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Geomagnetic micropulsations with periods 0.3-3 seconds Jolley, Edmund Joseph 1962

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GEOMAGNETIC MICROPULSATIONS WITH PERIODS 0. 3 - 3 SECONDS by EDMUND JOSEPH J O L L E Y B. Sc. , Carleton University, 1959 A THESIS SUBMITTED IN P A R T I A L F U L F I L L M E N T OF T H E REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS in the Department of PHYSICS We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA APRIL, 1962 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis f o r scholarly purposes may be granted by the Head of my Department or by his representatives. It i s understood that copying or publication of t h i s thesis f o r f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia, Vancouver 8, Canada. Date IQ (ZXAJ. ; tf{*L - i -A B S T R A C T j The c l a s s i f i c a t i o n and p o s s i b l e o r i g i n of geomagnetic m i c r o p u l -sations are d i s c u s s e d . In p a r t i c u l a r , p e a r l s are d e s c r i b e d in some detail and p r e v i o u s investigations reviewed. R e c o r d s f r o m V i c t o r i a and Resolute Bay, Canada; Uppsala, Sweden; Reykjavik, Iceland; Huancayo, P e r u ; Ruth, Nevada and Isabella and P a l o m a r , C a l i f o r n i a are examined and the times of commencement and t e r m i n a t i o n of p e a r l a c t i v i t y determined. The c o n c l u s i o n is reached that p e a r l s i n mid-latitudes are l o c a l mean time dependent and tend to o c cur during two p e r i o d s of the day. These periods c o r r e s p o n d roughly to s u n r i s e and sunset, the t i m e s of r a p i d change in the c r i t i c a l f r equency in the F2 l a y e r . P e a r l s s e e m to occur most often when the geomagnetic Kp index is l e s s than 4o and g r e a t e r than G>. No c o r r e l a t i o n is evident between o c c a s i o n a l p e a r l - l i k e signals at Huancayo and p e a r l s observed at other stations. It is suggested that the appearance of p e a r l s is to a c e r t a i n extent c o n t r o l l e d by l o c a l i o n o s p h e r i c conditions. - i i -T A B L E O F C O N T E N T S A B S T R A C T i T A B L E O F C O N T E N T S i i A C K N O W L E D G E M E N T S . i i i C H A P T E R I I N T R O D U C T I O N 1 1.1 Micropulsations - pre I. G . Y . Classifications 1 1.2 -Micropulsations - post I. G . Y . Classifications 2 1.3 Geomdrphology of Micropulsations 5 1.4 Origin of Micropulsations 7 C H A P T E R II P E A R L S 9 2. 1 Introduction 9 2. 2 Previous Investigations 9 C H A P T E R III I N S T R U M E N T A T I O N 13 C H A P T E R IV E X A M I N A T I O N O F R E C O R D S 15 4. 1 Stations and Components 15 4.2 Method of Examination & Description of Records 16 C H A P T E R V R E S U L T S 19 5.1 General Discussion of Pear ls - Possible L . M . T . Dependence 19 5. 2 Consecutive Day Occurences 20 5. 3 Occurence and Duration . . . 22 5.4 Diurnal and Seasonal Variations . . . 22 5.5 Relationship with Other Geomagnetic and Ionospheric Phenomena . . .24 5.6 P e a r l - l i k e Signal at Huancayo 25 C H A P T E R VI C O N C L U S I O N S 27 F I G U R E S 1 - 24 30 B I B L I O G R A P H Y 31 - i i i -A C K N O W L E D G E M E N T S I wish to sincerely thank Professor J . A . Jacobs for suggesting the topic of this thesis and for guidance throughout the investigation. Thanks are also due to M r . A. Shand of the Pacif ic Naval Laboratory, V i c t o r i a for the use of their records , to Professor H . Benioff for copies of records obtained at the other stations, and to D r . T . Yoshimatsu, Director of the Kakioka Magnetic Observatory for data f r o m Memambetau, This work was supported by the Office of Naval Research under Contract Nonr 3116(00). CHAPTER I INTRODUCTION 1. 1 Micro-pulsations - pre I. G. Y. Classifications Small periodic variations of the Earth's geomagnetic field are known as micropulsations and may be separated into different classes. The usual criteria for this division are amplitude, frequency, time of occurence and duration. Micropulsations range in amplitude from fractions of a gamma to tens of gammas on occasions. Their periods range from 0.3 seconds to several minutes. They may occur anytime throughout the 24 hours of the day depending upon the specific type and may last anywhere from a very few minutes to several hours at a time. Prior to the International Geophysical Year (I. G. Y . ) , micropul-sations were divided into three classes: Pc, Pt and Pg. However, data obtained during the I. G . Y. has led investigators to realize that this classification is too broad and does not contain all pulsations evident on the records. In this classification, Pc's are defined as continuous series of pulsations, roughly sinusoidal in shape, with amplitude of the order of tenths of a gamma, and with periods ranging from 10 to 60 seconds. They are a daylight phenomenon and have a maximum frequency of occurency just before local noon. Pt's are trains of pulsations or pulsations occuring in series, each lasting a few minutes, the total duration be ing less than an hour. - 5 * 1 gamma (r) - 10 gauss (P) - 2 -They are w e l l damped and have periods in the range between 40 seconds and a few minutes. Their amplitude is greater than that of Pc's, i.e. , about half a gamma. These pulsations are nocturnal and have a maxi-mum frequency of occurence around l o c a l midnight. Geomagnetic bays are frequently accompanied by Pt's. Pg's a re giant pulsations with amplitudes up to tens of gammas and periods as long as several minutes. The duration of a P g is of the order of an hour or more. They only occur i n or near the a u r o r a l zones. 1. 