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A theory for the generation of "intervals of pulsations of diminishing period" Roxburgh, Kenneth R. 1970

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A THEORY FOR THE GENERATION OF "INTERVALS OF PULSATIONS OF DIMINISHING PERIOD" by KENNETH R. ROXBURGH B.Sc. (Hons), U n i v e r s i t y o f A l b e r t a , 1966 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department o f GEOPHYSICS We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA August, 1970 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r equ i r emen t s f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I ag ree tha t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and S tudy . I f u r t h e r ag ree tha t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y pu rposes may be g r an t ed by the Head o f my Department or by h i s r e p r e s e n t a t i v e s . It i s u n d e r s t o o d t h a t c o p y i n g or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f G e o p h y s i c s The U n i v e r s i t y o f B r i t i s h Co lumbia Vancouver 8, Canada Date September 4, 1970 ABSTRACT Micropulsation data recorded at Palo A l t o , C a l i f o r n i a during 1963-4 and Ralston, Alberta during 1967 have been used to study "Intervals of pulsations of diminishing period" (IPDP). IPDP's are found to be generated in the dusk-midnight quadrant of the magnetosphere at an equatorial distance of about 6 earth r a d i i . An intensive study of the Ralston data reveals that IPDP's occur during the expansive phase of magnetospheric sub-storms. It i s proposed that IPDP's are generated by a cyclotron i n s t a b i l i t y between energetic protons and left-hand ion cyclotron waves. Their main ch a r a c t e r i s t i c s are determined by the per-turbations of the dusk-midnight sector of the magnetosphere by magnetospheric substorms. One of the main disturbances in that region is a slow decrease and then sudden increase in the magnetic f i e l d corresponding to the buildup and decay of a p a r t i a l ring current. IPDP's show an increase in midfrequency due to the change in the cyclotron i n s t a b i l i t y frequency produced by the increasing magnetic f i e l d . This theory i s tested by a comparison of frequency increase of IPDP's observed at Ralston and magnetic f i e l d increase in the magnetosphere observed by the ATS-1 s a t e l l i t e . Other conditions necessary for IPDP generation are then discussed. It i s shown that d i f f e r e n t combinations of these conditions result in the generation of hm emissions and band type micropulsations. - i i i -TABLE OF CONTENTS Page ABSTRACT i i LIST OF FIGURES v LIST OF TABLES v i i ACKNOWLEDGEMENTS v i i i CHAPTER I INTRODUCTION 1 CHAPTER II DATA SOURCES, ANALYSIS AND INSTRUMENTATION 8 11.1 Micropulsation Data Source and Analysis 8 11.2 Magnetic F i e l d Data 10 11.3 Analysis of Micropulsation Data 11 CHAPTER III REVIEW OF POLAR MAGNETIC SUBSTORMS 15 111.1 Introduction 15 111.2 Polar Magnetic Substorms 16 CHAPTER IV PROPERTIES OF IPDP'S 25 IV.1 Selection of IPDP Events 25 IV.2 Characteristics of IPDP's 27 IV.3 Occurrence of IPDP's 30 IV.4 Occurrence with Hm Emissions 35 IV.5 Relationship to Magnetospheric Substorms 39 IV.6 Magnetic F i e l d Control of Frequency Change 50 i - i v -CHAPTER V DISCUSSION OF IPDP THEORIES 61 V . l Increasing Magnetic F i e l d Theory 61 V.2 Other IPDP Theories 68 CHAPTER VI DISCUSSION OF FUTURE EXPERIMENTS 77 BIBLIOGRAPHY 80 APPENDIX I Specifications of Kay E l e c t r i c Sonagraph 7030A 87 APPENDIX II Ion Cyclotron I n s t a b i l i t y Frequency Versus Magnetic F i e l d 88 APPENDIX III Use of Ion Cyclotron Dispersion Equation with a Changing B F i e l d 90 APPENDIX IV D e f i n i t i o n of Magnetic Components 91 V -LIST OF FIGURES Figure Page 1 Typical Pc 1 micropulsation 3 2 Pi 1 type micropulsations a) Pi burst followed by Pi(c) event (after Heacock 1967b) b) 4-sec. period micropulsation (after Heacock 1966) 5 3 Typical Ralston IPDP 6 4 Magnetograms showing the s p a t i a l v a r i a t i o n of magnetic bays 17 5 Polar magnetic substorm equivalent current systems with a) two c e l l s b) one c e l l (after Akasofu et a l . 1965b) 18 6 An equatorial plane view from above the north geomagnetic pole of 3-dimensional current systems thought to be responsible for polar magnetic substorms (after a) Cummings et a l . 1968, and b) Akasofu and Meng 1969) 21 7 Magnetograms showing the behavior of magnetic f i e l d at ATS-1 during polar magnetic substorms 24 8 IPDP with d i s t i n c t s t r u c t u r a l elements 28 9 IPDP with large noise band c h a r a c t e r i s t i c 29 10 Occurrence of IPDP's at Ralston versus l o c a l time 31 11 Occurrence of IPDP's at Palo Alto versus l o c a l time 32 12 Occurrence of IPDP's at Ralston and Palo Alto versus 3 hour Kp index 34 - v i -13 An example of an IPDP which changes into an hm emission 37 14 IPDP generation region sketched i n an equatorial plane view of magnetosphere 40 15 Example of IPDP occurrence during a polar magnetic substorm 42 16 Example of IPDP occurrence during a compli-cated substorm period 43 17 IPDP occurrence during two c l o s e l y spaced polar magnetic substorms 46 18 IPDP event occurring during substorm shown in Fig. 16 47 19 IPDP event occurring during substorm shown in Fig. 17 48 20 Occurrence of Ralston IPDP's r e l a t i v e to time of substorm expansion 49 21 Ralston IPDP frequency increase r e l a t i v e to ATS-1 magnetic f i e l d change with time as the parameter 55 22 Diurnal v a r i a t i o n of H component of magnetic f i e l d at ATS-1 for a quiet and a disturbed day 57 2 3 IPDP frequency increase r e l a t i v e to ATS-1 magnetic f i e l d change with a correction for s a t e l l i t e ' s motion 59 24 P a r t i a l ring current ex i s t i n g during polar magnetic substorms as viewed from the dusk-midnight quadrant (after Cummings et a l . 1968) 63 25 Integration contour (c) and surface area (s) for c a l c u l a t i o n of e l e c t r i c f i e l d 71 26 Graphic representation of the elements of a magnetic vector: X, Y, Z (geographic north, east, and v e r t i c a l components), H (horizontal i n t e n s i t y ) , D (declination), I ( i n c l i n a t i o n ) , and F ( t o t a l i n t e n s i t y ) . 91 - v i i -LIST OF TABLES Table Page 1.1 C l a s s i f i c a t i o n of Micropulsations 1 11.1 Location of Micropulsation Stations 8 11.2 Location and Magnetic Elements of Magnetic Observatories 12 IV.1 IPDP's Used for Frequency Versus Magnetic F i e l d Study 53 V . l Inward D r i f t V e l o c i t i e s and E l e c t r i c F i e l d Necessary for Explanation of IPDP 75 - v i i i -ACKNOWLEDGEMENTS I wish to thank Dr. T. Watanabe for his constant advice and encouragement and for many hours of discussion during the progress of this work. I am indebted to him for many c r i t i c i s m s and comments and for c a r e f u l l y reviewing the f i n a l manuscript. Many persons have contributed i n one way or another to this work. The Palo Alto micropulsation data were recorded by the Physics Research Laboratory of Lockheed M i s s i l e s and Space Company and I am indebted to a l l people involved i n that operation. In p a r t i c u l a r I would l i k e to thank Dr. A. C. Fraser-Smith now at Radioscience Laboratory, Stanford University for many suggestions and comments and for help in the reduction of Palo Alto data. The ATS-1 magnetic data were made available through the co-operation of the Department of Planetary and Space Science, University of C a l i f o r n i a , Los Angeles. I am indebted in p a r t i -cular to the people who did the reduction of s a t e l l i t e data to the form of magnetic f i e l d p l o t s . I wish to thank Dr. R. L. McPherron for helpful discussions on the ATS-1 data and proposed IPDP generation theory. I also thank my wife, Marja, for her patience over the l a s t few years and for c a r e f u l l y reviewing the f i n a l manuscript. T h i s s t u d y was p a r t i a l l y s u p p o r t e d by a N a t i o n a l Research C o u n c i l o f Canada r e s e a r c h g r a n t t o Dr. T. Watanabe. The a u t h o r g r a t e f u l l y acknowledges f i n a n c i a l a s s i s t a n c e i n the form o f an I n t e r n a t i o n a l N i c k e l Company o f Canada F e l l o w -s h i p f o r one y e a r , and a N a t i o n a l Research C o u n c i l S c h o l a r s h i p f o r t h r e e y e a r s . CHAPTER I Introduction Early researchers i n the f i e l d of geomagnetic micropulsations generated many d i f f e r e n t names for the diverse and complicated phenomena observed. In 1964 the nomenclature was s i m p l i f i e d by r e c l a s s i f i c a t i o n of a l l micropulsations into two groups (Jacobs et a l . 1964). Micropulsations with a continuous waveform were denoted by Pc , while i r r e g u l a r impulsive waveform micropulsations were denoted by Pi Each group was subdivided on the basis of frequency (see Table 1.1), but the d i v i s i o n was based on the major morpho-l o g i c a l properties of the micropulsations. Table 1.1 C l a s s i f i c a t i o n of Micropulsations Type Range of Periods (sec) Continuous Pulsations Pc 1 Pc 2 Pc 3 Pc 4 Pc 5 0.2 5 5 10 45 150 600 10 45 150 Irregular Pulsations Pi 1 Pi 2 1 40 40 150 - 2 -It i s now known that some of the subgroups (namely Pc 1, Pi 1) contain several morphologically d i s t i n c t micro-pulsations. Figure 1 i s the sonagram representation, which displays frequency as the ordinate, time as the abscissa, and amplitude as the darkness, of a t y p i c a l Pc 1 event. Such micropulsation signals displaying a regular r e p e t i t i o n of r i s i n g tones have been c a l l e d hydromagnetic (hm) emissions (Tepley and Wentworth, 1962), hm whistlers (Obayashi, 1964, Jacobs and Watanabe 1964b) and micropulsation whistlers (Jacobs and Watanabe 1964a). Jacobs and Watanabe (1967) argue, how-ever, for the existence of at least two prototypes. One type displays the regular dispersion effects of an ion cyclotron mode wave (left-hand polarization) bouncing between a pair of magnetically conjugate areas under the guidance of the magnetic l i n e of force and i s thus named hm whistlers by Jacobs and Watanabe. The other type of Pc 1 signal i s c a l l e d periodic hm emission after i t s s i m i l a r i t y to periodic VLF emissions. The s t r u c t u r a l elements of these signals do not show any regular dispersion. Short intervals of pulsations (SIP), (Troitskaya 1961) Pi (c) events (Heacock 1967b) , and 4-sec. period micropulsa-tions (Heacock 1966) are examples of morphologically d i s t i n c t Pi 1 micropulsations. SIP or Pi bursts (Heacock 1967b) are impulsive broadband events of short duration occurring near l o c a l midnight. Pi (c) events are observed in the midnight-dawn quadrant and have a more continuous, nonimpulsive character. - 3 -Fig. 1. T y p i c a l Pc 1 m i c r o p u l s a t i o n - 4 -Figure 2a i s a sonagram of a Pi burst at about 0200 l o c a l time (L.T.) followed by a Pi (c) event of about three hours duration. A 4-sec. period micropulsation has a constant f r e -quency noise band character as i l l u s t r a t e d in Fig. 2b, and i s observed most often i n the afternoon L.T. (Heacock 1966). Intervals of pulsations of diminishing period, hereafter c a l l e d IPDP, were f i r s t extensively studied by Troitskaya (1961). They have also been studied under the name of solar whistles (Duffus et a l . 1959), gurglers (Tepley and Amundsen 1964, Tepley 1966) and sweepers (Heacock 1967a, Fukunishi 1969). IPDP's may have the waveform c h a r a c t e r i s t i c s of either Pc 1 or Pi 1 micropulsation groups. In the sonagram representation, they consist of a diffuse noise band on which i r r e g u l a r l y spaced s t r u c t u r a l elements are sometimes superimposed. Both the noise band and st r u c t u r a l elements display a r i s e i n midfrequency during the event which las t s from 10 to 45 minutes. The Pc or Pi waveform character is determined by the amount of noise, and i r r e g u l a r i t y of structure. Figure 3 i s an IPDP shown in shaded and contoured sonagrams (see Chapter II for d e t a i l s ) . It has many s t r u c t u r a l elements as seen in the shaded sonagram, but they occur in three major groups as indicated in the con-toured sonagram. The waveform of the IPDP shown i n F i g . 