Report on the U.S. Program for the International Geophysical Year: July 1, 1957 - December 31, 1958 (1965)

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V I IONOSPHERIC PHYSICS PROGRAM The Model C-4 Ionospheric Recorder used during the IGY

IONOSPHERIC PHYSICS PROGRAM Page A. Organization of Technical Panel on Ionospheric Physics 255 B. Summary of Panel Actions 256 C. Project Objectives and Results 260 6.1 Ionosphere Sounder Procurement 261 6.2 South American Sounding Program 262 6.3 A n t a r c t i c Sounder Program 265 6.5 Data Q u a l i t y Control and T r a i n i n g 267 6.6 Equatorial VHP Forward Scatter 268 6.7 Radio Noise Measurement , 272 6.8 Ionospheric Absorption-Pulse Method 275 6.9 True Height Determination 276 6.10 Whistler Program - West 279 6.11 Whistler Program - East 287 6.12 Fixed Frequency Backscatter Measurements 292 6.14 Oblique Incidence Sporadic-E (Eg) Measurements 297 6.19 A r c t i c D r i f t i n g S t a t i o n Sounder 301 6.20 Ionospheric Absorption, Cosmic Noise Method 301 6.21 Ionospheric Absorption, Cosmic Noise Method 302 5.22 Radio Amateur Reports on Unusual Propagation 303 6.23 Radio Star S c i n t i l l a t i o n 307 6.24 Ionospheric Data Processing & P u b l i c a t i o n 308 6.26 Signal Corps Ionospheric Sounder Stations 309 6.27 Whistler Stations - Alaska 310 6.28 Fixed Frequency Backscatter - Alaska 313 254

V I . IONOSPHERIC PHYSICS PROGRAM A. Organization of Technical Panel on Ionospheric Physics 1. Establishment of the Panel. L e t t e r s were w r i t t e n i n November 1954 t o ionospheric p h y s i c i s t s i n v i t i n g them to p a r t i c i p a t e i n the planning of the US-IGY program by serv- ing as members of the Technical Panel on Ionospheric Physics; A. H. Shapley convened the f i r s t meeting a t which i t was decided t o postpone organization and e l e c t i o n of o f f i c e r s . At a l a t e r meeting, M. G. Morgan was elected chairman and H. W. Wells, r e - cording secretary. Mr. Wells was elected vice-chairman a t a l a t e r date. N. C. Gerson and R. C. Peavey were I n v i t e d , a t a l a t e r time, to membership and several consultants were asked to j o i n i n the work of the Panel. The Department of Defense appointed l i a i - son members to the Panel from the three services; some of the DOD representatives were also members of the Panel. 2. Composition of the Panel. ( A f f i l i a t i o n a t time of appointment.) a. Panel Members M. G. Morgan, Chairman H, W. Wells, Rec. Secy. and Vice-chairman H. G. Booker Frederic H. Dickson N, C. Gerson Robert A. H e l l i w e l l Wolfgang P f i s t e r Alan H. Shapley Ralph J. Slutz Arthur H. Waynick Dartmouth College Department of T e r r e s t r i a l Magnetism, Carnegie I n s t i t u t i o n of Washington Cornell U n i v e r s i t y U. S. Army Sig. Radio Propagation Agcy. Geophysics Research D i r e c t o r a t e Stanford U n i v e r s i t y Geophysics Research D i r e c t o r a t e , AFCRL Central Radio Prop. Lab., NBS Central Radio Prop. Lab., NBS Pennsylvania State U n i v e r s i t y b. Consultants H. W. C u r t i s Harold E. Dinger Roger G a l l e t N. J. O l i v e r , J r . A. M. Peterson J. C. Seddon H. G. S e l l e r y Dartmouth College U. S. Naval Research Lab. Central Radio Prop. Lab., NBS Geophysics Research D i r e c t o r a t e , AFCRL Stanford U n i v e r s i t y U. S. Naval Research Lab. Central Radio Prop. Lab., NBS c. Secre t a r i a t (IGY S t a f f ) R. C. Peavey ( t o July 1957) P. W. Mange (July 1957 - Feb. 1959) Stanley Ruttenberg (from Feb. 1959) 3. Panel Meetings. Twelve meetings of the panel were held. F i r s t December 3, 1954 Washington, D. C. Second December 20, 1954 Washington, D. C. Thir d January 16, 1955 Boulder, Colorado Fourth torch 4/5, 1955 Boston, Mass. F i f t h May 6, 1955 Washington, D. C. S i x t h August 19/20, 1955 S p r i n g f i e l d , Mass. Seventh December 14/17, 1955 G a i n e s v i l l e , F l o r i d a Eighth May 4, 1956 March 14/15, 1957 Washington, D. C. Ninth Washington, D. C. 255

IONOSPHERIC PHYSICS Tenth August 17, 1957 Boulder, Colorado Eleventh November 6, 1957 Boulder, Colorado Tw e l f t h A p r i l 8, 1958 Washington, D. C. B. Summary of Panel Actions 1. O r i g i n a l Program. I n accordance w i t h suggested programs developed by CSAGI, and through the a i d of the U. S. National Committee f o r URSI, H. G. Booker, A. H. Shapley and N. C. Gerson formulated proposals f o r the U. S program f o r discussion of the U. S. National Committee. The proposed program, as developed f o r the I l n d meeting of CSAGI, Rome, 1954, contained three p r i n c i p a l sets of i n v e s t i g a t i o n s . a. A series of v e r t i c a l incidence sounding s t a t i o n s . I n a d d i t i o n to the normal network s t a t i o n s operated by the National Bureau of Standards, i t was proposed to ex- tend the network northward to Thule, Greenland, and southward to three locations i n the A n t a r c t i c . Several s t a t i o n s i n South America to be operated i n cooperation w i t h s c i e n t i s t s of various countries were contemplated to help f i l l the 75° W meridian pole-to-pole l i n e . I t was also planned to i n s t a l l several s t a t i o n s i n e q u a t o r i a l r e - gions, perhaps i n the Western P a c i f i c , to study anomalous e f f e c t s near the geomagnetic equator. The pole-to-pole chain would give observations on the l a t i t u d e v a r i a t i o n s r e l a t i v e l y free from any longitude e f f e c t . The high southern and northern l a t i t u d e s t a t i o n s would a f f o r d the opportunity to study the e f f e c t of prolonged absence of s u n l i g h t . Special a t t e n t i o n was to be given to the c a l i b r a t i o n and meticulous operation of the equipment m securing data of as high a q u a l i t y as possible. I t was hoped to obtain u n i f o r m i t y i n the data and to achieve t h i s i t was proposed t h a t a team of ex- perts t r a v e l to the s t a t i o n s to consult w i t h the observers i n maintenance, operation and record i n t e r p r e t a t i o n , b. A series of back s c a t t e r soundings using f i x e d and m u l t i p l e frequencies. The techniques of high frequency back sc a t t e r sounding had been s u f f i c i e n t l y advanced as to suggest e x p l o i t a t i o n of these techniques f o r the IGY program. Sweep frequency soundings i n several d i r e c t i o n s and f i x e d frequency soundings w i t h r o t a t i n g antennas would provide two methods to o b t a i n valuable information t o be added t o observations obtained w i t h f i x e d frequency v e r t i c a l soundings. c. Some studies of basic properties of the ionosphere. I t was hoped to undertake i n v e s t i g a t i o n s t o study the motion of p a r t i c l e s and patches of i o n i z a t i o n ( i . e . iono- spheric winds), w i t h the o b j e c t i v e to achieve a b e t t e r understanding of the dynamics of the ionized atmospheric regions. Other experiments were contemplated to attempt the determination of the i n t e r a c t i o n of p a r t i c l e s i n the ionosphere, namely, the c o l - l i s i o n a l frequency. From t h i s i t was hoped t o deduce temperatures and radio wave ab- s o r p t i o n c o e f f i c i e n t s . I n a d d i t i o n t o these three basic programs, a number of other observations and experiments were contemplated. These included, f o r example, a network f o r obtaining absolute noise power l e v e l data i n a wide range of frequencies. Exploratory work on w h i s t l e r s had also progressed to the point where i t seemed desirable to include ob- servations of t h i s phenomenon i n at least a few l o c a t i o n s . 2. Early Work of the Panel. a. Terms of reference. The Panel reviewed the proposed U. S, program as prepared by the U. S. National Committee and undertook to make recommendations from the budget- ary and s c i e n t i f i c viewpoint, as to the organizations to carry out the program, and as 256