2 Micropulsations - post I. G. Y. C l a s s i f i c a t i o n s T r o i t s k a y a (1959b) has suggested a di v i s i o n of Pc's into three separate classes; the f i r s t consisting of those with periods between 5 - 1 5 seconds, the sejcond with periods between 20 - 40 seconds, and the t h i r d with periods between 50 - 90 seconds. She found Pc's in the f i r s t of these divisions to be c h a r a c t e r i s t i c of polar regions exhibiting a different diurnal variation f r o m those with periods i n the 20 - 40 seconds range. The number of occurences of Pc's with periods between 20 - 30 seconds was observed to decrease sharply during the middle months of the long polar night. Troitskaya noted that Pt's in the A n t a r c t i c are s i m i l a r to those in the A r c t i c and that these polar region Pt's exhibit different char-a c t e r i s t i c s f r o m those in mid-latitudes. The occurency frequency of Pt's appears to be a maximum at the equinoxes. - 3 -Jacobs and Sinno (1960a) have r e p o r t e d that o r d i n a r y Pc's co n s i s t of two di f f e r e n t wave bands. Those Pc's with 15 - 30 seconds p e r i o d constitute the f i r s t band. They have maximum amplitudes i n m i d - latitude regions. The second band includes those pulsations with a 30 - 90 second p e r i o d . These l a t t e r r e a c h m a ximum amplitudes in p o l a r regions and, unlike the sh o r t e r p e r i o d band, are synchronous over wide a r e a s . In addition to these two bands, Jacobs and Sinno p r o p o s e d a new c l a s s , L P c ' s . These are continuous pulsations of longer p e r i o d than o r d i n a r y Pc's and u s u a l l y o c cur at the same time as Pc's i n p o l a r regions. They are f a i r l y synchronous over a wide a r e a and have a s i m i l a r l a t i t u d i n a l d i s t r i b u t i o n of amplitude to that of the 30 - 90 second Pc's The d i u r n a l v a r i a t i o n of L P c ' s is the same as that of Pc's. Jacobs and Sinno found that Pt's accompanying negative bays in the a u r o r a l zone have a different latitude d i s t r i b u t i o n of amplitude f r o m those accompanying positive bays and those o c c u r i n g without bays. They, t h e r e f o r e , c l a s s i f i e d Pt's as P t ~ and P t + . Both types have synchronous wave f o r m s over a range of r e c o r d i n g stations. Benioff (i960) examined r e c o r d s obtained at a number of stations f o r m i c r o p u l s a t i o n s i n the p e r i o d range 0. 3 - 120 seconds. He divided his findings into four types: A, B, C and D. Type A co n s i s t s of those o s c i l l a t i o n s with 0.3 -2.5 seconds p e r i o d . These have been designated as p e a r l s by T r o i t s k a y a (1957) and are the subject of this t hesis and w i l l be d i s c u s s e d i n detai l l a t e r . - 4 -Type B o s c i l l a t i o n s have p e r i o d s i n the 3 - 8 seconds range. T h ey are appr o x i m a t e l y s i n u s o i d a l i n appearance and, at the latitude of southern C a l i f o r n i a , appear to be a s s o c i a t e d with l o c a l a u r o r a and large values of the magnetic K index. Type C includes pulsations of 7 - 30 seconds p e r i o d , which are a l s o roughly s i n u s o i d a l i n f o r m . A daylight phenomenon, they have a m aximum occurence frequency at l o c a l noon. They show v e r y good c o r r e l a t i o n with the e l e v e n y e a r sunspot c y c l e . Between stations only 291 km. apart, Benioff observed that the phase may di f f e r by as much as a few seconds and the shapes of these o s c i l l a t i o n s may a l s o be different. He, t h e r e f o r e , suggested that these p a r t i c u l a r pulsations may be a l o c a l i o n ospheric phenomenon. Type D c o n s i s t s of single pulses or t r a i n s of s e v e r a l pulsations, the p e r i o d s of which are i n the 40 - 120 seconds range. T h e y are nocturnal i n southern C a l i f o r n i a with a m a x i m u m time of occurence at l o c a l midnight. O s c i l l a t i o n s of about 2 seconds p e r i o d were often o b s e r v e d to be su p e r i m p o s e d on the much longer p e r i o d s i g n a l . Type D, also, shows a pos s i b l e a s s o c i a t i o n with the sunspot c y c l e . Benioff found that the number of occurences of this type of o s c i l l a t i o n reaches a maximum at the s o l s t i c e s and a m i n i m u m near the equinoxes. T h i s is opposite to the occurence frequency of a u r o r a s and to what T r b i t s k a y a has r e p o r t e d f o r Pt's. Maple (1959), like Jacobs and Sinno, divided daytime Pc's into two bands, one with periods ce n t e r i n g around 20 seconds and the other - 5 -around 70 seconds. He observed a positive correlation between the 20 second band and the K index, but a negative correlation between the 70 second band and K. He also found a nocturnal 8 second band exhibiting a positive correlation with K. This band is equivalent to Benioff's Type B oscillations. Maple suggested that all three of these bands were dependent upon local time. 1. 3 Geomorphology of Micropulsations (a) Pc's Most investigations of geomagnetic micropulsations have dealt with Pc's, particularly those in the 5-40 seconds period range. Campbell (1960a) has summarized their general characteristics. As already mentioned, they have a maximum occurence frequency near local noon and are related to the K index. In addition Campbell et alia observed a 27 day recurrence tendency, i.e. , these particular pulsations are dependent upon the rotation of the sun. A relationship between the 5-30 seconds period Pc's and pulsating aurora and ionospheric absorption was also observed (Campbell, 1960b). An increase in the signal of pulsations in this period range simultaneous with meteor showers in 1958 was also noticed (Campbell, 1960c). Campbell (I960d) suggested that ionospheric electron density and collisional frequency may be the determining parameters of micro-pulsation amplitudes. Jacobs and Sinno (1960b) observed that the occurence frequency of Pc's increases towards the poles, reaching a maximum in the - 6 -a u r o r a l zones. They a l s o noted that the time of d i u r n a l m a x i m u m was e a r l i e r at higher latitudes. Duncan (1961) r e p o r t e d that the p e r i o d of Pc's exhibits a d i u r n a l v a r i a t i o n . T h i s v a r i a t i o n is continuous throughout the day and does not occur in d i s c r e t e jumps as other i n v e s t i g a t o r s have suggested. The evidence f o r l o c a l mean time (L. M. T. ) dependence of Pc's is widely accepted 1. '.. However, many o b s e r v e r s believe that there is al s o a u n i v e r s a l time (U.T.) dependence, i . e . , Pc's are simultaneous over large a r e a s . Jacobs and Sinno (1960b) found that the U. T. maximum time of occurence is 2100 i n the n o r t h e r n hemispheres, T r o i t s k a y a (1959b) has al s o maintained that Pc's are U. T. dependent but with a maximum time of occurence d i f f e r i n g by 7 hours f r o m that obtained by Jacobs and Sinno. The latte r i n v e s t i g a t o r s have e s t i m a t e d that the U. T. fac t