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An analysis of short period (10-30 seconds) geomagnetic micropulsations Hassett, John Henry 1960

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AN'-ANALYSIS OF SHORT PERIOD (10 - 30 SECONDS) GEOMAGNETIC MICROPULSATIONS by JOHN HENRY HASSETT B.A., University of B r i t i s h Columbia, 1950 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE In the Department of PHYSICS We accept th i s thesis as conforming to the reauired standard THE UNIVERSITY OF BRITISH COLUMBIA APRIL, I960 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n 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 agree t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by t h e Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f FHVSIC5 The U n i v e r s i t y o f B r i t i s h Columbia, Vancouver #, Canada. Date 13 APR (>D  - i -ABSTRACT Geomagnetic micropulsations are described and possible o r i g i n s discussed. Previous work in Canada i s reviewed with p a r t i c u l a r attention to the normal daytime Pc o s c i l l a t i o n s with periods from 10 - 30 seconds. A description i s given of the work done correlating the amplitude and d i r e c t i o n of the exciting vector at two stations. F i e l d work at Ralston, Alberta during July -August 1959 i s described i n d e t a i l . A d i g i t a l computer i s used to obtain the auto-correlation c o e f f i c i e n t and the covariance of the horizontal components of the vector. From these two paramenters the dominant frequency, amplitude, and p o l o r i z a t i o n of the vector are obtained. The conclusion i s reached that normal daytime Pc's seem to occur i n a small band centred around a dominant frequency. Two such dominant frequencies may occur simultaneously and the vectors can have d i f f e r e n t p o l a r i z a t i o n . The amplitude and d i r e c t i o n of a given Pc seems to follow a closed diurnal pattern reaching a maximum s l i g h t l y before l o c a l noon. - i i -TABLE OF CONTENTS Abstract i Table of Contents i i Acknowledgements i i i Chapter I I n t r o d u c t i o n 1 (a) Morphology of Geomagnetic M i c r o p u l s a t i o n s .. 1 (b) O r i g i n of M i c r o p u l s a t i o n s 3 I I Previous I n v e s t i g a t i o n s i n Canada 6 (a) Defence Research Board 6 (b) Subsequent I n v e s t i g a t i o n s by P.N.L 12 (c) U n i v e r s i t y of B r i t i s h Columbia 13 I I I F i e l d Work, Ralston A l b e r t a , I J u l y - 15 August 1959 14 (a) Equipment 14 (b) S t a t i o n Locations 16 (c) F i e l d Work H i s t o r y 17 IV E v a l u a t i o n of Data 20 (a) Choice of Records For A n a l y s i s 20 (b) S t a t i s t i c a l A n a l y s i s of Data 21 V Re s u l t s 24 (a) Dominant Frequencies 24 (b) D i r e c t i o n and Amplitude of the H o r i z o n t a l Vector 25 VI Conclusions 27 B i b l i o g r a p h y 29 DIAGRAMS Figure Facing Page (1) Examples of Micropulsations . 2 (2) (a) Block Diagram Station o< (b) Block Diagram Station p 15 15 (3) Auto-Correlation Function 31 24 (4) Auto-Correlation Function 9 24 (5) Auto-Correlation Function Showing Two 24 (6) 25 (7) Relative Amplitudes 31 July, 7 August, 26 (8) Polqr Plot 31 July, 7 August, , 10 August . 26 ACKNOWLEDGMENTS The author wishes to thank the s t a f f of the P a c i f i c Naval Laboratory for permitting him to take part in the f i e l d work and for t h e i r prompt transmission of the recorded data whenever possible. Thanks are extended to the' s t a f f of the Univers i t y of B r i t i s h Columbia Computing Center and in p a r t i c u l a r to Mr. R. Debell for his assistance in programming the data. Dr. J.A. Jacobs i s thanked for suggesting the investigation, and for his constructive help i n evaluating the data. F i n a n c i a l support from the National Research Council of Canada i s also g r a t e f u l l y acknowledged. CHAPTER I INTRODUCTION -Morphology o f Geomagnetic M i c r d p u l s a t i o n s .. Geomagnetic m i c r o p u l s a t i o n s a r e s m a l l s c a l e p e r i o d i c changes i n the e a r t h ' s magnetic f i e l d . The a m p l i t u d e s o f th e s e f l u c t u a t i o n s have an o r d e r o f magnitude o f C l ^ t o , on o c c a s i o n , as much as 20 or 3 0 ^ ( 1 ^ - 1 gamma - 10 *~ o e r s t e d ) . They o c c u r throughout a f r e q u e n c y range o f from about .001 cps up to about s e v e r a l c p s . Such m i c r o p u l s a t i o n s have been known s i n c e l 8 6 l and some o b s e r v a t i o n a l s t u d i e s were made d u r i n g the f i r s t h a l f o f t h i s c e n t u r y , a l t h o u g h most e x p e r i m e n t a l and t h e o r e t i c a l work has been c a r r i e d out d u r i n g the past t e n y e a r s . M i c r o p u l s a t i o n s have been b r o a d l y c l a s s i f i e d i n t o t h r e e groups but r e c e n t d a t a o b t a i n e d d u r i n g the I.GkY. (Ja c o b s I960) i n d i c a t e t h a t t h e s e c l a s s i f i c a t i o n s a r e too g e n e r a l and f u r t h e r s u b - c l a s s i f i c a t i o n s p o s s i b l y u s i n g d i f f e r e n t c r i t e r i a t h a n i n the p a s t , may be n e c e s s a r y . These t h r e e t y p e s o f m i c r o p u l s a t i o n s a re Pc's ( p u l s a t i o n s c o n t i n u e ! ) , P t ' s ( t r a i n s de p u l s a t i o n s ) , and P g 1 s ( g i a n t p u l s a t i o n s ) . In a d d i t i o n to any observed s i g n a l t h e r e i s always a g e n e r a l background made up, p a r t l y o f i n s t r u m e n t a l n o i s e , p a r t l y o f induced power f r e q u e n c y sub-harmonics, and p a r t l y o f v e r y low a m p l i t u d e P c ' s . When d i s c u s s i n g a p a r t i c u l a r f r e q u e n c y e s p e c i a l l y towards the higher end o f t h e f r e q u e n c y spectrum i t i s w e l l t o remember t h a t a s i g n a l i s not u s u a l l y made up o f the one FIG. I TYPICAL SIGNAL BASE STATION RALSTON, ALTA 0024Z II AUG, 59 oo 332 Xcc Yet X SHOWING MODULATION FROM LONGER PERIOD SIGNAL 0I56Z II AUG, 59 02 07Z MATV4 INITIATION