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Related investigations of pi 2 micropulsations Smith, Brian Paul 1972

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c i  RELATED INVESTIGATIONS OF P i 2 MICROPULSATIONS by BRIAN PAUL SMITH B . S c , University of B r i t i s h Columbia, 1 9 7 0  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of GEOPHYSICS  We accept t h i s thesis as conforming t o the required standard  THE UNIVERSITY OF BRITISH COLUMBIA August, 1 9 7 2  In presenting this thesis in p a r t i a l fulfilment of the requirements for an advanced degree.at the University of B r i t i s h Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives.  It i s understood that copying or publication  of this thesis for financial gain shall not be allowed without my written permission.  Department of  Geophysics  The University of B r i t i s h Columbia Vancouver 8, Canada  Date  August 29 1972 r  ii  ABSTRACT Related investigations of i r r e g u l a r , nighttime, type P i 2 micropulsations were undertaken with regards t o the source and occurrence of these geomagnetic f l u c t u a t i o n s . In p a r t i c u l a r , the l o c a l times of P i 2's recorded by a global network of stations, during 1964, were determined. From t h i s , the P i 2 d a i l y occurrence maximum was observed near 2230 LMT. For t h i s same year (1964), rapid-run magnetograms from Memambetsu, Japan and Wingst, Germany were analyzed.  The i n i t i a l orientation of the impulsive P i 2  disturbance vectors was observed t o be primarily northeast (north-west) before (after) 2230 LMT. These results suggest that P i 2 source f i e l d lines l i e near the 2230 LMT meridian. Further investigations of the globally observed P i 2's were made regarding variations i n morphology with magnetic a c t i v i t y . The d a i l y occurrence maximum of P i 2 was found e a r l i e r ( l a t e r ) at 2030 (2330) LMT during i n t e r vals of high (low) magnetic a c t i v i t y .  In t h i s manner, the  longitudinal s h i f t of the P i 2 source i s revealed. A s t a t i s t i c a l study of solar wind protons observed by Explorer 34 s a t e l l i t e was made during the i n t e r v a l s of high, and of low, magnetic a c t i v i t y . This study showed that the P i 2 source s h i f t may be due t o a change i n the solar wind flow  iii  d i r e c t i o n and/or processes a s s o c i a t e d w i t h changes i n the s o l a r wind proton p r e s s u r e . Pi 2 s f  are a t r a i n of p u l s a t i o n s having q u a s i -  p e r i o d s ranging from 40 t o 150 seconds and each s e r i e s l a s t s about 10 minutes.  The  p e r i o d s of P i 2 m i c r o p u l s a t i o n s  recorded at R a l s t o n , Canada d u r i n g 196? were c o r r e l a t e d w i t h simultaneous, A l o u e t t e 2 s a t e l l i t e r e c e i v e d , VLF r a d i o signals.  Some of these VLF e m i s s i o n phenomena, known as  ' w h i s t l e r c u t o f f * and  'lower h y b r i d resonance  breakup', i n d i c a t e d the l o c a t i o n of the plasmapause.  n o i s e band  magnetospheric  Other e m i s s i o n s , known as ELF, were b e l i e v e d  t o i n d i c a t e the plasma sheet i n n e r boundary.  The  vari-  a t i o n of the p e r i o d of the P i 2's w i t h the i n d i c a t e d magn e t o s p h e r i c subregion l o c a t i o n s showed t h a t P i 2 p e r i o d v a r i e s s y s t e m a t i c a l l y w i t h p o s i t i o n s of the plasma sheet i n n e r boundary d u r i n g i n t e r v a l s of magnetic The r e s u l t s imply a l a t i t u d i n a l  quiescence.  ( r a d i a l ) movement of the  P i 2 source i n a r e g i o n near the plasma sheet i n n e r boundary. L a s t l y , the r a t e o f P i 2 occurrence w i t h magnetic a c t i v i t y , d u r i n g 1964  and 1967, was  found t o be maximum  when the p l a n e t a r y index of magnetic a c t i v i t y , Kp, was t o 2-.  1+  The mean Kp index most c l o s e l y approaches t h i s  optimum l e ^ e l d u r i n g the years of sunspot  minimum*  Thus,  the r a t e of occurrence r e s u l t i s c o n s i s t e n t w i t h the i n v e r s e  iv  relationship of P i 2 yearly occurrence with the solar cycle. In summation, the source studies revealed a •dynamic* P i 2 source, i n the sense that i t varies both l a t i t u d i n a l l y and l o n g i t u d i n a l l y .  An association was shown  between P i 2 and nightside magnetospheric subregions.  processes and  The occurrence study indicated that processes  generating P i 2*s are not clear but approach optimum when the Kp l e v e l i s between 1+ and 2-.  V  TABLE OF CONTENTS Page ABSTRACT  i i  LIST OF TABLES  vi  LIST OF FIGURES  vi  ACKNOWLEDGEMENTS CHAPTER I  viii  A BACKGROUND TO INVESTIGATIONS? OF P i 2  1  a.  Introduction  1  b.  P i 2 Morphology  4  c.  Subregions of the Magnetosphere  7  d.  Theories of P i 2  12  CHAPTER I I , RELATED INVESTIGATIONS OF P i 2 MICROPULSATIONS a.  VLF Emissions and P i 2 Period  20  b. c.  P i 2 Diurnal Variations P i 2, Solar Wind and Geomagnetic Activity  2g 30;  d«  P i 2 Rate of Occurrence  39  CHAPTER I I I DISCUSSION OF THE RESULTS  CHAPTER IV BIBLIOGRAPHY  20  43  a.  P i 2 and Magnetospheric Subregions  43  b.  P i 2 Source  46  c.  P i 2 Source Variations  4#  d.  On the P i 2 Rate of Occurrence  49  SUMMARY AND CONCLUDING REMARKS  53 57  vi  LIST OF TABLES Page Date, UT, type of r a d i o s i g n a l r e c e i v e d by, and p o s i t i o n of A l o u e t t e 2 c o r r e l a t e d w i t h P i 2 p e r i o d at R a l s t o n  25  LIST OF FIGURES 1  Magnetospheric subregion L v a l u e a t i o n s of P i 2 p e r i o d  2  Magnetograms at i n i t i a l l y (X+,  3 4 5  6  7  & 9  Y-I  vari-  northwest  Pi 2  Magnetograms of i n i t i a l l y (X+, Y+7 P i 2  26  31 northeast 32  D i u r n a l v a r i a t i o n of i n i t i a l l y northwest and northeast P i 2 occurrence f r e q u e n c i e s  33  D i u r n a l v a r i a t i o n of t h e i n i t i a l l y n o r t h east P i 2 occurrence p r o b a b i l i t y and t h e t o t a l P i 2 occurrence frequency  34  D i u r n a l v a r i a t i o n o f P i 2 occurrence frequency d u r i n g high and low magnetic activity  36  S o l a r wind streaming angle v a r i a t i o n of p a r t i c l e pressure d u r i n g high and low magnetic a c t i v i t y  3#  Kp v a r i a t i o n of t h e P i 2 occurrence d u r i n g 1964 and 1967  41  rate  N i g h t s i d e e q u a t o r i a l magnetospheric conv e c t i v e system, near t h e plasmapause, d u r i n g low magnetic a c t i v i t y  50  vii  Nightside equatorial magnetospheric cpnvective system, near the plasmapause, during high magnetic a c t i v i t y Motion of magnetospheric plasmas due to an implosion (Smith and Watanabe, 1972)  viii  ACKNOWLEDGEMENTS I wish to thank Professor Tomiya Watanabe of the University of B r i t i s h Columbia f o r suggesting and encouraging much of the work undertaken i n t h i s t h e s i s .  His many  discussions and h e l p f u l comments oh the thesis were greatly appreciated. The Alouette 2 data was prepared by Drs. R. E . Barrington and F. H. Palmer of the Communications Research Centre, Ottawa.  I would l i k e to thank them f o r providing  t h i s information, and also Dr. R. E. Horita of the Univ e r s i t y of V i c t o r i a f o r h i s h e l p f u l comments regarding t h i s study. The 1967 micropulsation data recorded at Ralston was kindly provided by S i r Charles S. Wright, Dr. J . E . Lokken and h i s s t a f f at the Defense Research Establishment P a c i f i c , Esquimalt.  I also wish t o thank Mr. H. Ueda f o r  his assistance i n reproducing t h i s micropulsation data. The Explorer 34 solar wind data were supplied by the World Data Centre A", Rockets and S a t e l l i t e s , Goddard Space F l i g h t Centre, NASA, Greenbelt, Maryland.  The  Memambetsu and Wingst rapid-run magnetograms were supplied by the World Data Centre A, f o r S o l a r - T e r r e s t r i a l Physics, National Oceanic and Atmospheric Administration, Boulder, Colorado.  I wish to thank these centres f o r providing t h i s  ix  service. This thesis was supported by National Research Council operating grant  A3564,  major equipment grant E2032  and Defense Research Board grant Watanabe.  9511-112  to Dr. T.  CHAPTER I A BACKGROUND TO INVESTIGATIONS OF P i 2  a.  Introduction Pi 2 type geomagnetic micropulsations are i r r e g u l a r  f l u c t u a t i o n s , having a quasi-period between 40 and 150 seconds.  They are primarily nighttime phenomena, appearing  as a series of impulsive o s c i l l a t i o n s which usually last 5 to 10 minutes.  They are often associated with geomagnetic  bay disturbances (Angenheister,  1913; Terada, 1917), f l u c -  tuations i n auroral luminosity (Fukunishi and Hirasawa, 1970)  and intensity fluctuations of charged p a r t i c l e s pre-  c i p i t a t i n g upon the ionosphere (Milton, McPherron, Anderson and Ward,  1967). The frequency of occurrence of t h i s type  of micropulsation i s maximum during the years of minimum sunspot a c t i v i t y (Yanagihara,  1956). I t i s observed that  Pi 2 tends to occur with a quasi-period similar t o the sunspot rotation period, 26 to 29 days (Saito and Matsushita,  196S). The interaction of the solar wind and the t e r r e s t r i a l magnetic f i e l d can possibly give r i s e to geomagnetic micropulsations. reported.  Much evidence of t h i s i n t e r a c t i o n has been  The magnetopause, or boundary of t h i s solar-  t e r r e s t r i a l i n t e r a c t i o n , has been observed with the a i d of s a t e l l i t e experiments  ( C a h i l l and Amazeen,  1963; Ness, 1965).  2  Hydromagnetic i n t e r a c t i o n between solar wind d i s c o n t i n u i t i e s and the t e r r e s t r i a l magnetic f i e l d have also been reported (Oglivie and Burgala, 1970).  Yet the solar wind stimulates  not only geomagnetic a c t i v i t y , such as large scale magnetic storms but also causes variations i n the structure of the region inside the magnetopause, v i z . the magnetosphere. Carpenter (1970), Hones, Asbridge and Bame (1971) have observed changes i n magnetospheric subregions with varying magnetic a c t i v i t y , v i z . the e x t r a t e r r e s t r i a l r i n g current, the plasmapause bulge and the magnetotail plasmasheet, r e spectively.  These observations  tween micropulsations exist.  