o r affects the mod-ulation of d i u r n a l occurence by 50%. C a m p b e l l and M a t s u s h i t a (1962) concluded that 5 - 30 seconds p e r i o d m i c r o p u l s a t i o n s may be detected almost continuously throughout the world. (b) Pt's The c h a r a c t e r i s t i c s of Pt's and Pg's have not been i n v e s t i -gated as thoroughly as those of Pc's. T h i s is p r o b a b l y due to the lack of suitable data. T h e r e appears to be a close r e l a t i o n s h i p between Pt's and bays and, both exhibit a p p r o x i m a t e l y the same v a r i a t i o n of amplitude with latitude. Y a n a g i h a r a (19 59) re p o r t e d that the occurence - 7 -frequency of Pt's i n c r e a s e s with i n c r e a s i n g magnetic act i v i t y , whereas, the r e l a t i o n between P t occurence and s o l a r a c t i v i t y is an inv e r s e one. Jacobs and Westphal suggest that Pt's like Pc's are proba b l y both U. T. and L.M.T. dependent, U.T. c o n t r o l l i n g the frequency of occurence and L. M. T. the modulation of the s i g n a l amplitude. (c) Pg's Pg's are e s s e n t i a l l y high latitude phenomena, o c c u r i n g in or near the a u r o r a l zones. Sucksdorff (1939), an e a r l y investigator of these pulsations, separated them into two c l a s s e s : A-type and B-type, both o c c u r i n g m a i n l y d u r i n g the m o r n i n g hours. The A-type have a maximum frequency of occurence in the e a r l y hours while that of the B-type is near l o c a l noon. He found the occurence of Pg's to be more dependent on s o l a r a c t i v i t y than on magnetic a c t i v i t y . L a t e r investigations tend to c o n f i r m Suckdorff's a n a l y s i s . K o robkova et a l i a (1959) noticed a t r e n d f o r an L.M.T. dependence of Pg's 1.4 O r i g i n of M i c r o p u l s a t i o n s The o r i g i n of m i c r o p u l s a t i o n s i s not as yet c l e a r l y understood. M o s t i n v e s t i g a t o r s agree that they can most l i k e l y be explained i n t e r m s of hydromagnetic waves, i . e . , they are sign a l s r e c o r d e d on the ground f r o m hydromagnetic waves generated i n the upper atmosphere - ex a c t l y where i n the upper atmosphere is not c e r t a i n . Such hydro-magnetic waves are probably due to the i n t e r a c t i o n of s o l a r c o r p u s c u l a r s t r e a m s with the upper atmosphere. - 8 -Obayashi and Jacobs (1958), among others, have a s s o c i a t e d Pg's with t o r o i d a l o s c i l l a t i o n s of the outer atmosphere since they both exhibit l a t i t u d i n a l dependence. A n association between Pt's, longer p e r i o d Pc's, and p o l o i d a l o s c i l l a t i o n s has a l s o been investigated (Jacobs and Sinno, 1960a). C H A P T E R II P E A R L S 2. 1 Introduction Geomagnetic m i c r o p u l s a t i o n s at the high frequency end of the spectrum, with p e r i o d s in the 0 . 3 - 4 seconds range, have been c a l l e d p e a r l s by T r o i t s k a y a (1957). The name is indicative of the f o r m of this type of s i g n a l . T h ey are s i n u s o i d a l o s c i l l a t i o n s which undergo amplitude modulation i n such a way as to re s e m b l e oval beads or p e a r l s on a s t r i n g . A n i n d i v i d u a l " p e a r l " may l a s t anywhere f r o m 5 to 30 seconds while a p e a r l occurence may be a separate burst of 1 or 2 minutes duration or a continuous in t e r m i t t e n t s e r i e s of bursts l a s t i n g f o r s e v e r a l hours. The amplitudes of p e a r l s , as a r u l e , are v e r y s m a l l , l y i n g between thousandth's and hundredth's of a gamma. 2. 2 P r e v i o u s Investigations (a) U.S.S.R. T r o i t s k a y a (1957) f i r s t noticed these o s c i l l a t i o n s on r a p i d - r u n e a r t h c u r r e n t r e c o r d s obtained i n 1952-53 at two Soviet N stations i n smid-Asia. Subsequent r e c o r d i n g s using a tra c e speed of 30 mm/min. and v e r y high s e n s i t i v i t y were made d u r i n g 1957-58 at a number of Soviet stations. F r o m an an a l y s i s of the r e c o r d s T r o i t s k a y a (1959a) was able to recognize c e r t a i n c h a r a c t e r i s t i c s of these pulsations. A s u m m a r y of her findings is given below. P e a r l occurences i n mid-latitudes u s u a l l y c o n s i s t of a continuous s e r i e s while short bursts are more pr e v a l e n t i n the A r c t i c . The data f r o m the A n t a r c t i c indicate that both s e r i e s and bursts of p e a r l s may - 10 -occur. In mid-latitudes p e a r l s are r e c o r d e d m a i n l y d u r i n g the evening, night, and morning.' hours. Two occurence f r e q u e n c y m a x i m a are evident, one between 1900 and 2300 L. M. T. and a m a i n m a x i m u m between 03 00 - 0700 L.M.T. In p o l a r regions, however, p e a r l s s e e m to o ccur at a l l hours of the day and night with s e v e r a l occurence maxima. T r o i t s k a y a suggests that these d i f f e r e n c e s i n d i u r n a l v a r i a t i o n may be connected with a different mode of appearance i n the two regions. The amplitude of p e a r l s i n the p o l a r regions i s g r e a t e r than that of those observed i n m i d - l a t i t u d e s . P e a r l s with p e r i o d s g r e a t e r than 4 seconds are v e r y r a r e , u s u a l l y o c c u r i n g only on days of magnetic s t o r m s and i n separate b u r s t s . P e a r l s with p e r i o d s l e s s than one second can appear under a l l magnetic f i e l d conditions. A n a s s o c i a t i o n b etween p e a r l s and such m a c r o s c o p i c geomagnetic events as bays, pu l s a t i o n t r a i n s , and sudden commencements on quiet days is not indicated. However, T r o i t s k a y a b e l i e v e s that they r e p r e s e n t a m i c r o s t r u c t u r e of the greatest magnetic s t o r m s i n r e s p e c t of pulsations. Under quiet f i e l d conditions p e a r l a c t i v i t y often o c c u r s during p e r i o d s when c o s m i c - r a y intensity i n the stratosphere is i n c r e a s i n g sharply. In mid-latitudes long s e r i e s of p e a r l s show an i n v e r s e relationship.with s o l a r a c t i v i t y v a r i a t i o n . D u r i n g magnetic s t o r m s , there appears to be a r e l a t i o n between p e a r l s and c e r t a i n high a t m o s p h e r i c phenomena, e.g. , mid-latitude a u r o r a , sharp d e c r e a s e s in the F 2 l a y e r c