3 resembles Pc 1 waveform. When the noise band dominates over the structure the IPDP waveform becomes i r r e g u l a r . F i g . 2. P i 1 type m i c r o p u l s a t i o n s a) P i b u r s t f o l l o w e d by P i ( c ) event ( a f t e r Heacock 1967b) b) 4-sec. p e r i o d m i c r o p u l s a t i o n ( a f t e r Heacock 1966) F i g . 3. T y p i c a l Ralston IPDP - 7 -The occurrence of IPDP's i s related to the occurrence of other micropulsations and geomagnetic phenomena. Heacock (1967) has noted that a 4-sec. micropulsation band sometimes terminates i n an IPDP. Gendrin et a l . (1967) have observed the occurrence of hm emissions d i r e c t l y following an IPDP. It is thus l i k e l y that the generation processes for these three types of micropulsations have some common connection. IPDP's also occur in conjunction with magnetospheric substorms (Troitskaya 1961 and others). A knowledge of IPDP ch a r a c t e r i s t i c s and generation mechanism w i l l be very useful in furthering the understanding of the magnetospheric substorm process. This thesis w i l l show that IPDP's are produced by a s p e c i f i c combination of conditions existing in the dusk-midnight quadrant of the magnetosphere during magnetospheric substorms. Different combinations of these conditions w i l l be shown to lead to other Pc 1 frequency micropulsations. The magnetospheric substorm process is reviewed i n Chapter I I I . Chapter IV presents the experimental data and develops the IPDP generation mechanism. Chapter V i s a discus-sion of the proposed and other IPDP theories. There the r e l a -tionship of IPDP's, hm emissions, and band type micropulsations w i l l also be discussed. - 8 -CHAPTER II Data Sources, Analysis and Instrumentation II.1 Micropulsation Data Source and Instrumentation Micropulsation data from two separate research projects have been used i n t h i s thesis. The Ralston 1967 data were recorded through a cooperative f i e l d operation by Radio Science Laboratory, Stanford University, the P a c i f i c Naval Laboratory (now D.R.E.P.), and the University of B r i t i s h Columbia. The Physics Research Laboratory of Lockheed M i s s i l e s and Space Company recorded the Palo Alto 1963-64 micropulsation data. Table II.1 gives the location of both recording stations. Table II.1  Location of Micropulsation Stations Station Geographic Geomagnetic Lat. (N) Long. (W) Lat. (N) Long. (E) Ralston 51°12' 111°07' 58.8° 305.5° Palo Alto 37°26' 122°10' 43.5° 299.0° The Ralston micropulsation detection system consisted of mumetal cored solenoids i n the geographic north-south (X), east-west (Y), and in the v e r t i c a l (Z) di r e c t i o n s . The signals from these c o i l s were fed through dc chopper amplifiers to a slow speed FM recording system using a c a r r i e r of 22.5 hertz and having a band pass of 0 to 4 hertz. The tape speed for - 9 -recording was 0.025 inches per second whereas the reproduction speed i s 3.75 inches per second, giving a frequency m u l t i p l i -cation of 150. At these speeds, 10 days of data recorded on 1800 feet of tape can be played back i n 1.6 hours. Channels 1, 2, and 3 of the magnetic tapes contain the X, Y, and Z micropulsation components. Also, minute and hour marks were multiplexed pn channels 1 and 2 respectively and are available as separate outputs on reproduction. Fre-quency c a l i b r a t i o n was achieved by p e r i o d i c a l l y recording a c a l i b r a t i o n tone consisting of frequencies in steps from 0.03 to 6.0 hertz. A simultaneous recording of the Y component was made on a Helicorder chart operating at 3 cm. per minute. Weir (1966) and Gibb (1968) give a complete description of the micropulsation recording system. The Palo Alto micropulsation system uses mumetal cored solenoids in the X and Y di r e c t i o n s . The c o i l signals are fed to the recording system through galvanometer photo-tube amplifiers. The signals which are then i n the 0.02 to 7 hertz band are recorded on an AM tape system running at 0.03 inches per second by amplitude modulating a 1000 hertz bias s i g n a l . Both channels are also recorded on Helicorder charts operating at 6 cm. per minute. Time and frequency c a l i b r a t i o n are achieved by recording a two-minute tone of known frequency at the beginning of every hour. Tepley (1961, 1962) f u l l y describes the in s t r u -mentation at the Palo Alto s t a t i o n . The data made available to this author was rerecorded on AM tapes which, when played at - 10 -3.75 inches per second, had a frequency m u l t i p l i c a t i o n of 2000. II.2 Magnetic F i e l d Data Magnetograms from the ATS-1 s a t e l l i t e were made a v a i l -able through the cooperation of the Department of Planetary and Space Science, University of C a l i f o r n i a , Los Angeles. The ATS-1 s a t e l l i t e i s i n a synchronous equatorial orbit at 151°W and 6.6 Re geocentric distance. The magnetometer experiment consists of two orthogonal flux gates, coplanar with s a t e l l i t e spin axis, but with t h e i r sensing axes i n c l i n e d 45° to the spin axis. The magnetic f i e l d s perpendicular and p a r a l l e l to the spin axes are determined by taking the sum and difference of the outputs of the two detectors. The magnetic f i e l d i s then converted into H, D, and Z components as for an earth based mag-netic observatory - H i s pos i t i v e northward, D po s i t i v e eastward, and Z posit i v e outward. The r e l a t i v e accuracy of in d i v i d u a l measurements i s ±0.1 y but the absolute value of D and Z is ±1 y and H i s ±10 y (Cummings et a l . 1968). For a complete description of the s a t e l l i t e experiment see Barry and Snare (1966). (See Appendix IV for explanation of magnetic components.) - 11 -A l l the data analysis has been done by the U.C.L.A. group. The data were made available i n the form of 15 sec. and 6 min. average plots of the H, D, and Z components. Magnetograms from World Data Center observatories have also been extensively used for the research presented i n this thesis. Table II.2 i s a l i s t of the magnetic observatories used with t h e i r geographic and geomagnetic co-ordinates. II.3 Analysis of Micropulsation Data A spectral representation or sonagram i s the most useful form for micropulsation data. A sonagram displays f r e -quency as the ordinate, time as the abscissa and amplitude as the darkness of shading. The Helicorder charts are used only to locate the micropulsation event and for a quantitative measure of i t s magnitude. Time and frequency measurements are made d i r e c t l y from the sonagrams. The i n i t i a l data analysis therefore consists of the production of suitable sonagrams for a l l the events being studied. For the Ralston data, the channel to be analysed (X, Y or Z) i s combined with the hour marks through a r e s i s t o r net-work and then fed into a Kay E l e c t r i c 7030 A sonagraph (see Appendix I for s p e c i f i c a t i o n s ) . Later in the research a second channel was added to the sonagraph. Then the time signal was recorded separately on this channel and displayed at the bottom of the sonagram. Table II.2 Location and Magnetic Elements of Magnetic Observatories Station Geographic Lat. (N) Co-ordinates Long. (W) Geomagnetic Lat. (N) Co-ordinates Long. (E) Average X Total F i e l d (Y) Y Z Ft. C h u r c h i l l (CH) 58°48' 94°06' 68.8° 322.5° 6,857 409 60,692 Baker Lake (BL) 64 018 , 96°23' 73.9° 314.8° 4,059 253 60,389 Leirvogur (LEI) 64°11» 21°42' 70.1° 70.2° H 11,688 D 336°19' Z 49,348 Great Whale River (GW) 55°16' 77°47' 66.8° 342.2° 9,450 338°21» 58,700 Meanook (MEA) 54°37 f 169°50' 61.8° 301.0° 12,500 23°31' 57,700 College (COL) 64°52' 147°50' 64.6° 256.5° 12,610 28°07' 55,227 Sitka (SIT) 57°04» 135°20» 60.0° 275.3° 15,418 28°09' 54,712 Barrow (BA) 71°18» 156°45' 68.5° 241.1° 8,850 22°40' 56,050 V i c t o r i a (VIC) 48°31' 123°25' 54.3° 292.7° 18,803 22°11' 53,090 Boulder (BOU) 40°08» 105°14' 49.0° 316.5° 21,135 13°43' 51,805 Fredericksburg (FRED) 38°12' 77°22» 49.6° 349.8° 19,367 6°59' 52,808 Dallas (DA) 32°49» 96°45» 43.0° 327.7° 24,282 8°39» 47,415 Tuscon (TU) 32°1S' 110°50' 40.4° 312.2° 25,785 12°58' 4 3,615 - 13 -The sonagraph analyses the signal by f i r s t recording i t on the edge of a turntable which i s d i r e c t l y connected to the drum on which the sonagram i s produced. This arrangement provides automatic time synchronization. The sonagram frequency i s calibrated by recording a short i n t e r v a l of a 50 hertz signal along with i t s harmonics. In the reproduce mode the sonagraph turntable rotates at a speed such that the recorded signal varies from 0.96 to 96 KHz. The sonagram i s traced by a stylus which advances upward on the reproduce drum, at the same time changing an o s c i l l a t o r frequency from 200 to 296 KHz. This variable c a r r i e r frequency i s mixed with the recorded signal producing frequencies which are the sum and difference of the two signals. The modulator output i s f i l t e r e d by a band pass f i l t e r set at 200 KHz. This process of mixing and f i l t e r i n g enables the sonagraph to scan the recorded s i g n a l . Two types of amplitude displays are available. The conventional display indicates the amplitude by the r e l a t i v e darkness of the sonagram. The recording paper has a dynamic range of 10 db but 40 db signals may be compressed on i t by use of an AGC c i r c u i t . The second display contours the ampli-tude of the frequency time plots in steps of 6 db with a dynamic range of 42 db. The contoured inter v a l s are also r e l a t i v e l y shaded for ease of i d e n t i f i c a t i o n . The Palo Alto micropulsation tapes were analysed on a Kay E l e c t r i c M i s s i l i z e r which i s very s i m i l a r to a Kay E l e c t r i c - 14 -7030 A Sonagraph. However, a contour display i s not available with this machine. The anlysis procedure was much the same as for Ralston data. The tapes had an hour mark at a known fr e -quency, however, providing automatic time and frequency c a l i b r a -tion of the sonagrams. - 15 -CHAPTER III Review of Polar Magnetic Substorms I I I . l Introduction In order to better understand the implications of some of the data to be presented in Chapter IV, a very short review of polar magnetic substorms w i l l be given here. This review is in no way intended to be comprehensive but w i l l concentrate on the gross s p a t i a l and temporal variations of substorm asso-ciated magnetic f i e l d changes. A magnetospheric substorm i s an explosive process occurring throughout the magnetosphere and ionosphere, l a s t i n g from 1 to 3 hours. It i s an int e g r a l part of a magnetospheric storm, but also occurs during more magnetically quiet periods. Akasofu (1968) divides the magnetospheric substorm as manifested in the polar upper atmosphere into seven parts - auroral, polar magnetic, ionospheric, X-ray, proton aurora, VLF emission, and micropulsation substorms. In the magnetosphere, substorms are manifested by magnetic disturbances and proton and electron flux variations. Each substorm component has i t s own s p a t i a l and temporal c h a r a c t e r i s t i c s and at present the relationship between them i s not adequately understood. In this chapter, only polar magnetic substorms and associated magnetic disturbances i n the magnetosphere w i l l be reviewed. - 1 6 -III.2 P o l a r Magnetic Substorms A t y p i c a l magnetic d i s t u r b a n c e at the e a r t h ' s s u r f a c e during a magnetospheric substorm i s a sudden d e v i a t i o n from the normal b a s e l i n e l a s t i n g up to three hours (magnetic bay). The magnitude, d i r e c t i o n , and form of the bay depend on the l a t i t u d e and l o c a l time of the observatory as w e l l as the temporal charac-t e r i s t i c s o f the substorm. The gross s p a t i a l v a r i a t i o n o f magnetic bays i s w e l l i l l u s t r a t e d by the substorm on October 6, 1967 ( F i g . 