OF PC AFTER QUIET PERIOD X^ 05 HZ Pt SHOWING DAMPING - 2 -d i s c r e t e frequency but of a small band centred around t h i s dominant frequency, Pc's as t h e i r name suggests are continuous wave t r a i n s w i t h amplitudes a few tenths of a / and periods from about ten seconds to under a minute. They occur most f r e q u e n t l y during d a y l i g h t hours p a r t i c u l a r l y during the l a t e morning and a s e r i e s of Pc's may cover a time period l a s t i n g s e v e r a l hours. (See f i g u r e 1) Pt's u s u a l l y occur as a s e r i e s of o s c i l l a t i o n s and appear to be w e l l damped wi t h l a r g e r amplitudes and longer periods than Pc's. They appear i n groups at night with a t o t a l d u r a t i o n of from ten minutes to l e s s than an hour. Amplitudes are around one h a l f gamma and periods of the order f o r t y seconds to s e v e r a l minutes. (See f i g u r e 1 ) . Pg's are s e r i e s of regular p u l s a t i o n s w i t h l a r g e amplitudes up to tens of gammas and periods of a few minutes o c c u r r i n g only i n the a u r o r a l zones. The p u l s a t i o n s described cover the frequency spectrum up to 0 . 1 cps. From 0 . 1 to 10 cps the observed p u l s a t i o n s are i n general very weak although there are c h a r a c t e r i s t i c t r a i n s of o s c i l l a t i o n s , which 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). S t i l l higher frequencies are caused f o r the most part by l i g h t n i n g discharges (Goldberg 1956) or a r i s e from man-made background of electromagnetic r a d i a t i o n . Despite the large amount of recent work on - 3 -micropulsations i t i s d i f f i c u l t to draw more than very general conclusions about such p r o p e r t i e s as frequency of occurrence, d i u r n a l and seasonal v a r i a t i o n , l a t i t u d e dependance, and whether the incidence of a given p u l s a t i o n Is l o c a l or widespread. Often the experimental data reported by d i f f e r e n t observers i s c o n t r a d i c t o r y or seems to f i t no reg u l a r p a t t e r n . Among the p o s s i b l e reasons f o r t h i s i s the use of instruments with d i f f e r e n t s e n s i t i v i t i e s , and recording f o r periods of too short a d u r a t i o n . Another d i f f i c u l t y i s the choice of method f o r a n a l y s i s of data and choice of c r i t e r i a f o r d i f f e r e n t i a t i n g between the d i f f e r e n t types of m i c r o p u l s a t i o n s . In t h i s respect i t now appears l i k e l y that Pg's can be div i d e d i n t o two groups depending on the wave form and time of maximum frequency of occurrence. Also a group of Russian i n v e s t i g a t o r s (Jacobs i 9 6 0 ) suggest the d i v i s i o n of Pc's i n t o three groups w i t h periods i n the range from 5 - 1 5 seconds, 20 - 40 seconds, and 50 - 90 seconds. O r i g i n of M i c r o p u l s a t i o n s There i s l i t t l e doubt that the source of the disturbance which causes mic r o p u l s a t i o n s i s e i t h e r i n the earth's ionosphere, i n the outer atmosphere extending out to s e v e r a l earth r a d i i , or i n both depending on the type of p u l s a t i o n . I t i s also g e n e r a l l y accepted that these v a r i a t i o n s are due to a f l u x of s o l a r p a r t i c l e s , probably i o n i z e d hydrogen, which are i n c i d e n t upon the earth's atmosphere e i t h e r i n the form of an io n i z e d cloud or as a steady j e t whose i n t e n s i t y and v e l o c i t y depend on the s t a t e of the sun's corona. Anart from these rather general ideas, there are s e v e r a l c o n f l i c t i n g t h e o r i e s d e a l i n g w i t h the exact cause of the micropulsations themselves. Bennett and Hulburt (1954) have suggested that these streams of protons from the sun undergo magnetic s e l f -f o c using and s p i r a l i n towards the earth along the magnetic l i n e s of force causing the aurora when stopped by c o l l i s i o n s w i t h the heavier gas molecules. M i c r o p u l s a t i o n s might be caused by i o n i z e d p a r t i c l e s f o l l o w i n g o r b i t s i n the earths magnetic f i e l d . I f an i o n i z e d cloud of s o l a r o r i g i n enters the earths upper atmosphere then i t i s p o s s i b l e that hydromagnetic o s c i l l a t i o n s would be ex c i t e d and A l f v e n waves propogated along the magnetic l i n e s of for c e causing m i c r o p u l s a t i o n s w i t h periods comparable to those of Pt - type o s c i l l a t i o n s . C a l c u l a t i o n s based on observed data and assuming that the mic r o p u l s a t i o n s are caused by A l f v e n waves (Obayaski and Jacobs 1958) gives ion d e n s i t i e s f o r the outer atmosphere comparable wi t h f i g u r e s obtained from other sources. Giant p u l s a t i o n s may be caused by t o r s i o n a l o s c i l l a t i o n s i n the outer atmosphere (Kato and Akasofu 1956? Kato and Watanabe 1957) and Pc's by r>oloidal o s c i l l a t i o n s . Pc's would then be i n i t i a t e d i n the s u n l i t part of the - 5 -i o n o s p h e r e by t u r b u l e n t s h o c k waves f r o m t h e sun's c o r o n a . T h e r e i s however some e x p e r i m e n t a l d a t a ( D u f f u s and Shand 1958) w h i c h shows t h a t P c ' s and P t ' s a r e o f t e n n o t c o n t i n e n t - w i d e i n o c c u r r e n c e , and e v e n when w i d e s p r e a d a r e o f t e n o u t o f p h a s e . T h i s would n o t seem t o f a v o u r t h e p o l o i d a l o s c i l l a t i o n t h e o r y o f t h e J a p a n e s e i n v e s t i g a t o r s . CHAPTER I I PREVIOUS INVESTIGATIONS IN CANADA  Defence Research Board A group from the P a c i f i c Naval Laboratory (P.N.L.) at Esquimalt B.C. have been recording Pc's and P t 1 s since 1954. Most of t h e i r experimental work has been c a r r i e d on at A l b e r t Head, a s t a t i o n on the coast near V i c t o r i a , although data has also been recorded by a mobile s t a t i o n at v arious i n l a n d l o c a t i