r i t i c a l frequency, bursts of -11 -X-rays in the atmosphere and periods of full absorption in the iono-sphere. The amplitudes of pearls are strongly enhanced during storms and Troitskaya points out that there seems to be a shortening of period for successive series. Also on days following magnetic storms pearls may sometimes be detected. The geographic distribution of pearls appears to indicate both ah L. M.T. and a U. T. dependence. On occasions pearls have been recorded simultaneously at Soviet stations separated by 120° of longitude (particularly during magnetic storms). The most favourable times for this were between 1600 and 2000U. T. and 2200 and 0200 U. T. Also, simultaneity of pearl occurence was noted at Arctic and Antarctic stations during the greatest magnetic storms and, very occasionally, on quiet days. On the other hand, there were occasions when.pearls were recorded at one station only. A tendency for pearls to occur at the same time on successive days at any one station was also noticed. Troitskaya suggests that they might be excited on a world wide scale (i. e. , U. T. dependent) although the probability of their being recorded is dependent upon local time. On highly disturbed days the local time control is weakened. She remarks that the atmosphere may be transparent to micropulsations of 0. 3 - 4 seconds period at certain times and not at others. Troitskaya considers pearls to be a main constituent of I. P. D. P. (i.e. intervals of pulsations diminishing by periods, a form of pulsation activity which occurs during great magnetic storms) and to originate in - 12 -the outer atmosphere beyond the ionosphere. In a l a t e r paper (1961) the c o n c l u s i o n is drawn that p e a r l s are a v e r y sen s i t i v e i n d i c a t o r of high a t m o s p h e r i c response to c o r p u s c u l a r i n t r u s i o n s . (b) N o r t h A m e r i c a The Type A o s c i l l a t i o n s of Benioff are p e a r l s . He found them to be n o c t u r n a l at the latitude of southern C a l i f o r n i a although o c c u r i n g throughout the 24 hours of the day at Uppsala (Sweden). In C a l i f o r n i a there is a m i n i m u m occurence around 2200 L. M. T. and a m aximum around 0500 - 0600 L.M.T. P e a r l s begin quite r a p i d l y after sunset and cease s h o r t l y after s u n r i s e . A t Uppsala the occurence m aximum is around 0700 - 1000 L.M.T. These t i m e s of Benioff are not i n complete agreement with those given by T r o i t s k a y a . A negative c o r r e l a t i o n with sunspot numbers i s evident and at the southern C a l i f o r n i a latitudes, p e a r l a c t i v i t y c o i n c i d e s with quiet f i e l d conditions. Benioff suggests that the ionosphere may act as a s h i e l d against p e a r l s f or most of the t i m e . He a l s o noted that the c o r r e l a t i o n between two C a l i f o r n i a stations was a l m o s t per f e c t . Duffus et a l i a (i960) e x a m i n i n g r e c o r d s f r o m A l b e r t Head, B.C. and R a l s t o n , A l b e r t a , two stations some 515 m i l e s apart found occasions of simultaneous p e a r l occurence. T h e y suggested, t h e r e f o r e , that the source must be beyond the ionosphere or else has f a i r l y l a r ge dimensions. C H A P T E R III I N S T R U M E N T A T I O N The r e c o r d i n g equipment at V i c t o r i a c o n s i s t s of an induction c o i l , a m p l i f i e r , and a v i s u a l r e c o r d e r . The c o i l is a m e tal c o r e d solenoid, s i x feet in. length, wound with 20, 700 turns of wire. The c r o s s s e c t i o n a l a r e a of the core is 0. 5 in. and the d-c r e s i s t a n c e of the c o i l is about 50 ohms. F o r c a l i b r a t i o n purposes 10 turns are wound s e p a r a t e l y f r o m the m a i n windings. The c o i l is e n c l o s e d i n a w aterproofed container and b u r i e d i n the ground. The induced s i g n a l is fed through a sensitive chopper a m p l i f i e r before e n t e r i n g the r e c o r d e r . The l a t t e r c o n s i s t s of a rotating drum, single channel B r u s h pehmotor and a m p l i f i e r . A r e c o r d i n g speed of 0.5 mm/sec. is employed. At the stations o r g a n i z e d by Benioff, the magnetic pick-up c o i l s c o n s i s t of c i r c u l a r a l u minum forms, 192 cm. in diameter, would with 750 turns of w i r e . The inductance and r e s i s t a n c e of each c o i l i s a p p r o x i m a t e l y 2. 75 henries and 55 ohms r e s p e c t i v e l y . These c o i l s are connected to 1. 0 second p e r i o d galvanometers f r o m which the r e c o r d i n g is done p h o t o g r a p h i c a l l y using s e i s m o g r a p h drums.with a r e c o r d i n g speed of lmm/sec. P r o v i s i o n is made f o r the c a l i b r a t i o n of the c o i l - g a l v a n o m e t e r s y s t e m with r e g a r d to frequency response and s e n s i t i v i t y . F o r the r e c o r d i n g of t e l l u r i c c u r r e n t s at I s a b e l l a and P a l o m a r two lead e l e c t r o d e s are employed. They are p l a c e d 305 m e t e r s apart - 14 -buried to a depth of about one meter. The actual recording is done by a single heated stylus visible-writing recorder. On both types of installation accurate timing is effected by causing the recording trace to be offset once per minute. C H A P T E R IV EXAMINATION OF RECORDS 4. 1 Stations and Components F o r this investigation, micropulsation records were examined initially from Victoria, B.C. The records covered the interval between September 23, I960 and February 28, 1961. Definite occurences of pearls were picked out and records for the days on which they occured at certain other stations were obtained from Professor H. Benioff of the California Institute of Technology. These stations were Uppsala, Sweden; Reykjavik, Iceland; Resolute Bay, Canada; Huancayo, Peru; Ruth, Nevada and Isabella and Palomar, California. In addition, Dr. K. Yanagihara of the Kakioka Magnetic Observatory kindly furnished data of telluric current recordings made at Memambetsu, Japan. Table I gives the geographic and geo-magnetic co-ordinates of these stations. At Victoria only the vertical ( Z) component of the geomagnetic field was recorded. The records from Palomar and Isabella included all three magnetic components, i.e., north-south (X), east-west n ( (Y) and vertical ( z ) . On some occasions telluric current records were also available from the California stations. The records from Ruth, Resolute, Reykjavik, Uppsala and Huancayo were all of the X component Table II gives a list of the magnetic components recorded and the sensitivities of the equipment at the various stations. At Palomar and Isabella, where all three magnetic components were recorded, the Z component was always the smallest in amplitude. T A B L E I Stati on Ge ogr aphi c Latitude Longitude Resolute Bay- N 47°41< W 94°55' R e y k j a v i k ' N 64°11« W 221°42' Uppsala N 59°53' E 17°39' V i c t o r i a N 48°25 1 W 123°22' Me mambetsu N 43°55' E 144°12' Ruth N 39 016' W 114°59' Isab e l l a N?3'5°40' W 118°28' P a l o m a r N 33°22' W 116°50' Huancayo S 12°03 I W 75°20' Geomagnetic Latitude Longitude N 82°. 