4). The magnetic d i s t u r b a n c e , s t a r t i n g at about 03:30 U.T. , i s l a r g e and complex near the a u r o r a l zone (GW, CH, MEA, COL). The maxi-mum di s t u r b a n c e occurs near l o c a l midnight (GW, CH). M i d l a t i -tude s t a t i o n s (BOU, VIC) observe s m a l l e r magnitude bays w i t h u s u a l l y a simple form. A l s o both p o s i t i v e and n e g a t i v e bays are observed s i m u l t a n e o u s l y at d i f f e r e n t o b s e r v a t o r i e s (MEA, VIC, COL). I t i s customary to re p r e s e n t a p o l a r magnetic sub-storm by a c u r r e n t system l o c a t e d i n the ionosphere. The o r i g i n a l c u r r e n t c o n f i g u r a t i o n ( S i l s b e e and V e s t i n e 1942) was based on the average o f many bays and tended to p o i n t to the e x i s t e n c e of two a u r o r a l e l e c t r o j e c t s , one f l o w i n g eastward b e f o r e midnight and one f l o w i n g westward a f t e r midnight ( F i g . 5a). More r e c e n t l y , Akasofu et a l . (1965b, 1966a) and F e l d s t e i n (1966) have found that the j e t c u r r e n t flows c o n t i n u o u s l y westward along the F i g . 4. Magnetograms showing the s p a t i a l v a r i a t i o n o f magnetic bays - 18 -SUN t a) b) F i g . 5. P o l a r magnetic substorm e q u i v a l e n t c u r r e n t systems w i t h a) two c e l l s b) one c e l l ( a f t e r A k a s o f u e t a l . 1965b) - 19 -auroral oval (Fig. 5b). In both models the return currents are of much lower surface density than the primary e l e c t r o j e t s . A detailed study by Best et a l . (1968) shows that both types of current systems may occur during the same disturbed period but in d i f f e r e n t phases of i t . Thus the temporal behaviour of magnetospheric substorms changes the form as well as the mag-nitude of the current systems. Recently i t has been shown that f i e l d aligned currents are also important i n the production of magnetic disturbances (Zmuda et a l . 1966, Atkinson 1967, Cummings et a l . 1968). Cummings et a l . (1968) showed that substorm magnetic f i e l d changes i n the dusk-midnight quadrant at ATS-1 (6.6 Re) and Honolulu were in the same d i r e c t i o n and of comparable magnitude. The f i e l d changes must thus be of magnetospheric o r i g i n as ionospheric currents would produce magnetic f i e l d s of opposite sign. Also Atkinson (1967) has been able to explain complicated magnetic disturbances near the auroral bulge by the use of f i e l d aligned currents. The existence of magnetospheric currents means that a three dimensional current system must be used to explain substorm associated magnetic f i e l d changes. The current systems sketched in Fig. 5 must be considered to be equivalent current systems i . e . they symbolize the substorm magnetic disturbance by assuming that the causative current is flowing i n the ionosphe - 20 -Two contradictory 3-dimensional current systems have been proposed for polar magnetic substorms. Cummings et a l . (1968) used ATS-1 magnetic f i e l d data to deduce the existence of a p a r t i a l ring current i n the dusk-midnight quadrant of the magnetosphere at a distance greater than 6.6 Re (Fig. 6a). The ring current i s completed by currents flowing along the f i e l d lines into the ionosphere at about 1800 L.T. and out of the ionosphere at 2400 L.T. It would exist i n addition to ionospheric currents with the general form of F i g . 5. Meng and Akasofu (1969) used ground magnetic data to deduce a p a r t i a l ring current with a gap near l o c a l midnight (Fig. 6b). This model i s not consistent with ATS-1 magnetic f i e l d measurements, which do not indicate a ring current on the day side of the magnetosphere. For this reason, Cummings' et a l . model for substorm magneto-spheric currents w i l l be used in this thesis. The exact nature of the temporal changes in the mag-nitude and form of current systems i s unknown. However, mag-netic disturbances in the auroral zone near l o c a l midnight are closely associated with auroral a c t i v i t y , namely the formation and motion of the auroral bulge and westward t r a v e l l i n g surge (Akasofu et a l . 1966a, b). At the time of auroral substorm expansive phase the currents which are flowing along the direc-tion of auroral arcs (Sobuti 1961, Feldstein 1964 and others) are suddenly enhanced. The e l e c t r o j e t current then moves pole-ward with the expanding auroral bulge. The sudden and large F i g . 6. An equatorial plane view from above the north geomagnetic pole of 3-dimensional current systems thought to be responsible for polar magnetic substorms (after a) Cummings et a l . 1968, and b) Akasofu and Meng 1969) - 22 -magnetic disturbances seen in the v i c i n i t y of this moving elec-t r o j e t can be used to i d e n t i f y the substorm expansive phase. Ideally one auroral zone observatory near l o c a l midnight i s s u f f i c i e n t for this purpose, but p r a c t i c a l l y a network of auroral zone observatories must be used since many substorms do not con-form to the average substorm discussed above. Some substorms have l o c a l i z e d magnetic f i e l d disturbances as w i l l be shown i n Chapter IV. Also the lati t u d e range over which the e l e c t r o j e t moves during substorm expansion depends on the in t e n s i t y of the substorm (Akasofu et a l . 1966b). The substorm temporal changes i n the dusk region of the auroral zone are dominated by the passage of the westward t r a v e l l i n g surge. (Akasofu et a l . 1965a, Akasofu and Meng 1967). The magnetic disturbance in the dawn region i s much less complex than that in either the dusk or midnight regions. It i s dominated by the growth and decay, rather than the motion, of the current system. Major magnetic disturbances occur during the substorm expansive phase, but there i s evidence of s i g n i f i c a n t magnetic a c t i v i t y previous to expansion. Rostoker (1968) has shown that the major excursion of the bay i s often preceded by a smaller excursion having a duration of less than 20 minutes. Thus he argues that substorms occur in two stages, the second usually corresponding to auroral substorm expansive phase. - 23 -Cummings et a l . (1968) noticed that when ATS-1 i s in the dusk-midnight quadrant, the magnetic f i e l d slowly decreases, corresponding to the buildup of a p a r t i a l ring current. At the time of, or shortly a f t e r the st a r t of auroral substorm expansion, the f i e l d recovers to i t s pre-substorm value. The behaviour of the f i e l d at ATS-1 i s i l l u s t r a t e d i n the magneto-grams shown i n F i g . 7. For both substorms occurring on May 11 the f i e l d at ATS-1 decreases previous to the time of substorm expansion as defined by the sudden changes at Great Whale. Polar magnetic substorms then consist of three phases - the quiet or buildup phase, the expansive phase and the recovery . phase. The times of the expansive and recovery phases correspond to the times of the same phases for the auroral substorm. Fig. 7. Magnetograms showing the behavior of magnetic f i e l d at ATS-1 during polar magnetic substorms - 25 -CHAPTER IV Properties of IPDP's IV.1 Selection of IPDP Events A continuous chart or magnetic tape recording of geo-magnetic micropulsations may include many ph y s i c a l l y and morpho-l o g i c a l l y d i f f e r e n t types. Therefore, i n order to study a p a r t i c u l a r type of micropulsation such as IPDP, i t must f i r s t be i d e n t i f i e d and separated from a l l other micropulsations. This i d e n t i f i c a t i o n i s based on the d i s t i n c t morphological properties of the micropulsation as observed i n eith e r the amplitude-time (paper chart) or frequency-time-amplitude (sonagram) displays. Different researchers may use a d i f f e r e n t s e lection process, thereby possibly influencing the f i n a l r e s u l t s . Because of this p o s s i b i l i t y , the process of IPDP selection for this thesis w i l l be described i n d e t a i l . Troitskaya (1961) used the term "Irregular pulsations of diminishing periods" to c l a s s i f y a group of micropulsations whose frequency increased from approximately 0.1 to 1.0 hertz during i t s continuance of about t h i r t y minutes. Further work by Gendrin et a l . (1967), Heacock (1967a), and others revealed that the amount of frequency change is quite variable and that i r r e g u l a r l y spaced s t r u c t u r a l elements are sometimes superimposed on the r i s i n g frequency noise band. - 26 -Heacock (1966) a l s o o b s e r v e d s o - c a l l e d 4-sec. p e r i o d m i c r o p u l s a t i o n s w h i c h sometimes appear v e r y s i m i l a r t o IPDP's but have a c o n s t a n t f r e q u e n c y . S h o r t i n t e r v a l s o f p u l s a t i o n s , ( S . I . P . ) , ( T r o i t s k a y a 1961), are an example o f p u l s a t i o n s h a v i n g an i n f i n i t e r a t e o f f r e q u e n c y i n c r e a s e ; i . e . , they are an i m p u l s i v e event w i t h a l l f r e q u e n c i e s observed s i m u l t a n e o u s l y . S i n c e the v a r i a t i o n o f the f r e q u e n c y i n c r e a s e o f IPDP's extends almost t o the extreme cases o f 4-sec. p u l s a t i o n s and S.I.P., one must r e a l i z e t h a t the d i v i s i o n becomes d i f f i c u l t . H e l i c o r d e r c h a r t s as d e s c r i b e d i n Chapter II were s e a r c h e d f o r events i n the 0.1 t o 1.0 h e r t z f r e q u e n c y range whose average f r e q u e n c y i n c r e a s e d w i t h t i m e . A l l these events were put i n t o sonagram form and the IPDP sample was s e l e c t e d by e l i m i n a t i o n o f e v e n t s t h a t : 1) had no measurable f r e q u e n c y i n c r e a s e and thus were p r o b a b l y 4-sec. p e r i o d type m i c r o p u l s a -t i o n s , 2) more c l o s e l y resembled SIP o r P i ( c ) (Heacock 1967b), 3) were c l e a r l y r e c o g n i z a b l e as hydromagnetic e m i s s i o n s ( T e p l e y 1962) by t h e i r r e g u l a r r e p e t i t i o n o f r i s i n g s t r u c t u r a l e l ements. In cases (2) and (3) the f r e q u e n c y i n c r e a s e though o b s e r v e d on paper c h a r t s was due t o the complex f r e q u e n c y - t i m e s t r u c t u r e o f the e m i s s i o n . An a n a l y s i s o f P a l o A l t o d a t a f o r 1963-4 produced 35 IPDP's, 10 o f which were too c o m p l i c a t e d t o y i e l d any mean-i n g f u l f r e q u e n c y measurements. R a l s t o n d a t a f o r 1967 produced 39 IPDP's, o f which 16 had a v e r y c o m p l i c a t e d form. r 27 -IV.2 C h a r a c t e r i s t i c s o f IPDP's The c h a r a c t e r i s t i c s o f IPDP's are b e s t o b s e r v e d i n the s p e c t r o g r a m r e p r e s e n t a t i o n . F i g . 8 and 9 are examples o f two q u i t e d i f f e r e n t IPDP's shown i n b o t h shaded and c o n t o u r e d sonagrams. One can e a s i l y see the f r e q u e n c y i n c r e a s e o f the broad-band n o i s e i n t h i s r e p r e s e n t a t i o n . S t r u c t u r a l elements superimposed on t h i s n o i s e band v a r y i n number and form as shown by F i g . 8 and 9. U n l i k e hydromagnetic e m i s s i o n s , a l s o known as hydromagnetic w h i s t l e r s , or m i c r o p u l s a t i o n w h i s t l e r s , the s t r u c t u r a l elements do not have a s i m p l e r e p e t i t i v e p e r i o d . The d u r a t i o n o f an IPDP i s t y p i c a l l y 20 t o 30 minutes but some have been found t o l a s t o n l y 10 m i n u t e s . Events l a s t -i n g l e s s than 10 minutes would not l i k e l y be c l a s s i f i e d as IPDP's because o f the l a c k o f an i d e n t i f i a b l e f r e q u e n c y i n c r e a s e ; but they may be r e l a t e d i n o r i g i n . When two r i s i n g f r e q u e n c y e v e n t s were observed i n one c o n t i n u o u s m i c r o p u l s a t i o n e m i s s i o n , they were c l a s s i f i e d as s e p a r a t e IPDP's. T h e i r s t a r t i n g times were s e l e c t e d , as i n the case o f a l l IPDP's, a t the b e g i n n i n g o f the r i s i n g f r e q u e n c y segments. F i g . 8 and 9 a l s o i l l u s t r a t e the v a r i a b i l i t y o f the minimum, maximum, and m i d f r e q u e n c y o f IPDP n o i s e band. For R a l s t o n IPDP's, the minimum f r e q u e n c y v a r i e d from a low v a l u e t o 0.3 h e r t z . The maximum f r e q u e n c y v a r i e d from about 0.6 h e r t z t o above 1.0 h e r t z . O f t e n t h e r e i s no sharp c u t - o f f i n e i t h e r - 28 RALSTON 21 JAN. 67 F i g . 