IONOSPHERIC PHYSICS to the soundness of the program. The Panel was also assigned the task of coordinating the execution of the program. b. Working groups. At an e a r l y meeting, the Panel appointed several ad hoc sub- committees to study s p e c i f i c problems and make recommendations to the Panel as f o l - lows . ( i ) To review the proposed program i n back-scatter soundings and to suggest mod i f i c a t i o n s . (R. A. H e l l i w e l l and N. C. Gerson w i t h A. M. Peterson, R. S i l b e r s t e i n and J. T. de Bettencourt as co n s u l t a n t s ) ; ( i i ) To recommend a program of forward-scatter measurements. (H. Wells and R. Bateman, c o n s u l t a n t ) , ( i l l ) To consider a program i n " w h i s t l e r s . " (R. A. H e l l i w e l l and M. G. Morgan w i t h A. G. Jean as c o n s u l t a n t ) ; ( i v ) To consider a program i n absorption. (W. P f i s t e r w i t h R. E. Jones as consultant. R. A. H e l l i w e l l was asked to confer w i t h A T. Waterman, J r . , on t h i s area and report to the subcommittee.) 3. Recommendations f o r Programs. a. Sweep frequency back-scatter sounder. The Panel recommended t h a t t h i s e x p e r i - ment be considered f o r operation a t Dartmouth College i n view of the decision by CRPL to withdraw i t s proposal to conduct t h i s program. This p r o j e c t was included i n the f i n a l program but owing to the burden of work a t Dartmouth College i n connection w i t h g e t t i n g the expanded w h i s t l e r program i n t o operation, the sweep frequency back-scatter program was not implemented and was withdrawn from the program. b. Absorption. I n view of the r e s u l t s obtained by Unive r s i t y of Alaska scien- t i s t s w i t h instruments to record g a l a c t i c noise, the Panel recommended the i n c l u s i o n of a program of ionospheric absorption using the riometer equipment. This k i n d of work was also included i n the program of the Technical Panel on Aurora and Airglow. The projects implemented by both panels were i d e n t i c a l i n objective and merely d i v i d e d the load of supporting an adequate network of s t a t i o n s . c. D r i f t s . While some discussions have taken place on the measurement of iono- spheric d r i f t s by fading and meteoric Doppler techniques, the Panel f e l t t hat some unc e r t a i n t i e s m the i n t e r p r e t a t i o n s of observations needed to be c l a r i f i e d before a program should be planned. I t was also decided to see whether there was i n t e r e s t shown i n the i n t e r n a t i o n a l community i n organizing a synoptic program on d r i f t s . The Panel eventually included two proj e c t s m atmospheric d r i f t s i n i t s program. d. Ionospheric absorption, pulse method. The Panel f e l t t hat at least some ab- sor p t i o n measurements should be made using the v e r t i c a l incidence pulse sounder and recommended that one pro j e c t a t the Pennsylvania State Uni v e r s i t y be included i n the program. e. Equatorial sounder program. Plans f o r operation of sounders i n e q u a t o r i a l regions went through several phases during the development of the program. Considera- tions were given to operations i n the Western P a c i f i c and the Marianas Islands (Yap, Palau, Guam), i n the Line Islands i n the East Central P a c i f i c , or a t locations i n South America where l o g i s t i c and operational problems would be expected t o be s i m p l i - f i e d . I t was f i n a l l y decided to incorporate a close-spaced network of s t a t i o n s i n South America, centered a t the observatory at Huancayo. 257

IONOSPHERIC PHYSICS f . Other experiments. During the development of the ionospheric physics program, discussion was held regarding proposals on forward s c a t t e r experiments bearing on a reported east-west longitude e f f e c t i n sporadic E, and on tr a n s e q u a t o r i a l s c a t t e r ex- periments f o r E and F region phenomena. These experiments were eventually Included i n the program. The p o s s i b i l i t y of u t i l i z i n g r a dio amateur reports of unusual propa- gation was also i n v e s t i g a t e d ; a j o i n t p r o j e c t of ARRL and GRD developed and was i n c l u - ded. 4. Programs Not D i r e c t l y Supported by IGY Funds. The Panel discussed the I n c l u s i o n i n the program of work th a t might be appropriate to Include i n the IGY program t h a t was already supported by other agencies. Several suggestions were reviewed and i n - cluded i n the f i n a l l i s t of projects as non-funded or contributed programs. 5. S a t e l l i t e Experiments. An ad hoc committee c o n s i s t i n g of A. H. Shapley, A. H. Waynlck, and H. W. Wells was set up to discuss programs f o r radio observations of s a t e l l i t e transmissions. The committee was e x p l i c i t l y d i r e c t e d to consider only pro- posals f o r experiments leading to new ionospheric or radio propagation information as d i s t i n c t from observational programs f o r the purpose of obtaining o r b i t a l data. The Panel endorsed a recommendation that a U. S. s a t e l l i t e be launched w i t h m u l t i p l e f r e - quency transmission on a t least two frequencies, a high frequency such as 108 mc, and a lower one such as 20 mc. The Panel suggested t h a t s a t e l l i t e transmission frequency s t a b i l i t y of one part i n 10^ was necessary f o r the determination of the Integrated e l e c t r o n density over the path between the s a t e l l i t e and observer. I t was suggested also that r e f r a c t i o n measurements should be as synoptic as possible. As a conse- quence of the i n t e r e s t i n using s a t e l l i t e transmissions f o r ionospheric experiments, a group of pro j e c t s was developed and Incorporated i n the s a t e l l i t e program, as d i s - cussed i n chapter 14. 6. A n t a r c t i c Program. Preliminary plans f o r s t a t i o n layouts were brought t o the a t t e n t i o n of the Panel w i t h the view to obtaining comment from the s c i e n t i f i c p r o j e c t d i r e c t o r s as t o requirements f o r power, space, c o r o l l a r y f a c i l i t i e s , e t c . The Panel agreed t h a t R. C. Peavey and H. G. S e l l e r y should discuss the needs of the ionospheric program and make requirements known to U S. Navy Task Force 43 which had been assigned r e s p o n s i b i l i t y f o r a n t a r c t i c l o g i s t i c support. The Panel recommended that a proposed f i x e d frequency s c a t t e r sounder a t an ant- a r c t i c l o c a t i o n be eliminated from the program. The plans f o r the v e r t i c a l incidence sounders a t a l l s t a t i o n s were approved but the Panel recommended th a t i f the proposed s t a t i o n i n the Weddell Sea could not be established more than 300 miles from the United Kingdom s t a t i o n , the v e r t i c a l incidence equipment and the personnel be returned to the U. S. f o r use elsewhere. The penetration of the Weddell Sea was greater than expected but a s t a t i o n could not be located a t the greatest depth of penetration be- cause of the conditions a t the ice b a r r i e r . The f i n a l l o c a t i o n of the s t a t i o n was judged to be s u f f i c i e n t l y f a r from the U, K. s t a t i o n to warrant the i n s t a l l a t i o n of the v e r t i c a l Incidence sounding equipment. The Panel recommended to the USNC A n t a r c t i c Committee th a t arrangements be made w i t h the Department of Defense f o r the establishment of communication centers a t each a n t a r c t i c l o c a t i o n and t h a t consideration be given on an i n t e r n a t i o n a l basis t o the coordinated use of frequencies f o r communication w i t h s t a t i o n s outside A n t a r c t i c a . A request was addressed to CRPL to assess the radio t r a f f i c needs of the ionospheric physics a n t a r c t i c program f o r the use of the Academy's IGY s t a f f . The Panel a t a l a t e r date approved the i n c l u s i o n of radio noise and w h i s t l e r ob- servations i n the A n t a r c t i c . 7. A r c t i c Program. When a coordinated program of research i n the A r c t i c Basin was incorporated i n t o the U. S. program, the Panel approved the I n c l u s i o n of v e r t i c a l 258