9 289°. 3 N 70°. 2 71°. 0 N 58°. 7 104°. 5 N 54°. 1 292°. 6 N 34°. 1 208°.3 1 N 46°. 4 305°. 3 N 42°. 6 303°. 1 N 40°. 5 304°. 1 S 0°. 6 353°. 8 Station T A B L E II Sensitivity in Gamma/sec/mm X Y 2 Resolute Bay 0.23 Reykjavik 0. 1 -Uppsala 0. 095 Ruth Similar to Isabella and Palomar Isabella 0.069 0.064 0.061 Palomar 0. 052 0. 046 0. 046 Huancayo 0. 140 - 16 -T h e r e f o r e , on the following graphs, the r e s u l t s f r o m these stations are r e p r e s e n t e d by eit h e r t h e i r X or Y components, u s u a l l y X. The correspondence between the three A m e r i c a n stations i s v e r y good in r e s p e c t to the time of p e a r l occurence, duration and amplitude. The r e s u l t s f r o m V i c t o r i a , however, are not always i n good a g r e e -ment with them despite the fact that there i s lit t l e d i fference in (geographic) longitude and n d too much difference i n latitude. T h i s may be due to the fact that the observations at V i c t o r i a were of the Z component. _^  4. 2 Method of E x a m i n a t i o n and D e s c r i p t i o n of R e c o r d s The r e c o r d s were ex amined to determine the t i m e s (to the neare s t minute) of the i n i t i a t i o n and c e s s a t i o n of p e a r l a c t i v i t y at the in d i v i d u a l stations. A t y p i c a l occurence of p e a r l a c t i v i t y c o n s i s t s f i r s t of a p e r i o d of undeveloped p e a r l s , i . e . , the amplitude modula-tio n t y p i c a l of p e a r l s is just b a r e l y evident. T h i s is followed by definite p e a r l s which i n t u r n decrease to the undeveloped state. The duration of e a c h of these three phases depends upon the duration of the o v e r a l l occurence. On some occasio n s , p e a r l s occur with v e r y lit t l e undeveloped phase before and after the main s i g n a l . However, on other occasions, the a c t i v i t y never exceeds that of the undeveloped stage. T h i s is often the case at V i c t o r i a even whe n there is good simultaneous p e a r l a c t i v i t y on the A m e r i c a n r e c o r d s . Thus, the undeveloped phase may be c o n s i d e r e d legitimate p e a r l a c t i v i t y but with s m a l l e r r e c o r d e d amplitude due e i t h e r to the s i g n a l amplitude i t s e l f or, as is the case at V i c t o r i a , to the fact that the low amplitude Z component was r e c o r d e d . The t i m i n g of a b u r s t of p e a r l a c t i v i t y on the r e c o r d s can, at t i m e s , be d i f f i c u l t . A s a working r u l e , the time of i n i t i a t i o n was chosen to be that when v e r y s m a l l amplitude s i g n a l s , s e e m i n g l y r e g u l a r i n shape and frequency, could be c l a s s i f i e d as undeveloped p e a r l a c t i v i t y r a t h e r than just r i p p l e s . The e s t i m a t e d po s s i b l e e r r o r f o r this p r o c e d u r e is ± 1 minute f o r the A m e r i c a n , Uppsala and Re y k j a v i k r e c o r d s , more for those f r o m V i c t o r i a and l e s s f o r those f r o m Huancayo. A s indicated i n the introduction, p e a r l s do not occur on e v e r y day of the month nor do they occur i n any appparent o r d e r e d fashion. T h i s is borne out by the r e c o r d s examined f r o m the A m e r i c a n stations, V i c t o r i a , Uppsala and to a l e s s e r extent f r o m Reykjavik. The l a s t station, however, is a high latitude station and u s u a l l y has a v e r y active t r a c e despite the f a i r l y low r e c o r d i n g s e n s i t i v i t y . T h e r e f o r e , when p e a r l s are c l e a r l y evident at Uppsala, they are often not seen at Reykjavik. Resolute has the lowest s e n s i t i v i t y of a l l the stations, the r e c o r d s being l i t t l e more than smooth h o r i z o n t a l t r a c e s and thus, p e a r l s cannot be distinguished at this station.. The r e c o r d i n g s e n s i t i v i t y at Huancayo was lower than that at R e y k j a v i k and, the r e c o r d s there are a l s o e x t r e m e l y quiet. However, p e a r l - l i k e signals are evident on the r e c o r d s . The s i g n a l almost always consists of - 18 -only a few o s c i l l a t i o n s , being l e s s than a half minute in duration. On many occasions, two or more of these signals occur on the same day but, the s e p a r a t i o n between them is u s u a l l y of the order of hours. The r e c o r d s f r o m Huancayo w i l l be d i s c u s s e d again l a t e r . C H A P T E R V R E S U L T S 5. 1 G e n e r a l D i s c u s s i o n of P e a r l s - P o s s i b l e L. M. T. Dependence F i g u r e s 1 to 22 show the time of p e a r l occurence (U. T. ) plotted against geographic longitude. The duration of a c t i v i t y at e ach station is r e p r e s e n t e d by a v e r t i c a l l i n e . A l s o included on e ach plot is a line whose i n v e r s e slope r e p r e s e n t s the rate at which the E a r t h rotates, i . e . , 15° per hour. P l o t s were only drawn f o r those days on which there was good or wide s p r e a d p e a r l a c t i v i t y at U p p s a l a and at the A m e r i c a n stations or f o r those days when the s i g n a l appeared to be L. M. T. dependent. A s a r u l e , these c r i t e r i a were one and the same. F r o m these plots it can be seen that when p e a r l s are observed at stations f a i r l y w e l l separated in longitude, the more we s t e r n stations r e c o r d t hem p r o g r e s s i v e l y l a t e r . The rate of this p r o g r e s s i o n f o r a given occurence can be roughly d etermined by c o m p a r i n g it with the l i n e , the i n v e r s e slope of which is 15° per hour. T h i