imply that associations be-  and magnetospheric subregions may also  One of the investigations reported i n t h i s thesis  shows a systematic v a r i a t i o n i n P i 2 period with the l o c a t i o n of a subregion of the magnetosphere. The morphology of geomagnetic  micropulsations  should, i n some manner, r e f l e c t the nature of the source responsible f o r these fluctuations of the earth's f i e l d . review of the subject of micropulsations  (Jacobs,  A  1967)  reveals that P i 2 morphology has been considerable well i n vestigated.  Yet studies of variations of P i 2 morphology  with magnetic a c t i v i t y have been less consistent.  Such  studies may provide more information on the source mechanism of P i 2.  In t h i s t h e s i s , a correlated investigation  of P i 2 morphology i s reported.  Also reported i s a morpho-  3  logic v a r i a t i o n study of the change i n the most probable time of P i 2 occurrence, with magnetic a c t i v i t y and with the solar wind.  As mentioned, morphologic v a r i a t i o n  studies have been less consistent and some investigators have reported  contradicting observations.  To s e t t l e some  of these contradictions, the v a r i a t i o n i n the rate of P i 2 occurrence with the three hour planetary  index of magnetic  a c t i v i t y , K p , has been investigated and reported  i n the  l a s t part of t h i s t h e s i s . The existence  purpose of t h i s thesis i s t o e s t a b l i s h the  of relationships among P i 2 micropulsations^; the  magnetosphere, and the solar wind.  This i s achieved through  the investigations into P i 2 which were previewed i n the above.  In some of these studies, correlations were made  with s a t e l l i t e observations of VLF radio signals i n the magnetosphere and also of protons i n the solar wind. The implications of these studies are discussed with regards t o the source and generation of P i 2 micropulsations.  However,  interpretations of experimental r e s u l t s often d i f f e r . For t h i s reason i t i s necessary t o outline the established morphology of P i 2.  In order t o understand the implied  association of P i 2 micropulsations with the magnetosphere, a review of the observed dynamics of magnetospheric subregions i s also presented.  Lastly, various theories sug-  gesting the mechanism of P i 2 generation are developed.  4  Some of these theories, based on certain i n v e s t i g a t i o n a l r e s u l t s , require different locations f o r the P i 2 source. A discussion of these theories i s then useful, to more f u l l y comprehend the generation and source of P i 2 micropulsations.  b.  P i 2 Morphology In general, P i 2 amplitude increases with l a t i t u d e ,  reaching maximum near the auroral zones (Saito and Sakur8i, 197Q).  Although a few investigators have found an equa-  t o r i a l enhancement of P i 2, the maximum amplitude i s found at regions higher than 50° geomagnetic latitude (Jacobs and Sinno, I960).  The amplitude of P i 2 i s shown to be maximum  near midnight (Saito et a l . , 1968).  Yet, P i 2's are not  sinusoidal continuous o s c i l l a t i o n s , but rather of an impulsive and i r r e g u l a r nature.  Thus a discussion of the occur-  rence of such micropulsations i s more enlightening than discussing amplitude features. As mentioned, P i 2*s are often associated with geomagnetic bays or baylike phenomena (Saito, 1961).  Pi 2  occurrence has also been connected with impulsive geomagnetic H component variations, during magnetic storms (Fukunishi et a l . , 1970).  The l o c a l time at which P i 2 occur most  frequently i s near 2230 LMT, i n low and middle latitudes  5  (Yanagihara, 1957a; Rostoker, 1967a).  This occurrence  frequency maximum tends to s h i f t from midnight towards dusk longitudes as the Kp index increases (Yanagihara, I960), though t h i s v a r i a t i o n i s not well established and Fernando, 1969).  (Kannangara  Also, some investigations have found  the r8te of P i 2 occurrence t o increase l i n e a r l y with the Kp index (Kannangara et a l . , 1969; Channon and Orr, 1970). Observations by Yanagihara (1956) show that the yearly occurrence frequency of night pulsations* i s inversely T  proportional to the solar a c t i v i t y .  Reports by Afanasieva  (1961) and Saito et a l . (1968) suggest that the peak time of P i 2 occurrence i s found near midnight (2300 to  0100)  during sunspot maximum and at e a r l i e r times (2000 to 2300) during sunspot minimum.  As shown i n Chapter I I , these  occurrence observations imply apparent contradictions. Saito et a l . (1970) gave two examples showing that P i 2 period i s common from middle latitudes through polar regions.  On a random noise type background, Fukunishi et  a l . (1970) observed an 80 second, P i 2 spectral peak at the auroral zone.  This peak was also observed at low 8nd  middle l a t i t u d e s . The evidence suggests that the period of P i 2 micropulsations does not change with l a t i t u d e , presumably even up to the latitudes which divide the magnetotail from the region of closed magnetic l i n e s of force.  A  diurnal v a r i a t i o n of P i 2 period has been shown, with the  6  period increasing towards midnight and decreasing towards noon (Hirasawa and Nagata, 1966; Troitskaya, 1967).  Saito  et a l . (196£) showed that the period of P i 2 associated with geomagnetic bays, i s dependent upon the bay i n t e n s i t y . However Fukunishi et a l . (1970) showed the P i 2 spectral peak decreases i n period with magnetic storm  development.  Troitskaya (1967) showed that P i 2 period decreases with increasing Kp index.  Yet, Rostoker (1967b) observed that  two or more prominent P i 2 spectral peaks may  appear,  especially f o r those events occurring during higher Kp values.  The relationships among bay i n t e n s i t y , storm devel-  opment and Kp are not c l e a r l y understood.  This combined  with the above f a c t s , suggests that there i s not always a direct association of P i 2 with geomagnetic bays and/or with the  Kp index, although such associations are often observed. At  low and middle l a t i t u d e s , the f i r s t pulse of  a P i 2 series on the north-south geomagnetic  component i s  always northward ( B i l l u a d , 1953; Grenet, Kato, Ossaka and Okuda, 1954; Saito, 1961).  The movement of the P i 2 d i s -  turbance vector i s usually north-east (north-west) p r i o r to  (after) midnight (Kato, Ossaka, Watanabe, Okuda and  Tamao, 1956; Yanagihara, I960; Saito et a l . , 1968).  This  i n i t i a l disturbance vector has been shown to converge to the  northern auroral zone on the midnight meridian (Saito  et a l . , 1968).  In middle l a t i t u d e s , the p o l a r i z a t i o n of  7 the P i 2 magnetic disturbance f i e l d tends to be counterclockwise (clockwise) i n the northern (southern) hemisphere ( C h r i s t o f f e l and Linford, 1966; Sakurai, 1970).  Sakurai  also observed that at College, located at a lower auroral zone l a t i t u d e , P i 2 p o l a r i z a t i o n was counterclockwise i n the pre-midnight hours and clockwise i n the hours.  post-midnight  Yet at Point Barrow, located at a higher auroral  zone l a t i t u d e , P i 2 polarization was either clockwise or indeterminate.  As shown i n Chapter III of t h i s t h e s i s ,  p o l a r i z a t i o n morphology can y i e l d information about the o r i g i n of P i 2 micropuisations.  c.  Subregions of the Magnetosphere The magnetospheric plasmapause i s a boundary  which marks an abrupt change i n plasma density at an average equatorial radius of about 4 Re, where 1 Re i s a length equal to the radius of the earth.  At the plasma-  pause, the equatorial electron density changes by a f a c t o r of 10 to 100 (or from approximately 100/crn^ to 1/cv?) within a distance of about 0.15 Re (Angerami and 1966).  Carpenter,  The plasmapause i s asymmetric and has an outward  bulge near the dusk meridian.  The bulge region has been  associated with an interaction between the plasma moving towards the sun from the magnetotail and the flow due to  8  the  earth's rotation (Brice, 1967).  region i s characterized by a  R  -/f  The plasma i n t h i s  density p r o f i l e .  For t h i s  reason, Chappell, Harris and Sharp (1970) suggested that the  bulge i s slowly f i l l e d by p a r t i c l e s from the ionosphere.  During times of low magnetic a c t i v i t y , the plasmapause bulge may be located at distances out to 9 Re and near l o c a l midnight.  However, when a large surge of substorm a c t i v i t y  occurs the bulge moves inward t o distances of about 4 Re and to an e a r l i e r l o c a l time near dusk.  The r a d i a l speed  of t h i s nightside plasmapause motion i s of the order of 0.3 Re/hour (Carpenter and Stone, 1967).  Thus the bulge region  i s l o s t during the main phase of a magnetic storm.  Yet the  dayside plasmasphere appears shielded from storms, as there i s very seldom any r a d i a l movement reported there (Carpenter, 1970).  During the recovery phase, the bulge begins to be  f i l l e d again.  The plasmasphere bulge i s i n an everchanging  state towards dynamic equilibrium, constantly undergoing a supply and loss process by the modulating t a i l plasma flow. One possible mechanism suggested by Carpenter (1970) attributes the loss process to the westward convection d r i f t s of the plasmasphere bulge by the increasing t a i l field.  The described motion and asymmetry of the plasma-  pause i s of p a r t i c u l a r importance to certain P i 2 theories. The equatorial magnetic f i e l d at a distance of 6.6 Re was observed with the ATS 1 s a t e l l i t e .  During  9  magnetic substorms, the f i e l d  at ATS  1 was  observed t o be  depressed i n the dusk t o midnight quadrant.  Partial ring  c u r r e n t s , formed by the inward c o n v e c t i o n of charged part i c l e s near t h e midnight m e r i d i a n , was b e l i e v e d r e s p o n s i b l e f o r the observed d e p r e s s i o n (Cummings, 1966). by S c h i e l d  Computations  (1969) showed t h a t an e x t r a - t e r r e s t r i a l  c u r r e n t weakens (enhances) the geomagnetic f i e l d ( o u t s i d e ) the c u r r e n t s i t e .  ring  inside  D u r i n g magnetic storms, an  asymmetric enhancement of the i n c r e a s i n g r i n g c u r r e n t p r o t o n i n t e n s i t i e s occurs.  The i n c r e a s e s were observed t o be  g r e a t e s t i n the dusk t o midnight quadrant (Frank, 1967 and 1970).  At the same time, no i n c r e a s e s were observed near  l o c a l noon.  