IONOSPHERIC PHYSICS incidence soundings a t the s t a t i o n to be established on T-3 (Fletcher's Ice I s l a n d ) . 8. Equipment. a. V e r t i c a l incidence equipment. At an e a r l y meeting, the Panel discussed the se l e c t i o n of v e r t i c a l sounding equipment. I t was stated that although the Canadian Marconi was the best q u a l i f i e d company to provide t h i s equipment i n the shortest pos- s i b l e time, the d i f f i c u l t i e s involved i n buying from another country might r e s u l t i n i n t o l e r a b l e delay. The Panel concluded t h a t the best s o l u t i o n under the circumstances was the con s t r u c t i o n of a new model using the Canadian sounder, model LG17, as a pro- totype. I t was assumed t h a t , i f necessary, a l i c e n s i n g arrangement w i t h Canadian Mar- coni could be worked out. The Panel decided t h a t bids be requested f o r ( i ) a new model using the LG17 as the " p r i n c i p l e prototype" and the C3 as "another example," ( i i ) a copy of the LG17. I n both cases, sealed components and t r o p i c a l i z a t i o n were required. The components were to be of U. S. manufacture to insure easy replacement. The d e s i r a b i l i t y of " u n i t c o n s t r u c t i o n " was emphasized by the Panel. The Panel placed a t CRPL the r e s p o n s i b i l i t y f o r the w r i t i n g of the s p e c i f i c a t i o n s and handling of bids. W. P f i s t e r , H. W. Wells and A. H. Shapley were delegated as a sub-committee to make recommendations f o r l o c a t i o n of any surplus v e r t i c a l incidence recorders t h a t might become ava i l a b l e and t o take i n t o consideration possible losses of equipment and the need f o r replacement, b. Equipment f o r other countries. The Panel considered requests f o r ionospheric sounding equipment from Indonesia and Chile to e s t a b l i s h s t a t i o n s on Java and Easter Island r e s p e c t i v e l y and, based upon the CSAGI recommendation f o r a s t a t i o n on Java and the obvious s c i e n t i f i c m e r i t of a s t a t i o n on Easter I s l a n d , authorized and encouraged CRPL to negotiate w i t h these countries i f i t had equipment to be replaced by the new models and not otherwise committed t o the IGY program. The Panel agreed to the f o l l o w i n g order of p r i o r i t y f o r requests f o r assistance i n e s t a b l i s h i n g v e r t i c a l incidence ionosphere s t a t i o n s : ( i ) Easter Is l a n d ( C h i l e ) , ( i i ) I s r a e l , ( i i i ) Indonesia, i n the event a l l such requests could not be supported. c. Radio noise equipment. At another meeting the Panel agreed t o recommend the use of the Crichlow atmospheric noise measuring equipment, modified to measure a se- cond parameter (the log mean value of i n t e n s i t y ) , and w i t h p r o v i s i o n f o r a second band- width of about 50 cycles, but went on record as noting t h a t present noise recording equipment was more s u i t a b l e f o r engineering studies than geophysical research and tha t DOD might w e l l conduct noise measurements where the Panel had not recommended the ex- penditure of USNC funds f o r t h i s purpose, but where r e l a t e d a c t i v i t i e s would be con- ducted. d. Visual recorders f o r magnetic disturbances. The Panel agreed to r e f e r the fo l l o w i n g to the Technical Panel f o r Geomagnetism: the i n s t a l l a t i o n of inexpensive v i s u a l l y - r e c o r d i n g magnetic variographs at ionosphere s t a t i o n s . The Technical Panel on Ionospheric Physics noted t h a t the Technical Panel on Geomagnetism had planned the i n s t a l l a t i o n of equipment of t h i s type a t s i x ionosphere s t a t i o n s . The existence of a much less expensive instrument had come to the a t t e n t i o n of the Technical Panel on Ionospheric Physics, and t h i s Panel understood t h a t there were other s i m i l a r i n s t r u - ments which had been developed by other sources. The Technical Panel on Ionospheric Physics saw the p o s s i b i l i t y of having instruments i n s t a l l e d a t a larger nvmiber of ionospheric s t a t i o n s and asked the Technical Panel on Geomagnetism to evaluate t h i s p o s s i b i l i t y and advise. e. D i s p o s i t i o n of equipment. The Panel considered at a l a t e meeting the d i s p o s i - t i o n of equipment a f t e r the IGY and suggested t h a t an ad hoc committee be set up to survey the general question. A c t i o n was deferred, however, to a l a t e r date, and, i n 259

IONOSPHERIC PHYSICS f a c t , t h i s question was not d e a l t w i t h by the Panel. 9. Publications, The Panel deferred a c t i o n on recoiranendations w i t h regard t o p u b l i - c a t i o n of ionospheric data u n t i l t h i s matter was discussed i n the CSAGI and i n t e r n a - t i o n a l recommendations were developed. The Panel recommended th a t the CSAGI be urged to require t h a t information on equipment and operating c h a r a c t e r i s t i c s accompany iono- spheric data and record interchanges i n IGY operations. CRPL offered several proposals f o r t r e a t i n g the ionospheric data which ranged from the f u l l CSAGI recommendations, which would be to reduce and publ i s h i n s t a t i o n booklet form d a i l y f - p l o t s and hourly values of some 12 c h a r a c t e r i s t i c s f o r each of 34 sta- t i o n s , to p a r t i a l treatment wherein data from some selected s t a t i o n s would be published i n f u l l and data from other s t a t i o n s would be published only p a r t i a l l y . The Panel recommended t h a t the f u l l p u b l i c a t i o n program be c a r r i e d out i f possible, and suggested t h a t some of the costs could be covered by the sale of data booklets a f - ter the requirements had been met f o r the usual free i n t e r n a t i o n a l exchange. C. Proje c t Objectives and Results 1. Summary of Program. The ionospheric physics program was composed of synoptic studies t h a t included v e r t i c a l - i n c i d e n c e soundings, oblique Incidence soundings w i t h r o t a t i n g antennas, studies of radio noise, and the recording of w h i s t l e r s and other low frequency phenomena. Special studies, i n a d d i t i o n , included s c a t t e r experiments, true height c a l c u l a t i o n s , s c i n t i l l a t i o n s and d r i f t s , absorption, and r e p o r t i n g of un- usual radio propagation v i a amateur channels. There were also some pr o j e c t s f o r equip- ment procurement and data processing. Ionospheric physics experiments were also car- r i e d out using rockets and s a t e l l i t e s , and by analyzing s a t e l l i t e telemeter signals received by special configurations of ground equipment. These experiments are re- ported i n Chapters X and XV, ROCKETRY and EARTH SATELLITE PROGRAM, 2. Order of Pr o j e c t Description. The pr o j e c t s t h a t are described m the f o l l o w i n g pages are i n numerical order to correspond w i t h the o r i g i n a l formulation of the pro- gram. For convenience, the proj e c t s are grouped below to r e f l e c t s i m i l a r i t y of pur- pose. V e r t i c a l Incidence 6.2, 6.3, 6.5, 6.19, 6.26 Oblique Incidence Backscatter 6.12, 6.28 Radio Noise 6.7 Whistlers 6.10, 6.11, 6.27 Scatter Experiments 6.6, 6,14 True Heights 6.9 S c i n t i l l a t i o n 6.23 Absorption 6.8, 6.20, 6.21 Unusual Propagation 6.22 Equipment Procurement 6.1 Data Processing and 6.24 Pub l i c a t i o n 3. Cancelled Projects. Former projects bearing the f o l l o w i n g numbers were eliminated from the program or combined w i t h other p r o j e c t s : 6.4, 6,13, 6.15 to 6.18, and 6.25. 260