8. IPDP w i t h d i s t i n c t s t r u c t u r a l elements F i g . 9. IPDP w i t h l a r g e n o i s e band c h a r a c t e r i s t i c * 30 -the minimum or maximum frequencies observed so the above estimates are only approximate. Palo Alto IPDP's had approxi-mately the same l i m i t s except for a few cases having a larger maximum frequency 2.0 hertz). This suggests some geomagnetic control of IPDP frequency and confirms the observation of Knaflich and Kenney (1967) that IPDP's at Seattle (53.6°geo-magnetic latitude) extend to higher frequencies than the same IPDP at College (64.6° geomagnetic l a t i t u d e ) . Care must be taken in any comparison though, as d i f f e r e n t recording equip-ment has been used at a l l four stations. The rate of increase of IPDP midfrequency varies from a very small value to about 5 hertz/hour, 0.3 hertz/hour being a t y p i c a l value. The rate of increase i s generally large for IPDP's near l o c a l midnight but large rates of increase also occur at other times. No relationship has been found between rate of frequency increase and l o c a l time, Kp index, or amplitude of event. IV. 3 Occurrence of IPDP's The occurrence of IPDP's depends strongly on the l o c a l time of the observing s t a t i o n . Fig. 10 and 11 show the number of IPDP's observed i n any one hour i n t e r v a l versus the l o c a l time. Most IPDP's occur in the 16 to 22 hour l o c a l time i n t e r v a l which is the dusk to midnight quadrant in the magnetosphere. This - 31 -R A L S T O N 1967 - I — ' ' 1 1 1 1 — 1 1 4 8 12 16 20 24 LOCAL TIME F i g . 10. Occurrence of IPDP's at R a l s t o n versus l o c a l time 32 -UJ O z U J or or 3 O a o 8 1 P A L O A L T O 1 9 6 3 - 4 6n" lx. O or LU co z> z 8 " T -12 16 i— 20 24 L O C A L TIME F i g . 1 1 . Occurrence of IPDP's at Palo Alto versus l o c a l time - 33 -s t r o n g maximum a l s o means t h a t any one IPDP i s v i s i b l e o n l y over a r e s t r i c t e d l o n g i t u d i n a l range. T h i s range may be as l a r g e as 30° though, s i n c e the same IPDP has been obse r v e d at C o l l e g e and S e a t t l e ( K n a f l i c h and Kenney 1967). An e a s t -west l i n e o f m i c r o p u l s a t i o n s t a t i o n s would be n e c e s s a r y t o d e f i n e the e x a c t l o n g i t u d i n a l e x t e n t o f IPDP's. R a l s t o n and P a l o A l t o o c c u r r e n c e f r e q u e n c i e s are v e r y s i m i l a r but P a l o A l t o IPDP's o c c u r d u r i n g more m a g n e t i c a l l y d i s t u r b e d c o n d i t i o n s as F i g . 12 shows. The s o l i d l i n e s show the number o f IPDP o c c u r r e n c e s v e r s u s Kp i n d e x (a measure o f p l a n e t a r y magnetic a c t i v i t y ) , whereas the dashed l i n e s are the number o f o c c u r r e n c e s n o r m a l i z e d t o the number o f 3 hour Kp i n d i c e s o b s e r v e d between 1800-2400 L.T. f o r the y e a r ( s ) i n q u e s t i o n . The s c a l e f o r the n o r m a l i z e d o c c u r r e n c e r a t e s i s g i v e n on the r i g h t hand s i d e o f the f i g u r e . Upon e x a m i n a t i o n , F i g . 12 shows t h a t the average Kp i n d e x f o r IPDP events at P a l o A l t o ( 5 e ) i s l a r g e r t h a n f o r e v e n ts a t R a l s t o n ( 4 - ) . At b oth s t a t i o n s , however, the nor-m a l i z e d o c c u r r e n c e o f IPDP's i n c r e a s e s f o r i n c r e a s i n g Kp i n d e x . A l s o , the t o t a l number o f IPDP's obse r v e d i s l a r g e r a t R a l s t o n and s t i l l l a r g e r at C o l l e g e (Heacock 1967a). Thus, IPDP's must be a r e l a t i v e l y h i g h l a t i t u d e phenomena or o c c u r on h i g h l a t i t u d e f i e l d l i n e s . They are c o r r e l a t e d t o magnetic a c t i v i t y as measured by the Kp i n d e x , and d u r i n g times o f l a r g e magnetic d i s t u r b a n c e s , the g e n e r a t i o n r e g i o n l i k e l y - 34 -15-RALSTON 1967 co UJ o z Ul cr. 3 O o o I I ! - 4 0 — r -3 4 ~T~ 6 20 y z UJ cr _ 3 O o o 3 Hr. Kp Index tr tu m 3 Z 15-PALO A L T O 1963-4 o LU NJ -J < cr • 4 0 o z IO' i " 2 0 —r-2 — r — 3 3 Hr. Kp Index F i g . 12. Occurrence of IPDP's at R a l s t o n and Palo A l t o versus 3 hour Kp index - 35 -moves towards the equator (inward i n the magnetosphere). Low latitude stations would observe IPDP's due to t h e i r propagation through the ionospheric duct (Tepley and Landshoff 1966, Manchester 1966, Greifinger and Greifinger 1968). No corre-l a t i o n has been found between magnitude of the IPDP and Kp index. By incorporating the results of Section IV.5 in which IPDP's are found to be d i r e c t l y correlated with the occurrence of magnetospheric substorms, one can e a s i l y understand the,increase in normalized occurrence rate versus Kp index. The Kp index i s determined by averaging the K index (magnetic disturbance a f t e r various corrections) for 12 observatories which are located bet-ween 47.7 and 62.5 degrees geomagnetic l a t i t u d e . By far the most important disturbance i n this latitude range i s magnetic bay a c t i v i t y which i s a manifestation of the magnetospheric substorm process. Magnetospheric substorms thus govern both the Kp index and the generation of IPDP's. IV.4 Occurrence with Hm Emissions Occasionally IPDP's are observed with an hm emission following the increasing frequency noise band. Gendrin et a l , (1967) mention this occurrence but do not give any quanti-tative figures. S. Lacourly (personal communication) reports that eleven, or 20% of the IPDP's observed at Kerguelen in 1965, were followed by an hm emission. However, for six months - 36 -of available data i n 1967, only 1 of 15 events ended i n an hm emission. No such cases were found in the 1967 Ralston data, but one case was found i n the Palo Alto data. Knaflich and Kenney (1967) also have reported a couple of examples of this occurrence. Thus i t has been firmly established that occasionally an hm emission d i r e c t l y follows an IPDP. Fig. 13 shows the Palo Alto example indicating that the two types of pulsations are continuous i n time. The IPDP starts at 07:40 U.T. and the hm emission starts at about 08:00 U.T., and i s c l e a r l y v i s i b l e at the end of the event. The gap preceding the frequency-time mark at 08:00 U.T. i s not of natural o r i g i n . Hydromagnetic emissions have been extensively studied, and are generally believed to originate from, or be amplified by, a cyclotron i n s t a b i l i t y process between energetic protons and ion cyclotron waves (left-hand polarization) which are bouncing between a p a i r of magnetically conjugate areas under the guidance of the magnetic l i n e of force connecting those areas (Jacobs and Watanabe 1964a, Obayashi 1965, Jacobs and Watanabe 1966). The continuity of the two events in Fig. 13 makes i t l i k e l y that energetic protons are involved in the generation process of IPDP's, perhaps also v i a a cyclotron i n s t a b i l i t y process. - 37 -F i g . 13. An example o f an IPDP which changes i n t o an hm e m i s s i o n - 38 -Hydromagnetic emissions of the dispersive type, or hydromagnetic whistlers (Jacobs and Watanabe 1966) , have been used to determine the equatorial radius to the guiding geo-magnetic f i e l d l i n e as well as the electron density at that point (Watanabe 1965, Dowden and Emery 1965). The December 3, 1963, example yielded a r a d i a l distance of 6.5 earth r a d i i (Re) using Watanabe's (1965) method. Because of the short duration of the hm emission and the small amount of dispersion measured, the possible error w i l l be quite large, say ±1 Re or more. This estimate of generation region for IPDP's agrees closely with that of previous researchers. Gendrin et a l . (1967) made an estimate of 3 to 6 Re by studying the occurrence of an IPDP at stations of varying l a t i t u d e . They mention, how-ever, ,that t h e i r estimate could be low due to the p o s s i b i l i t y ; of signal propagation i n the ionospheric waveguide. Knaflich and Kenney (1967) studied the s t r u c t u r a l elements of IPDP's and arrived at an estimate of 6 to 13 Re to the generation region. They had to assume that IPDP st r u c t u r a l elements are half-hop micropulsation whistlers generated by a broad band impulse at the equatorial plane. Also, the plasma density d i s t r i b u t i o n and magnetic f i e l d configuration was assumed to be undisturbed by the occurrence of a magnetospheric substorm. Both assumptions may not be v a l i d . In order to obtain an accurate estimate of distance to generation region, more examples of IPDP's followed by hm - 39 -emissions are needed. But, by using the r a d i a l estimate made here and the occurrence of IPDP's versus l o c a l time, one can deduce the generation region of IPDP's. This region i s i l l u s t r a t e d i n Fi g . 14 which i s an equatorial plane view of the magnetosphere. IV.5 Relationship to Magnetospheric Substorms Troitskaya (1961), Heacock (1966), Gendrin et a l . (1967) and others have noted that IPDP's generally occur during times of magnetospheric a c t i v i t y . Since a great many phenomena are observed during the li f e t i m e of a substorm, a more exact corr e l a t i o n must be looked for between some substorm process and the occurrence of IPDP's. The analysis of magnetograms from auroral zone observatories i s one of the most common ways of observing and studying magnetospheric substorms. Chapter III showed that mag-netograms from a world-wide network of observatories can be used to i d e n t i f y the various phases of substorms. In this section i t w i l l be shown how the expansive phase has been picked for both simple and complex substorms and how the occurrence of IPDP's is related to this phase. Magnetograms from a l l the observatories l i s t e d in Table II.2 were used to i d e n t i f y the expansion phases of substorms studied. For ease of i l l u s t r a t i o n only a few magnetograms are shown for each example. F i g . 14. IPDP g e n e r a t i o n r e g i o n s k e t c h e d i n an e q u a t o r i a l p l a n e view o f magnetosphere - 41 -Fig. 15 i s a set of magnetograms for January 21, 1967 with the corresponding IPDP shown i n F i g . 8. Although this substorm produced a r e l a t i v e l y simple magnetic bay i n the dusk region, the two stations nearest midnight, Churchill (not shown) and Great Whale, do not show any clear evidence of the substorm. However, a sharp change in several magnetograms i s seen at 05:25 U.T., thus indicating the s t a r t of the expansive phase at that time. The slow increase i n College horizontal f i e l d from 05:00 to time of expansion i s l i k e l y associated with the quiet or build-up phase of the polar magnetic substorm. This is an example of a r e l a t i v e l y simple substorm but the absence of a magnetic disturbance at Chu r c h i l l and Great Whale might mean that the equivalent current system, and thus the real current system, i s unusual. o Fig. 15 also shows the H component of magnetic f i e l d at ATS-1. Note that the f i e l d recovery at ATS-1 started at 05:25 which i s pr e c i s e l y the s t a r t i n g time of the Ralston IPDP and the expansive phase as defined by ground magnetograms. The magnetograms of F i g . 16 i l l u s t r a t e a more compli-cated substorm period occurring on March 18, 1967. The substorm s t a r t i n g at 03:25 U.T. is evident at a l l stations shown as well as at Boulder, Fredericsburg, and Baker Lake and thus conforms to the idea of a large equivalent current system. At 04:20 U.T. another substorm i s v i s i b l e at Great Whale, C h u r c h i l l , Boulder and Baker Lake but not at other stations. However, Fredericsburg, - 42 -21 JAN. 1967 F i g . 15. Example o f IPDP o c c u r r e n c e d u r i n g a p o l a r magnetic substorm - 43 -18 MARCH 1967 RALSTON - j \Wm | , , IPDP 0 3 06 U.T. F i g . 