u l a t e d . O t h e r s , such as the f i r s t phase of a storm, t h a t i s , the p e r i o d of i n c r e a s e d H-component which may precede the main phase of a storm, can c o n t r i b u t e t o the i n d e x , however. The e f f e c t of the DP 2 i r r e g u l a r v a r i a t i o n , q u a s i - p e r i o d i c f l u c t u a t i o n s w i t h a p e r i o d of =1 hour, c o u l d s i g n i f i c a n t l y i n t e r f e r e w i t h the Dst index near the e q u a t o r , but i t s e f f e c t i s m i n i m i z e d by not u s i n g e q u a t o r i a l s t a t i o n s i n the c a l c u l a t i o n of the i n d e x . A u r o r a l d i s t u r b a n c e s c o u l d a l s o a f f e c t t h i s i n d e x , though, the e f f e c t of the westward e l e c t r o j e t i s minor a t low l a t i t u d e s , and the eastward e l e c t r o j e t i s r e c o g n i z e d as b e i n g due t o the p a r t i a l r i n g c u r r e n t a l l o w i n g i t s e f f e c t s t o be c o n s i d e r e d p a r t of the phenomenon b e i n g m o n i t o r e d (Mayaud, 1980). The r e g u l a r d a i l y v a r i a t i o n s must a l s o be removed i n o r d e r t o a c c u r a t e l y c a l c u l a t e the Dst i n d e x . T h i s i s a c c o m p l i s h e d by computing a s t a t i s t i c a l v e r s i o n of t h i s d a i l y v a r i a t i o n from the f i v e q u i e t e s t days of each month, and then s u b t r a c t i n g t h i s from 229 the observed d a t a f o r each day of t h a t month. S i n c e the d a i l y v a r i a t i o n s are not c o n s t a n t from day t o day, t h e r e are n e c e s s a r i l y e r r o r s i n t r o d u c e d by t h i s p r o c e s s though these s h o u l d be reduced somewhat when a l l the s t a t i o n s a r e averaged t o g e t h e r t o produce the a c t u a l Dst i n d e x . Note a l s o t h a t these d a i l y v a r i a t i o n s do not a f f e c t the s t a t i o n s when they are on the n i g h t s i d e of E a r t h . L a s t l y , s e c u l a r v a r i a t i o n s must a l s o be removed i f the Dst index i s t o be u s e f u l f o r l o n g term s t u d i e s . B e f o r e a c t u a l c a l c u l a t i o n of the Dst index can b e g i n , a r e f e r e n c e l e v e l must be s e t . T h i s i s d e t e r m i n e d from the H-component annual means c a l c u l a t e d from the f i v e q u i e t e s t days of each month (Mayaud, 1980). Note t h a t t h i s r e f e r e n c e l e v e l i s not a z e r o l e v e l , s i n c e the r i n g c u r r e n t always e x i s t s , and t h e r e f o r e o n l y p r o v i d e s a r e f e r e n c e t o r i n g c u r r e n t i n t e n s i t y i n v e r y q u i e t t i m e s . For each s t a t i o n , a raw Dst e s t i m a t e i s then c a l c u l a t e d as f o l l o w s : Dst = H o b s - S q ( t ) - H 0 ( t ) (C.I) where H ^ i s the o b s e r v e d H-component of the magnetic f i e l d , S q ( t ) i s the e s t i m a t e d d a i l y v a r i a t i o n , and H 0 ( t ) i s the r e f e r e n c e l e v e l . These Dst e s t i m a t e s from each s t a t i o n a r e averaged t o remove l o c a l e f f e c t s and then c o r r e c t e d f o r l a t i t u d e i n o r d e r t o y i e l d the r i n g c u r r e n t e f f e c t a t the 230 e q u a t o r . T h i s l a s t s t e p r e q u i r e s t h a t the s t a t i o n s a l l be a t s i m i l a r l a t i t u d e s . The a c t u a l o b s e r v a t o r i e s used a r e H o n o l u l u ( H a w a i i ) , San Juan ( P u e r t o R i c o ) , Hermanus (South A f r i c a ) , and K a k i o k a ( J a p a n ) . They a r e w e l l s p r e a d out i n l o n g i t u d e i n o r d e r t o m i n i m i z e l o c a l e f f e c t s , and average about 28\u00C2\u00B0 from the geomagnetic e q u a t o r . T h i s i s a t a low enough l a t i t u d e t o be near the r i n g c u r r