IONOSPHERIC PHYSICS Project 6.1 - Ionosphere Sounder Procurement 1. Objectives. This p r o j e c t of the Central Radio Propagation Laboratory, Boulder Laboratories, National Bureau of Standards, provided f o r the purchase of 14 improved ionosphere v e r t i c a l incidence sounders, model C-4. Two model C-3 sounders were d i - verted by CRPL t o IGY use. Three portable sounders were purchased f o r i n t e r i m use a t U. S. st a t i o n s so th a t C-4's could be sent to remote l o c a t i o n s , and as emergency backup. ^ 2. Personnel. The purchase and a l l o c a t i o n of these instruments was supervised by Harry G. S e l l e r y , CRPL. 3. Results. The C-3 sounders were i n s t a l l e d a t Bjnrd and Amundsen-Scott s t a t i o n s i n A n t a r c t i c a . C-4 equipments were located a t H a l l e t t , Byrd, L i t t l e America, E l l s w o r t h and Wilkes s t a t i o n s , A n t a r c t i c a ; Huancayo and Chirabote, Peru; La Paz, B o l i v i a ; Bogota, Colombia; Concepcion, C h i l e ; N a t a l , B r a z i l , Maui, Hawaiian Islands; Boulder, Colorado, Grand Bahama Is l a n d , Federation of the West In d i e s , and Thule, Greenland. While the C-4 instruments represented a considerable advance over the e a r l i e r models, some modifications of cameras and c i r c u i t s (oscilloscope power supply and de- f l e c t i o n c i r c u i t s ) were made to improve performance and r e l i a b i l i t y . 261

IONOSPHERIC PHYSICS Project 6.2 - South American Sounding Program 1. Objectives. This p r o j e c t a t CRPL, National Bureau of Standards, provided f o r supplies, spare parts and some operations a t s i x s t a t i o n s i n South America. C-4 sounders were supplied from p r o j e c t 6.1. Four of the locations were to f i l l i n the 70-80°W Meridian chain; the other two were part of a close-spaced network, centered at Huancayo, as part of a study of anomalous behavior of the F-layer near l o c a l noon, i n the v i c i n i t y of the magnetic equator. 2. Operations. Mr, H. Go l l e r , I n s t i t u t o Geoffsico de Huancayo, completed a t r a i n i n g program a t CRPL and a t Barker-Williamson, manufacturer of the C-4. A l b e r t Gieseke, J r . , D irector of Huancayo, and Mateo Casaverde of the I n s t i t u t o , also v i s i t e d CRPL f o r the purpose of f a m i l i a r i z i n g themselves w i t h the equipment and observing techniques. Observers from the various South American countries were t r a i n e d a t Huancayo. Per- sonnel from CRPL v i s i t e d the s t a t i o n s and assisted i n i n s t a l l a t i o n of equipment. Operations commenced by the s t a r t of IGY w i t h the exception of one s t a t i o n which was delayed f o r a few months and a second s t a t i o n where the delay was somewhat longer, inasmuch as t h i s s t a t i o n was included i n the program a t a l a t e date. 3. Personnel. Harry G. Selle r y supervised t h i s p r o j e c t ; E. V i o l e t t e and E. E. Fer- guson collaborated. 4. Data. lonograms were scaled a t the s t a t i o n s and sent to Huancayo f o r checking. F i n a l grams and scalings were sent to WDC-A: Ionosphere (CRPL) and published i n i n - d i v i d u a l s t a t i o n books, according to CSAGI recommendations. 5. Results. From a reduction of e l e c t r o n density values to true heights f o r the close-spaced chain (Talara, Chiclayo, Chimbote, Huancayo and La Paz), i t was seen t h a t the e l e c t r o n density r i s e s sharply a t sunrise and maximum density i s obtained e a r l i e r a t intermediate levels than at higher l e v e l s . For the low l e v e l s , e l e c t r o n density i s p r o p o r t i o n a l to the square r o o t of the cosine of the solar z e n i t h angle, as predicted by Chapman i n h i s theory of ionosphere behavior. The e l e c t r o n density drops, a t a p a r t i c u l a r a l t i t u d e l e v e l , sharply a t sunrise, f a s t e r , i n f a c t , than ex- pected from considering recombination alone. I t was also observed t h a t sporadic E occurs during most d a y l i g h t hours. The extent of Es i s very sharply r e l a t e d to mag- n e t i c d i p . the frequency of occurrence i s greater than 35% i n the region + 5.5° of the magnetic equator but drops t o 5% a t 8° from the equator. This agrees w i t h the magne- t i c observations of Forbush (see p r o j e c t 3,16). Occasionally Ej disappeared suddenly fo r periods of minutes t o hours e a r l y I n the afternoon. Analysis of Es observations of Knecht tend to confirm Matsushita's explanation of a lunar dependence f o r t h i s e f f e c t . V e r t i c a l cross-sections of the ionosphere across the geomagnetic equator and along the 75°W meridian were prepared from e l e c t r o n density p r o f i l e s by J. W. Wright. F i g . 1 shows these cross-sections as contours of plasma frequency ( f j j ) . The daytime d i s - tension of the e q u a t o r i a l ionosphere, and the great increases i n e l e c t r o n density a t neighboring l a t i t u d e s were suspected p r i o r to the IGY, however those shown i n F i g . 1 are the f i r s t q u a n t i t a t i v e and f u l l y d e s c r i p t i v e representations to become a v a i l a b l e . An explanation f o r these p e r s i s t e n t features of the e q u a t o r i a l ionosphere i s being sought i n terms of t i d a l a c t i o n causing v e r t i c a l " l i f t i n g " of the daytime e q u a t o r i a l i o n i z a t i o n followed by meridional downward d i f f u s i o n to higher l a t i t u d e s . 262

U> PUEBTPIWO 1200-75-W 10 SEPT -57 IXOan S « L E JX HOSrKWTM. S U L E ) nam SCALE) 2200-75-W 10 SEPT '57 cornoum O F f ( H C C H T SCALE SX HORIZONTAL S C A L E ) Figure 1. Contours, of Electron Density Along 75° W Meridian. § o CO