s was done for a number of the plots and the average rate of p r o g r e s s i o n w a s found to lie between 15° and 16° per hour. Such a value suggests that the p e a r l s examined here are L. M. T. dependent. T r o i t s k a y a (1959a) has pointed out this p o s s i b i l i t y and, i n addition, has indicated that p e a r l s may depend on U.T. as w e l l , i . e . , they may be simultaneous over a wide a r e a . T h i s s i m u l t a n e i t y o c c u r s u s u a l l y on highly disturbed days and m a i n l y d u r i n g two time i n t e r v a l s , v i z . , 1600 - 2000 U. T. and 2200 - 0200 U. T. , which would c o r r e s p o n d to - 20 -0800 - 1200 L.M.T. and 1400 - 1800 L.M.T. at the A m e r i c a n stations. However, simultaneity appears to be r a r e between Uppsala and stations i n the we s t e r n hemisphere. F i g u r e s 4, 5, 6, 12 and 14 \Show po s s i b l e c a s e s of p e a r l a c t i v i t y at Uppsala and at the A m e r i c a n stations o c c u r i n g at the same time. N e v e r t h e l e s s , c l o s e r examination of these p a r t i c u l a r r e c o r d s r e v e a l s that the Uppsala signals c o r r e s p o n d more c l o s e l y to A m e r i c a n signals o c c u r i n g about nine hours l a t e r . F u r t h e r m o r e , v e r y li t t l e p e a r l a c t i v i t y is observed on the r e c o r d s f r o m Isabella, P a l o m a r , Ruth and V i c t o r i a d u r i n g the times mentioned by T r o i t s k a y a . T h i s a l s o applies, to a large extent, to Uppsala. A s al r e a d y pointed out by Benioff (i960), p e a r l s or Type A oosdallations are nocturnal at the latitude of the southern C a l i f o r n i a stations. No evidence f o r U. T. dependence of p e a r l s has been obtained f r o m this investigation. P e a r l s do appear si m u l t a n e o u s l y at a l l four mid-latitude N o r t h A m e r i c a n stations. T h i s could, however, be indicative of the extent of the source or of the effective a r e a over which sim u l t a n e i t y can occur, since the stations d i f f e r but li t t l e i n longitude. 5. 2 Consecutive Day O c c u r e n c e s L. M. T. dependence is strengthened by the occurence of p e a r l s on consecutive days at approximately the same time on each day. T h i s - 2 1 -can be seen i n F i g u r e s 15, 16, 17, 19, 20, 21 and 22. A l s o f r o m these p a r t i c u l a r plots, the p r o g r e s s i o n mentioned e a r l i e r can be seen to continue on occasions f o r at l e a s t one revol u t i o n of the E a r t h . F i g u r e 22 shows the appearance of p e a r l s at Uppsala on F e b r u a r y 23 at a p p r o x i m a t e l y 0300 U. T. On the same day p e a r l s were r e c o r d e d at around 1200 U. T. at Isa b e l l a and at Memambetsu at about 2100 U.T. On F e b r u a r y 24, the Uppsala station r e c o r d e d p e a r l s again l a s t i n g f r o m 0200 t i l l 0700 U. T. and at Isa b e l l a they were r e c o r d e d f r o m 0900 to 1200 U.T. T h i s p a r t i c u l a r plot shows the w e s t e r l y p r o g r e s s i o n of the onset of p e a r l a c t i v i t y extending f o r more than one r e v o l u t i o n of the E a r t h . T h e r e i s no evidence f o r any other w e l l developed p e a r l a c t i v i t y on these days. The difference i n duration of the s i g n a l at the var i o u s stations i s p r e s u m a b l y caused e i t h e r by v a r y i n g source amplitude or by l o c a l i o n o s p h e r i c conditions. If F i g u r e s 19 and 20 are combined; then a p r o g r e s s i o n s t a r t i n g i n i t i a l l y at Uppsala and l a s t i n g f o r two revolutions of the E a r t h i s obtained. A s i m i l a r r e s u l t is obtained f r o m F i g u r e s 15 and 16 except that, i n this case, p e a r l s are r e c o r d e d f i r s t at Isabella. F i g u r e s 17 and 18 indicate a L.M.T. dependence t r e n d although the s i g n a l on both occasions is not v e r y intense. U p p s a l a and C a l i f -o r n i a r e c o r d s were not available f o r October 31. However, ass u m i n g p e a r l s to have o c c u r e d on this day f o r both or e i t h e r of these stations or sets of stations, a plot could be constructed which would show L.M.T. dependence continuing oyer five days. - 22 -5. 3 Occurence and Duration To be observed both at Uppsala and at the American stations, the signal need not be of long duration at either or both locations (See Figures 3, 6, 8 and 10), although it usually lasts for two hours or more at one or other of the stations. Also, continuous activity at one station does not always imply the appearance of activity at the other. As a rule, the duration of pearls is longer at the Calif-ornia stations than at Uppsala. When pearls occur for more than one hour at the latter station, they are usually recorded nine hours later in California and thus exhibit an L. M. T. dependence. F r o m these plots for mid-latitude stations, it appears that when pearls are recorded at one particular station, they may aaot necessarily be observed at the other stations. It depends on the amplitude of the source and local ionospheric conditions at the various stations. However, if they are observed over a wide area, they occur at such times as to indicate an L. M. T. dependence. i 5.4 Diurnal and Seasonal Variations Figures 23 and 24 show pearl occurence (L. M. T.) plotted against the days of the year. As before, the duration of each pearl event is represented by a vertical line. These plots are only representative of the time of year between September 23 and February 28. It is evident from these plots, particularly Figure 24 (Uppsala), that there is a trend for pearls to occur during two periods of the day. These - 23 -p e r i o d s exhibit a s e a s o n a l v a r i a t i o n and c o r r e s p o n d to times around s u n r i s e and sunset. The l i m i t for the commencement of p e a r l s in the late afternoon is between one and two hours before sunset; that for the t e r m i n a t i o n of p e a r l a c t i v i t y i n the m o r n i n g is between one and two hours after s u n r i s e . F o r m i d - l a t i t u d e s , p e a r l s occur no c t u r n a l l y between these two p e r i o d s but, v e r y r a r e l y d u r i n g the day-time. A t the winter s o l s t i c e the two p e r i o d s at U p p s a l a a l m o s t coincide just before l o c a l noon. T h i s is on account of the high latitude of