16. Example o f IPDP o c c u r r e n c e d u r i n g a c o m p l i c a t e d substorm p e r i o d - 44 -V i c t o r i a and s e v e r a l o t h e r o b s e r v a t o r i e s show a P i 2 event s t a r t i n g a t 04:15 w h i c h , a c c o r d i n g t o A n g e n h e i s t e r ( 1 9 1 2 ) , Terada (1917) and R o s t o k e r (1966) , i s g e n e r a t e d at the s t a r t o f a substorm. The C h u r c h i l l magnetogram has a n o t h e r major e x c u r s i o n a t 05:25 U.T. b u t no o t h e r s t a t i o n r e c o r d s a s i g -n i f i c a n t magnetic f i e l d change a t t h a t t i m e . However, a p o s s i b l e P i 2 event i s o b s e r v e d a t about 05:30 U.T. on the R a l s t o n m i c r o p u l s a t i o n c h a r t r e c o r d i n g . The l a r g e d i f f e r e n c e between Great Whale and C h u r c h i l l magnetograms and the l a c k o f a d i s -t u r b a n c e a t o t h e r o b s e r v a t o r i e s i n d i c a t e s the u n u s u a l c h a r a c t e r o f the 05:25 substorm. For March 18, e x p a n s i v e phases would be at 03:25, 04:20 and 05:25 U.T. even though the l a t t e r two cases are anomalous. The ATS-1 magnetogram f o r March 18 a l s o does not f o l l o w the g e n e r a l p i c t u r e g i v e n i n Chapter I I I . The f i r s t two substorms are combined i n t o one a t ATS-1. No l a r g e change i s o b s e r v e d u n t i l 03:50 at which time the f i e l d s t a r t s d e p r e s s i n g . The r e c o v e r y s t a r t s a t 04:00 and l a s t s u n t i l 04:30 or l a t e r . T h i s d e p r e s s i o n and r e c o v e r y i s l i k e l y due t o the 03:25 substorm, the r e c o v e r y a t ATS-1 b e i n g d e l a y e d 35 minutes from the s t a r t o f the substorm e x p a n s i v e phase. The second substorm a t ATS-1 has i t s r e c o v e r y phase at 05:30 and thus c o r r e s p o n d s t o the sub-storm o b s e r v e d o n l y a t C h u r c h i l l . W h i l e the ground magnetic changes were obse r v e d o n l y a t C h u r c h i l l (23 L . T . ) , the asymmetric r i n g c u r r e n t was o b s e r v e d i n the dusk r e g i o n (18 L.T. a t ATS-1). What i s most i m p o r t a n t t o observe f o r t h i s complex case i s t h a t IPDP's o c c u r r e d s i m u l t a n e o u s l y w i t h the f i e l d r e c o v e r y a t ATS-1. - 45 -F i g . 17 i s a s e t o f magnetograms f o r A p r i l 17, 1967. The Great Whale magnetogram shows two substorms s t a r t i n g a t 02:45 U.T. and 03:10 U.T., w h i l e the C h u r c h i l l magnetogram i n d i c a t e s o n l y one substorm at 03:05 U.T. The R a l s t o n slow speed m i c r o p u l s a t i o n r e c o r d i n g r e v e a l s t h a t P i 2 p u l s a t i o n s o c c u r r e d a t 02:48 and 03:09 U.T., i n d i c a t i n g two c l o s e l y spaced substorms. The p o s i t i v e D bay a t B o u l d e r c o i n c i d e s w i t h the f i r s t substorm. An IPDP was o b s e r v e d a t R a l s t o n p r e c i s e l y d u r i n g the time o f m i d - l a t i t u d e D bay and t h i s c o r r e l a t i o n has been n o t e d f o r the m a j o r i t y o f IPDP's. The d i f f e r e n c e between the magnetic e f f e c t s o f the two substorms at B o u l d e r , which i s w e l l s o u t h o f the a u r o r a l zone, means t h a t the c u r r e n t systems o f the substorms were a l s o q u i t e d i f f e r e n t . A g a i n the R a l s t o n IPDP o c c u r r e d d u r i n g the time o f f i e l d r e c o v e r y a t ATS-1. However, an IPDP was not o b s e r v e d d u r i n g the second f i e l d r e c o v e r y . The s i g n i f i c a n c e o f t h i s o b s e r v a t i o n w i l l be d i s c u s s e d i n S e c t i o n V . l . The sonagrams f o r the IPDP's d i s c u s s e d i n the p r e v i o u s two examples are shown i n F i g . 18 and 19. The p r e c e d i n g examples i n d i c a t e a c orrespondence between IPDP o c c u r r e n c e and the e x p a n s i v e phase o f a substorm. F i g . 20 p l o t s the s t a r t i n g time o f a l l R a l s t o n IPDP's r e l a t i v e t o the time o f substorm e x p a n s i o n . I t c l e a r l y shows t h a t IPDP's s t a r t at the time o f substorm e x p a n s i o n o r s h o r t l y t h e r e a f t e r . The ATS-1 f i e l d r e c o v e r y i s a s s o c i a t e d w i t h the substorm expan-s i o n (Cummings e t a l . 1968), so F i g . 20 a l s o i m p l i e s t h a t IPDP's - 4 6 -F i g . 17. IPDP o c c u r r e n c e d u r i n g two c l o s e l y spaced p o l a r magnetic substorms - 47 -RALSTON 18 MARCH 67 TYPE B/63 SONAGRAM 0 KAY ELECTRIC CO. PINE BROOK. N. J. F i g . 18. IPDP event o c c u r r i n g d u r i n g substorm shown i n F i g . 16 48 RALSTON 17 APRIL 67 TYPE B/63 SONAGRAMS KAY ELECTRIC CO. PINE BROOK. N. J. F Hz 2.0-U.T. 02 03 I i I i i i L_ L.T. 19 20 F i g . 19. IPDP event o c c u r r i n g d u r i n g substorm shown i n F i g . 17 - 49 -12 10 8 to UJ o z LU CC CC _> o u o u. o CQ 2 _> z - 60 START OF EXPANSION + 60 MINUTES Fig. 20. Occurrence of Ralston IPDP's r e l a t i v e to time of substorm expansion - 50 -occur during the time of magnetic f i e l d increase in the dusk-midnight quadrant. Many other phenomena also occur during the substorm expansive phase but i t w i l l be shown in Section IV.6 that the magnetic f i e l d increase as observed by ATS-1 produces the frequency increase of IPDP's. IV.6 Magnetic F i e l d Control of Frequency Change Section IV.4 pointed out that IPDP's are l i k e l y asso-ciated with a cyclotron i n s t a b i l i t y between an ion cyclotron wave and energetic protons. Section IV.5 noted a correspondence between IPDP's and an increasing magnetic f i e l d at ATS-1. It is now proposed that the noise band of IPDP's is produced by a cyclotron i n s t a b i l i t y process between energetic protons and an ion cyclotron left-handed wave. The increase in noise band midfrequency results from an increase i n the background mag-netic f i e l d in the IPDP generation region. In order to test this proposal the cyclotron i n s t a b i l i t y process must be examined. The dispersion equation for a left-handed ion cyclotron wave propagating p a r a l l e l to the background mag-netic f i e l d i s : (Astrom 1950) a)2 - C 2 k 2 - I P n = 0 (1) comp - 51 -where fi2 = i--± p m 0 - ^ mc and N , m , q are the number d e n s i t y , mass, and charge ( w i t h s i g n ) o f the plasma components, and B q i s the background magnetic f i e l d . The summation i s o v e r the components o f the plasma wh i c h i n the IPDP g e n e r a t i o n r e g i o n can be c o n s i d e r e d t o be e l e c t r o n s and p r o t o n s . The u s u a l assumption o f a n e u t r a l plasma i s a l s o made, i . e . , N = N. . e 1 A resonance can t a k e p l a c e between an i o n c y c l o t r o n L.H. wave and b o t h p r o t o n s and e l e c t r o n s . However, e n e r g e t i c p r o t o n s are chosen as they have been proven t o be the i n t e r -a c t i n g p a r t i c l e i n the case o f hm e m i s s i o n s ( C o r n w a l l 1965, G e n d r i n 1965, Jacobs and Watanabe 1965, 1966). P r o t o n s w i l l r e s o n a t e w i t h the hydromagnetic wave when t h e i r r o t a t i o n about the f i e l d l i n e s i s a t the same f r e q u e n c y as the wave f r e q u e n c y d o p p l e r s h i f t e d t o the v e l o c i t y o f the p r o t o n s p a r a l l e l t o the magnetic f i e l d l i n e s . T h i s i s e x p r e s s e d m a t h e m a t i c a l l y as ku - ai (2) where u i s the p r o t o n s ' p a r a l l e l v e l o c i t y and i s the i o n c y c l o t r o n f r e q u e n c y . - 52 -U s i n g the resonance c o n d i t i o n (2) and the d i s p e r s i o n e q u a t i o n ( 1 ) , a r e l a t i o n s h i p between the background plasma den-s i t y N i , magnetic f i e l d B Q , the wave f r e q u e n c y w , and the p a r a l l e l energy o f e n e r g e t i c p r o t o n s can e a s i l y be d e r i v e d (Appendix I I ) 3 N W„ = —±1 ( l - SL_) _ ° - ( 3 ) 1 8ir m, 2 c 2 V n . / a 2 I E q u a t i o n (3) can be used t o f i n d the i n s t a b i l i t y f r e -quency i f a l l the o t h e r parameters are known. A much more complex a n a l y s i s must be performed t o determine the c o n d i t i o n s f o r wave growth. T h i s a n a l y s i s has been performed by many au t h o r s ( C o r n w a l l 1965, Liemohn 1967, J a c k s 1966) and i s not n e c e s s a r y f o r t h i s s t u d y . The v a r i a t i o n o f the i n s t a b i l i t y f r e q u e n c y u> can be seen more e a s i l y i f we assume t h a t u << fi^ . Then: B 2 w •« ° — (4) The i n s t a b i l i t y f r e q u e n c y w i l l i n c r e a s e i f B q i n c r e a s e s o r i f o r W„ d e c r e a s e s . E q u a t i o n (3) can how be used t o t e s t the h y p o t h e s i s t h a t an i n c r e a s e i n B Q produces the f r e q u e n c y i n c r e a s e o f an IPDP. M a g n e t i c f i e l d d a t a were a v a i l a b l e from the ATS-1 s a t e l -l i t e f o r n i n e IPDP's (Table IV.1) o b s e r v e d a t R a l s t o n . For each - 53 -Table IV.1 IPDP's Used for Frequency Versus Magnetic F i e l d Study Date Jan. 21 March 18 March 27 A p r i l 17 May 7 May 16 May 17 Aug. 14 Sept. 13 Start Time L.T. 22:25 22 :30 21:15 19:55 21:15 22 :20 21:55 19:50 21:35 Af hertz .22 .06 .13 .28 .24 .11 .18 .12 .03 AB Y 38 10 13 15 6 7 8 3 7 AT Min. 15 10 20 15 15 5 20 10 - 54 -event the midfrequency was measured from the contoured sona-grams at intervals of five minutes. The frequency thus deter-mined was plotted against the observed t o t a l magnetic f i e l d at ATS-1 with time as the parameter (Fig. 21). (See Appendix III.) The s o l i d curves i n Fig . 21 represent lines of constant N^W„ . The plasma density i n the IPDP generation region i s of the order of 1 particle/cm 3 (Carpenter 1966) so the curves represent approximately p a r a l l e l energy (kev) of resonating protons. If the IPDP's observed at Ralston were generated i n the v i c i n i t y of the ATS-1 s a t e l l i t e and i f a l l the frequency change observed was due to an increase in the background mag-netic f i e l d , the ind i v i d u a l events should follow the curves of constant NW„ . Many of the events do approximately follow the theore t i c a l curves. For these events, a l l the observed frequency increase i s explained by the magnetic f i e l d increase as observed by ATS-1. For some IPDP's the magnetic f i e l d seen by the reso-nating protons may not be the f i e l d measured by ATS-1. A cor-rection must be made for the s a t e l l i t e ' s motion, and thus DB* -*• measurement of ^ due to (f'V)B . Also, i f the IPDP is not generated near the s a t e l l i t e a p o s i t i o n a l correction w i l l be needed. Only the f i r s t correction can be made on a quantitative basis. - 55 r-F i g . 21. R a l s t o n IPDP f r e q u e n c y i n c r e a s e r e l a t i v e t o ATS-1 magnetic f i e l d change w i t h time as the parameter - 56 -The magnetic f i e l d measured by ATS-1 exhibits a diurnal v a r i a t i o n just as a ground magnetic observatory does. However, the v a r i a t i o n i s not constant but depends on the parameters of the magnetosphere such as subsolar distance to magnetopause, distance to t a i l current sheet, and t a i l magnetic f i e l d strength. The diurnal v a r i a t i o n for March 18, 1967 i s i l l u s t r a t e d i n Fig. 22. The H component at ATS-1 decreases from a maximum of 155 y at noon to a minimum of less than 50 y at midnight. The dashed l i n e i s a Mead's model (Mead 1964, Williams and Mead 1965) approximation of the diurnal v a r i a t i o n . The parameters used are subsolar distance to magnetopause 8.0 Re, distance to t a i l current sheet 9.6 Re, termination of current sheet 117 Re, and t a i l f i e l d 60 y. The diurnal v a r i a t i o n on a magnetic quiet day (March 11) i s also shown in Fig. 22. Two important facts are evident. The large decrease i n the dusk region i s due to the s a t e l l i t e ' s motion into regions of lower magnetic f i e l d . This decrease must be taken into consideration when the f i e l d change at one p o s i t i o n i s desired. Secondly, the amount of correction necessary varies extremely as evidenced by March 11 and 18. The correction for March 18 at 04:00 U.T. i s +14 y/hour which is the negative slope of the tangent to Mead's model curve at that time, while the correc-tion for March 11 is only +1.5 y/hour. Unfortunately not a l l days exhibit steady magneto-spheric conditions as does March 18. Often a major change such - 57 -4 8 12 16 20 U.T. (HOURS) F i g . 