IONOSPHERIC PHYSICS Bibliography. a. Papers Presented a t Meetings. R. W. Knecht, D. W. S c h l i t t - "Early Results from the Equatorial Close-Space Chain of Ionospheric V e r t i c a l Incidence Soundings Stations." Vth CSAGI Assembly, August 1958, Moscow. (Also published i n NBS Report No. 5587 and i n press i n the "Annals of the IGY".) b. Published Papers. R. W. Knecht. "An A d d i t i o n a l Lunar Influence on Equatori a l Es at Huancayo." J. Atm. and Terr. Phys., v o l . 14, 1959, pp. 348-49 R. W. Knecht: "On the P o s s i b i l i t y of Detecting Ionospheric D r i f t s from the Occurrence of Spread F Echoes a t Low Lat i t u d e s , " Nature, v o l . 187, 1960, p. 927. R. W. Knecht, R. E. McDuffie: "On the Width of the Equatorial Es B e l t . " (To be published i n an Es Monograph, Pergamon Press). R. W. Knecht: "Temporal and S p a t i a l V a r i a t i o n s of Low Lat i t u d e Spread F Occurrence." ( I n p r e p a r a t i o n ) . J. W. Wright: "Note on Quiet-Day V e r t i c a l Cross-sections of the Ionosphere Along 75°W Geographic Meridian." J. Geophys. Res., v o l . 64, 1959, pp. 1631- 1634. J. W, Wright: "The NBS Electron Density P r o f i l e Program, Some Features and Early Results," Proceedings of a Symposium organized by the URSI/AGI Commit- tee, Brussels, September 1959, "Some Ionospheric Results Obtained During the I n t e r n a t i o n a l Geophysical Year." by W. J. G. Beynon, E d i t o r . J, W. Wright: "A Model of the Ionosphere Above hmaxF2," J. Geophys. Res,, v o l . 65, 1960, pp. 185-191. 264

IONOSPHERIC PHYSICS Project 6.3 - A n t a r c t i c Sounder Program 1. Objectives. This p r o j e c t at CRPL, National Bureau of Standards, provided f o r per- sonnel, supplies, and operation of C-4 sounders a t s i x a n t a r c t i c s t a t i o n s where, u n t i l the IGY, no such program had previously been attempted. Of p a r t i c u l a r i n t e r e s t was the behavior of the ionosphere over the polar cap, i n response to a seasonal rather than d i u r n a l cycle of the sun. 2. Operations. CRPL personnel assisted i n assigning the f a c i l i t i e s a t the a n t a r c t i c locations — L i t t l e America, Byrd, Pole, H a l l e t t , Wilkes and El l s w o r t h . S p e c i f i c a t i o n s were prepared f o r power, w i r i n g and antenna i n s t a l l a t i o n s . Personnel were r e c r u i t e d and t r a i n e d a t CRPL. The f i l m ionograms were processed and scaled a t the s t a t i o n s . Telegraphic summaries of data were r e g u l a r l y sent to CRPL f o r study and suggestions f o r improving performances were sent back to A n t a r c t i c a . A l l s t a t i o n s were i n opera- t i o n i n e a r l y 1957 i n advance of the opening date of the IGY. 3. Personnel. Harry G. S e l l e r y supervised t h i s p r o j e c t . 4. Data. A l l data have been processed and submitted to WDC-A Ionosphere, and pub- li s h e d i n s t a t i o n book form according to CSAGI s p e c i f i c a t i o n s . 5. Results. For the f i r s t time, observations o f the ionosphere were obtained a t the geographic pole throughout a complete seasonal cycle. The monthly median values of foF2 are shown f o r the South Pole i n F i g . 2. F-region i o n i z a t i o n p e r s i s t e d during the six-month dark w i n t e r ; marked d i u r n a l v a r i a t i o n s were observed even though, on a d a l l y basis, the solar e l e v a t i o n remained constant. A small but s i g n i f i c a n t d i - urna l v a r i a t i o n was also found f o r f o F l , w h i l e , i n c o n t r a s t , foE ex h i b i t e d no regu- l a r d a l l y f l u c t u a t i o n but seemed t o depend to a greater extent on the l e v e l of solar a c t i v i t y . Possible mechanisms to expl a i n maintenance of s i g n i f i c a n t mid-winter i o n i z a t i o n a t the South Pole include: a) h o r i z o n t a l d r i f t from lower l a t i t u d e s ; b) increasing solar corpuscular r a d i a t i o n ; and c) subsidence from higher, i l l u m i n a t e d l e v e l s . These three mechanisms were examined to see whether they could also ex p l a i n the d i u r n a l v a r i a t i o n . While each mechanism could r e s u l t i n d i u r n a l f l u c t u a t i o n s , predicted features d i d not agree w i t h a l l observed d e t a i l s , and suggestions were made as to what f u r t h e r observa- t i o n could help i l l u m i n a t e t h i s problem. At Wilkes and E l l s w o r t h s t a t i o n s , the normal temperate l a t i t u d e v a r i a t i o n (maximum around mid-day) of foF2 was found while a t L i t t l e America and Byrd s t a t i o n the maximum was reached i n the evening hours. A study of newly discovered sporadic E type i n the a u r o r a l zones was undertaken by Olesen and Wright. Designated Es-d, t h i s phenomenon appears c l o s e l y r e l a t e d to the occurrence of a u r o r a l zone absorption, and t o the region responsible f o r VHD D-scatter i n the a r c t i c , the Es-d observations appear to be the f i r s t d e f i n i t i v e evidence on the height of the VHF D-scatter region. A study by Wright of magnetoionic phenomena on ionograms obtained near the magnetic d i p poles disclosed several new coupling e f f e c t s which permit the observation and mea- surement of " v a l l e y " minima above the E layer. 6. Bibliography. a. Papers Presented a t Meetings. R. W. Knecht, R. E. McDuffie, Y. Aono: "Preliminary Results from the U. S.- IGY A n t a r c t i c Network of Ionospheric Soundings Stations." Vth CSAGI Confer- ence, August 1958, Moscow ("Annals of the IGY", v o l . 11, i n press). 265

IONOSPHERIC PHYSICS b. Published Papers. R. W. Knecht: "Observations of the Ionosphere Over the South Geographic Pole." JGR, v o l . 64, no. 9, September 1959, pp. 1243-50. J. K. Olesen, J. W. Wright: "The Relation of Low-height lonosonde Echoes to Auroral Zone Absorption and VHF D-Scatter." JGR. v o l . 66, 1961, pp. 1127-1134. J. W. Wright: "Some Magnetoionic Phenomena of the A r c t i c E Region. Terr. Phys.. v o l . 98, 1960, pp. 276-289. J. Atmos. J. W. Wright: "Two Magnetoionic Phenomena Permitting Observation of Valley Minima i n the A r c t i c E Region." Proceedings of a Symposium Organized by the URSI/AGI Committee, Brussels, September 1959, "Some Ionospheric Results Ob- tained During the I n t e r n a t i o n a l Geophysical Year." W, J. G. Beynon, E d i t o r . i9ii m umastt m mam m Figure 2. Monthly median f6F2, south pole. 266

IONOSPHERIC PHYSICS Project 6.5 - Data Qu a l i t y Control and Training 1. Objectives. The p r i n c i p a l o b j e c t i v e o f _ t h i s p r o j e c t c a r r i e d on a t CRPL was to en- sure t h a t the ionospheric data coming out of the IGY v e r t i c a l soundings program were of the highest possible q u a l i t y . This was accomplished through four a c t i v i t i e s : a) the preparation of a manual of ionospheric v e r t i c a l soundings (Annals of the IGY, v o l . I l l , Part 1 ) , b) the preparation ( f o r the World-Wide Soundings Committee of URSI) of an At l a s of lonograms, c) t r a i n i n g of f i e l d personnel f o r the program, and d) data q u a l i t y c o n t r o l operations. 2. Operations. Ionospheric data from the 33 st a t i o n s associated w i t h the U. S. IGY soundings program were r e g u l a r l y sent to Boulder f o r review and processing. The o r i - g i n a l ionograms were also inspected as soon as they could be obtained from the s t a t i o n . From these analyses, experienced personnel a t CRPL could determine whether the s t a t i o n s were operating s a t i s f a c t o r i l y and what measures might be taken to b r i n g the data q u a l i - t y to a high standard. Upwards of 40 f i e l d personnel spent periods ranging from 3 days to 4 months i n Boulder undergoing t r a i n i n g i n the v e r t i c a l soundings work. Of the t o t a l number of station-months of IGY data p o t e n t i a l l y a v a i l a b l e (33 sta - t i o n s X 18 months r 594), a l l but about 17 (3%) were successfully obtained. The bulk of the l o s t data can be a t t r i b u t e d to unavoidably l a t e s t a r t s of several of the new South American s t a t i o n s . 3. Personnel. A. H. Shapley maintained o v e r a l l supervision of the p r o j e c t . R. W. Knecht and J. W. Wright p a r t i c i p a t e d as senior personnel, w i t h the assistance of S. C. Gladden, L. S. Hayden, I . Brophy, K. Davies and J. P i t t s . 4. Bibliography. J. W. Wright, R. W. Knecht, and K. Davies: "Ionospheric V e r t i c a l Soundings." Vol. I l l , Part I , Annals of the IGY. J. W. Wright, R. W. Knecht: "IGY At l a s of Ionograms." CRPL, June 1957. 267