The i n c e s s a n t r i n g c u r r e n t of p r o t o n s , u s u a l l y  found at v a l u e s o f L (an e q u a t o r i a l d i s t a n c e i n u n i t s of e a r t h r a d i i ) g r e a t e r t h a n , o r about 6, p e n e t r a t e s t o s m a l l e r L values d u r i n g magnetic storms (Frank and Owens, 1970). The i n t e n s e asymmetric part o f the storm time r i n g decays much more r a p i d l y than the symmetric part 1966).  The r i n g c u r r e n t has been c o n s i d e r e d  currents  (Cummings,  asymmetric  from the s s c t o the main phase minimum of a storm, and symmetric d u r i n g t h e r e c o v e r y phase 1968).  (Hoffman and C a h i l l ,  In c o n j u n c t i o n w i t h the r a p i d asymmetric  ring  c u r r e n t decay, sudden r e c o v e r i e s o f t h e f i e l d at ATS 1 have been a t t r i b u t e d currents  t o abrupt d i s r u p t i o n s of t h e p a r t i a l r i n g  (Cummings, B a r f i e l d , and Coleman, 1968).  This  10 thesis w i l l show that the unique features of t h i s magnetospheric subregion provide information r e l a t i n g to P i 2 micropulsations. The plasma sheet i s a region of magnetic f i e l d reversal, or neutral sheet, between the northern and southern  halves of the magnetotail.  In t h i s equatorial sheet,  a low intensity magnetic f i e l d having a non-zero v e r t i c a l component, i s observed.  Since a pressure balance must be  maintained, a decrease i n the f i e l d pressure i s balanced by an increase i n p a r t i c l e pressure i n the plasma sheet. An enhanced p a r t i c l e energy density i s one of the sharp boundaries e x i s t i n g between the plasma sheet and the higher latitude magnetotail region.  Comparisons of the average  p a r t i c l e energy,-density and energy density have been made (Bame, 1967).  The greater energy of the plasma sheet resides  i n the protons,  l u r i n g the main phase of a negative bay, a  decrease i n the electron average energy density occurs i n the:plasma sheet (Hones et a l . , 1971).  This was  shown to  be due to a decrease i n the thickness of the plasma sheet by a net loss of t a i l p a r t i c l e s .  Ah increase i n the t a i l  current i s also observed during t h i s phase of the bay (Coleman and Cummings, 1971).  As the bay recovers, the sheet  thickens again and the t a i l current decreases.  The inner  boundary of the plasma sheet (characterized by an expon e n t i a l decrease of electron energy density with decreasing  11  r a d i a l distance) was reported at positions out to 11.2 Re equatorial distance at times of low magnetic a c t i v i t y (Vasyliunas, 1968).  During the main phase decrease of a  storm, t h i s inner boundary moves close to 6 Re distance. The plasma sheet inner boundary returns to i t ' s quiet time p o s i t i o n immediately following the main phase minimum of a storm (Goleman et a l . , 1971).  One of the investigations of  t h i s t h e s i s correlates the period of P i 2's with the observed position of the plasma sheet inner boundary. The trapping boundary of energetic electrons (for E greater than &0 kev) was found t o be located within the proton r i n g current, near i t ' s outward edge (Frank, 1971). This trapping boundary was either coincident with the plasma sheet inner boundary or i n the plasma sheet i t s e l f .  The  plasma sheet "inner boundary was found coincident with the plasmapause i n the post midnight quadrant, and 1 to 3 Re beyond the plasmapause i n the pre-midnight quadrant. A low energy density electron trough l i e s between.  The r i n g  current was observed t o penetrate 0.5 t o 1 Re distance into the plasmasphere. The plasma sheet inner boundary and electron trough are within the proton ring current.  During  the main phase of a storm, the trough disappears and the entire structure moves inward, towards the earth.  The  inner edge of the symmetric part of the storm time r i n g current continues t o move inward into the plasmasphere,  12  during the recovery phase of a storm (Coleman et a l . , 1971). With the abrupt disruption of the p a r t i a l ring currents during storm recovery, the plasma sheet and ring currents disconnect.  The ring currents l i k e l y move inward and the  plasma sheet r e t i r e s outward.  The close and complicated  interaction of the magnetospheric subregions makes i t d i f f i c u l t to ascertain the l o c a t i o n of the P i 2 source.  d.  Theories of P i 2 The i n i t i a l kick of either component of a P i 2  event often has the same sign as the corresponding component of an accompanying bay.  Jacobs et a l . (I960)  suggested t h i s kick may be represented by an equivalent overhead current system i n the dynamo region of the ionosphere.  Such a current system suggests a nightside  auroral zone source f o r P i 2.  Jacobs (1970) stated that  solar wind-geomagnetic f i e l d interaction i n the t a i l region gives r i s e to a broadband hydromagnetic (abbreviated  here-  after with hm) impulse which t r a v e l s t o the auroral zones. The impulse contains periods ranging from P i to bay.  Near  the auroral zone source, a l l frequencies arrive at the same time and the leading edge of the bay i s very steep. ionosphere  The  disperses the waves t r a v e l l i n g t o lower l a t i t u d e s .  This ionospheric dispersion causes high frequencies t o  13 propagate f a s t e r than lower frequencies and consequently, the leading edge of the bay i s l e s s steep at low and middle latitudes than at the auroral zone.  Thus Jacobs regarded  the bay and i n i t i a l P i 2 pulse as a r e s u l t of modification by the ionosphere, of solar plasma generated hm d i s t u r bances.  An objection to the idea of P i 2's as fluctuations  of an ionospheric current system was voiced by Saito et a l . (1968) who  noted the l a t i t u d i n a l v a r i a t i o n of bay magnitude  i s not always the same as that of the amplitude of concurrent Pi 2.  Furthermore, observations of occassional  clockwise p o l a r i z a t i o n i n the northern hemisphere led Jacobs (1970) to believe that P i 2 could not be described by a single current system.  He then suggested that P i 2 may  caused by a disturbance propagating E-region.  The  i n the  ionospheric  close r e l a t i o n s h i p between auroral lumin-  osity f l u c t u a t i o n s and micropulsations 1961)  be  (Campbell and l e e s ,  and observed P i 2 phase s h i f t s between two  separate  stations (Herron, 1966) were cited by Jacobs as further evidence of ionospheric propagation  effects.  Rostoker  (1967a), suggested that P i 2*s originate as e i g e n - o s c i l lations of auroral f i e l d l i n e s which then propagate through the ionospheric E-region.  Thus, the p o l a r i z a t i o n of the  f i e l d would be effected by ionospheric screening, dependent on the location of the s t a t i o n r e l a t i v e to the P i 2 source. There are certain reported d i s s i m i l a r i t i e s between  14 Pi 2's observed i n the auroral zone and those observed at low latitudes (Fukunishi et a l . , 1970).  Observed auroral  latitude P i 2 i s more i r r e g u l a r i n waveform than the damped, mid-latitude P i 2 .  L i k e l y , t h i s i s because the  effect of injected, energetic p a r t i c l e s i s more prevalent i n the auroral zone.  As mentioned already, the power  spectrum of auroral l a t i t u d e P i 2 during a magnetospheric substorm was found to have a background random noise type of dependence with frequency.  This random noise i s less  prevalent at lower latitudes and t h i s might imply that auroral l a t i t u d e P i 2's may be generated by a mechanism different from that f o r low and middle latitude P i 2 s . r  Also, as the Kp index increased, the fundamental mode of the auroral l a t i t u d e P i 2 became obscured and the amplitude of the higher frequency P i 1 r i d e r s increased.  A funda-  mental mode of period greater than 40 seconds was not c l e a r l y observable f o r Kp greater than 3 .  Yet the fundamental mode  was shown t o decrease i n period as Kp increased f o r middle latitude P i 2 . According t o Hirasawa et a l . (1966), the s i m i l a r diurnal variations of P i 2 period and Pc 4 period (a continuous micropulsation of period from 45 t o 150 seconds) imply a similar generating mechanism at low and middle l a t i t u d e s .  Hirasawa et a l . had attributed Pc 4 to  hm o s c i l l a t i o n s at the plasmapause.  Fukunishi et a l . (1970)  calculated the Kp dependence of P i 2 period from formulae  15  expressing the l a t i t u d e v a r i a t i o n i n the eigen-period of hm o s c i l l a t i o n s (Obayashi and Jacobs, 1958)  and the Kp  v a r i a t i o n of the plasmapause ( l a t i t u d e ) p o s i t i o n (Blnsack, 1967).  The Kp versus P i 2 period r e l a t i o n obtained by  them agrees w e l l with the Kp-Pi 2 period observations of Troitskaya (1967).  They also observed a decrease i n P i 2  period corresponding to the suggested inward motion of the plasmapause, from 4.6 to 4.2 Re, during the expansive phase of a magnetospheric substorm.  Pukunishi et a l . (1970) thus  concluded that lower l a t i t u d e P i 2 i s a transient surface o s c i l l a t i o n on the plasmapause, excited by hm  disturbances.  The auroral latitude P i 2's are considered to be f l u c tuations of ionospheric current produced by the i n f l u x of energetic p a r t i c l e s to the upper atmosphere.  Yet i t may  be that only P i fluctuations of period less than 40 seconds, or P i 1, are caused by ionospheric current disturbances. Heacock, Mullen and Hessler (1971) showed that when a strong Pi (Pi 1 and 2) occurs at College, i n the auroral zone, a f a i n t P i also occurs at Anchorage, a lower l a t i t u d e s t a t i o n . However, at Anchorage, P i 1 at a period about 2.5 seconds was  enhanced compared to other periods.  This implies that  P i 1 may. propagate as hm waves i n the ionospheric horizontal waveguide.  Also, the v a r i a t i o n i n Pi 2 period with the  suggested plasmapause p o s i t i o n does not prove that P i 2 occur there.  As previously mentioned, other magnetospheric  16  subregions, such as the r i n g currents and the plasma sheet inner boundary, also vary with magnetic a c t i v i t y . Kato (1971) analyzed geomagnetic micropulsations associated with sudden storm commencements (abbreviated hereafter with ssc) by dividing the signal into several frequency channels.  He showed that the i n i t i a l predominant  P i 2 had periods of about 200 seconds.  