22. D i u r n a l v a r i a t i o n o f H component o f magnetic f i e l d a t ATS-1 f o r a q u i e t and a d i s t u r b e d day - 58 + as the magnetic storm on May 7, 1967, makes i t impossible to determine a diurnal correctipn. However, May 7 was the only example of the events used in Fig. 21 for which a correction could not be determined. The correction for r e l a t i v e p o s i t i o n of s a t e l l i t e and IPDP generation region i s d i f f i c u l t because the s p a t i a l v a r i a t i o n of magnetic f i e l d changes during a magnetospheric sub-storm i s unknown. But the three hour L.T. difference between Ralston and ATS-1 could be important since there i s sometimes a delay i n f i e l d recovery at ATS-1 from the time of substorm expansion. When the s a t e l l i t e i s at midnight the f i e l d recovery starts simultaneously with the substorm expansive phase (Cummings et a l . 1968). Thus i f an IPDP i s generated in a longitudinal zone subs t a n t i a l l y closer to midnight than the position of ATS-1, a time delay might also be seen between the s t a r t of IPDP at Ralston and f i e l d recovery at ATS-1. The May 17 example of Fig. 21 may be such a case since the f i e l d recovery at ATS-1 occurs 25 minutes aft e r s t a r t of substorm expansion and 15 minutes after s t a r t of Ralston IPDP. A cor-rection of this type must be considered speculative at this time. Fig. 23 is a repeat of Fig. 21 with corrections made for movement of s a t e l l i t e assuming IPDP's are generated at a fixed point i n the magnetosphere. Also shown i s the possible change in the May 17 example with a 15 minute time s h i f t . The correspondence between the theoreti c a l curves and experimental - 59 -F i g . 23. IPDP f r e q u e n c y i n c r e a s e r e l a t i v e t o ATS-1 magnetic f i e l d change w i t h a c o r r e c t i o n f o r s a t e l l i t e ' s motion - 60 -data i s greatly improved. The May 7 example has been omitted since no correc-tion was possible. During that time magnetospheric conditions were very disturbed as evidenced by the low magnetic f i e l d at ATS-1 (30 y at 18:00 L.T.) and the s a t e l l i t e was l i k e l y not in IPDP generation region. It can now be stated that the p r i n c i p a l cause for the frequency r i s e observed i n IPDP's i s an increase in the background magnetic f i e l d thus changing the conditions for the cyclotron i n s t a b i l i t y process. Other conditions influencing the production of an IPDP w i l l be considered i n the following chapter. 61 -CHAPTER V D i s c u s s i o n o f IPDP T h e o r i e s V. 1 I n c r e a s i n g M a g n e t i c F i e l d Theory Chapter IV showed t h a t the g e n e r a t i o n o f IPDP's c o u l d be e x p l a i n e d by a c y c l o t r o n i n s t a b i l i t y between p r o t o n s and i o n c y c l o t r o n l e f t - h a n d p o l a r i z e d waves under the c o n t r o l o f an i n c r e a s i n g magnetic f i e l d . C o n d i t i o n s on the r e s o n a t i n g p a r t i c l e s , the magnetic f i e l d , and o t h e r magnetospheric p r o p e r t i e s n e c e s s a r y f o r the i n i t i a t i o n o f an IPDP w i l l be d i s c u s s e d i n t h i s s e c t i o n . The r e l a t i o n s h i p between IPDP's and o t h e r m i c r o p u l s a t i o n s thought to be g e n e r a t e d or a m p l i f i e d by a c y c l o t r o n i n s t a b i l i t y p r o c e s s w i l l then be d i s c u s s e d . The magnetic f i e l d i n c r e a s e i n the g e n e r a t i o n r e g i o n o f IPDP's produces t h e i r major d i s t i n g u i s h i n g f e a t u r e , i . e . the r i s e i n average f r e q u e n c y o f n o i s e band. The g e n e r a l f e a t u r e s o f substorm a s s o c i a t e d , magnetic f i e l d changes, as measured by ATS-1, w i l l be summarized here f o r a comparison w i t h IPDP d a t a . Major magnetic f i e l d changes a s s o c i a t e d w i t h substorms are seen o n l y i n the dusk-midnight quadrant o f the magnetosphere. The f i e l d s l o w l y becomes depr e s s e d some time b e f o r e a substorm e x p a n s i o n o c c u r s and a t the time o f e x p a n s i o n the f i e l d r a p i d l y r e c o v e r s . The r e c o v e r y i s g r a d u a l i n the dusk r e g i o n , q u i c k e s t j u s t b e f o r e m i d n i g h t , but c o m p l e t e l y absent a f t e r m i d n i g h t l o c a l time (Cummings and Coleman 1968). - 62 -Cummings e t a l (1968) propose a p a r t i a l r i n g c u r r e n t i n the d u s k - m i d n i g h t quadrant as s k e t c h e d i n F i g . 24 t o e x p l a i n t h e s e e f f e c t s . The m a g n e t o s p h e r i c c u r r e n t i s composed o f e n e r g e t i c p r o t o n s d r i f t i n g westward due t o the g r a d i e n t and c u r v a -t u r e o f the magnetic f i e l d . I t i s assumed t h a t the e l e c t r o n s are e i t h e r p r e c i p i t a t e d more q u i c k l y than the p r o t o n s o r t h a t t hey are c o n s i d e r a b l y l e s s e n e r g e t i c . The c u r r e n t i s c a r r i e d t o the i o n o s p h e r e , and from the i o n o s p h e r e a l o n g the e a r t h ' s f i e l d l i n e s . T h i s p a r t i a l r i n g c u r r e n t would e x i s t m a i n l y out-s i d e the o r b i t o f ATS-1 and as i t i n c r e a s e s i n magnitude, the magnetic f i e l d would become d e p r e s s e d at ATS-1. A t the time o f the substorm e x p a n s i v e phase a major p o r t i o n o f the r i n g c u r r e n t near m i d n i g h t would be s u d d e n l y removed. The r i n g c u r r e n t a t dusk would then d e c r e a s e s l o w l y due t o the absence o f a s o u r c e o f p r o t o n s . Note t h a t t h e s e magnetic e f f e c t s are c o n f i n e d t o the IPDP g e n e r a t i o n r e g i o n as d e f i n e d i n S e c t i o n IV.4. A l s o n o t e the sharp c u t - o f f n e a r m i d n i g h t o f the o c c u r r e n c e o f IPDP's at b o th R a l s t o n and P a l o A l t o ( F i g . 10 and 11) c o r r e s p o n d i n g t o the c u t - o f f o f magnetic f i e l d e f f e c t s as o b s e r v e d a t ATS-1. E n e r g e t i c p r o t o n s are a l s o n e c e s s a r y f o r the genera^-t i o n o f an IPDP as they s u p p l y the energy f o r growth o f the i o n c y c l o t r o n waves. An e x a m i n a t i o n o f F i g . 23 r e v e a l s t h a t 10 to 1000 kev p r o t o n s are most l i k e l y r e s p o n s i b l e f o r IPDP genera-t i o n ( s i n c e the background plasma d e n s i t y , N ^ 1/cm3 i n IPDP genera-t i o n r e g i o n ) . S t u d i e s o f c y c l o t r o n - i n s t a b i l i t y a m p l i f i c a t i o n - 63 -N Fig. 24. P a r t i a l ring current existing during polar magnetic substorms as viewed from the dusk-midnight quadrant (after Cummings et a l . 1968) - 64 -of hm emissions (Cornwall 1965, Liemohn 1967, Jacks 1966) reveal that 200 to 500 kev protons at L=4, or lower energy protons at larger L values, provide an e f f i c i e n t amplification of ion cyclotron waves. An anisotropic proton v e l o c i t y d i s t r i b u t i o n i s needed for wave amplification but the existence of hm emis-sions of long duration i s evidence for the existence of suitable protons i n the magnetosphere. Since hm emission occurrence i s enhanced after a magnetic storm (Tepley 1966) , the protons may have been injected during times of strong substorm a c t i v i t y . Substorm associated anisotropic proton v e l o c i t y dis-tributions have been observed by Konradi (1967, 1968) and Brown et a l (1968). Measurements by Konradi (1967) indicate that the protons were injected into the night side of the magnetosphere from the t a i l region 15 to 20 minutes before the substorm expansive phase. These protons would d r i f t westward and would be in IPDP generation region at time of substorm expansion. It i s not known i f the proton events observed by Konradi are the main source of IPDP energy but there c e r t a i n l y i s no lack of protons with the proper energies at times of substorm a c t i v i t y . Generally disturbed magnetospheric conditions may also influence the generation of IPDP's. Hydromagnetic emissions, 4-sec. period micropulsations, and IPDP's are a l l believed to be generated or amplified by a cyclotron i n s t a b i l i t y process. Hydromagnetic emissions show a regular r e p e t i t i o n of r i s i n g elements whereas 4-sec. period micropulsations and IPDP's consist - 65 -of a n o i s e band w i t h i r r e g u l a r l y spaced s t r u c t u r e s . The r e l a -t i v e l y q u i e t c o n d i t i o n s e x i s t i n g d u r i n g an hm e m i s s i o n may a l l o w the a m p l i f i c a t i o n o f an i n i t i a l i o n c y c l o t r o n "seed" wave t o dominate the p r o d u c t i o n o f new waves. Under c o n d i t i o n s o f more magnetic n o i s e , background plasma p e r t u r b a t i o n s , and d i v e r s i t y o f e n e r g e t i c p a r t i c l e s , i o n c y c l o t r o n waves may be c o n t i n u o u s l y g e n e r a t e d r e s u l t i n g i n a n o i s e band. Only o c c a s i o n a l l y would a l a r g e s t r u c t u r a l element be g e n e r a t e d . The s i m u l t a n e o u s e x i s t e n c e o f r e s o n a t i n g p r o t o n s , i n c r e a s i n g magnetic f i e l d , and magnetic n o i s e or plasma t u r -b u l e n c e would r e s u l t i n an IPDP. D i f f e r e n t c o m b i n a t i o n s o f the t h r e e v a r i a b l e s would r e s u l t i n o t h e r types o f m i c r o p u l s a -t i o n s such as hm e m i s s i o n s or 4-sec. m i c r o p u l s a t i o n s . M a g n e t o s p h e r i c substorms produce a l l t h r e e c o n d i t i o n s i n the d u s k - m i d n i g h t quadrant and thus IPDP's would be g e n e r a t e d t h e r e . C o nstant f r e q u e n c y e m i s s i o n s o f t e n seen b e f o r e or a f t e r IPDP's would be produced by a c y c l o t r o n i n s t a b i l i t y p r o c e s s u s i n g the same p r o t o n s o u r c e but w i t h a s t a t i c magnetic f i e l d . A good example o f t h i s magnetic f i e l d c o n t r o l o f e m i s s i o n f r e -quency i s seen i n the March 18 event ( F i g . 16 and 1 8 ) . A c o n s t a n t f r e q u e n c y e m i s s i o n r e s e m b l i n g 4-sec. m i c r o p u l s a t i o n s s e p a r a t e s the IPDP's o c c u r r i n g at 21:00 and 22:30 L.T. The magnetic f i e l d at ATS-1 was a l s o a p p r o x i m a t e l y c o n s t a n t d u r i n g t h i s p e r i o d . - 66 -Heacock (1967a) has p u b l i s h e d some e x c e l l e n t examples of 4-sec. m i c r o p u l s a t i o n s t e r m i n a t i n g i n an IPDP. In those cases the r e s o n a t i n g p r o t o n s are i n t r o d u c e d s u b s t a n t i a l l y b e f o r e the substorm e x p a n s i v e phase. At the time o f e x p a n s i o n the 4-sec. m i c r o p u l s a t i o n changes i n t o an IPDP. Not a l l magnetic f i e l d i n c r e a s e s o b s e r v e d a t ATS-1 produced an IPDP at R a l s t o n . For example, o f the two f i e l d r e c o v e r i e s on A p r i l 17 ( F i g . 17) o n l y the f i r s t r e s u l t e d i n an IPDP. The l a c k o f any Pc 1 f r e q u e n c y m i c r o p u l s a t i o n s d u r i n g the second f i e l d i n c r e a s e would be due t o the absence o f s u i t -a b l e p r o t o n s f o r c y c l o t r o n i n s t a b i l i t y wave g e n e r a t i o n . A most i n t e r e s t i n g c o m b i n a t i o n o f v a r i a b l e s o c c u r s when hm e m i s s i o n s are o b s e r v e d d u r i n g a magnetic storm sudden commencement ( s s c ) . The q u i e t m a g n e t o s p h e r i c c o n d i t i o n s p r e -v a i l i n g are s u d d e n l y changed t o d i s t u r b e d c o n d i t i o n s by a sharp i n c r e a s e i n the magnetic f i e l d . Heacock and H e s s l e r (1965) show the sonagrams f o r hm e m i s s i o n s o c c u r r i n g d u r i n g t h i s p e r i o d ( F i g . 