IONOSPHERIC PHYSICS Project 6.6 - Equatori a l VHF Forward Scatter 1. Objectives. This research, performed by the Central Radio Propagation Laboratory of the National Bureau of Standards, was organized to study radio wave s c a t t e r i n g phenomena r e s u l t i n g from e l e c t r o n i r r e g u l a r i t i e s i n the ionosphere near the magnetic equator. During the IGY a number of ionospheric forward s c a t t e r paths i n the v i c i n i t y of the magnetic equator i n South America were established. [These transmissions also provided signals which were monitored by radio amateurs i n North America f o r studying unusual VHF propagation phenomena ( c f . p r o j e c t 6.22)]. 2. Operations. Among these s c a t t e r paths there were two basic t r a n s e q u a t o r i a l chan- nels to in v e s t i g a t e e q u a t o r i a l Sporadic E and e q u a t o r i a l Spread F, re s p e c t i v e l y . Col- l a t e r a l observations of the e q u a t o r i a l ionosphere were conducted a t the I n s t i t u t o Geo- f i s i c o de Huancayo, which i s located near the magnetic equator near the midpoints of the basic paths. The f i r s t path, Arequipa, Peru to T r u j i l l o , Peru, was 1230 km i n length, corresponding to s i m i l a r forward-scatter c i r c u i t s studied e a r l i e r i n temperate and a r c t i c l a t i t u d e s . The second path, Antofagasta, Chile to Guayaquil, Ecuador, was about twice t h i s separation f o r suppressing s c a t t e r i n g i n the E-region i n order to examine possible oblique s c a t t e r i n g e f f e c t s i n the F-region associated w i t h Spread F. The ionosphere above Huancayo was e s s e n t i a l l y the medium propagating the VHF sc a t t e r signals on these two paths, while to examine ionospheric regions a t other l a t i t u d e s near the equator, other s c a t t e r paths were established from Antofagasta to Huancayo, Arequipa t o Guayaquil, Antofagasta to T r u j i l l o , and Arequipa to Guayaquil, u t i l i z i n g e x i s t i n g or r e a d i l y a v a i l a b l e receiving and t r a n s m i t t i n g l o c a t i o n s . For the purpose of monitoring the s c a t t e r i n g e f f e c t s observable by t r a n s m i t t i n g i n a d i r e c t i o n p a r a l - l e l to the magnetic equator, part of the Antofagasta r a d i a t i o n was beamed to the east and received a t cooperative s t a t i o n s operated f o r NBS i n Clorlnda, Argentina and Sao Paulo, B r a z i l . The t r a n s m i t t e r s operated a t frequencies near 50 Me/s at about 3 k i l o w a t t s of power, and rhombic antennas were employed f o r both transmission and reception. The four p r i n c i p a l f i e l d s i t e s consisted of laboratory t r a i l e r s manned by CRPL personnel. The p r o j e c t s c i e n t i s t s made an exploratory advance t r i p to South America p r i o r t o equipment i n s t a l l a t i o n i n order to discuss the program w i t h t h e i r colleagues i n the countries concerned and t o locate appropriate f i e l d s i t e s . S c i e n t i s t s and IGY Commit- tees of these c o u n t r i e s handled the indi s p e n s a b l e governmental and l o c a l arrangements, 3. Personnel. Kenneth L. Bowles and Robert S. Cohen were the senior s c i e n t i s t s and proj e c t d i r e c t o r s f o r t h i s research program. 4. Data. Inasmuch as t h i s was a special experiment, not covered e x p l i c i t l y by CSAGI recommendations f o r r o u t i n e data exchange, the data are retained a t CRPL f o r study and an a l y s i s . However, the s i g n a l s trength data obtained have been processed by machine methods and are being made a v a i l a b l e to in t e r e s t e d workers through the IGY World Data Centers. 5. Results. The remarkable strength of the E-reglon e q u a t o r i a l s c a t t e r , as e x h i b i t e d by the Arequipa to T r u j i l l o , Antofagasta to Huancayo and Huancayo to Guayaquil s i g n a l strength records, i s considerably greater than t h a t observed and u t i l i z e d i n temperate l a t i t u d e s . Thus i t has been established t h a t a great n a t u r a l resource Is p o t e n t i a l l y a v a ilable to nations located i n e q u a t o r i a l zones, who w i l l be enabled, by e x p l o i t i n g the high I n t e n s i t y of the e q u a t o r i a l E-reglon propagation e f f e c t s , to r e a l i z e new radio communication p o t e n t i a l i t i e s of the ionospheric VHF forward s c a t t e r technique. Other r e s u l t s established by the p r o j e c t regarding the e q u a t o r i a l E-region are that a close r e l a t i o n s h i p e x i s t s between the magnetic manifestations of the e q u a t o r i a l 268