These 200  second  fluctuations c l e a r l y exhibited a damped type of o s c i l l a t i o n and were of a global scale.  Periods of about 100 seconds  were shown to be of a more impulsive or resonant nature, occurring on a semi-global scale.  Kato showed the f i l t e r e d  waveforms recorded simultaneously at College and Onagawa during a ssc are s i m i l a r . i t was  From such a frequency analysis,  concluded that P i 2 i s f i r s t excited by an hm burst.  This i s due to a solar wind shock front impacting the magnetopause, on the dayside.  The damped 200 second f l u c -  tuations which are thus excited, t r a v e l along f i e l d l i n e s to high l a t i t u d e s and also across f i e l d l i n e s to the nightside of the magnetosphere.  Yet, i f t h i s were the case,  these 200 second fluctuations having a f i n i t e propagation v e l o c i t y , would not arrive simultaneously at two  stations  separated by 50 degrees of longitude and 36 degrees of l a t i t u d e , as they were observed.  Following the burst, Kato  suggested P i 2's are excited i n the magnetosphere nightside and occur with the growth of the substorm.  At t h i s  17  time, the p a r t i c l e flow pressure increases against the magnetic f i e l d pressure near the ring current s i t e .  The  mechanism proposed by Kato (1971) c a l l s f o r a hm burst impacting the f i e l d i n the v i c i n i t y of the inner boundary of the p a r t i a l ring current.  Such an inward burst requires  a sudden disruption of p a r t i a l r i n g currents.  As w i l l be  discussed i n Chapter I I I , a sudden p a r t i a l r i n g current disruption gives r i s e to a plasma implosion.  Another theory  of P i 2 generation by an implosion of plasmas i n the nighttime magnetosphere was  proposed by Atkinson  (1966).  This  idea i s based on the theory of reconnection of open t a i l f i e l d l i n e s proposed by Dungey (1961, 1962, by Axford, Petschek and Siscoe (1965).  1967)  and also  Atkinson suggested  that intermittent f i e l d l i n e reconnection gives r i s e to the implosion of t a i l plasmas towards closed magnetic lines of f o r c e . Heacock et a l . (1971) reported that 95$ of the time when P i events occur at College or at Sodankyla, the plasmapause i s located inside the f i e l d l i n e connected to these auroral zone stations.  This implies that most Pi 2 s f  occur outside the plasmapause, since Pi 2 amplitude i n i t ' s latitudinal variation  becomes maximum i n the auroral zones.  Evidence has been offered by Saito et a l . (1970) to show that P i 2 micropulsations associated with a small substorm are due to o s c i l l a t i o n s of the f i e l d lines through the  IB  plasma sheet inner boundary.  The f i e l d l i n e s connected to  the maximum amplitude P i 2 l a t i t u d e s , i n two examples, were shown to pass through the equatorial plane of the nightside magnetosphere at distances of 9.5 and 6.5 Re, respectively.  These distances were near the predicted plasma  sheet inner boundary.  V/asyliunas (1968) found that the  plasma sheet inner boundary on the nightside moves inward, towards the earth, as the Kp index increases from G to 3. Saito et a l . (1970) gave an empirical formula f o r the r e l a t i o n of Kp to the geocentric distance of the plasma sheet inner boundary, Rps,  (1)  A formula was given by Rycroft and Thomas (1970) f o r the r e l a t i o n between Kp and the equatorial distance of the nightside plasmapause, Rpp,  (2)  From the two formulae, Saito et a l . (1970) found that P i 2 peak amplitude latitudes mapped closer to the •inferred* plasma sheet inner boundary than to the 'inferred* plasmapause p o s i t i o n , f o r Kp indices less than 4*  At the i n i t i a l  stage of a magnetospheric substorm, P i 2's are observed to  19  have a period common from middle latitudes to polar  regions.  At auroral latitudes however, t h i s period may be observed overlapping the noise-like background.  The prominent  spectral peak of t h i s P i 2 i s frequently seen i n the spectrum of auroral zenith i n t e n s i t y f l u c t u a t i o n s . (1970) f e l t that i f P i 2 at plasma sheet inner  Saito et a l . boundary  latitudes (auroral zone) were due to the auroral e l e c t r o j e t f l u c t u a t i o n s , then the usual coincident set of P i 2 patterns at conjugate stations would not be observed.  They consider  auroral e l e c t r o j e t fluctuations to be a secondary phenomenon produced by a possible Alfven wave modulation of the p r e c i p i t a t i o n of auroral p a r t i c l e s . P i 2 are considered to be primarily due to a transient t o r s i o n a l o s c i l l a t i o n of the f i e l d l i n e s through the inner boundary of the plasma sheet.  CHAPTER II RELATED INVESTIGATIONS OF P i 2 MICROPULSATIONS  a.  VLF Emissions and P i 2 Period This research i s aimed at locating the region of  generation of P i 2 micropulsations.  Previous investigators  have reported the v a r i a t i o n of the plasmapause (Rycroft et a l . , 1970) and the plasma sheet inner boundary (Saito et a l . , 1979) positions with the three hour planetary K index.  The  period of P i 2 has been observed to decrease with increasing Kp (Troitskaya, 1967).  Hence i t i s reasonable to assume the  dependence of P i 2 period upon the nightside position of a magnetospheric  subregion.  However, there i s a considerable  degree of uncertainty as to which subregion generates P i 2. Some authors (Saito et a l . , 1970) indicate the plasma sheet inner boundary while others (Hirasawa et a l . , 1966) suggest the plasmapause as the generating subregion.  The hypoth-  esis of Saito and Sakurai i s based on a result of t h e i r analysis, showing that the l a t i t u d e of maximum P i 2 amplitude maps along the f i e l d l i n e to the equatorial plane, near the predicted plasma sheet inner boundary.  Hirasawa  and Nagata s hypothesis i s founded on the comparison of ;,  t h e i r observations of the diurnal v a r i a t i o n of the equat o r i a l distance of the plasmapause position (Carpenter, 1966) with the diurnal v a r i a t i o n of P i 2 period. Further-  21  more, Fukunishi et a l . (1970) calculated the Kp v a r i a t i o n of P i 2 period from formulae expressing the latitude v a r i ation i n the eigen-period of hm o s c i l l a t i o n s (ObayaShi et a l . , 1958) and the Kp v a r i a t i o n of the plasmapause position (Binsack, 1967).  The Kp versus P i 2 period r e l a t i o n  obtained by them agrees reasonably well with observations by Troitskaya (1967). In the investigation reported here, the variations of P i 2 period with changes i n equatorial distances of the nightside magnetospheric examined.  subregion boundaries, were d i r e c t l y  These boundaries, v i z . the plasmapause and  plasma sheet inner boundary, were determined by observing sudden changes i n the c h a r a c t e r i s t i c s of certain types of VLF radio signals received by the Alouette 2 s a t e l l i t e . The polar orbit of t h i s s a t e l l i t e was almost c i r c u l a r and i t scanned a wide latitude range.  The VLF receiver on  board often observed a sudden change i n the c h a r a c t e r i s t i c s of VLF radio signals.. As the s a t e l l i t e moved to higher l a t i t u d e s , a common type of change observed, most frequently at invariant latitudes of about 60°, i s a cutoff i n whistler activity.  'Breakups* i n the lower hybrid resonance  (abbre-  viated hereafter with LHR) noise band were also observed, often concurrent with a cutoff i n whistler a c t i v i t y ,  LHR  'breakup* involves abrupt frequency and bandwidth changes as well as a t r a n s i t i o n from a smooth to an i r r e g u l a r  22  appearance on frequency-time  records.  The whistler cutoff  and LHR 'breakup events take place when the s a t e l l i t e 1  crosses the plasmapause l a t i t u d e (Carpenter, Walter, Barrington and McEwen, 1968).  In addition to these types  of events, a sudden change i n ELF emission strength was detected by the Alouette 2 receiver.  It i s tentatively  assumed that such a change takes place when the s a t e l l i t e crosses the plasma sheet inner boundary.  This assumption  w i l l be discussed further i n Chapter I I I . During 1967, the magnetospheric subregion boundary crossing events were collected with respect to the s a t e l l i t e orbits within ± 2 hours of longitudinal distance from Ottawa. in t o t a l .  Approximately  sixty examples were obtained  The geomagnetic micropulsation data were obtained  at Ralston, southeast of Calgary, Alberta.  In t h i s research,  the, following conditions were met with regards t o the selection of P i 2. i ) P i were considered only i f they were observed within an i n t e r v a l of ± 2 hours about the time of a s a t e l l i t e 'boundary crossing' event.  A shorter i n t e r v a l would y i e l d  an i n s u f f i c i e n t number of P i 2 events and a longer i n t e r v a l may make a comparison between P i 2 and subregion boundary positions meaningless. i i ) Selected P i 2 must have occurred within the l o c a l time i n t e r v a l of 1430 to 0530 at Ralston (or approx-  23  imately 2200 to 1300 UT).  Pi 2 i s primarily a nighttime  phenomena with optimum occurrence being near 2230 LMT. During the daytime, P i 2 are generally smaller i n amplitude and often contaminated with other types of micropulsations (mostly Pc3 and Pc4). i i i ) The average Kp index, during a 9 hour i n t e r v a l about the event, must not be greater than 3 .  During times  of greater magnetic a c t i v i t y , the magnetospheric  subregions  often become coincident i n location (Frank, 1971).  Thus  intervals of magnetic quiescence suit t h i s research purpose and since P i 2 occur most frequently when 1+ ^ Kp £ 2- (as w i l l be shown i n section II.d), few examples are eliminated by t h i s c r i t e r i o n . The period of each of the selected P i 2 series was scaled from the north-south component.  I f more than one  series of coherent P i 2 occurred i n the time i n t e r v a l , then the mean value of a l l the P i 2 was considered t o indicate the period corresponding to the s a t e l l i t e event.  The P i 2  periods were correlated with the boundary crossings. During most crossing events, any possible events due to wide band VLF intensity changes were suppressed with the use of an automatic gain control (abbreviated hereafter with AGC). It i s again pertinent to mention that P i 2 period does not change with l a t i t u d e .  