o n s . Whenever the mobile s t a t i o n was operated, the base s t a t i o n at A l b e r t Head recorded as w e l l f o r comparison. Measurements were made of the three components X, Y, and Z where X (geographical n o r t h ) , and Y (east) are the components of the h o r i z o n t a l f i e l d H and Z i s the v e r t i c a l component ( p o s i t i v e downwards). Duffus and Shand (1958) obtained m i c r o p u l s a t i o n records at A l b e r t Head i n the frequency range .001 to .1 cps on 150 days between 1954 and 1957. The magnitude and d i r e c t i o n of the mic r o p u l s a t i o n s were noted and i n t e r -p r e t a t i o n s made of the d i u r n a l v a r i a t i o n , the d i r e c t i o n of the e x c i t i n g v e e t o r j and i t s geographical d i s t r i b u t i o n . The r e s u l t s were compared w i t h data published by other i n v e s t i g a t o r s i n d i f f e r e n t p a r ts of the world (Chernosky et a l 1954,Haimberg 1953, T r o i t s k a y a 1955). Duffus and Shand found a trend f o r i n c r e a s i n g amplitude w i t h i n c r e a s i n g period and found that the p r o b a b i l i t y of occurrence depended both on frequency (and hence also on amplitude) and on L.M.T. The d i u r n a l variations showed only general trends and often the results conflicted with those from other investigators. This i s p a r t l y due to i n s u f f i c i e n t data but also, to a large extent, to d i f f e r e n t detection and amplification equipment. Often equipment w i l l tend to discriminate against certain frequencies i n favour of others or have d i r e c t i o n a l char-act e r i s t i c s thus giving incomplete r e s u l t s . There Is also the problem of Interpreting data obtained i n d i f f e r e n t geographical locations p a r t i c u l a r l y i n d i f f e r e n t l a t i t u d e s . Despite these d i f f i c u l t i e s a general peak in the Pc a c t i v i t y was found s l i g h t l y before l o c a l noon and a peak i n Pt a c t i v i t y before l o c a l midnight. The quietest time was from 1800 to 2200 L.M.T. Most of the pulsations had phase differences between two or a l l three of the components. The general trend was for X and Z to be i n phase while Y led or lagged. This was not i n accord with e a r l i e r work in Janan (Terada 1917) where the horizontal components were i n phase and Z lagged. The data for signals which were i n phase gave a rather wide scatter for the d i r e c t i o n of the vector as a function of frequency. There was s l i g h t l y less scatter i n both the azimuth and the i n c l i n a t i o n for the very low frequency end of the spectrum. It was noticeable that the greater the azimuth the greater was the angle of i n c l i n a t i o n . Inclinations ranged from 10° to 70° and azimuths from 260° to 20° true. L i t t l e c o r r e l a t i o n was found between the v e r t i c a l - 8 -components at A l b e r t Head and H a l i f a x Nova S c o t i a where some data had been recorded with i d e n t i c a l equipment. The s i g n a l s were u s u a l l y d i f f e r e n t i n frequency and phase. When s i m i l a r p u l s a t i o n s did occur they seemed to be e i t h e r e x a c t l y i n phase or 180°out of phase with some evidence of a d i u r n a l v a r i a t i o n . This c o n f l i c t s w i t h some observations i n d i c a t i n g that i n i t i a t i o n i s world-wide ( T r o i t s k a y a 1955). Because of the o f t e n c o n t r a d i c t o r y data from records at widely separated s t a t i o n s the group at P.N.L. sub-sequently decided to i n v e s t i g a t e short range geographical v a r i a t i o n s i n m i c r o p u l s a t i o n s . Simultaneous records were made at two s t a t i o n s , the base s t a t i o n at A l b e r t Head and the mobile f i e l d s t a t i o n which occupied various l o c a t i o n s between May 1958 and February 1959. Observations were i n i t i a l l y r e s t r i c t e d to the frequency band between 0.001 and 0.1 cps which was l a t e r extended to include frequencies up to 1 cps. Measurements were made of the three components X, Y, and Z, and a n a l y s i s was by v i s u a l i n s p e c t i o n of the amplitudes and periods on s t r i p - c h a r t r e c o r d i n g s . No attempt was made to determine phase r e l a t i o n s h i p s . There was a s e l e c t i v e choice of data f o r a n a l y s i s and s i g n a l s w i t h phase d i f f e r e n c e s between components of IT/A or more were not processed. The f i r s t f i e l d s t a t i o n was at Bear Creek some 25 miles from A l b e r t Head and twelve miles from the sea. - 9 -Duffus et a l (1959) found that f o r periods under two minutes the X component at Bear Creek was as much as 50 per cent l a r g e r than X at A l b e r t Head while the Y and i n p a r t i c u l a r the Z component at Bear Creek became smaller w i t h i n c r e a s i n g frequency. I f the amplitudes of the three components are summed v e c t o r i a l l y the " t o t a l p u l s a t i n g v e c t o r " i s obtained. The amplitude of the t o t a l p u l s a t i n g vector at Bear Creek was l e s s than that at A l b e r t Head f o r periods under 50 seconds but greater f o r periods over 100 seconds. Thus the vector at the s t a t i o n by the sea had a much greater i n c l i n a t i o n and i t s azimuth was more w e s t e r l y than that at the in l a n d s t a t i o n . Also w i t h i n c r e a s i n g frequency the amplitude by the sea became greater than the amplitude i n l a n d . I t seems probable that these e f f e c t s are due to the higher e l e c t r i c a l c o n d u c t i v i t y of the sea. The second f i e l d s t a t i o n was set up at Summerland B.C. 250 miles from A l b e r t Head and 185 miles from the sea. Records from Summerland d i f f e r e d from those at A l b e r t Head much more than those at Bear Creek (Shand et a l 1959). There were s t i l l however many s i m i l a r i t i e s and corresponding s e c t i o n s of the records could be compared. The X and Y components