IONOSPHERIC PHYSICS e l e c t r o j e t current above Huancayo, the occurrence on Huancayo lonograms of e q u a t o r i a l Sporadic E, and the i n t e n s i t y of VHF signals propagated by the ionosphere over Huanca- yo. The zone i n which E-region e f f e c t s of the e q u a t o r i a l current-stream are apparent extends over some 10° of l a t i t u d e . Also, the scatter propagation i n the e q u a t o r i a l ionosphere i s characterized by higher s i g n a l l e v e l s and by more r a p i d fading rates than are observed m the ionosphere a t temperate l a t i t u d e s , and s i g n a l strengths r e - main high throughout the n i g h t . Curiously, ionospheric s c a t t e r propagation a t VHF s i m i l a r to t h a t associated w i t h Sporadic E formations m temperate l a t i t u d e s i s ob- served from time to time j u s t to the n o r t h and south of the magnetic equator, but i t s occurrence appears to be excluded i n the immediate v i c i n i t y of t h a t equator. I t has been demonstrated by experiments performed i n Huancayo subsequent to the IGY t h a t the e l e c t r o n i r r e g u l a r i t i e s present i n the e q u a t o r i a l e l e c t r o j e t are of a d i f f e r e n t nature than had been expected. Because of s i m i l a r i t i e s between the s c a t t e r i n g e f f e c t s pro- duced by these i r r e g u l a r i t i e s i n the e q u a t o r i a l ionosphere and radio s c a t t e r i n g associated w i t h the aurora, and to the r e l a t i v e l y simpler but analogous geometry a v a i l - able at the magnetic equator compared to t h a t i n the a u r o r a l zone, i t appears t h a t many aspects of the a u r o r a l phenomena could be deduced by studying the e q u a t o r i a l e f - f e c t s . This resemblance i s i n d i c a t i v e t h a t the conditions producing the a u r o r a l e f - f e c t s are comparable to those g i v i n g r i s e to the e q u a t o r i a l i r r e g u l a r i t i e s , and sug- gests that the e q u a t o r i a l region might w e l l be used as a laboratory m which to study the c l o s e l y simulated but more t r a c t a b l e analogues of a u r o r a l i r r e g u l a r i t i e s t h a t seem to be occurring there. Further, the a p p l i c a t i o n of radio techniques f o r studying the e q u a t o r i a l e l e c t r o j e t promises to a f f o r d the a d d i t i o n a l p o s s i b i l i t y of r e s o l v i n g the v a r i a t i o n i n current flow i n t o i t s c o n s t i t u e n t s , changes m v e l o c i t y and/or charge. Considerable information has been established regarding i r r e g u l a r i t i e s m the F- region of the e q u a t o r i a l ionosphere by measurements over the Antofagasta to Guayaquil path and by various special experiments. Propagation over t h i s path v i a F s c a t t e r was infrequent, being present only about 10% of the time, and only a t ni g h t t i m e . A c o n d i t i o n c l o s e l y r e l a t e d to the occurrence of F s c a t t e r propagation was the presence of e q u a t o r i a l Spread F configurations on the Huancayo lonograms. The height of the propagation medium supporting t h i s F s c a t t e r was usually i d e n t i f i a b l e w i t h the lowest height of the associated e q u a t o r i a l Spread F on the lonograms. The e q u a t o r i a l Spread F has been shown to a r i s e from s c a t t e r i n g by r e l a t i v e l y t h i n sheets of i r r e g u l a r i t i e s i n the e l e c t r o n density which occur a t the bottom of the F-layer or as much as 100 km lower. The thickness of these patches was estimated a t the order of 50 km. The scat- t e r i n g i r r e g u l a r i t i e s comprising these patches were found to be elongated along the earth's magnetic l i n e s of force. Electron i r r e g u l a r i t i e s of scale 10 meters or smal- l e r , measured i n a t l e a s t one dimension transverse to the magnetic f i e l d l i n e s , and 1000 meters or longer, measured along the magnetic f i e l d l i n e s , were shown to e x i s t as high as 450 km i n the nocturnal e q u a t o r i a l F-region during e q u a t o r i a l Spread F con- d i t i o n s . Equatorial Spread F echoes observed a t Huancayo were demonstrated to be ar- r i v i n g at a l l e l e v a t i o n angles i n the magnetic east-west plane. The geographical ex- tension of a given s c a t t e r i n g sheet i n the magnetic east-west d i r e c t i o n was a t times as great as 1000 km. An observational procedure has been suggested f o r d i s t i n g u i s h i n g two fundamental v a r i e t i e s of Spread F echoes appearing on e q u a t o r i a l lonograms. A ne- cessary c o n d i t i o n , t h a t the contours of mean e l e c t r o n density be p a r a l l e l to the mag- ne t i c l i n e s of f o r c e , has been proposed as a c o n t r o l l i n g f a c t o r f o r the occurrence of Spread F m the e q u a t o r i a l ionosphere. 6. Bibliography. a. Papers Presented a t Meetings. R. S. Cohen and K. L. Bowles: "50-Mc Oblique Transmission Experiment Near the Magnetic Equator." Spring meeting, URSI, 23-26 A p r i l 1958, Washington, D. C. Abstract published i n Trans. IRE PGAP, AP-6, no. 3, 316 ( J u l y , 1958). 269

IONOSPHERIC PHYSICS K. L. Bowles and R. S. Cohen: "Observations of F Layer Scatter Near the Mag- n e t i c Equator." Spring meeting, URSI, 4-7 May 1959, Washington, D. C. Ab- s t r a c t published m Trans. IRE PGAP, AP-7, no. 3, 291 ( J u l y , 1959). Kenneth L. Bowles and Robert Cohen: "Studies of Scattering Phenomena i n the Equatorial Ionosphere Based upon VHF Transmissions Across the Magnetic Equa- t o r . " Brussels meeting of the URSI-AGI Committee, 1-3 September 1959, Brus- se l s , Belgium. Abstract i s on pp. 192-194 of the book "Some Ionospheric Re- s u l t s Obtained During the I n t e r n a t i o n a l Geophysical Year." W. J. G. Beynon, ed. (El s e v i e r , 1960). Kenneth L. Bowles and Robert Cohen: "A Study of the E q u a t o r i a l E l e c t r o j e t by Radio Techniques." Spring meeting, AGU, 27-30 A p r i l 1960, Washington, D. C. Abstract published i n JGR, v o l . 65, no. 8, pp. 2476-2477 (August, 1960). Wynne Calvert and Robert Cohen: "The I n t e r p r e t a t i o n and Synthesis of Certain Spread F Configurations Appearing on Equatori a l lonograms." Spring meeting, URSI, 2-4 May 1961, Washington, D. C. Abstract probably to appear i n Trans. IRE PGAP, AP-9. no. 4 ( J u l y , 1961). Robert Cohen, Kenneth L. Bowles and Wynne Calvert: "On the Nature of Equato- r i a l Slant Sporadic E." Spring meeting, URSI, 2-4 May 1961, Washington, D. C. Abstract probably to appear i n Trans. IRE PGAP, AP-9, no. 4 (Jul y 1961). b. Published Papers. Kenneth Bowles and Robert Cohen: "NBS Equatorial Region VHF Scatter Research Program f o r the IGY." QST, v o l . 41, pp. 11-15 (August 1957). Kenneth Bowles y Robert Cohen. "Programa de inve s t i g a c i 6 n d e l N. B. S. sobre l a dispersion en VHF e c u a t o r i a l para e l aflo g e o f f s i c o i n t e r n a c i o n a l . " Revista T e l e g r ^ f i c a Electr6nica (Argentina), v o l . 46, no. 541, pp. 655-658 (Noviembre 1957). (Translation of the above a r t i c l e . ) David M. Gates: "Preliminary Results of the National Bureau of Standards Radio and Ionospheric Observations during the I n t e r n a t i o n a l Geophysical Year," J. Research of the NBS, v o l . 63D, no. 1, 1-14 (July-August 1959). K. L. Bowles, R. Cohen, G. R. Ochs, B. B. Balsley. "Radio Echoes from F i e l d - Aligned I o n i z a t i o n Above the Magnetic Equator and Their Resemblance to Auroral Echoes." JGR., v o l . 65, no. 6, pp. 1853-1855 (June 1960). R. Cohen and K. L. Bowles: "On the Nature of Equatorial Spread F." JGR.. v o l . 66, no. 4, pp. 1081-1106 ( A p r i l 1961). Wynne Calvert and R. Cohen: "The I n t e r p r e t a t i o n and Synthesis of Certain Spread F Configurations Appearing on Equatori a l lonograms." JGR., v o l . 66, no. 10, pp. 3125-3140 (October 1961). K. L. Bowles and R. Cohen: "A Study of Radio Wave Scattering from Sporadic E Near the Magnetic Equator." Ionospheric Sporadic E, E. K. Smith and S. Matsushita, E d i t o r s , Pergamon Press, 1962. M. L. V. Pitteway and R. Cohen: "A Waveguide I n t e r p r e t a t i o n of 'Temperate- Lat i t u d e Spread F* on Equatorial lonograms." JGR., v o l . 66, no. 10, pp. 3141-3156 (October 1961). 270