Saito et a l . (1970) gave  two examples showing that P i 2 period i s common from middle  24  latitudes through polar regions.  On the other hand, Fuku-  n i s h i et a l . (1970) mentioned that the wave forms of • i. '  •  -  .  auroral zone P i 2 have a nearly random noise type of power spectrum, whereas the P i 2 spectrum i n low and middle latitudes i s characterized by an outstanding peak near 80 seconds.  Yet, they showed that auroral zone P i 2 spectrum  has three peaks overlapping the noise-like background.  One  of the peaks i s centered at about 80 seconds as i n low and middle l a t i t u d e s .  The other two spectral peaks exist near  20 and 10 seconds.  The common peak at about 80 seconds  seems t o indicate that hm o s c i l l a t i o n s of that period are of the fundamental mode prevailing i n a l a t i t u d i n a l range from low t o auroral zone, presumably even up to the latitudes which divide the magnetotail from the region of closed magnetic l i n e s of f o r c e . The periods of the selected P i 2 series are l i s t e d i n Table 1. Also l i s t e d are the time, nature and equatorial distance (an L. value i n units of earth r a d i i ) of each of the correlated subregion boundary crossings.  Based on t h i s  table, Figure 1 shows a plot of the P i 2 period change with the: equatorial distance of the plasmapause and/or the plasma sheet inner boundary.  An open c i r c l e represents a plasma-  pause event and a s o l i d (dark) c i r c l e , a plasma sheet inner boundary event.  A t r i a n g l e represents a coincidence i n  location of these two subregions.  25  Table I Alouette 2 events and the correlated P i 2 periods at Ralston during 1967.  Date  U.T.  Events  L value  Pi 2 period  Feb. 28  0937  LHR, ELF, AGC  4;88  66 (sec.)  March 4 March 11  0837 0836 0602  LHR, ELF, AGO  48  ELF LHR, ELF, AGC  2.90 2.86 2.82  0959  LHR, AGC  3.26  0715 0510 0916  ELF, AGC ELF, AGC ELF, AGC  5.06 6.28  55 80 76  0433 0205 0215 1236  LHR, ELF, AGC ELF, AGC ELF, AGC  ,4.83 8.50 4.38  ELF, AGC  5.52  1152  ELF, AGC  Sept. 10  0807  Whsl ., ELF, AGC  3.45 4.18  Sept. 12  Whsl., LHR  4.57  Sept. 25  1041 0603  3.99  Oct. 5  0849  Whsl ., ELF LHR, ELF, AGC  Nov. 23 Nov. 28  0949 0910  LHR, AGC LHR, ELF  4.33  47 72  Dec. 6  0913  ELF, AGC  6.87  81  Dec. 8  1151 1206  ELF, AGC  3.43 3.56  61  April 7 May 12 June 8 June 8 June 8 June 13 July 11 July 26 Sept. 4 Sept. 9  Dec. 9  LHR, ELF  4.80  7.64 3.62  43 65  59 48 92 58 66 72 69 69 56 95  67  26  r  r~~—i  1  1  I  I  • INNER PLASMA SHEET BOUNDARY EVENT O PLASMAPAUSE EVENT A COMBINED EVENT  0  1  L _  40  50  _J 60  !_ 70 PERIOD  Fig.  1.  80  90 . 100  (SEC.)  Magnetospheric subregion L value variations of P i 2 period  27  The curve marked with 'plasmapause  1  i s a theo-  r e t i c a l one t o show how P i 2 period i s expected to change with the location of the plasmapause i f P i 2's are due to plasmapause f l u c t u a t i o n s . i c a l formulae.  The curve i s based on two empir-  One relates P i 2 period t o Kp index:  T - 109 - 14 Kp  ( ± 5 ) ,  (for Kp  where T i s the P i 2 period ( i n seconds).  £ 5 0 )  (1)  The formula i s a  least squares f i t t o a scatter plot showing the Kp v a r i a t i o n of P i 2 period (Troitskaya, 1967, F i g . V I I . g). The other formula represents the Kp v a r i a t i o n of the nightside plasmapause position:  Rpp•- 5.64 - 0.7&jKp~, (for Kp ^ 5 0 )  (2)  given by Rycroft et a l . (1970), where Rpp i s the equatorial distance of the plasmapause.  The 'plasma sheet inner bound-  ary' curve i s also a t h e o r e t i c a l one t o show how P i 2 period i s expected to change with the l o c a t i o n of the inner boundary, i f P i 2 are generated at t h i s subregion boundary. It was obtained by combining  (1) and the following empirical  relation:  Rps - 15  - 6/Kp , (for Kp £  3o).  (3)  28  This equation relates Kp to Rps, the equatorial distance of the plasma sheet inner boundary i n units of earth r a d i i . It was derived by Saito et a l . (1970) from s i x data points about the position of the plasma sheet inner boundary which were obtained by Vasyliunas (1968). For Pi 2 periods less than 70 seconds, the two curves approach one another.  The closeness of these curves  i s consistent with the observed coincidence of the plasmapause and inner boundary during periods of greater magnetic a c t i v i t y (Frank, 197!)••  However, the 'plasma sheet inner  boundary* curve was derived from data which occurred primar i l y during times of low Kp.  In t h i s range (periods> 70  seconds), the curves separate s u f f i c i e n t l y t o substantiate an agreement between the •plasma sheet inner boundary' curve and the data from direct observations. The implication of t h i s r e s u l t i s discussed i n Chapter I I I .  b.  P i 2 Diurnal Variations The purpose of t h i s investigation i s to more  c l e a r l y e s t a b l i s h the source f i e l d lines of P i 2 micropulsations.  As previously mentioned (Chapter I ) , the mor-  phology of micropulsations should r e f l e c t the nature of the source responsible f o r these f l u c t u a t i o n s . t e r i s t i c s of P i 2 have been observed.  Various charac-  F i r s t l y the maximum  29  amplitude of P i 2 tends to occur near midnight and at geomagnetic latitudes i n the auroral zone (Saito et a l . , or at least higher than 50° (Jacobs et a l . , I960).  1970),  Secondly,  the d i r e c t i o n of the i n i t i a l movement of the P i 2 d i s t u r bance vector at low and middle latitudes i s usually northeast (north-west) p r i o r to (after) midnight (Kato et a l . , 1956; Yanagihara, I960).  This disturbance vector has been  shown t o converge to the northern auroral zone on the midnight meridian (Saito, 1961).  T h i r d l y , the l o c a l time at  which P i 2 occur most frequently i s near 2230 (Yanagihara, 1957a; Rostoker, 1967a).  When these three factors are  considered, i t i s reasonable to expect the source of Pi 2 to be found on auroral zone f i e l d meridian.  l i n e s near the midnight  The investigation reported here compares the  diurnal v a r i a t i o n i n the occurrence frequency of i n i t i a l l y north-east oriented P i 2 s with that of north-west P i 2. f  From these observations, the diurnal v a r i a t i o n i n the probability of occurrence of north-east P i 2 i s found. This- d i s t r i b u t i o n i s compared with the diurnal v a r i a t i o n i n the occurrence frequency of a l l the observed P i 2 events. Pi 2 events occurring from January t o May  1964  were selected from the rapid run magnetograms at Wingst, Germany and Memambetsu, Japan.  The i n i t i a l impulsive  movements of the horizontal disturbance vector were observed. In p a r t i c u l a r , the i n i t i a l north-south component of each  30  Pi 2 event was compared with the east-west component.  As  Pi 2's are primarily nightside, dusk to dawn, phenomena, only events occurring from 1400 to 08.00. LMT were used. The i n i t i a l movement of a l l of these events was either north-east or north-west. are  shown i n Figure 2 and 3.  usually  Examples of these events  For each of these two groups,  the diurnal v a r i a t i o n i n the number of P i 2 (occurring i n hourly i n t e r v a l s ) i s plotted i n Figure 4.  The diurnal  v a r i a t i o n i n the occurrence probability of north-east P i 2 i s compared with the v a r i a t i o n i n the occurrence frequency of a l l observed P i 2 events, i n Figure 5. The most probable l o c a l time of occurrence of initially  north-east (north-west) Pi 2 i s at 1930 (2330) as  i s shown i n Figure 4.  From Figure 5, i t can be seen that  Pi 2 occurrence i s centered about 2205 LMT.  This i s near  2300 LMT a f t e r which the probability of i n i t i a l north-east orientation becomes less than 50$ (also shown i n Figure 5). Thus, P i 2 i s found t o occur about 2205 LMT, p r i o r to (after) which the i n i t i a l P i 2 orientation i s primarily north-east (north-west).  c.  P i 2. Solar Wind and Geomagnetic A c t i v i t y Studies of morphologic variations i n micropulsations  may provide information on variations i n the source of these  31 ^^AyvvvN/vv\/V\y^—/V*  AA/^^/^ j^/\Ayvv^v\ V\/\A/\/\A/  05-.4-1 LT  X  •"1  MARCH 2  05'-51 LT  MARCH 11  0Z-4L LT  JANUARY 2,6  •—•VWvyvy\A/v\/\/^  09-11 LT  yvvVAA MARCH 2  NAARCU 1 0  Fig. 2 .  Magnetograms of i n i t i a l l y north-west (X+, Y-T P i 2  X  y  19-Z 6 LT  W\NGST  MARCH 10  X Y  20-01  LT  WINGST  19-36  LT  Y WINGST  MARCH 16  X  F i g . 3.  APRIL 2.8  Magnetograms of i n i t i a l l y north-east (X-*v)Y+) P i 2  33  17  20  23 LOCAL  Fig.  4.  02  05  TIME  Diurnal v a r i a t i o n of i n i t i a l l y north-west and north-east P i 2 occurrence frequencies  34  Fig.  5.  23 LOCAL TIME Diurnal v a r i a t i o n of the i n i t i a l l y norjbh-east P i 2 occurrence probab i l i t y and the t o t a l P i 2 occurrence frequency  35  fluctuations.  Yanagihara (I960) noted a tendency f o r the  most probable time of P i 2 occurrence to s h i f t from midnight to about 2200 LMT with increasing magnetic a c t i v i t y .  In  t h i s investigation the tendency i s further substantiated by comparing the most probable l o c a l time of P i 2 occurrence during periods of low magnetic a c t i v i t y with the most probable time during high a c t i v i t y .  In t h i s manner, the  •dynamic* behaviour of the P i 2 source i s demonstrated.  In  order to account f o r t h i s behaviour, the d i r e c t i o n and pressure of the solar wind protons i s examined during periods of high, magnetic a c t i v i t y . The l o c a l time d i s t r i b u t i o n of P i 2 events observed by a global network of stations during 1964 (Romana and Veldkamp, 1968) was determined f o r periods of magnetic quiescence (Kp - 3+) and also f o r periods of high magnetic a c t i v i t y (Kp - 4-).  The diurnal v a r i a t i o n i n the  Pi 2 occurrence was thus determined f o r each group (one of nigh Kp, the other low). Figure 6.  These variations are shown i n  Next, a study of the solar wind proton streaming  angle and pressure was undertaken, i n the b e l i e f that the most probable time of P i 2 occurrence may be conditioned by solar wind.  The streaming angle, fl, i s measured positive  eastward from the sun-earth l i n e to the d i r e c t i o n of the solar wind flow.  