at Summerland were s i m i l a r to those at A l b e r t Head except that amplitudes at Summerland averaged 50 per cent higher. The Z component at Summerland was very d i f f e r e n t i n appearance and had a much smaller amplitude. At Summerland the i n c l i n a t i o n was much l e s s - 10 -and the azimuth s l i g h t l y more n o r t h e r l y than at A l b e r t Head. The amplitude f o r the t o t a l vector was about the same at each s t a t i o n . A t h i r d f i e l d s t a t i o n was e s t a b l i s h e d at R a l s t o n , A l b e r t a 515 miles from A l b e r t Head and 470 miles from the sea. The number of record s e c t i o n s which could be compared was r e l a t i v e l y few although the onset and disappearance of bursts of a c t i v i t y appeared simultaneously and the envelopes of a s e r i e s of p u l s a t i o n s were s i m i l a r at the two s t a t i o n s . The X components were s i m i l a r i n appearance w i t h the amplitude at Ra l s t o n u s u a l l y about double that at A b l e r t Head. The Y components were only seldom s i m i l a r although again the s i g n a l a t R a l s t o n was u s u a l l y double that at A l b e r t Head. The Zcomponents were d i s s i m i l a r w i t h a much lower amplitude at R a l s t o n , p a r t i c u l a r i l y at the higher f r e q u e n c i e s . The azimuth was a l i t t l e more n o r t h e r l y at Ra l s t o n than at A l b e r t Head and the i n c l i n a t i o n much l e s s -- even l e s s than that at Summer land. The mean amplitude of the t o t a l vector at Ra l s t o n was 50 per cent greater than at A l b e r t Head. When t r a i n s of Pc a c t i v i t y were compared between Ra l s t o n and A l b e r t Head they almost always occurred simultaneously d e s p i t e a d i f f e r e n c e i n longitude of 13° . There was also no i n d i c a t i o n of any d i u r n a l v a r i a t i o n i n the amplitude of the t o t a l vector at Ra l s t o n as compared to A l b e r t Head. - 11 -The f o u r t h and l a s t f i e l d s t a t i o n i n t h i s s e r i e s was e s t a b l i s h e d at Borrego Springs, C a l i f o r n i a , 960 miles from A l b e r t Head and o n l y 70 miles from the sea. The s i g n a l at Borrego, the lower l a t i t u d e s t a t i o n , was simpler i n form to that at A l b e r t Head and the X and Y components showed fewer phase d i f f e r e n c e s . I n d i v i d u a l p u l s a t i o n s at the two s t a t i o n s were seldom s i m i l a r but again the envelopes of s e r i e s of p u l s a t i o n s were very s i m i l a r . The amplitudes of the X and Y components at Borrego averaged 3/4 those at A l b e r t Head. The Z component at Borrego was much smaller than that at A l b e r t Head. There were l a r g e and frequent changes i n azimuth at Borrego -the p r e ferred d i r e c t i o n of the t o t a l vector was northeast w i t h a s l i g h t i n c l i n a t i o n . Summarizing the data from the four f i e l d s t a t i o n s and the base s t a t i o n at A l b e r t Head, i t seems f e a s i b l e to d i v i d e the s i g n a l i n t o three bands wi t h periods i n the ranges I - 8, 10 - 30, and above 40 seconds. The lower l i m i t of 1 second i s an instru m e n t a l l i m i t a t i o n . The group above 40 seconds would in c l u d e P t ' s . The group from 10 - 30 seconds occurred most r e g u l a r i l y and included Pc's recognized as the normal daytime s i g n a l . Almost without exception t h i s group occurred simultaneously at both the f i e l d s t a t i o n and at A l b e r t Head. The t o t a l vector f o r t h i s middle group of Pc's maintained a preference f o r d i r e c t i o n , time of day, and amplitude at the f i e l d s t a t i o n d i f f e r e n t to that at A l b e r t Head. - 12 -T o t a l Pc a c t i v i t y does not appear to be r e l a t e d s o l e l y to L.M.T., despite the preference f o r daytime of the 10 - 30 second group. The s t a t i o n at R a l s t o n which was c l o s e s t to the a u r o r a l zone and f u r t h e s t i n l a n d , and si t u a t e d i n the most uniform topography had the smallest Z component and the l a r g e s t amplitude of the t o t a l v e c t o r . The s t a t i o n at Borrego f u r t h e s t from the a u r o r a l zone had the smallest amplitude f o r the t o t a l vector and was the only s t a t i o n w i t h a n o t i c e a b l y d i f f e r e n t azimuth. The s t a t i o n at A l b e r t Head by the sea and al s o i n non-uniform topography had the l a r g e s t Z component. Subsequent I n v e s t i g a t i o n s by P.N.L. Continuation of the research i n t o short range geographical v a r i a t i o n s of the character of micr o p u l s a t i o n s has been c a r r i e d out by P.N.L. I t was suspected that earth currents (Cagniard i 9 6 0 ) accompanying Pc's and Pt's might a f f e c t the amplitude, d i r e c t i o n , and even phase of the magnetic v e c t o r . This would be p a r t i c u l a r i l y t r u e ' f o r a s t a t i o n by the sea or i n mountainous t e r r a i n and i't was decided to c o r r e l a t e data from two s t a t i o n s over a m a g n e t i c a l l y homogeneous area. The s i t e chosen was near Ralston i n eastern A l b e r t a . This t h e s i s Is mainly concerned w i t h the a n a l y s i s of some of the data obtained on t h i s i n v e s t i g a t i o n . Records were made of the three components X, Y, and Z over the frequency range . 