this station. Thus, it might be expected that p e a r l a c t i v i t y would be l i m i t e d around the summer s o l s t i c e at Uppsala. V i c t o r i a and the A m e r i c a n stations are situated i n lower latitudes and, as a r e s u l t , would not be expected to show such an extreme change in the t i m e s of these p e r i o d s between the s o l s t i c e s , as is the case at Uppsala. That this is so, is c l e a r f r o m F i g u r e 23 where at I s a b e l l a the p r e - s u n s e t l i m i t of p e a r l a c t i v i t y on December 21 is at about 1500 L.M.T. while the post s u n r i s e l i m i t , although not as w e l l defined, is at about 0930 L.M.T. P o o r e r s i g n a l r e c e p t i o n prevented the drawing of a s i m i l a r plot f o r V i c t o r i a . F o r both Uppsala and Is a b e l l a there is a nocturnal m i n i m u m of p e a r l occurence at 2400 L.M.T. The r e were no occasions on which p e a r l s were r e c o r d e d at U p p s a l a near this m i n i m u m zone. However, v e r y extensive p e a r l a c t i v i t y at Isabella on s i x occasions r e s u l t e d i n p e a r l s being r e c o r d e d through this m i n i m u m zone and f o r almost the whole night. - 24 -5. 5 Rel a t i o n s h i p with Other Geomagnetic and Ionospheric Phenomena These two p r e f e r r e d p e r i o d s f o r p e a r l occurence a l s o coincide with and exhibit seasonal v a r i a t i o n s s i m i l a r to those p e r i o d s of the day when the c r i t i c a l frequency of the T2 l a y e r in the ionosphere is changing r a p i d l y . P e a r l s appear du r i n g the night when the F 2 l a y e r c r i t i c a l frequency i s much lower than the mid-day value. T h i s is in agreement with the r e s u l t s of B o d v a r s s o n (Benioff I960) who examined the southern C a l i f o r n i a data f r o m 1955 to 1957 and found that p e a r l s o c c u r e d only when the F l a y e r e l e c t r o n density was at a minimum. T r o i t s k a y a (1959a) has a l s o indicated that p e a r l s o c c u r when there is a sharp drop'in the F ^ l a y e r c r i t i c a l f r equency during magnetic s t o r m s . It seems reasonable to assume that p e a r l s are in t i m a t e l y connected with other upper a t m o s p h e r i c phenomena. However, the two per i o d s of changing c r i t i c a l f r equency ( c o r r e s -ponding to s u n r i s e and sunset) occur d a i l y while p e a r l s u s u a l l y occur only four or five t i m e s a month. Thus there must be other f a c t o r s i n v o l v e d w hich affect the appearance of p e a r l s on the ground. P r e v i o u s investigations have r e v e a l e d that p e a r l s u s u a l l y occur when the geomagnetic f i e l d i s r e l a t i v e l y quiet. P e a r l occurences determined f r o m the r e c o r d s examined were compared with the pla n e t a r y geomagnetic a c t i v i t y index, Kp. It was found that p e a r l s o c c u r e d only f o r Kp l e s s than 6- and only r a r e l y f o r Kp as high as that. On two occasions only were p e a r l s r e c o r d e d on days which were - 25 -c l a s s i f i e d as disturbed days of the month. E x c e p t i o n a l l y c l e a r p e a r l a c t i v i t y u s u a l l y o c cured when Kp was l e s s than 4- and o r d i n a r y a c t i v i t y when Kp was 36 or l e s s . L.M.T. dependence was evident at t i m e s when the index was l e s s than 4o. P e a r l s do not n o r m a l l y occur on e x t r e m e l y quiet days, i . e . , when Kp is l e s s than 0+. T r o i t s k a y a found a tendency f o r p e a r l s to occur on days following magnetic s t o r m s . T h i s is p a r t i a l l y supported by r e s u l t s obtained f r o m this investigation. F o l l o w i n g days of high Kp values, p e a r l s sometimes occur and, c o n v e r s e l y , on days p r o c e d i n g wide-sp r e a d p e a r l a c t i v i t y , Kp has been l a r g e r than on most other days of the month. The i n t e r v a l between l a r g e Kp values and p e a r l occurence is of the o r d e r of one to three days. U s u a l l y when Kp values are high f o r more than one day, p e a r l s appear and are w i d e s p r e a d during the c o u r s e of a day and sometimes for more than a day. However, there are many occasions when there i s no such c o r r e l a t i o n between high Kp values and p e a r l a c t i v i t y . 5. 6 P e a r l - l i k e Signals at Huancayo If the p e a r l - l i k e s i g n a l s r e c o r d e d at Huancayo are indeed p e a r l s , then they are a s p e c i a l type. A s a l r e a d y mentioned, this type of a c t i v i t y lasts f o r about 10 to 30 seconds only. L i k e true p e a r l s , these pulsations have two p r e f e r r e d p e r i o d s of occurence - f r o m 0700 - 0800 L.M.T. and 1600 - 1800 L.M.T. Unlike p e a r l s , however, they do not occur between 1800 and 0700 but during the daylight hours. - 26 -As can be seen f r o m F i g u r e s 1, 4, 6, 9, 11, 12 and 13 the signals f r o m Huancayo do not show any c o r r e l a t i o n with p e a r l s at other stations. M o r e o v e r , no seasonal t r e n d i s evident. T h i s i s what might be expected at an e q u a t o r i a l station, if the latitude dependent s e a s o n a l trends at Uppsala and Isa b e l l a are r e a l . C H A P T E R VI C O N C L U S I O N S P e a r l s i n mid-latitudes appear to be L. M. T. dependent. F o r a single occurence observed at a number of widely separated stations, the more w e s t e r l y stations r e c o r d the sig n a l s p r o g r e s s i v e l y l a t e r . The average rate of p r o g r e s s i o n is a p p r o x i m a t e l y 15° per hour, the rate of rotation of the E a r t h . P e a r l s occur i n t e r m i t t e n t l y at any one station but sometimes appear on two or more consecutive days at about the same time. A n L. M. T. dependence is often evident throughout these days. Such occasions are u s u a l l y p r e c e d e d by days of high values of the Kp index. No evidence f o r U. T. dependence is found i n this investigation. Two p r e f e r r e d times of p e a r l occurence are indicated. These c o r r e s p o n d roughly to s u n r i s e and sunset, the p e r i o d s of the day when the c r i t i c a l f r equency of the F2 l a y e r undergoes r a p i d changes. P e a r l a c t i v i t y d u r i n g the mid-day is e x t r e m e l y r a r e but, may occur anytime throughout the