Data was obtained, from the World Data  Center A, Greenbelt, Md.,  f o r the Explorer 34 experiment,  36  UJ 03  IE z  400  Kp = 0 ~ 3+ o  300  200  100 \—  0  17  F i g . 6.  20  23 LOCAL TIME  02  05  Diurnal v a r i a t i o n of P i 2 occurrence frequency during high and low magnetic a c t i v i t y  37  of which t e c h n i c a l i t i e s have been described elsewhere (Oglivie, 1968).  The proton flow d i r e c t i o n , v e l o c i t y and  density data were observed at three minute i n t e r v a l s . Approximately  2,000 such datum points, selected from June  to November, 1967 when the s a t e l l i t e was outside the  bow  shock, were selected during times of high Kp (£4.-).  The  number of points i n each flow d i r e c t i o n ( i n a 22.5 degree interval) were recorded and the average proton pressure i n each of these d i r e c t i o n a l flow intervals was  calculated.  This procedure was repeated during times of low Kp (- 3+). Thus the probability of occurrence of each d i r e c t i o n a l i n t e r v a l , P(jrf), was found and the product of P(jz0 and the 2  average proton pressure (NmV  ) i n that d i r e c t i o n a l i n t e r v a l o  was  calculated.  This value, P(^)«(NmV ), represents the  'expected' solar wind proton pressure, i n that d i r e c t i o n a l flow i n t e r v a l during the prescribed magnetic a c t i v i t y .  The  solar wind streaming angle v a r i a t i o n of t h i s solar wind proton pressure during times of high and of low Kp i s shown in Figure 7. The combined results (for low plus high Kp) of the P i 2 occurrence frequencies shown i n Figure 6 y i e l d a peak time near 2230.  The most probable l o c a l time of  occurrence of P i 2 during low (high) Kp i s after (prior to) t h i s time.  In p a r t i c u l a r , P i 2 occurs most frequently at  2030 (2330) LMT during high;(low) Kp.  This westward s h i f t  38  S O L A R WIND S T R E A M I N G  F i g . 7.  ANGLE, *  Solar wind streaming angle variation of p a r t i c l e pressure during high and low magnetic a c t i v i t y  39  i s i n agreement with Yanagihara's observation.  The  streaming angle v a r i a t i o n i n the solar wind proton pressure has a pressure peak directed at an angle of 188° (165°) during low (high) Kp.  Thus, during periods of low  magnetic  a c t i v i t y , P i 2's occur most frequently near 2330 LMT, when the solar wind protons at 1 AU are streaming at an angle of 188°.  During periods of high magnetic a c t i v i t y , t h i s  streaming d i r e c t i o n i s 165° and P i 2's occur most frequently at an e a r l i e r time of 2030.  As expected, the proton stream-  ing pressure i s greater during high Kp than during low  d.  Kp.  P i 2 Rate of Occurrence Observations of changes i n Pi 2 morphology with  magnetic a c t i v i t y and the solar cycle have been less consistent and even appear contradictory at times.  As men-  tioned i n section I.b, the rate of P i 2 occurrence was reported to increase with Kp (Yanagihara 1957b, Kannangara e t ' a l . , 1969; Shannon et a l . , 1970).  This might imply that  the occurrence of P i 2 should increase during sunspot maximum  (when the Kp index i s higher). Yet, Yanagihara  (1956)  reported that the yearly occurrence frequency of 'night pulsations* i s inversely proportional to the solar a c t i v i t y . In section I I . c , the peak time of Pi 2 occurrence was shown to s h i f t westward with increasing magnetic  activity.  40  Together, t h i s s h i f t and the increasing rate of P i 2 with Kp may imply that the peak time of P i 2 occurrence should be observed e a r l i e r during sunspot maximum.  Yet, Afanasieva  (1961) and Saito et a l . (1968) show that the Pi 2 peak time of occurrence i s found near midnight (2300 to 0100) during sunspot maximum and at e a r l i e r times (2000 to 2300s) during sunspot minimum.  In an attempt to explain these two  apparent contradictions, an investigation was made of the Kp v a r i a t i o n i n the rate of Pi 2 occurrence near sunspot minimum (1964) and at a more active year (1967). The P i 2 events used i n t h i s investigation were those observed by a global network of stations during 1964 (Romana et a l . , 1968) and 1967 (Romana and Van Sabben, 1970). For each of these years the t o t a l number of P i 2 events was found f o r each three hour Kp l e v e l .  The rates of occurrence  f o r d i f f e r e n t Kp levels were obtained by d i v i d i n g the t o t a l number at each l e v e l by .the t o t a l number of times that the p a r t i c u l a r l e v e l occurred during that year.  The rates of  Pi 2 occurrence, f o r both 1964 and 1967 were calculated using over 3,000 reported P i 2 events from each year.  The  rates, showing a s t a t i s t i c a l deviation about each point, are plotted i n Figure 8. The Kp v a r i a t i o n i n the P i 2 occurrence rate, -shown i n Figure 8, i s s i m i l a r f o r both years despite the fact that the average Kp index was higher during 1967.  In  41  1964  0o  10  2  3  o K  F i g . £.  p  o  4  o  5Q  6C  INDEX  Kp v a r i a t i o n of the Pi 2 occurrence rate during 1964 and 1967  42  both years, i t can be seen that the P i 2 occurrence rate increases with Kp f o r Kp values between Oo and 1+. The occurrence rate does not keep increasing beyond Kp = 2o, contrary to results presented by the investigators mentioned e a r l i e r .  Thus, during years of both sunspot minimum  (1964) and of higher magnetic a c t i v i t y (1967), P i 2 occurs most frequently during intervals when 1+ - Kp - 2-.  CHAPTER I I I DISCUSSION OF THE RESULTS  a.  Pi 2 and Magnetospheric  Subregions  The results of the investigation presented i n section II.a and depicted i n Figure 1 show an agreement between the 'plasma sheet inner boundary * curve and the data from direct observations. A l l of the f i v e subregion boundary crossings corresponding to P i 2 periods longer than about 75 seconds were detected with a sudden cutoff i n ELF emission strength and accordingly assumed to i d e n t i f y the plasma sheet inner boundary.  In the case corresponding  to the P i 2 period of 95 seconds (December 6th event), a LHR breakup was observed simultaneously. A l l of these f i v e crossings were i d e n t i f i e d when the s a t e l l i t e was on the nightside of the earth and at invariant latitudes not lower than 63.6°, v i z . , L s- 5.06.  The l o c a l times as well as  the larger L values indicate that ELF emissions i n these cases may be a type of auroral zone VLF h i s s .  ELF hiss  and chorus, which are often concurrent, take place mostly on the dayside, and at latitudes lower than those at which auroral zone VLF hiss i s observed.  Although dayside VLF  hiss occurs i n the polar cusp region, nightside auroral zone VLF hiss i s also observed. VLF hiss was observed at the auroral zone, near  44 and on the poleward side of the 'trapping boundary' f o r energetic electrons (E 5c 45 kev), i n l a t i t u d e range of about 7° (Gurnett and Frank, 1972).  Frank (1971) found  that the 'trapping boundary' i s beyond the outer boundary of the earthward edge of the plasma sheet.  In case that  the  'trapping boundary' i s beyond the outer boundary of  the  edge, i t i s within a range of about 1 Re from the outer  boundary of the edge.  The earthward edge i s a 'micro-  scopic' view of the inner boundary of the plasma sheet. Frank found that the plasma sheet inner boundary, or edge, has a f i n i t e width, 1 to 2 Re, within which the average energy of electrons i n the range 80 ev - E ^ 46 kev decreases exponentially with decreasing distance.  These  pieces of information relate auroral zone VLF h i s s , the 'trapping boundary* and the plasma sheet inner boundary t o one another. They indicate that the 'trapping boundary' as well as the plasma sheet inner boundary can be approximately located through observation of a sudden,cutoff i n auroral zone VLF hiss a c t i v i t y on the lower latitude side. The evidence that Saito et a l . (1970) presented to prove t h e i r plasma sheet theory was that the latitude of maximum P i 2 amplitude maps along the f i e l d l i n e to the equatorial plane near the plasma sheet inner boundary. The mapping was done based on a certain model of the average magnetic f i e l d configuration of the outer magnetosphere  45 ( F a i r f i e l d , 1968).  The latitude of maximum P i 2 amplitude  was determined from observations at eight stations d i s t r i buted over a range of geomagnetic 73.8°.  latitude from 40.4° to  Two P i 2 events f o r time i n t e r v a l s having d i f f e r e n t  Kp values were chosen and f o r each event the latitude of maximum amplitude was determined.  It was then mapped t o a  point on the equatorial plane which was found to be near the  position of the plasma sheet inner boundary,  from the equation II.a(3).  inferred  The approach of Saito et a l .  was i n d i r e c t , since i t depends on the inferred inner boundary l o c a t i o n .  In t h i s respect, the investigation  presented here i s a direct observation of the expected P i 2 v a r i a t i o n i n period with a magnetospheric subregion, v i z . , the  plasma sheet inner boundary.  The r e s u l t s presented i n  t h i s thesis i n d i r e c t l y suggest that the region of P i 2 generation, during times of magnetic quiescence, i s found near the plasma sheet inner boundary.  During times of  higher Kp, the P i 2 period v a r i a t i o n with subregion boundaries i s less discernable.  These ambiguous results are i n  agreement with the observed coincidence i n location of magnetospheric subregions during times of higher magnetic a c t i v i t y (Frank, 1971).  One method of establishing a more  direct association of P i 2 with the plasma sheet inner boundary might be t o determine the latitude of maximum P i 2 amplitude while simultaneously observing the location of  46  the inner boundary.  b.  P i 2 Source From sections II.b and c, i t was  occur most frequently around 2230 LMT,  shown that P i 2  east (west) of which  t h e i r i n i t i a l orientation i s primarily north-west (northeast).  These results and also those of section II.a imply  that the P i 2 source must l i e oh auroral zone f i e l d centered about the 2230 LMT time plasma implosion may  meridian.  lines  A theory of night-  account f o r the i n i t i a l movements  (Smith and Watanabe, 1972).  Two  theories of implosion  processes have been suggested (Atkinson, 1966;  Kato, 1971).  Atkinson's theory assumes that intermittent f i e l d reconnection takes place.  