0 1 to 30 cps. A permanent base s t a t i o n was e s t a b l i s h e d and a mobile f i e l d s t a t i o n i n a truck set up at g r a d u a l l y i n c r e a s i n g d i s t a n c e s . Both s t a t i o n s operated simultaneously w i t h the s i g n a l from the f i e l d s t a t i o n multiplexed over telephone l i n e using s e v e r a l c a r r i e r frequencies and recorded beside that from the base s t a t i o n . Simultaneous records were also made of v a r i a t i o n s i n the magnetic f i e l d and i n the associated earth c u r r e n t s . U n i v e r s i t y of B r i t i s h Columbia A n a l y s i s of data obtained during the I.G.Y. by s t a t i o n s throughout the world has been c a r r i e d out during the past year. R e s u l t s to date (Jacobs and Sinno i960) i n d i c a t e that the frequency of occurrence of Pc's increases w i t h l a t i t u d e as the a u r o r a l zones are approached. A d e f i n i t e s o l a r time dependance f o r the frequency of occurrence was found w i t h the maximum changing from e a r l y afternoon to l a t e morning w i t h i n c r e a s i n g l a t i t u d e . Observations at the same geomagnetic l a t i t u d e showed both a l o c a l and a u n i v e r s a l time dependance. The time of maximum occurrence of Pc's was about 21 hours G.M.T. i n the northern hemisphere. The u n i v e r s a l time f a c t o r was found to a f f e c t the modulation of.the d i u r n a l occurrency by about 50 per cent. CHAPTER I I I FIELD WORK, RALSTON ALBERTA, 1 JULY - 15 AUGUST 1959  Equipment The detectors f o r the X and Y components of the magnetic f i e l d were mumetal cored solenoids 5' i n length and 5" i n diameter. These solenoids had 35>000 turns of copper wire and a d.c, r e s i s t a n c e of 250 ohms. The detector f o r the Z component was a 20 ' diameter a i r cored shielded c o i l . This c o i l had 1100 turns of No.21 "Formel" covered copper w i r e . For higher frequencies of 1/3 - 1/30 cps the detectors f o r a l l three components were anhyster cored c o i l s using "Kronhite" f i l t e r s . A l l -detectors were l e v e l l e d and l i g h t l y buried when i n use wi t h the h o r i z o n t a l component detectors aligned geographic-a l l y north-south and east-west. The s i g n a l s from the det e c t o r s were fed to a j u n c t i o n box by buried cable and from there by shielded cable to d.c. chopper a m p l i f i e r s . The a m p l i f i e r outputs drove Esterline-Angus s t r i p - c h a r t pen recorders at a speed of 3/4" per minute. When desired the output from the a m p l i f i e r s could also be fed i n p a r a l l e l i n t o a 6 channel Brush s t r i p - c h a r t recorder and i n t o a 7 channel Ampex F.R.1100 F.M. tape recorder. A m p l i f i c a t i o n could be vari e d although i t was always necessary to give the Z component four times the a m p l i f i c a t i o n given to the h o r i z o n t a l components. Detect o r s , a m p l i f i e r s , and recorders were d u p l i c a t e d at the mobile s t a t i o n except the 6 channel Brush and 7 FIGURE 2 (b) BLOCK DIAGRAM STATION jB RALSTON, ALBERTA 27 JULY 59 D.C. CHOPPER AMPLIFIERS TRI FILTER COILf^M) X. C O I L j ^ ) Y. C0IL(20')Z_ 120 c/s FILTER TELEPHONE Y-STN.<* BRIDGE AMPLIFIER (INPUT 3 MIXER 2.Oh kc F.M. TELEPHONE BRIDGE X ,Z-STN.o4-^AMPLIFIEFf BIXER ILTER 1.0 kc F.M. 6.25 kc F.M. FIGURE 2 (a) BLOCK DIAGRAM STATION RALSTON, ALBERTA 27 JULY 5 9 c o i i | > g x Coilf/W) Y D.C. CHOPPER <M> C o i l ( 2 0 ' ) Z _ I A M P L I F I E R S [= E s t e r l l n e - A n g u s R e c o r d i n g Meters TRI FILTER 1 1 2 0 c/s F i l t e r 6 Channel Brush R e c o r d e r 7 Channel Tape E l e c t r i c ^hrdnometer F.M. Reproduce A m p l i f i e r Telephone Yjs A t t e n u a t o r F 0 M a S e p e r a t o F i l t e r Telephone Xj> , Z J _ A t t e n u a t o r F..M. S e p e r a t F i l t e r 3F-channel tape recorder. In a d d i t i o n the mobile s t a t i o n had f i l t e r i n g , a m p l i f y i n g , and frequency modulating equipment fo r m u l t i p l e x i n g the s i g n a l over two telephone l i n e s to the base s t a t i o n where i t was demodulated and fed to the Brush recorder and tape recorder. (See f i g u r e 2 ) . The d e t e c t o r s f o r earth currents were copper rods d r i v e n i n t o moist ground and connected by t h i n copper leads. One rod was d r i v e n i n at the s t a t i o n , another 500* to the south, and the t h i r d 5 0 0 ' to the east and changes i n p o t e n t i a l measured. The s i g n a l s were u s u a l l y measured on a Texas Instruments recorder and o c c a s i o n a l l y on the 6 channel Brush. For d a i l y c a l i b r a t i o n each mumetal detector ( h o r i z o n t a l ) components) had a s i n g l e c o i l around i t and the 2 0 ' v e r t i c a l component det e c t o r s had a 200 t u r n c o i l placed c e n t r a l l y w i t h i n . An a.c. current of . 8 1 m.a. at . 0 6 7 cps could be passed i n s e r i e s through the complete detector system i n c l u d i n g that at the mobile s t a t i o n . Such a current would induce a s i g n a l w i t h a peak to peak amplitude corresponding to a f i e l d change of 1Y at the h o r i z o n t a l component dete c t o r s and of 1/4 Y at the v e r t i c a l component d e t e c t o r s . Major c a l i b r a t i o n of the detectors was c a r r i e d out by p l a c i n g one of the 2 0 ' v e r t i c a l component detectors around the centre of a c i r c l e formed by an outer c a l i -b r a t i o n c o i l of 1 2 0 ' diameter. An inner one foot diameter c a l i b r a t e d search c o i l was placed at the centre of the c i r c l e . The current through the outer c a l i b r a t i o n c o i l - 16 -which induced a s i g n a l corresponding to a known f i e l d change at the inner c a l i b r a t i o n c o i l was recorded as was the amplitude of the s i g n a l on the 20' v e r t i c a l component d e t e c t o r . C a l i b r a t i o n of the h o r i z o n t a l component detectors was done by burying them v e r t i c a l l y at the centre of the c i r c l e and no t i n g the amplitude of the s i g n a l induced by passing the recorded current through the outer c a l i b r a t i o n c o i l . S t a t i o n Locations The base s t a t i o n was at s i t e cx:(50° l 6 . 5 * N , l l f 08 'W) and the mobile s t a t i o n moved i n turn to three s i t e s at £ ( 5 0 ° 1 8 . 