night. The l i m i t s f o r the commencement and ce s s a t i o n of p e a r l s appear to li e between one and two hours before sunset and after s u n r i s e r e s p e c t i v e l y . A m i n i m u m of occurence at 2400 L.M.T. is indicated. On m a g n e t i c a l l y d i s t u r b e d and on e x t r e m e l y quiet days p e a r l s are not l i k e l y to be observed but, show signs of o c c u r i n g 1 - 3 days after occasions of high values of the Kp index. U s u a l l y they are r e c o r d e d when K is l e s s than 4o and gre a t e r than 0+- . - 28 -The s i g n a l at Huancayo, although p e a r l - l i k e i n its s i n u s o i d a l f o r m , has not. the c h a r a c t e r i s t i c s of p e a r l s with respect to duration and d i u r n a l v a r i a t i o n . T h e r e appears to be no c o r r e l a t i o n between this s i g n a l and p e a r l s r e c o r d e d at other stations. It i s suggested that l o c a l i o n o s p h e r i c conditions play a sig n i f i c a n t role i n c o n t r o l l i n g the p r o b a b i l i t y of p e a r l s being r e c o r d e d . T h i s is indicated by t h e i r occurence at only one station on many occasions and, also, by the v a r i a t i o n i n t h e i r duration at different stations. The fact that p e a r l s appear s i m u l t a n e o u s l y at four mid-latitude stations of appro x i m a t e l y the same longitude i n N o r t h A m e r i c a may be indic a t i v e of the extent of the source or of the a r e a over which i o n o s p h e r i c conditions p e r m i t s i m u l t a n e i t y to occur. A n examination of m i c r o p u l s a t i o n r e c o r d s obtained d u r i n g the months between F e b r u a r y and October f r o m the stations used i n this i n v e s t i g a t i o n is needed to c o n f i r m the latitude dependent seasonal trends noticed i n this study. If these trends are r e a l , then i t is expected that d u r i n g the summer months t i m e s of p e a r l a c t i v i t y at U p p sala w i l l be l i m i t e d , i . e . , the p e r i o d of day between the commencement and c e s s a t i o n l i m i t s mentioned above w i l l be quite short. Stiations at lower latitudes should have c o r r e s p o n d i n g l y longer p e r i o d s when p e a r l a c t i v i t y could occur. M o r e analyses on a w o r l d wide scale are r e q u i r e d before it can be determined whether p e a r l s r e c o r d e d at high-latitude and at - 29 -e q u a t o r i a l stations are L.M.T. or U.T. dependent. - 30 -F i g u r e s 1 - 22 Ordinates r e p r e s e n t time (U. T.) A b s c i s s a e r e p r e s e n t longitude (geographic) u - Uppsala Rk - R e y k j a v i k H - Huancayo Re - Resolute R - Ruth P - P a l o m a r I - I s a b e l l a V - V i c t o r i a M Me mambetsu The dashed line r e p r e s e n t s the i n v e r s e gradient of 15° per hour. F i g u r e s 23 - 24 Ordinates r e p r e s e n t time (L. M. T. ) A b s c i s s a e r e p r e s e n t the days of the year between September 23, 1960 and F e b r u a r y 28, 1961. 2100 I80€H 1500-\200-\ 0900H 0600H 0300H V PR i i i FIGURE II Oct — i • — i m ° w 4 R ° w ' w w i es°w o ° I5°E I20°W I05°W 90°W 75°W 60°W 45°W 30°W TT ±1 ± T FIGURE 5 19 Nov. V i i i _! ,111 Re H 0600 +0300 Rk U i?n°w IPR ms°w qo°w 7 5 ° W 60°W 45°W 30°W I5°W 0 C I5°E V _ L _ I20°W FIGURE 6 25 Dec. P R R e L I I 1 u I05°W 90°W 75°W 60°W 45°W 30°W I5°E +2100 - 0 6 0 0 FIGURE 7  26 Dec. --0300 i V I PR Re H Rk U 1 | 1 1 1 : 1 1 1 1 1 : 1 1 — r 1 r — L I20°W I05°W 90°W 75°W 60°W 45°W 30°W I5°W 0° I5°E I 11 V I PR _ i i i i FIGURE 8 1-2 Jan. R e i H f 0 6 0 0 1 1 — I20°W I05°W 90° W 75°W 0 9 0 0 + 0 3 0 0 2 4 0 0 + 2100 R k _ i _ U 60°W 45°W 30°W I5°W 0° I5°E v I I J . I I I FIGURE 9 3 Jan. I — i r 30°W I5°W I 2 0 ° W , P R - I05°W 90°W 75°W 60°W 45°W 0° I5°E FIGURE 15 9-10 Oct. 40 W u — H " 10 E 60 E 110 E + 1200 + 0600 0400 + 1800 + 1200 --0600 160 E I 150 W 100 W 41200 + 060CK FIGURE 16  10-11 O c t . Rk _ J _ u JL . 2400 + 1800 4-1200 4-0600 40 W 60 E 160 E — i 100 w Rk I T 0 u _ l _ 1200 I J I i I FIGURE 17  2 9 - 3 0 Oct. Rk i u 40 W 60 E + 0600 2400 + 1800 + 1200 + 0600 160 E i — i — 100 w T" 0 u _1_ 1200 FIGURE 18 1-2 Nov. u 40 W 60 E 10600 2400 +1800 + 1200 +0600 160 E J L IOOW 0 u _!_ I r Re _ i _ I I FIGURE 19 2-3 Jan. Rk u 40 W 60 E +0600 •1200 2400 + 1800 + 1200 +0600 160 E I 100 w I I Rk U ' i L 0 I FIGURE 20  3 - 4 Jan, -H200 +0600 2400 + 1800 •1200 +0600 U 60E 160 E I Re ' I 100 w Rk U _ J ( L 0 1200 I I I I FIGURE 21  22-23-24 Jan. Rk i u -L 40 W 60 E +0600 + 2400 4-1800 + 1200 0600 + 2400 160 E i i P L _ 100 w Rk 1 0 --\ \ \ \ -1200 \ \ -0600 ^ > 2400 \ \ \ \ I -1800 -1200 1 I . FIGURE 22 23-24 Feb. u , r - l , M — , 1 — -0600 J— i , I u 1 1 ' 90W 40W 10 E 6 0 E II0E 160 E I50W IOOW 5 0 W 0 +0600 I I I I 10300 +2400 I I-I i i +2100 +1800 T FIGURE 23 ISABELLA + 1500 +1200 SEPT. OCT. — i — 16 31 NOV. 15 30 DEC. 15 30 J A N . — i — 14 29 FEB, — i — 13 I X I I I I FIGURE 24  UPPSALA OCT. NOV. I 1 1— 16 31 15 1 1 4-0600 +0300 1 4-2400 +•2100 DE +1800 + 1500 x +1200 C X I JAN, FEB. 15 30 29 13 - 31 -BIBLIOGRAPHY Benioff, H. , I960, J. Geophys. Res., 65, 1413 Campbell, W. H. , 1960a, J. Geophys. Res., 65, 1843 Campbell, W.H. , 1960b, J. Geophys.Res. , 65, 1833 Campbell, W. H. , 1960c, J. Geophys. Res., 65, 2241 Campbell, W.H. , 1960d, J. Geophys. Res. , 65, 2480 Campbell, W. H. , & Matsushita, S. , 1962, J. Geophys. Res., 67, 555 Duffus, H.J.., Shand, J.A. & Wright, C.S. , I960, Nature, 181, 141 Duncan, R.A., 1961, J. Geophys. Res., 66, 2087 Jacobs, J.A., & Westphal, K. O. , Phys. and Chem. of Earth. Vol. 5 (in press) Jacobs, J.A., & Sinno, K. 1960a, J. Geophys. Res., 65, 107 Jacobs, J.A., & Sinno, K. , 1960b, Geophys. J. , Roy. Astro. S o c , 3, 333 Korobkova, G. , Nikitina, N. , Zubareva, E. & Troitskaya, V. A., 1959, I. A.G. A. Symposium on Rapid Geomagnetic Variations, Utrecht Maple, E. , 1959, J. Geophys. Res., 65, 1395 Obayashi, T. , & Jacobs, J.A., 1958, Geophys. J. , Roy. Astro. Soc. , 1, 53 Sucksdorff, E., 1939, T e r r . Mag., 44, 157 Troitskaya, V.A., 1957, Ann. I. G. Y. , 4, 322 Troitskaya, V.A., 1959a, I. A.G. A. Symposium on Rapid Geomagnetic Variations, Utrecht Troitskaya, V.A., 1959b, I. A.G. A. Symposium on Rapid Geomagnetic Variations, Utrecht - 32 -Troitskaya, V. A, , 1961, J. Geophys. Res., 66, 5 Yanagihara, K., 1959, J. Geomag. Geoelec, 10, 172 i 

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