line  This gives r i s e to an implosion  of t a i l plasmas towards the region of closed magnetic l i n e s of force.  The implosion should cause the observed i n i t i a l  northward impulse.  The i n i t i a l eastward and westward move-  ments may be aided by the motion of the imploding  convecting  t a i l plasmas as they separate to flow about the closed f i e l d lines.  This convective  'flow separation' has been suggested  by superposing the magnetospheric convective and co-rotating potential f i e l d s (Axford and Hines, 1961; Brice, 1967).  Nishida,  The most e f f e c t i v e impact of the  1966;  imploding  plasmas might be at t h i s nightside 'flow separation' point  47  which could explain the diurnal v a r i a t i o n i n the P i 2 occurrence  frequency. As mentioned i n section I.d, the mechanism pro-  posed by Kato c a l l s f o r an hm burst impacting the f i e l d i n the v i c i n i t y of the inner boundary of the p a r t i a l r i n g currents.  Such an inward burst requires a sudden disruption  of p a r t i a l r i n g currents i n the dusk t o midnight quadrant, as observed by the abrupt f i e l d recovery at ATS et a l . , 1968).  1 (Cummings  The ring current weakens the magnetic f i e l d  inside the current s i t e and enhances i t outside.  From a  point of hydromagnetics, the ring current carries away some magnetospheric plasmas and frozen-in f i e l d l i n e s from the inner region to the outer region across the current site.  A sudden p a r t i a l ring current disruption i s expected  to l e t the carried away f i e l d l i n e s move back to t h e i r normal p o s i t i o n s , giving r i s e to a plasma implosion. f i e l d l i n e s are concentrated about the 2230 LMT  These  meridian.  When implosion occurs, the i n i t i a l movement of the f i e l d l i n e s immediately east (west) of t h i s meridian must move i n ward and veer eastward (westward).  This east and west  veering i s l i k e l y determined by Maxwell stress which the implosion exerts upon the f i e l d l i n e s , spreading away from 2230 LMT meridian.  F i e l d l i n e s f a r away from the a c t i v i t y  centre should move almost r a d i a l l y inward.  48  c.  P i 2 Source Variations From the r e s u l t s presented i n the Pi 2 source  v a r i a t i o n study of section I I . c , i t i s seen that the flow d i r e c t i o n and pressure of solar wind protons and the most probable l o c a l time of P i 2 occurrence during low magnetic a c t i v i t y are d i f f e r e n t from those, during high a c t i v i t y . It i s possible that the l o c a l time at which P i 2 occurs most frequently i s dependent upon the solar wind d i r e c t i o n . That i s , the solar wind streaming d i r e c t i o n may  determine  the d i r e c t i o n of the earthward convecting, t a i l plasma flow which could possibly a f f e c t the meridians of peak intensity p a r t i a l r i n g currents.  Indeed, Cummings (1966)  suggested the p a r t i a l ring currents are formed by the i n ward convection of charged p a r t i c l e s near the midnight meridian.  Yet, from low to high magnetic a c t i v i t y , the  peak streaming angle changes by only 23°.  This corres-  ponds to only about 1 hour t h i r t y minutes while the westward s h i f t i n peak P i 2 occurrence i s about 3 hours.  Thus  the streaming angle change may not f u l l y account f o r the peak P i 2 time s h i f t .  Processes associated with the  increased solar wind streaming pressure during high magnetic a c t i v i t y might give r i s e to the intense, p a r t i a l ring currents.  This increased plasma density, i n the dusk  to midnight quadrant, could also account f o r the westward  49  s h i f t i n the peak time of Pi 2 occurrence.  Thus, the  results of t h i s study display the *dynamic' behaviour of the P i 2 source which appears dependent upon the solar wind. The meridian of P i 2 generation then, i s closely associated with the earthward convecting plasmas i n the magnetotail.  This meridian has been considered to i n d i -  cate the 'flow separation' point of the inward convecting t a i l plasmas and/or the peak intensity of the p a r t i a l r i n g currents.  In view of t h i s discussion (and the one i n  section I l l . b ) , sketches are presented of the streamline pattern i n the equatorial plane of the magnetosphere during low and high magnetic a c t i v i t i e s .  Figures 9 and 10 depict  the results of t h i s investigation, showing the solar wind d i r e c t i o n and peak Pi 2 occurrence time ('flow separation* point) during low and during high magnetic a c t i v i t i e s , respectively. Carpenter  The plasmapause behaviour was reported by  (1970) and Chappell et a l . (1970).  The  partial  ring current belts were drawn from the information suggested by Frank (1967) and Coleman et a l . (1971).  d.  On the Pi 2 Rate of Occurrence The f i n d i n g (section II.d) that P i 2 occur most  frequently during intervals when the Kp i s between 1+ and  52  2-, i s unexpected.  Although t h i s result contradicts the  observations of previous investigators, i t i s f e l t to be • s t a t i s t i c a l l y ' s i g n i f i c a n t , due to the large amount of data used.  A direct consequence of t h i s f i n d i n g i s that  the yearly occurrence frequency of Pi 2 should reach maximum  when the average Kp index most closely  optimum l e v e l (1+ - Kp i 2-).  approaches  This would be during sunspot  minimum, i n agreement with the observations by Yanagihara (1956).  A further consequence of t h i s result i s that the  peak time of Pi 2 occurrence should not s h i f t during the sunspot cycle.  Yet such a s h i f t has been observed (Afana-  sieva, 1961; Saito et a l . , 1968).  It may be that  further  investigation i s necessary i n order to establish whether a systematic change exists (or should be expected) i n the Pi 2 peak time of occurrence during the solar cycle.  CHAPTER IV SUMMARY AND CONCLUDING REMARKS  The investigations presented i n t h i s thesis have shown that P i 2 micropulsations do r e f l e c t the nature of t h e i r source.  This source i s i n the auroral zone centered  near the 2230 LMT meridian, as indicated by P i 2 occurrence and i n i t i a l orientation studies. The actual source meridian i s 'dynamic* i n the sense that i t s h i f t s with changes i n magnetic a c t i v i t y .  Furthermore, the P i 2 period v a r i a t i o n  with the location of the plasma sheet inner boundary implies the association of the P i 2 source with a  magnetospheric  subregion, and also with the earthward convecting plasmas i n the magnetotail.  The 'dynamic* source i s also dependent  upon the solar wind, as evidenced by the correlated studies of solar wind and source variations with magnetic a c t i v i t y . Lastly, as suggested i n sections I.b and d regarding period morphology and nonsimilar l a t i t u d i n a l variations of P i 2 and bay amplitude, P i 2 are not always d i r e c t l y associated with magnetic a c t i v i t y (Kp) and/or magnetic storms (ssc and bays).  The relationship i s more complicated, as i s seen  iri the P i 2 rate of occurrence study.  In summation, the  Pi 2 phenomenon appears as a complex problem involving the solar wind, magnetospheric ditions.  subregions and ionospheric con-  The author f e e l s that t h i s thesis presents some  evidence that P i 2 micropulsations can provide information  % on the states of the solar wind, magnetosphere and ionosphere. It was suggested that P i 2 may be explained by a nightside plasma implosion process near the closed f i e l d l i n e boundary and/or the r i n g current.  Two theories  regarding implosion have been presented  (Atkinson, 1966;  Kato, 1971), as to which theory i s the more l i k e l y , i t i s d i f f i c u l t to decide.  Indeed, i t i s possible that the two  mechanisms each generate P i 2, and i n t h i s sense, they may be regarded as of a complementary nature.  Atkinson's  theory associated P i 2 with geomagnetic bay disturbances. Yet many P i 2's not related t o t h i s magnetic a c t i v i t y have been observed (Romana et a l . , 1968).  These non-related  Pi 2's could be due to p a r t i a l ring current disruptions required by Kato's theory. The P i 2 plasma implosion theory and also the theory of P i 2's as propagating  ionospheric disturbances,  discussed by Jacobs (1970), each explain much of the observed morphology.  An objection to P i 2 as the effect  of a current system was that occassional clockwise r o t a tions are observed when the p o l a r i z a t i o n i s usually counter-clockwise.  Yet, P i 2 p o l a r i z a t i o n may be due to  inward moving f i e l d lines which are veered eastward by the skewed position of the plasmasphere bulge (Smith and Watanabe, 1972).  This motion i s depicted i n Figure 11.  55  F i g . 11.  Motion of magnetospheric plasmas due to an implosion (Smith and Watanabe, 1972)  56  In such a s i t u a t i o n , the p o l a r i z a t i o n at meridians near the abrupt westward edge of t h i s bulge may occassionally be observed as clockwise ( i n the northern hemisphere). Another objection to P i 2 s due to a current system was f  that l a t i t u d i n a l v a r i a t i o n of bay magnitude i s not always the same as that of the amplitude of Pi 2 (Saito et a l . , 1968).  Yet Akasofu, Chapman and Meng (1965) proposed a  model current system f o r an intense polar magnetic storm which showed peak i n t e n s i t i e s i n the midnight t o dawn quadrant.  Thus, observation of occassional d i s s i m i l a r i t i e s  between P i 2 (occurring near 2230 LMT) and the magnetic bay should be expected on the basis that the a c t i v i t y may not be coincident.  centres  57  BIBLIOGRAPHY  Afanasieva, V. I., Short period o s c i l l a t i o n s of the geomagnetic f i e l d , IAGU B u l l . , 16G, 48, 1961. Akasofu, S. - I . S . Chapman and C. - I . Meng, The polar e l e c t r o j e t , J . Atmos. T e r r . Phys., 27, 1275, 1965.  ~  Angenheister, G., Ueber die Fortpflanzungs - Geschwindigkeit maghetischer Storungen und Pulsationen. Berecht uber die erdmagnetischen S c h n e l l r e g i s trierungen i n Apia (Samoa), Batavia, Cheltenham, und Tsingtau i n September 19ll'. Gottingen Nachr. Ges. Wiss., 565, 1913. Angerami, J. J. and D. L. Carpenter, Whistler studies pf the plasmapause i n the magnetosphere, 2, Electron density and t o t a l tube electron content near the knee i n magnetospheric i o n i z a t i o n , J . Geophys. Res., 21, 711, 1966. Atkinson, G., A theory of polar substorms, J. Geophys. Res., I I , 5157, 1966. Axford, W. I . and C. 0. Hines, A unifying theory ofthighl a t i t u d e geophysical phenomena and geomagnetic storms, Can. J . Phys., 3 9 , H 3 3 , 1961. Axford, W. I., H.E. Petschek and 0. L. Siscoe, T a i l of the magnetosphere, J . Geophys. Res., 70. 