5'N, l l f 08 'W), y(50°22'K, l l f 08.5'W)., and £(50°30 .5 ' N , 110°46 'W). S t a t i o n £ was 2 miles n o r t h , s t a t i o n V 5ir miles n o r t h , and s t a t i o n £ 25 miles n o r t h -east of the base s t a t i o n at <* . The geology of the area was uniform w i t h l i t t l e topographic r e l i e f . Sediments of uniform t h i c k n e s s l i e above the g e n t l y s l o p i n g pre-cambrian basement at a depth of 6000 f e e t . The base s t a t i o n at ©< was 2 miles from R a l s t o n and 1 mile from a t r a v e l l e d road. The-site was l e v e l w i t h a--~ po-wer l i n e running east-west 400 .yards to the north, where i t was joined by the l i n e supplying the s t a t i o n power. S i t e s f o r the mobile s t a t i o n were w e l l c l e a r of any i n t e r -ference except that s i t e p was only 100-yards from a t r a v e l l e d road. Power f o r the mobile s t a t i o n was supplied by a gas engine d r i v e n 60 c y c l e generator operated 50 - 17 -yards from the s t a t i o n and i n the opposite d i r e c t i o n to the d e t e c t o r s . Detectors at both the base and mobile s t a t i o n s were on l e v e l ground at a d i s t a n c e of about 100 yards. F i e l d Work H i s t o r y During the f i r s t two weeks of J u l y , the base s t a t i o n was set up at s i t e ©< , and major c a l i b r a t i o n of equipment c a r r i e d out. Another ten days were required to set up the mobile s t a t i o n at s i t e p , connect i t by telephone. l i n e to the base at s i t e o < , and to adjust the- a m p l i f y i n g and re c o r d i n g equipment. By the end of J u l y records were being taken at both s t a t i o n s and were al s o being multiplexed over telephone wire from s t a t i o n £ to s t a t i o n ©< where the three components from each s t a t i o n were recorded simultan-eously on magnetic tape and on the 6 channel Brush. One of the main problems was c o r r e c t timing of the records both f o r absolute time and f o r comparison of the s i g n a l s between two s t a t i o n s . For the main s t a t i o n at site<=>< the frequency r e g u l a t i o n of the l o c a l power system was deemed adequate i f o c c a s s i o n a l l y checked by radio s i g n a l s and a chronometer. The chronometer was wired to place a time s i g n a l on the 7 channel magnetic tape. For the mobile s t a t i o n frequent time s i g n a l s were obtained by r a d i o and the s t r i p - c h a r t records marked. A chronometer was used during periods of r a d i o blackout. When required the speed of the engine d r i v i n g the f i e l d generator could be v a r i e d . Despite a l l e f f o r t s there was a p o s s i b l e e r r o r - 18 -of several seconds between i n d i v i d u a l records of the base and mobile stations. Of course t h i s r e l a t i v e time _error did not apply for signals multiplexed over the telephone wire. Another d i f f i c u l t y was that s p e c i a l pre-amplifiers had to be used for recording signals around 1 - 3 cps. For s t i l l higher frequencies of 3 - 30 cps the anhyster rod detectors were required. This meant that when frequencies above 1 cps were recorded the broad band from . 0 0 1 - 1 cps was not received. Also there were frequent errors caused by the reversal of terminals as the components at one station could be given a 180° phase s h i f t r e l a t i v e either to each other or to the other station. There were even times when the sign a l from a eiven detector was fed to the wrong strip-chart record and then i n c o r r e c t l y l a b e l l e d . To minimize t h i s type of error a c o i l and battery could be placed beside each detector i n turn and a positive signal induced. Observation of the i n d i v i d u a l strip-chart records would not only confirm which component was being measured but would indicate whether the sign a l was i n phase or 180° out of phase r e l a t i v e to the other components. Another check was the c a l i b r a t i o n which was carried out d a i l y during the quiet period i n the early evening unless the signal was too large for such c a l i b r a t i o n to be fe a s i b l e . The c a l i b r a t i o n signal with a peak to peak amplitude corresponding to 1 Y for the horizontal components - 19 -and 1/4 Y for the Z component could then be measured on the i n d i v i d u a l records giving the scale constant for that component. Earth current records were made either at the base station or at the mobile station except on a few short occasions when they were recorded at both st a t i o n . There were a few simultaneous records made of earth currents from the base and mobile station on the 6 channel Brush but usually they were recorded on a Texas Instruments recorder. During the f i r s t week of August the mobile station was moved to s i t e / and records were again multiplexed over telephone l i n e to the base station. The station at s i t e ¥ was i n operation only a few days and on the 10 August the mobile station was moved to s i t e £ . Because of greater l i n e loss and what appeared to be lititercapacitance between the telephone l i n e s only one component could be transmitted at a time to the base s t a t i o n . This signal was very weak and showed signs of instrumental i n t e r -ference. CHAPTER IV EVALUATION OF DATA  Choice of Records For Analysis A l l data were kept at P.N.L. with the records for any given period available on a temporary loan basis. Therefore, i t was decided to work only on records from the 6 channel Brush where a l l three components at the base station at o< plus at times the components from the mobile station were recorded simultaneously. There were only comparatively short periods of more or less continuous operation on these records because of the frequent moves of the mobile st a t i o n . These operating periods were interrupted when higher frequencies or earth currents were recorded because of the d i f f e r e n t equipment used. Moreover large parts of the record were too disturbed for analysis due either to excessive magnetic a c t i v i t y such as occurred during the frequent thunderstorms or to i n s t r u -mental d i f f i c u l t i e s . With only limited data available the study was of necessity r e s t r i c t e d to the normal daytime Pc o s c i l l a t i o n s of 10 - 30 seconds period. The Z component was not used because of i t s n e g l i g i b l e amplitude. There were several hours of record on 31 July when the sign a l from s i t e jS showed almost complete c o r r e l a t i o n with that at the base station at©^. The envelope of the series of pulsations several times showed d i s t i n c t "pearls" indicating a possible beat frequency. There were several series of o s c i l l a t i o n s at s i t e Y on 7 August which could be - 21 -correlated with those at the base st a t i o n . The remaining signals studied are from the records on 10 August at the base station only. In figure I the top two records are the X and Y components respectively of a signal at base station °< on 10 August with the X component showing modulation from a longer period s i g n a l . The thi r d record shows the i n i t i a t i o n of a Pc at the base station and the bottom record i s of a longer period signal probably a Pt with signs of damping. S t a t i s t i c a l Analysis of Data The data selected on the strip-chart record from the 6 channel Brush showed f a i r to good v i s u a l c o r r e l a t i o n between components and between stations. There were either no obvious phase differences or one of 180° which could be explained as a reversal of terminals. A p l a s t i c template was centred over each component i n turn cover-ing the same time i n t e r v a l and the amplitude read every f i v e seconds for a t o t a l of 56 readings. No consideration was given to any phase difference since readings were only being taken approximately every quarter period and no correction was made for any constant value included due to placing of the template. The amplitudes of the nearest c a l i b r a t i o n signals were also read and the positive sense of the signal noted. A s t a t i s t i c a l analysis was made of each component by auto-correlation of i t s signal amplitudes to obtain - 22 -the dominant frequency and by ca l c u l a t i o n of the covariance to obtain the energy in that dominant f r e -quency. The auto-correlation c o e f f i c i e n t "r* " i s defined as: N-K N-K K =7= ZX-Xv* ~ J- Z X; £ Xi N-K 1=1 - = . — V N N-K \ / = / v / f Where the X i refer to r e l a t i v e amplitudes in any ar b i t r a r y units, N equals 56, and K has integer values from 1 - 9 representing phase displacements of 5 - 45 seconds. The covariance i s defined as the numerator of the above expression divided by N - K and multiplied by the appropiate c a l i b r a t i o n constant. The covariance corresponding to the maximum value of TK w i l l be pro-portional to the energy present for a dominant frequency with a period corresponding to thi s phase displacement. The amplitude of t h i s dominant frequency w i l l be pro-portional to the square root of the maximum value of the covariance. Calculations of the co r r e l a t i o n c o e f f i c i e n t s and of the covariance values were made by an Alwac III E d i g i t a l computer at the University of B r i t i s h Columbia - 23 -which required a punched tape data feed. An existing auto-correlation programme had to he modified for the purpose p a r t i c u l a r l y where scaling of the data was concerned. The programme required further modification to obtain the required covariance values. PHASE SHIFT IN SECONDS CHAPTER V RESULTS Dominant Frequencies The auto-correlation c o e f f i c i e n t r* was plotted as a function of phase displacement i n order to compare components and to obtain the dominant frequencies. (See figure 3 ) . Whenever the signals for two stations were compared a small band of Pc's seemed to centre around the same dominant frequency for both base and mobile stations. Except where d i f f e r e n t frequency signals occurred on the X and Y components the plots of the correlation c o e f f i c i e n t r* for the two components were very s i m i l a r . (See figure 4). Out of I? sets of data there were four occasions when the signal appearing on the Y component dif f e r e d i n p e r i o d i c i t y by at least two seconds and i n one case by as much as ten seconds from that on the X component. Where records had been obtained from both the base and mobile stations t h i s same difference i n p e r i o d i c i t y occurred at both stations, (See figure 5). The periods of the Pc's on 31 July we're-16 - 18 seconds except when a longer period of 19 - 20 seconds twice appeared on the Y component only. On 7 August the periods ranged from 16 - 21 seconds and on 10 August from 19 - 29 seconds except on one occasion when a shorter period of 17 seconds appeared on the Y component only. Maximum values of rk were between .4 and .9 with no apparent r e l a t i o n to frequency or amplitude of es. 6 RELATIVE ENERGY FOR SIGNALS COMMENCING 13 03 LM.T 31 JULY,59 - 25 -the s i g n a l . There seemed only a very general trend that the l a r g e r the amplitude of a s i g n a l the l a r g e r the maximum value of r* because of a smaller p r o p o r t i o n of noise or s i g n a l w i t h frequency outside the sm a l l band under c o n s i d e r a t i o n . U s u a l l y the Y component had a smaller amplitude and hence u s u a l l y a smaller value of r* . D i r e c t i o n and Amplitude of The H o r i z o n t a l Vector The r e l a t i v e values of the covariance as scaled by the computer programme were p l o t t e d as a f u n c t i o n of phase displacement, the curves reaching a maximum at the displacement corresponding to the dominant frequency. (See f i g u r e 6 ) . The amplitude of the vector i s then given by: Where^/x, x+k andJLfy, y + k are the values of the covariance at the dominant frequency f o r the r e s p e c t i v e h o r i z o n t a l components and: _ v5< /Maximum R e l a t i v e Amplitude of CovarianceJ Sx i s the combined s c a l i n g f a c t o r from c a l i b r a t i o n and s c a l i n g f o r the computer, N equals the number of readings ( 5 6 ) , and K i s the c l o s e s t integer value to the period d i v i d e d by f i v e . For the data with a d i f f e r e n t frequency s i g n a l appearing on the Y component, readings were taken at the average p e r i o d . The amplitude and d i r e c t i o n of 340' 350' FIG. 8 POLAR PLOT OF HORIZONTAL Pc VECTOR RALSTON ALBERTA 12 HR. L.M. T. STN." 31 JULY .30 P. 2 0 .10 P 3 2 STN. T 7 AUG. STN. B 31 JULY STN '«• 3/ JULY STN. « - 10 AUG. -t-0 6 0 0 0 8 0 0 (0 0 0 12 0 0 F/6. 