2 o f t h e i r p a p e r ) . The e m i s s i o n f r e q u e n c y t a k e s a sudden jump at the time o f s s c and then the s t r u c t u r a l elements d i s -appear l e a v i n g a n o i s e band. The jump i n f r e q u e n c y and l o s s of s t r u c t u r e o f the e m i s s i o n has been caused by the sharp i n -c r e a s e i n background magnetic f i e l d and r e s u l t i n g d i s t u r b a n c e of the plasma. - 67 -The s t r u c t u r a l elements obse r v e d i n IPDP's o f f e r s p e c i a l problems. They are u s u a l l y o b s e r v e d s i m u l t a n e o u s l y a t co n j u g a t e s t a t i o n s ( G e n d r i n e t a l 1967) but some elements o c c u r w i t h a s l i g h t time d i f f e r e n c e and o t h e r s appear o n l y a t one s t a t i o n . T h e r e f o r e , these elements cannot be g i v e n the same i n t e r p r e t a t i o n as those from hm e m i s s i o n s which appear a l t e r -n a t e l y at c o n j u g a t e s t a t i o n s . The d i s t u r b e d m agnetospheric c o n d i t i o n s e x i s t i n g i n IPDP g e n e r a t i o n r e g i o n can be used f o r a q u a l i t a t i v e e x p l a n a -t i o n o f IPDP s t r u c t u r e . The n o i s e g e n e r a t i o n p r o c e s s may be enhanced suddenly e i t h e r by an e x t e r n a l impulse o r by a change i n resonance c o n d i t i o n s at o r near the e q u a t o r i a l p l a n e . T h i s a m p l i t u d e enhancement o r s t r u c t u r a l element, would propagate i n b o th d i r e c t i o n s a l o n g the geomagnetic f i e l d l i n e . Due t o the d i s t o r t i o n o f f i e l d l i n e s and plasma d e n s i t i e s by the asym-m e t r i c r i n g c u r r e n t , the elements would a r r i v e s i m u l t a n e o u s l y or w i t h a s l i g h t d e l a y a t c o n j u g a t e s t a t i o n s . The energy r e -f l e c t e d by the i o n o s p h e r e i s p r o b a b l y i n s i g n i f i c a n t compared t o the wave energy c o n t i n u a l l y b e i n g g e n e r a t e d i n the e q u a t o r i a l r e g i o n . I f the wave ( s t r u c t u r a l element) was g e n e r a t e d s i g -n i f i c a n t l y o f f the e q u a t o r i a l p l a n e , the wave p r o p a g a t i n g back through the IPDP g e n e r a t i o n r e g i o n may be damped by d i f f e r e n t r e s o n a n t c o n d i t i o n s e x i s t i n g t h e r e and o n l y one hemisphere would see the element. - 68 -Certainly more experimental and t h e o r e t i c a l work needs to be done on IPDP structures but u n t i l the magnitude and extent of magnetospheric disturbances are established, no quantitative analysis can be performed. V.2 Other IPDP Theories Previous to this work, two major theories for IPDP generation had been proposed. Both are based on a cyclotron i n s t a b i l i t y between protons and ion cyclotron L mode waves, but d i f f e r e n t mechanisms are used to explain the noise band frequency increase. Heacock (1967a) and Gendrin et a l . (1967) explain the frequency r i s e by assuming that the resonating protons are d i f f u s i n g inward across the geomagnetic f i e l d l i n e s , thus moving into regions of larger magnetic f i e l d and background plasma density. The r e s u l t i n g change in IPDP frequency would be given by equation (4) of Chapter IV B 2 o to « In the magnetosphere under steady state conditions, « B Q , and i f one assumes that the p a r t i c l e s do not gain energy by the d i f f u s i o n process, the emission frequency w i l l be: u « B 3 / 2 (5) o v J - 69 -in which B is the earth's main f i e l d , o In both the inward d r i f t theory and increasing mag-netic f i e l d theory for IPDP, the change i,n emission frequency i s governed by the change in magnetic f i e l d . The connection between the two theories is shown by the t o t a l derivative DB 9B A * DY = + ( v . v ) B (6) DB A moving p a r t i c l e sees the f i e l d change ^ and i t is this quantity which determines the change in frequency. In the increasing magnetic f i e l d theory the p a r t i c l e s are assumed to remain at a fixed r a d i a l distance from the earth so (v»V)B = 0 DB 3 B Then ^ = -^j; which is measured by the s a t e l l i t e a f t e r correc-tions for i t s motion. The close correspondence of f versus B as measured by ATS-1, with time as the parameter and curves of constant NW„ (Fig. 23) means that 2 .^ i s determined by + UX. 3t i . e . ly^-l > | ( v A)B | for the resonating protons. -* •+ The term (v=vB) may be non-zero, however, due to the existence of the changing magnetic f i e l d . That i s , the magneto-hydrodynamic (MHD) equation o » |f = V x v x B (7) says that a changing magnetic f i e l d w i l l produce internal plasma -t-motions. To find the exact form of v , the whole set of MHD - 70 -e q u a t i o n s would have t o be s o l v e d t h r o u g h o u t the r e g i o n where * o at u * I t i s p o s s i b l e t o make a rough magnitude c a l c u l a t i o n f o r ( v»V)B i f an i d e a l i z e d model i s used. For t h i s c a l c u l a -t i o n i t i s assumed: ->• 9 B 1) t h a t i s c o n s t a n t i n the ma g n e t o s p h e r i c s e c t o r bounded by an angle <j>o and r a d i a l d i s t a n c e R (see F i g . 2 5 ) , 2) t h a t E ( e l e c t r i c f i e l d ) i s not a f u n c t i o n o f <|> Assumption (1) i s r e a s o n a b l e s i n c e i n the d u s k - m i d n i g h t s e c t o r •+ 3 R almost the same ^ i s r e c o r d e d at ATS-1 s a t e l l i t e and d i r e c t l y below i t a t H o n o l u l u (Cummings e t a l , 1968), Assumption (2) i s not c o m p l e t e l y v a l i d s i n c e i t means t h a t the e l e c t r i c f i e l d i s -V c i r c u l a r l y symmetric w h i l e the change which produces the -r E f i e l d i s c o n f i n e d t o the dus k - m i d n i g h t s e c t o r . T h i s model -> -> t h e r e f o r e w i l l produce o n l y an upper l i m i t f o r (v«V)B The e l e c t r i c f i e l d can be e v a l u a t e d from the Maxwell e q u a t i o n i n i n t e g r a l form. E o d l = - | _ 8 t B°da where c and s are the c o n t o u r and s u r f a c e o f the s e c t o r i n F i g . 25. The c o n t r i b u t i o n from AB and CA t o E->dl w i l l c a n c e l so F i g . 25. Integration contour (c) and surface area (s) for ca l c u l a t i o n of e l e c t r i c f i e l d - 72 -E R <J> 9 R 3 t B R2 <j> or E - - 1 R 3 B  or E* 1 R Ft An e l e c t r i c f i e l d in the minus <|> di r e c t i o n w i l l cause the plasma to d r i f t inward at a speed v = E/B . The f i e l d B i s taken as the earth's dipole f i e l d , i . e . the ring current f i e l d i s ignored. Under these conditions: | ( v - v ) B | = " v | | 3/2 — at The upper l i m i t of ( v v ) B i s of the same order of magnitude ->• a B as D u t t n e actual value of ( w ) B may be much smaller. The frequency increase of an IPDP due to inward d r i f t i s , in the extreme case, only comparable to the frequency increase due to i l at . The inward d i f f u s i o n theory takes the opposite approach. -> a B In i t -^ -z- i s assumed equal to zero. But to evaluate the theory i t i s also necessary to assume that the d i f f u s i o n process does not affect the background plasma. This is necessary since (from ( 7 ) ) motion of the background plasma w i l l produce a ->• n R •^-r which cannot be calculated e a s i l y . - 73 -Using these assumptions, the change in magnetic f i e l d seen by the d i f f u s i n g p a r t i c l e i s -»• BT = <vd-7)B- (8) The d i f f u s i o n v e l o c i t y v^ can be considered contained in the equatorial plane and directed inward. The magnetic f i e l d i s B the earth's dipole f i e l d ( B = ^§3- , where R i s the distance to IPDP generation region). The amount of inward d i f f u s i o n necessary to explain IPDP's can now e a s i l y be found from (8) DB „ 9B DT " " V d FR" _ 3 V d B R and from (5) Du _ 3 oi DB BT " 1 F DT 9 "Zd so 2 R Dm v d = 9* u BT (9 ) , 74 -The amount of inward d i f f u s i o n i s determined by measuring u and from the sonagrams and using the distance to IPDP generation region for R . The results of this ana-l y s i s for several Ralston IPDP's i s shown in table V . l . The average d i f f u s i o n v e l o c i t y of the events shown i s 6.1 x 10 3 m/sec. A value of 6 Re for R has been used and i f this is increased to 8 Re, the average d i f f u s i o n v e l o c i t y becomes 8.1 x 10 3 m/sec. Lacourly (1969) attributes this inward d i f f u s i o n to ->• an e l e c t r i c f i e l d E , producing a d r i f t v = E x B B 2 However, the cold background plasma w i l l also d r i f t at the same velo c i t y so the set of MHD equations would have to be solved before ^f and thus jj^- could be determined. Ignoring this e f f e c t Lacourly estimates an e l e c t r i c f i e l d of about 5 x 10"1* volts/m. The equivalent e l e c t r i c f i e l d for the average d r i f t v e l o c i t y determined above is |E| = |B v^ | = 8.8 x IO"1* volts/meter. The main c r i t i c i s m of the inward d i f f u s i o n theory i s that no d i f f u s i o n v e l o c i t i e s or azimuthal e l e c t r i c f i e l d s of the above magnitudes have been measured in the dusk region of the magnetosphere. Also the main assumption that •—• = 0 has been proven i n v a l i d by ATS-1 measurements. Fukunishi (1969) explains the IPDP frequency r i s e not by a changing magnetic f i e l d but by a decrease in energy of the - 75 -T a b l e V . l Inward D r i f t V e l o c i t i e s and E l e c t r i c F i e l d N e c essary f o r E x p l a n a t i o n o f IPDP Date L o c a l Time d f ar h e r t z / s e c x 104* x h e r t z Vd m/sec x 1 0 3 _E v o l t s / i x 10-J a n . 21 22:30 2.7 0.62 3.7 5.3 March 18 22:40 1.0 0.37 2.3 3.3 March 27 18:50 1.1 0.18 5.2 7.4 A p r i l 17 19:50 4.7 0.54 7.4 10.5 May 7 21:20 4.2 0.70 5.1 7.3 May 16 22 :20 3.7 0.45 7.0 10.0 May 17 22:00 1.6 0.58 2.3 3.3 Aug. 14 19:50 4.0 0.27 13.0 18.5 Sept. 13 22:40 0.5 0.14 3.0 4.3 Nov. 2 13:40 5.5 0.40 12.0 17.0 Average 6.1 8.8 - 76 -resonating protons. The protons are assumed to be impulsively injected into the nighttime magnetosphere at the star t of a substorm expansion. Due to the gradient and curvature of the magnetic f i e l d the protons d r i f t westward at the speed v = f v ^ B (Wx + 2W„ ) Since this v e l o c i t y varies d i r e c t l y with the proton energy, an observer at a fixed longitude would see a gradually soften-ing proton beam. If the protons have a suitable v e l o c i t y dis-t r i b u t i o n for cyclotron i n s t a b i l i t y wave amplification an IPDP w i l l be produced (w <* l//w^  ) Fukunishi does not take into account the changing magnetic f i e l d in the dusk-midnight sector of the magnetosphere. His c a l c u l a t i o n of proton d r i f t v e l o c i t i e s i s thus for a steady state magnetosphere, which is a poor approximation during mag-netospheric substorms. The d i f f e r e n t i a l d r i f t theory can not e a s i l y explain the intimate relationship between IPDP's, 4-sec. micropulsations and hm emissions. Fukunishi uses stably trapped protons for 4-sec. micropulsation generation and transi e n t l y trapped protons for IPDP generation. It is much simpler to consider a single p a r t i c l e source with a s t a t i c and then changing magnetic f i e l d producing the difference between the two types of micropulsations. - 77 -CHAPTER VI Discussion of Future Experiments The increasing magnetic f i e l d theory for IPDP relates the frequency change of IPDP noise band to the change i n the ion cyclotron i n s t a b i l i t y frequency due to an increasing mag-netic f i e l d . Hm emissions and band type micropulsations (4-sec. period micropulsations) are also generated by a cyclotron i n -s t a b i l i t y process, and the relationship between these three types of micropulsations has been discussed b r i e f l y i n Section V . l . In order to firmly establish the ideas presented there, further experimental and t h e o r e t i c a l work needs to be done. In p a r t i c u l a r , the c h a r a c t e r i s t i c s of band type emissions must be more extensively studied. One of the main problems i s to est a b l i s h the s i m i l a r i t i e s and differences i n the s t r u c t u r a l elements i n hm emissions, IPDP's and band type micropulsations. A conjugate pair of stations would be necessary for this purpose. Since there i s a d i r e c t relationship between IPDP's and magnetospheric substorms, IPDP's might provide valuable information on the substorm process. The increasing magnetic f i e l d theory relates the IPDP frequency change to a magnetic f i e l d change associated with a p a r t i a l ring current i n the dusk.