1231, 1965.  Bame, S., Plasmasheet and adjacent regions, i n Earth's P a r t i c l e s and F i e l d s (Ed. B. M. McCormac), p. 373. Reinhold Book Corp., New York, 1968. Binsack, J . H., Plasmapause observations with the M.I.T. experiment on Imp 2, J . Geophys. Res., 72,. 5231, 1967.  Brice, N. M., Bulk motion of the magnetosphere, J . Geophys. Res., 22, 5193, 1967. C a h i l l , L. J . and P. G. Amazeen, The boundary of the geomagnetic f i e l d , J . Geophys. Res., 68. 1835. 1963.  58  Campbell, W. H. and Rees, M. H., A study of auroral coruscations, J . Geophys. Res., 66, 41, 1961. Carpenter, D. L., Whistler studies of the plasmapause i n the magnetosphere, 1, Temporal v a r i a t i o n s . i n the position of the knee and some evidence on plasma motions near the knee, J. Geophys. Res., 21, 693, 1966. Carpenter, D. L., Whistler evidence of the dynamic behaviour of the duskside bulge i n the plasmapause, J. Geophys. Res., Jit 3^37, 1970. Carpenter, D. L., and K, Stone, Direct detection by, a whistler method of the magnetospheric e l e c t r i c f i e l d associated with a polar substorm, Planet. Space S c i . , 15_, 395, 1967. Carpenter, D. L., F. Walter, R. E. Barrington and D. J . McEwen, Alouette 1 and 2 observations of abrupt, changes i n whistler rate and of VLF noise v a r i ations at the plasmapause; a satellite-ground study, J. Geophys. Res., 21, 2929, 1968. Channon, M. J. and D. Orr, A study of equatorial geomagnetic micropulsations, Planet. Space S c i . , 18, 229, 1970. ~~ Chappell, C. R., K. K. Harris and G. W. Sharp, The morphology of the bulge region of the plasmasphere, J . Geophys. Res., 21, 3848, 1970. C h r i s t o f f e l , A. D. and J. G. Linford, Diurnal properties of the horizontal geomagnetic micropulsation f i e l d i n New Zealand, J . Geophys. Res., 2i> #91, 1966. Coleman, P. J. and W. D. Cummings, Stormtime disturbance f i e l d at ATS 1, J. Geophys. Res., 2£, 51, 1971. Cummings, W;. D., Asymmetric ring currents and the low l a t i tude disturbance d a i l y v a r i a t i o n , J. Geophys. Res., 21, 4495, 1966. Cummings, W. D,., J . N. B a r f i e l d and P. J . Coleman, Magnetospheric substorms observed at the synchronous o r b i t , J . Geophys. Res.. 73.. 6687. 1968. Dungey, J . H., Interplanetary magnetic f i e l d and the auroral zones, Phys. Rev. Letters, 6, £2, 1961.  59  Duhgey, J . W., The i n t e r p l a n e t a r y f i e l d and a u r o r a l t h e o r y , J . Phys. Soc. Japan, 12, S u p p l . A2, 15, 1962. Dungey, J . W.,. Theory o f t h e q u i e t magnetosphere, i n S o l a r T e r r e s t r i a l P h y s i c s (Ed. J . W. King and W. S. Newman), p. 91. Academic P r e s s , New York, 1967. Frank, L. A., On t h e e x t r a t e r r e s t r i a l r i n g c u r r e n t d u r i n g geomagnetic storms, J . Geophys. Res., 72, 3753,. 1967. Frank, L. A., D i r e c t d e t e c t i o n o f asymmetric i n c r e a s e s o f e x t r a - t e r r e s t r i a l r i n g current proton i n s t a b i l i t i e s i n t h e o u t e r r a d i a t i o n zone, J . Geophys. Res., 22, 1263, 1970. Frank, L. A., R e l a t i o n s h i p o f t h e plasma sheet, r i n g c u r r e n t , t r a p p i n g boundary and plasmapause near t h e magn e t i c equator and l o c a l midnight, J . Geophys. Res., 2°> 2265, 1971. Frank, L. A., and H. P. Owens, O m n i d i r e c t i o n a l i n t e n s i t y contours o f low-energy protons (0.5 - E - 50.kev) i n t h e e a r t h ' s outer r a d i a t i o n zone a t the magn e t i c equator, J . Geophys. Res., 21* 1269, 1970. F u k u n i s h i , H. and T. Hirasawa, P r o g r e s s i v e change i n P i 2 power s p e c t r a w i t h t h e development o f magnetos p h e r i c substorm, Rep. Ionos. Space Res. Japan, 2/fc, 45, 1970. Grenet, G., Y. Kato, J . Osaka and M. Okuda, P u l s a t i o n s , i n t e r r e s t r i a l magnetic f i e l d a t t h e time o f bay d i s t u r b a n c e , S-ci. Rep. Tohoku Univ., S e r . 5, Geophys., 6, 1, 1954. G u r n e t t , D. A. and L. A. Frank, VLF h i s s and r e l a t e d plasma o b s e r v a t i o n s i n the p o l a r magnetosphere, J . Geophys. Res., 77, 172, 1972. Heacock, R. R., A. J . M u l l e n , V. P. H e s s l e r , C. S u c k s d o r f f , M. K i v i n e n and E . K a t a j a , C o r r e l a t i o n s o f OGO-V plasmapause c r o s s i n g w i t h o b s e r v a t i o n s o f type P i m i c r o p u l s a t i o n s on t h e ground, Ann. Geophys., 22, 477, 1971. Herron, T. J . , Phase c h a r a c t e r i s t i c s of geomagnetic microp u l s a t i o n s , J . Geophys. Res., 2i» ^71, 1966.  60  Hirasawa, T. and T. Nagata, Spectral analysis of geomagnetic pulsations from 0.5 to 100 sec. period f o r the quiet sun condition, Pure and Appl. Geophys., 6£, 102, 1966. Hoffman, R. A. and L. J . G a h i l l , Ring current p a r t i c l e d i s t r i b u t i o n s derived from r i n g current magnetic f i e l d measurements, «J. Geophys. Res., 73, 6711, 1968. Hones, E. W., J . R. Asbridge and S. J . Bame, Time variations of the magnetotail plasmasheet at 18 Re determined from concurrent observations by a pair of Vela s a t e l l i t e s , J . Geophys. Res., 2°» 4402, 1971. Jacobs, J . A., Geomagnetic Micropulsations, Springer-Verlag, New York, 1970. Jacobs, J . A. and K. Sinno, World-wide c h a r a c t e r i s t i c s of geomagnetic micropulsations. Geophys. J . , 3, 333, 1960. Kannangara, M. L. and P. G. Fernando, Nighttime equatorial Pi 2 micropulsations, J. Geophys. Res., 74, 844, 1969. Kato, Y., Frequency analysis of geomagnetic micropulsations associated with ssc and P i 2, S c i . Rep. Tohoku Univ., Ser. 5, Geophys., 21, 37, 1971. Kato, Y., J . Ossaka, T. Watanabe, M. Okuda and T. Tamao, Investigation on the magnetic disturbance by the induction magnetogra.ph, Pt. V, On the rapid pulsation psc, S c i . Rep. Tohoku Univ., Ser. 5, Geophys., J* 136, 1956. Milton, D'. W., R. L. McPherron, K. A. Anderson and S. H. Ward, Direct correspondence between x-ray microbursts and impulsive micropulsations, J . Geophys. , Res., 22, 414, 1967. Ness, N. F., The earth's magnetic t a i l , J . Geophys. Res. 70. 2^89, 1965. Nishida, A., Formationof plasmapause, or magnetospheric plasma knee by Combined action of magnetospheric convection and plasma escape from t a i l , J . Geophys. Res., 71, 5669, 1966.  61  Obayashi, T. and J . A. Jacobs, Geomagnetic p u l s a t i o n s and the e a r t h ' s outer atmosphere, Geophys. J . , 3L, 53, 1958. O g l i v i e , K. W. and L. F . B u r g a l a , Hydromagnetic o b s e r v a t i o n s i n t h e s o l a r wind, i n P a r t i c l e s and F i e l d s i n t h e Magnetosphere, 82, R e i d e l P u b l i s h i n g Go., D o r d r e c h t , H o l l a n d , 1970. O g l i v i e , K. W., N. M c l l w r a i t h and T. D. W i l k e r s o n , A massenergy spectrometer f o r space plasmas, Rev. S c i . I n s t r . , 22, M l , 1968. Romana, A. and D. Van Sabben, Geomagnetic data 1967 r a p i d v a r i a t i o n s , IAGA B u l l . , 12v2, 1970. Romana, A. and J . Veldkamp, Geomagnetic data 1964. r a p i d v a r i a t i o n s , IAGU B u l l . , 12s2, 1968. Rostoker,  G., 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 o f P i 2 m i c r o p u l s a t i o n s and t h e i r r e l a t i o n t o t h e d e t e r mination o f p o s s i b l e source mechanisms f o r t h e p r o d u c t i o n of nighttime i m p u l s i v e m i c r o p u l s a t i o n a c t i v i t y . Can. J . P h y s i , 1319, 1967a.  Rostoker,  G., The frequency spectrum of P i 2 m i c r o p u l s a t i o n a c t i v i t y and i t s r e l a t i o n s h i p t o p l a n e t a r y magn e t i c a c t i v i t y , J . Geophys. Res.,JZ, 2032, 1967b.  R y c r o f t , M. J . and J . 0. Thomas, The magnetospheric; plasmapause and t h e e l e c t r o n d e n s i t y trough a t t h e A l o u e t t e I o r b i t , P l a n e t . Space S c i . , 18, 65, 1970. S a i t o , T., O s c i l l a t i o n o f geomagnetic f i e l d w i t h t h e progress of pt-type p u l s a t i o n , S c i . Rep. Tohoku Univ., S e r . 5, Geophys., 13_, 53, 1961. S a i t o , T, and S. M a t s u s h i t a , S o l a r c y c l e e f f e c t s on geomagnetic P i 2 p u l s a t i o n s , J . Geophys. Res., 73, 267, 1968. S a i t o , T. and T. S a k u r a i , Mechanism o f geomagnetic P i 2 pulsations i n magnetically quiet c o n d i t i o n , S c i . Rep. Tohoku Univ., S e r . 5, Geophys., 11, 53, 1970. S a k u r a i , T., 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 o f geomagnetic P i 2 m i c r o p u l s a t i o n s , S c i . Rep. Tohoku Univ., S e r 5, Geophys.,20, 107, 1970.  62  S c h i e l d , M. A., Pressure balance between s o l a r wind and magnetosphere, J . Geophys. Res., 2k>  1275,  1969.  Smith, B.P. and T. Watanabe, On the o r i g i n and p o l a r i z a t i o n of n i g h t t i m e i r r e g u l a r m i c r o p u l s a t i o n s , P i 2, P l a n e t . Space S c i . , (submitted f o r p u b l i c a t i o n ) , 1972. Terada, T., On r a p i d p e r i o d i c v a r i a t i o n s of t e r r e s t r i a l magnetism, J . C o l l e g e S e t . , I m p e r i a l Univ. Tokyo, May 25th, XXV i i , A r t . 9, .1917. T r o i t s k a y a , V. A., M i c r o p u l s a t i o n s and the s t a t e of the magnetosphere, i n S o l a r T e r r e s t r i a l P h y s i c s (Ed. J . W; King and W. S. Newman), p. 213, Academic P r e s s , New York, 1967. Yanagihara, K., On the c o r r e l a t i o n between the frequency of the e a r t h c u r r e n t p u l s a t i o n and the s o l a r a c t i v i t y , Mem. Kakioka Mag. Obs., 27, 1956. Yanagihara, K., E a r t h c u r r e n t p u l s a t i o n s observed at Kakioka, Mem. Kakioka Mag. Obs., 8, 49, 1957a. Yanagihara, K., Frequency of p u l s a t i o n and geomagnetic a c t i v i t y , Mem. Kakioka Mag. Obs., 8, 61, 1957b. Yanagihara, K., Geomagnetic p u l s a t i o n s i n middle l a t i t u d e s Morphology and i t s i n t e r p r e t a t i o n , Mem. Kakioka Mag. Obs., 2, 15, I960. V a s y l i u n a s , V. M., A survey of low-energy e l e c t r o n s i n the evening s e c t o r of the magnetosphere w i t h 0G01 and 0G0 3, J . Geophys. Res., 21t 2839, 1968.  

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