7 L.M.T. (4 0 0 (6 0 0 » 0 0 2 0 0 0 - 26 -the resultant vector was then biased in favour of the stronger component. The azimuth of the vector was calculated from the expression: iVhere-G-is the true bearing of the vector and the addition of 270° i s required since the c a l i b r a t i o n and observed signals indicate the azimuth i s northwest. Amplitudes obtained were of the order of magnitude 0 . 2 / a n d seemed to follow a diurnal pattern reaching th e i r peak shortly before l o c a l noon. (See figure 7 ) . The amplitude of the vector at s i t e P averaged 3 0 per cent greater than that at the base station ato<. With only two case's for comparison the amplitude at s i t e ^ was only 2 0 per cent greater than that at the base sta t i o n although s i t e Y was twice the distance of s i t e jB . The polar plot of the horizontal vector indicates that the d i u r n a l pattern i s a closed figure with the maximum excursion taking place during daylight hours caused mostly by changes i n amplitudes (See figure 8 ) . The azimuths are northwesterly, those at s i t e P being more northerly,than those at the base station ato(. This arises because the greater amplitude at the mobile station i s due to a larger X component. The d i r e c t i o n of motion of the di u r n a l pattern i s anti-clockwise except on 1 0 August when the d i r e c t i o n i s reversed. y? y+K -\- 270 CHAPTER VI CONCLUSIONS The normal daytime Pc o s c i l l a t i o n s with period from 10 - 30 seconds seem to occur i n a small frequency band centred around one dominant frequency. The observed signal may be made up of two or more small bands of Pc's with some instrumental noise and possibly low amplitude Pc of a d i f f e r e n t dominant frequency. At times two such small bands of Pc's with d i f f e r e n t dominant frequencies and equivalent amplitudes may occur with widely separated azimuths. On such occasions the X component has one dominant frequency and the Y component another. Beats should occur when two Pc's of d i f f e r e n t frequency but equivalent amplitude are present i n the s i g n a l . Pearls indicating such beats occurred on several occassions on the record for the 31 July including two sets of data when there were d i f f e r e n t dominant frequencies on the X and Y components. These pearls could have been caused by two signals beating with a difference i n period of a few seconds. The horizontal vector seems to follow a closed diurnal pattern with the greatest excursions occurring during daylight hours. The maximum amplitude seems to be reached shortly before l o c a l noon. I n i t i a t i o n of a signal at two stations separated by a few miles i s simultaneous and the signals show a high c o r r e l a t i o n except for differences i n amplitude - 28 -and azimuth of the horizontal vector. The amplitude averaged 30 per cent greater for a station 2 miles north of the base station although i t seemed to be only 2G per cent greater for a station 5 h miles north of the base. There i s no obvious explanation for t h i s difference i n amplitude since any l a t i t u d e effect should- increase with distance and the uniform geology precludes any difference due to changes in the earth currents. The small effect on the t o t a l vector of the associated earth currents i s also evident i n the n e g l i g i b l e Z component. The s t a t i s t i c a l analysis of the data gave s a t i s -factory r e s u l t s . If amplitudes could be read e l e c t -r o n i c a l l y possibly by including the data on magnetic tape then greater accuracy would be obtained. This would permit more exact determination of the dominant frequency, and of the amplitude and azimuth of the vector. When Pc's of d i f f e r e n t frequency occur, i t should then be possible to resolve the signals into two vectors with d i f f e r e n t periods and possibly d i f f e r e n t azimuths. There i s a need for simultaneous records from two stations over a long time i n t e r v a l . Only after s u f f i c i e n t data i s obtained should the distance between the two stations be increased. - 29 -BIBLIOGRAPHY B e n n e t t , W.H. and H u l b u r t , E.O. 195U. P h y s . Rev. 95,315. C a g n i a r d , L. 1956. Handbuch d e r P h y s i c , V o l . ^ 7 , P.l+07-l+69 ( S p r i n g e r V e r l o g , B e r l i n ) . D u f f u s , H.J. and Shand, J.A. 1958. Can. J . P h y s . , 36,508. D u f f u s , H .J., Nasmyth, P.W. , Shand, J.A., and W r i g h t , C . S . 195'8. N a t u r e , 1.81, 1258. D u f f u s , H .J., Shand, J.A., W r i g h t , C.S., Nasmyth, P.W., and J a c o b s , J.A. 1959. J . Geophys. 6k, 581. "" G o l d b e r g , P.A. 1956. N a t u r e , 177, 1219. J a c o b s , J.A. i960. P h y s . and Chem. o f E a r t h s V o l . 5. ( i n p r e s s ) . J a c o b s , J.A. and S i n n o , K. I960. J . Geophys. R e s e a r c h 65, 107. K a t o , Y. and A k a s o f u , S. 1957. S c i . R e p t s . , Tohoku U n i v . , S e r . 5, Geophys. 7, No. 2. K a t o , Y. and Watanabe, T. 1957. S c i . R e p t s . , Tohoku U n i v . , S e r . 5, Geophys. 8, No. 2. O b a y a s h i , T. and J a c o b s , J.A.. 1^58. G e o r h y s . J . , R c y . A s t r o . Soc-.-.,T1, <H. Shand, J.A., W r i g h t ^ ?C.S. 'j a n d : D u f f u s , -H.J. 1959. P a c i f i c N a v a l - L a b . , D.R .B j y Rep t -15. T e r a d a , J . 1917. C o l l e g e S c i . , T o k y o , 37, No. o. T r o i t s k a y a , V.A. D e f e n c e R e s e a r c h 1 B o a r d (Canada) T r a n s l a t i o n W + R , T r o i t s k a y a , . , V . A . 1957. A b s t r a c t s o f t h e R e p o r t s a t t h e XI G e n e r a l A s s e m b l y o f t h e : I . U . G . G . , p. 20. 

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