-midnight quadrant of the magnetosphere. Thus IPDP's can be used to help deduce the form of the three dimensional current system existing during magnetospheric substorms. More s p e c i f i c a l l y , - 78 -IPDP's are generated at the time of removal of this p a r t i a l ring current which l i k e l y corresponds to the formation of the auroral bulge and westward t r a v e l l i n g surge. A careful study of IPDP properties could lead to a better understanding of the complex dynamic processes occurring during magnetospheric substorms. To achieve the aims given above, multi-station micro-pulsation experiments must be performed. A l i n e of micropulsa-tion stations at approximately the same geomagnetic latitude could determine: 1) the longitudinal extent of individual IPDP's 2) IPDP frequency versus longitude (L.T.) for individual events and 3) the simultaneity of the same IPDP observed at d i f f e r e n t longitudes. A l i n e of stations at the same geomag-netic longitude could determine 1) the f i e l d l i n e on which the IPDP was generated and 2) IPDP frequency c h a r a c t e r i s t i c s versus l a t i t u d e . IPDP studies of this type would provide information which could be related to the magnetospheric substorm process. Data from a network of micropulsation stations would also further establish (or disprove) the increasing magnetic f i e l d theory. The increasing magnetic f i e l d theory predicts a r e l a t i v e l y s t a t i c region of IPDP generation whereas the inward d i f f u s i o n theory predicts an inward motion of this region. The motion, or lack of i t , might be established by detecting a change in latitude of maximum IPDP energy. However, this difference would be d i f f i c u l t to establish due to a number of unknowns - 79 -(ionospheric absorption, duct propagation, cr u s t a l conducti-v i t y , etc.)- The d i f f e r e n t i a l d r i f t theory predicts a time delay for an IPDP observed i n the dusk region r e l a t i v e to time of the same IPDP nearer midnight. The lack of a time delay would disprove that theory. - 80 -BIBLIOGRAPHY Akasofu, S. 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J a c o b s , J . A. and T. Watanabe, A m p l i f i c a t i o n o f hydromagnetic waves i n the magnetosphere by a c y c l o t r o n i n s t a b i l i t y p r o c e s s w i t h a p p l i c a t i o n s t o the t h e o r y o f hydromag-n e t i c w h i s t l e r s , B o e ing S c i e n t i f i c Research L a b o r a t o r i e s Report 01-82-0398, 1965. J a c o b s , J . A. and T. Watanabe, A m p l i f i c a t i o n o f hydromagnetic waves i n the magnetosphere by a c y c l o t r o n i n s t a b i l i t y p r o c e s s w i t h a p p l i c a t i o n s t o the t h e o r y o f hydromag-n e t i c w h i s t l e r s , J . A t m o s p h e r i c T e r r e s t . Phys., 28, 235, 1966. J a c o b s , J . A. and T. Watanabe, T h e o r e t i c a l notes on w h i s t l e r s and p e r i o d i c e m i s s i o n s i n the hydromagnetic r e g i m e , P l a n e t . Space S c i . , 1_5 , 799 , 1967. J a c o b s , J . A., Y. K a t o , S. M a t s u s h i t a , and V. A. T r o i t s k a y a , C l a s s i f i c a t i o n o f geomagnetic m i c r o p u l s a t i o n s , J . Geophys. Res., 69, 180, 1964. J e l l e y , D. H., and N. B r i c e , A s s o c i a t i o n between i n c r e a s e d r a d i a t i o n i n the o u t e r b e l t and p o l a r a u r o r a l sub-s t o r m s , T r a n s . Am. Geophys. U n i o n , 4_8 , 180 , 1967. K n a f l i c h , H. B., and J . F. Kenney, IPDP events and t h e i r g e n e r a t i o n i n the magnetosphere, E a r t h P l a n e t . S c i . L e t t . , 2, 453, 1967. K n a f l i c h , H. B., and J . F. Kenney, L o n g i t u d i n a l s p r e a d o f Pc 1 m i c r o p u l s a t i o n s i n the magnetosphere, N a t u r e , 217, 1134, 1968. K o n r a d i , A., P r o t o n e v e n t s i n the magnetosphere a s s o c i a t e d w i t h magnetic b a y s , J . Geophys. Res., 7_2 , 3829 , 1967. K o n r a d i , A., R a p i d i n c r e a s e s i n the p r o t o n and e l e c t r o n f l u x e s i n the magnetosphere, J . Geophys. Res., 7_3, 3449 , 1968. - 84 -Lacourly, S., Evaluation de certains parametres de l a magneto-sphere a p a r t i r des proprietes des pulsations hydromagnetiques i r r e g u l i e r e s (SIP et IPDP), Ann. Geophys., 2J_, 651 , 1969. Liemohn, H. B., Cyclotron-resonance amplification of VLF and ULF whistlers, J . Geophys. Res., 7_2, 39 , 1967, Lokhen, J . E., Natural Electromagnetic Phenomena Below 30Kc/s., Plenum Press, New York, 1964. Manchester, R. N., Propagation of Pc 1 micropulsations from high to low l a t i t u d e s , J . Geophys. Res., 71, 3749, 1966. McPherron, R. L., G. K. Parks and F. V. C o r o n i t i , Relation of correlated magnetic micropulsations and electron p r e c i p i t a t i o n to the auroral substorm, Conjugate Point Symposium, June 1967, Boulder, Colorado, p III-4-1, 15, ITSAMem., 72, July, 1967. McPherron, R. L., G. K. Parks, F. V. C o r o n i t i , and S. H. Ward, Studies of the magnetospheric substorm 2. Correlated magnetic micropulsations and electron p r e c i p i t a t i o n occurring during auroral substorms, J . Geophys. Res., 73_, 1697, 1968. Mead, G. D., Deformation of the geomagnetic f i e l d by the solar wind, J . Geophys. Res., 69_, 1181 , 1964. Meng, C. I. and S. I. Akasofu, A study of polar magnetic sub-storms, 2. Three dimensional current system, J . Geophys. Res., 74, 4035, 1969. Obayashi, T., Symp. Ul t r a low frequency electromagnetic f i e l d s , Boulder, Colorado, 1964. Obayashi, T., Hydromagnetic whistlers, J . Geophys. Res., 70, 1069, 1965. Rostoker, G., The c h a r a c t e r i s t i c s and world-wide propagation of Pi 2 micropulsations, Ph.D. thesis, University of B r i t i s h Columbia, 1966. Rostoker, G., Macrostructure of geomagnetic bays, J . Geophys. Res. , 7J-, 4217 , 1968. Selsbee, H. C. and E. H. Vestine, Geomagnetic bays, th e i r fre-quency and current systems, Terrest. Magnet. Atmospher Elec. , 47 , 195 , 1942. - 85 -Sobouti, Y., The relationship between unique geomagnetic and auroral events, J . Geophys. Res., 66, 725, 1961. Tepley, L. R., A study of hydromagnetic emissions, S c i . Rept. 2 (contract AF 19 (604)-5906, Electron. Res. Directorate, A i r Res. Devel. Command), A p r i l 14, 1961. Tepley, L. R., Structure and attenuation of hydromagnetic emis-sions, Vol. 1, S c i . Rept. 1 (contract AF 19(604)-5906, Electron. Res. Directorate, A i r Res. Devel. Command), A p r i l 6, 1962. Tepley, L. R., Recent investigations of hydromagnetic emissions. Part I. Experimental observations, J . Geomag. Geoelect., 18_, 227 , 1966. Tepley, L. R. and K. D. Amundsen, Notes on sub ELF emissions observed during magnetic storms, J . Geophys. Res., 69, 3749, 1964. Tepley, L. R. and R. C. Wentworth, Hydromagnetic emissions, X-ray bursts, and electron bunches, 1. Experimental r e s u l t s , J . Geophys. Res., <_7 , 3317, 1962. Tepley, L. R. and R. K. Landshoff, Waveguide theory for ionospheric propagation of hydromagnetic emissions, J. Geophys. Res., 7_1 , 1499, 1966. Tereda, T., On rapid periodic variations of t e r r e s t r i a l mag-netism, Journal of the College of Science, Imperial University of Tokyo, May 25th, XXVII, Art. 9. de Moidrey, S.J.: Pulsations magnetiques a Zi-Ka-Wei et a Lu-kiv-pang, Terr. Mag., 22_, 113, 1917. Troitskaya, V. A., Pulsations of the earth's electromagnetic f i e l d with periods of 1 to 15 seconds and t h e i r connection with phenomena in the high atmosphere, J. Geophys. Res., 66, 5, 1961. Troitskaya, V. A., and N. F. Mal'tseva, Possible influence of ionospheric conditions on the formation of pulsations on intervals of decreasing period in the electromag-netic f i e l d of the earth, Geomag. Aerom.„ 6, 915, 1967. Watanabe, T., Determination of the electron d i s t r i b u t i o n in the magnetosphere using hydromagnetic whistlers, J . Geophys. Res., 70, 5839, 1965. - 86 -Weir, R. C. , An FM slow-speed tape recorder system, P a c i f i c Naval Laboratory Technical Memorandum 66-2, 1966. Williams, D. J . and G. D. Mead, Nightside magnetosphere con-figurations as obtained from trapped electrons at 1000 kilometers, J . Geophys. Res., 70, 3017, 1965. Zmuda, A. J . , J . H. Martin, and F. T. Heuring, Transverse magnetic disturbance at 1100 km in the auroral region, J . Geophys. Res., 7_, 5033, 1966. - 87 -APPENDIX I SPECIFICATIONS OF KAY ELECTRIC SONAGRAPH 7030A FREQUENCY RANGE: 1 t o 16000 Hz i n e i g h t ranges Range (Hz) Record Time ( s e c . ) R e s o l u t i o n (Hz) 1 • - 100 192.5 0,56 3.8 4 • - 400 48.1 2.2 15.2 5 -• 500 38.4 2.8 19.0 10 • • 1000 19.2 5.6 $ 37.5 20 • • 2000 9.6 11.2 75 40 • • 4000 4.8 22.5 150 80 -• 8000 2.4 45 $ 300 160 -• 16000 1.2 90 $ 600 RESPONSE: ± 2db over e n t i r e range AGC RANGE: V a r i a b l e 20 t o 40 down t o lOdb AMPLIFIER CHARACTERISTICS: F l a t o r 13db h i g h shape INPUT IMPEDANCE: 200, 600, or 10,000 ohms s w i t c h a b l e ANALYSIS TIME: 1.3 min. DISPLAYS AVAILABLE: F r e q u e n c y - v s - a m p l i t u d e - v s - t i m e ( c o n v e n t i o n a l and c o n t o u r ) A m p l i t u d e - v s - f r e q u e n c y Amp1itude-vs-time - 8 8 -APPENDIX II ION CYCLOTRON INSTABILITY FREQUENCY VERSUS MAGNETIC FIELD The dispersion equation for a left-handed ion cyclotron wave propagating p a r a l l e l to the background magnetic f i e l d i s : w 2 . c 2 k 2 . y s o (!) comp , ' 2 4 wNe2 . _ q B o where = — - — , n P m ' mc For a plasma consisting of protons and electrons n2.oi a* ID ,2 . C 2 k 2 . _ p i pe a o ( 2 ) i e Using the approximations: m << m. e I e equation (2) becomes on algebraic manipulation 4TTN. e o i 2c - 89 -the resonance c o n d i t i o n f o r streaming protons a) - ku - flj = 0 (4) i s s u b s t i t u t e d i n t o (3) and using the approximation that the streaming v e l o c i t y u << c we get: N.W., = — ( 1 - M -2-1 STrm^c2 \ 0./ a , 2 where: - background plasma d e n s i t y B Q - background magnetic f i e l d W„ - p a r a l l e l energy of streaming protons - 90 -APPENDIX III USE OF ION CYCLOTRON DISPERSION EQUATION WITH A CHANGING B FIELD The frequency of an ion cyclotron i n s t a b i l i t y has been determined in Appendix II using the dispersion equation for ion cyclotron waves with a constant background f i e l d . The i n s t a b i l i t y frequency is then considered to change due to a changing background magnetic f i e l d . This procedure i s v a l i d due to the large difference in time scales of phenomena. T << T << T (1) oo g e 1 T^ ^ 1 sec period for ion rotation about magnetic f i e l d l i n e equal to doppler s h i f t e d wave period T 100 sec growth time for ion cyclotron i n s t a b i l i t i e s T ^ 2 x 10 3 sec time duration of IPDP e The v a l i d i t y of inequality (1) assures that B is approximately constant over 1) many cycles of the wave necessary for the growth of the cyclotron i n s t a b i l i t y 2) the time required to esta b l i s h a frequency from the sonagram for a comparison with ATS-1 data. 91 APPENDIX IV DEFINITION OF MAGNETIC COMPONENTS The e a r t h ' s magnetic f i e l d a t any p o i n t can be r e p r e s e n t e d by a v e c t o r which i s d e s c r i b e d by i t s magnitude and d i r e c t i o n r e l a t i v e t o a s e l e c t e d c o - o r d i n a t e system. F i g u r e 26 i l l u s t r a t e s seven magnetic elements (X, Y, Z, H, D, I , F) o f t e n used i n d e s c r i b i n g the magnetic f i e l d . \ + X ( N o r t h ) + Y ( E a s t ) + Z F i g . 26. G r a p h i c r e p r e s e n t a t i o n o f the elements o f a magnetic v e c t o r : X, Y, Z ( g e o g r a p h i c n o r t h , e a s t , and v e r t i c a l components), H ( h o r i z o n t a l i n t e n s i t y ) , D ( d e c l i n a t i o n ) , I ( i n c l i n a t i o n ) , and F ( t o t a l i n t e n s i t y ) . S u r f a c e o b s e r v a t o r i e s commonly measure e i t h e r H, D, and Z or X, Y, Z u s i n g v a r i o m e t e r s p l u s an a b s o l u t e measurement to e s t a b l i s h the b a s e l i n e . In t h i s p r o c e d u r e D i s measured 92 as a magnetic f i e l d change perpendicular to H d i r e c t i o n . It can be expressed thus either as a magnetic f i e l d change or converted into an angle change in declination. 

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