e n t and t o m i n i m i z e a u r o r a l e f f e c t s , and s t i l l f a r enough from the e q u a t o r t o a v o i d DP 2 i n t e r f e r e n c e . W i t h t h i s p r o c e s s , a f i n a l Dst i s c a l c u l a t e d , i n 7, f o r each h o u r l y i n t e r v a l , l e a v i n g a s i m p l e s e t of 24 Dst v a l u e s per day. The index can be e i t h e r p o s i t i v e or n e g a t i v e . Large n e g a t i v e v a l u e s are i n d i c a t i v e of l a r g e magnetic f i e l d d e p r e s s i o n s a t the e q u a t o r , common d u r i n g storm t i m e s when the r i n g c u r r e n t becomes s t r o n g l y enhanced by substorm plasma i n j e c t i o n s . Kp Index The Kp index c o n s i s t s of a q u a s i - l o g a r i t h m i c s c a l e i n d i c a t i v e of mid t o h i g h l a t i t u d e geomagnetic a c t i v i t y on a p l a n e t - w i d e b a s i s . I t i s d e r i v e d from l o c a l K i n d i c e s c a l c u l a t e d a t 11 geomagnetic o b s e r v a t o r i e s r a n g i n g from 45\u00C2\u00B0 t o 63\u00C2\u00B0 c o r r e c t e d geomagnetic l a t i t u d e (Hakura, 1965). The K index a t each o b s e r v a t o r y i s d e t e r m i n e d f o r each 3-hour p e r i o d , f o r example, 0000-0300 UT, from the component, e i t h e r H or D, showing the l a r g e r range of 231 i r r e g u l a r v a r i a t i o n s w i t h i n t h a t p e r i o d . The index i s i n t e n d e d t o be s e n s i t i v e t o i r r e g u l a r v a r i a t i o n s o n l y and, as w i t h the Dst i n d e x , the r e g u l a r d a i l y v a r i a t i o n must be removed. The range from the chosen component, the d i f f e r e n c e between the maximum and minimum l e v e l s of t h a t component w i t h i n the s p e c i f i e d i n t e r v a l , i s then a s s i g n e d t o a c l a s s of ranges, each w i t h an a s s o c i a t e d number from 0 t o 9. The d i v i d i n g l i n e s between th e s e range c l a s s e s i n c r e a s e q u a s i - l o g a r i t h m i c a l l y and a r e a d j u s t e d by l a t i t u d e , s i n c e the a m p l i t u d e of the ranges d i s p l a y e d v a r i e s s t r o n g l y w i t h l a t i t u d e . T h i s adjustment makes the d i s t r i b u t i o n of K i n d i c e s u n i f o r m a t each o b s e r v a t o r y . B e f o r e the Kp index can be d e t e r m i n e d from the K i n d i c e s produced by the 11 o b s e r v a t o r i e s , f u r t h e r s t a n d a r d i z a t i o n of the v a r i o u s K's must t a k e p l a c e . Beyond l a t i t u d i n a l e f f e c t s , t h e r e e x i s t f u r t h e r d i f f e r e n c e s i n the K's from each of the o b s e r v a t o r i e s , and a l s o from a s i n g l e o b s e r v a t o r y i n d i f f e r e n t seasons. These a r e removed by d e t e r m i n i n g c o n v e r s i o n t a b l e s f o r each o b s e r v a t o r y which enable t h e i r K's t o be c o n v e r t e d i n t o a s t a n d a r d i z e d form, termed Ks. The Kp index i s then j u s t an average of the Ks i n d i c e s f o r each 3-hour p e r i o d from the 11 o b s e r v a t o r i e s d i s t r i b u t e d around the g l o b e . The Kp s c a l e i s a c t u a l l y d i v i d e d i n t o f i n e r i n t e r v a l s than the whole numbers mentioned above. Each K range c l a s s i s s p l i t i n t o t h i r d s , 232 g i v i n g a s c a l e where the Kp = 2 range, f o r example, i s d i v i d e d e q u a l l y i n t o Kp = 2 . , 2 0 , and 2 + s e c t i o n s . A c t i v e storm t i m e s t y p i c a l l y have Kp's of between 3 and 6, w h i l e Kp's of =8 or more, r e p r e s e n t i n g e x t r e m e l y a c t i v e t i m e s , a re q u i t e r a r e . C o n v e r s e l y , v e r y q u i e t p e r i o d s , which a r e much more common than Kp > 6 t i m e s , have Kp's of l e s s than 1. AE Index The AE index i s d e s i g n e d t o be a measure of g l o b a l a u r o r a l e l e c t r o j e t a c t i v i t y . The e l e c t r o j e t s a r e the predominant form of a u r o r a l - z o n e magnetic v a r i a t i o n . Thus, as i n the case of the Dst index but d i f f e r e n t from the Kp in d e x , a w e l l d e f i n e d c l a s s of i r r e g u l a r v a r i a t i o n s i s b e i n g m o n i t o r e d . A g l o b a l network of up t o 13 o b s e r v a t o r i e s a t or near a u r o r a l zone l a t i t u d e s , of =70\u00C2\u00B0 c o r r e c t e d GM L a t . , i s used t o d e t e r m i n e the AE i n d e x . The c u r r e n t d i r e c t i o n s of the eastward and westward e l e c t r o j e t s make the H-component the l o g i c a l one t o use i n d e t e r m i n i n g t h i s i n d e x , w i t h the eastward e l e c t r o j e t p r o d u c i n g p o s i t i v e AH d e v i a t i o n s and the westward e l e c t r o j e t n e g a t i v e AH d e v i a t i o n s . For each month, the r e f e r e n c e l e v e l from which th e s e d e v i a t i o n s a r e c a l c u l a t e d i s de t e r m i n e d u s i n g an average of the H-component of the f i v e q u i e t e s t days of t h a t month. A f t e r removal of the r e f e r e n c e l e v e l , the H-component t r a c e s from a l l of thes e s t a t i o n s a re superimposed, y i e l d i n g upper and lower 233 e n v e l o p e s . The upper envelope i s the AU i n d e x , and m o n i t o r s the eastward e l e c t r o j e t , w h i l e the lower envelope i s the AL i n d e x , which m o n i t o r s the westward e l e c t r o j e t . T h i s envelope t e c h n i q u e means t h a t , f o r any s p e c i f i c t i m e , each index i s a c t u a l l y g i v e n by the one s t a t i o n b e s t s i t u a t e d t o observe t h a t e l e c t r o j e t a t t h a t t i m e . Note t h a t t h e s e i n d i c e s a r e produced i n a d i g i t a l form w i t h a 2.5 minute sam p l i n g r a t e . The AE index i s s i m p l y the d i f f e r e n c e between the AU and AL i n d i c e s , t h a t i s : AE = AU - AL. T h i s o p e r a t i o n removes r i n g c u r r e n t c o n t a m i n a t i o n , which i s s i g n i f i c a n t o n l y i n v e r y a c t i v e t i m e s , from the AU and AL i n d i c e s , l e a v i n g the AE index dependent o n l y on the e l e c t r o j e t s . A c t u a l l y , the r e g u l a r d a i l y v a r i a t i o n s t i l l i n t e r f e r s w i t h the AE i n d e x , but i s q u i t e s m a l l , =*10S of 7, compared t o e l e c t r o j e t AH a m p l i t u d e s of -100s of 7. Other d i f f i c u l t i e s which can i n t e r f e r e w i t h t h i s index i n c l u d e v a r i o u s , and unknown, ground i n d u c t i o n e f f e c t s a t the o b s e r v a t o r i e s , the H-component not b e i n g n e c e s s a r i l y p r e c i s e l y normal t o the c u r r e n t d i r e c t i o n s , and a l e s s than i d e a l d i s t r i b u t i o n w i t h r e s p e c t t o l a t i t u d e and l o n g i t u d e of the o b s e r v a t o r y network as caused l a r g e l y by the uneven d i s t r i b u t i o n of l a n d masses. S i n c e the a u r o r a l e l e c t r o j e t s a r e a d i r e c t r e s u l t of magnetospheric storms, the AE index reaches l a r g e v a l u e s , o f t e n >10007, i n stormy p e r i o d s , w h i l e v e r y q u i e t t i m e s can have AEs of <1007. "@en . "Thesis/Dissertation"@en . "10.14288/1.0052627"@en . "eng"@en . "Geophysics"@en . "Vancouver : University of British Columbia Library"@en . "University of British Columbia"@en . "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en . "Graduate"@en . "The generation of IPDP micropulsations, with special attention to frequency shift mechanisms"@en . "Text"@en . "http://hdl.handle.net/2429/29132"@en .