IONOSPHERIC PHYSICS R. Cohen, K. L. Bowles and Wynne Calvert: "On the Nature of E q u a t o r i a l Slant Sporadic E." JGR., v o l . 67, no. 3, pp. 965-972 (March 1962). * K. L. Bowles and R. Cohen: "Ionospheric VHF Scattering Near the Magnetic Equator During the I n t e r n a t i o n a l Geophysical Year." J. of Research of the NBS, v o l . 67D, no. 5, pp. 459-480 (September-October 1963). * R. Cohen and K. L. Bowles: "The Association of Plane-Wave Electron-Density I r r e g u l a r i t i e s w i t h the E q u a t o r i a l E l e c t r o j e t . " JGR.. v o l . 68, no. 9, pp. 2503-2525 (May 1963). ** k. L. Bowles, B. B. Balsley and Robert Cohen: "Field-Aligned E-Region I r r e - g u l a r i t i e s I d e n t i f i e d w i t h Acoustic Plasma Waves." JGR., v o l . 68, no. 9, pp. 2485-2501 (May 1963). * Papers given t o URSI f a l l meeting i n Ottawa, October 1962. ** Paper presented a t URSI spring meeting, Washington, D. C, May 1963. 271

IONOSPHERIC PHYSICS Project 6.7 - Radio Noise Measurement 1. Objectives. This p r o j e c t at CRPL, National Bureau of Standards, provided f o r r a - dio noise recorders and a u x i l i a r y equipment f o r e x i s t i n g noise recorders i n order to expand f o r the IGY the scope of the CRPL noise program already i n operation. The ob- j e c t i v e of t h i s program was the measurement of the average radio noise ( t e r r e s t r i a l , g a l a c t i c , man-made) power, voltage, and logarithm of the noise envelope received a t a number of geographic l o c a t i o n s . These parameters were chosen to be measured since they adequately describe the character and l e v e l of the radio noise. The operation of the radio noise recorders during IGY provided d e t a i l e d information of received a t - mospheric noise l e v e l s to be used as an engineering basis f o r frequency a l l o c a t i o n s , and are also of great value and i n t e r e s t as a new t o o l f o r i n v e s t i g a t i n g the ionosphere. The data obtained were also of some i n t e r e s t i n the f i e l d of meteorology since they provided an integrated p i c t u r e of the received noise i n t e n s i t y from world-wide thunder- storm a c t i v i t y . A d d i t i o n a l i nformation was supplied concerning the d i r e c t i o n of a r r i - v a l of the noise by the use of DF equipment a t some s t a t i o n s . The r a d i o noise record- ing s t a t i o n s continued i n operation a f t e r the close of IGY as part of the regular net- work being established by CRPL. 2. Operations. A number of new s t a t i o n s were i n s t a l l e d f o r the IGY program i n c l u d i n g Byrd S t a t i o n , A n t a r c t i c a . Equipment was also i n s t a l l e d a t locations i n other countries through the cooperation of l o c a l i n s t i t u t i o n s and the IGY committees of the countries concerned. The mean power of the noise, averaged over several minutes, was the basic parame- t e r measured and was expressed as an e f f e c t i v e antenna-noise f i g u r e . This i s defined as the noise power a v a i l a b l e from an equivalent lossless antenna i n decibels (db) a- bove the thermal-noise (white-noise) power of a passive resistance. The NBS r a d i o - noise recorder. Model ARN-2, has an e f f e c t i v e bandwidth of 150 to 300 cps. A v e r t i c a l antenna, 66 m long, was used i n conjunction w i t h an elevated ground-plane. Eight channels between 13 kc and 20 Mc were used, two channels being recorded simultaneously. A 15-minute recording was made on each frequency each hour, and was taken as represen- t a t i v e of the noise conditions during the hour. Instantaneous amplitude p r o b a b i l i t y d i s t r i b u t i o n s were obtained a t Boulder, Colorado, to provide i n f o r m a t i o n concerning the d e t a i l e d character of the noise from which i t s i n t e r f e r e n c e p r o p e r t i e s can be determined. 3. Personnel. This p r o j e c t was supervised by W. Q. Crichlow, R. T. Disney, and C. A. Samson. 4. Data. A l l data recorded during the IGY were published i n IGY data booklets and q u a r t e r l y summaries have been issued as NBS reports g i v i n g trends and t e n t a t i v e con- clusions. These are a v a i l a b l e from WDC-A, Ionosphere (CRPL). 5. Results. Preliminary r e s u l t s would i n d i c a t e that the world-wide p r e d i c t i o n s as presented by the C. C. I . R. Report No. 65 are too s i m p l i f i e d . The behavior of ra d i o noise, as a f u n c t i o n of the frequency, time of day and season, d i f f e r s widely from l o c a t i o n to l o c a t i o n . Specific l o c a l conditions need to be w e l l understood i n order to make accurate p r e d i c t i o n s . As a few examples of t h i s one can point out the f o l l o w i n g : afternoon noise l e v e l s i n areas of high l o c a l thunderstorm a c t i v i t y may be 20 t o 30 db higher than i n d i c a t e d by the p r e d i c t i o n s . Boulder, Colorado, i s a good example of t h i s , since i t i s located near one of the most a c t i v e thunderstorm regions i n the United States, the f r o n t range of the Rocky Mountains. On c e r t a i n days the v a r i a t i o n may be as much as 70 db, on some frequencies. I n co n t r a s t , a t Kekaha, Hawaii, the minimum noise l e v e l s f o r the low f r e - 272

IONOSPHERIC PHYSICS quencies tend t o occur near sunset instead of a few hours a f t e r sunrise as a t most sta- t i o n s . As a r e s u l t , the 160-kc afternoon noise levels appear to be 20 to 30 db lower than predicted a t t h i s l o c a t i o n . The nighttime noise l e v e l s a t Boulder are o f t e n lower than predicted while a t Kekaha they agree rather w e l l w i t h the p r e d i c t i o n s . 6. Bibliography. a. Papers Presented a t Meetings. Robert C. Davis: " P r e d i c t i o n of Atmospheric Noise Levels from Thunderstorm Counts." URSI-IRE F a l l Meeting, December 12-14, 1960, Boulder, Colorado. Charles J. Roubique: "Instrumentation f o r Recording Spectrum Occupancy and Radio Noise Levels." URSI-IRE F a l l Meeting, December 12-14, 1960, Boulder, Colorado. Charles J. Roubique and A. D. Spaulding: "Bandwidth Conversion of Amplitude- P r o b a b i l i t y D i s t r i b u t i o n of Atmospheric Radio Noise." URSI, May 4, 1960, Washington, D. C. Robert T. Disney. "A Comparison of Man-Made Radio Noise w i t h Noise of Natural O r i g i n a t Several Fixed Locations." URSI, May 4, 1960, Washington, D. C. Wil l i a m Q. Crlchlow "NBS Radio Noise Program." Colorado Cooperative I n t e r - ference Committee, January 20, 1960, Denver, Colorado. C. A. Samson: "E f f e c t s of High-Altitude Nuclear Explosions on Radio Noise." URSI, October 19-21, 1959, San Diego, C a l i f o r n i a . Robert T. Disney: "Layman's Course on IGY: Atmospheric Radio Noise." Unive r s i t y of Colorado Extension Center, A p r i l 30, 1958, Colorado Springs, Colorado. A. D. Spaulding and J. Halton: "Determination of Binary Error Rates f o r the D i f f e r e n t i a l l y Coherent PSK Communication System Acting i n Non-Gausian Noise," URSI, A p r i l 15-18, 1964, Washington, D. C. C. A. Samson: "Some Recent Noise Measurements and Comparisons w i t h Predic- t i o n s . " URSI, A p r i l 24-26, 1958, Washington, D. C. R. T. Disney: "Radio Noise and the IGY." Arvada Science Club, Arvada High School, November 20, 1957. b. Published Papers. W. Q. Crlchlow, C. A. Samson, R. T. Disney, and M. A. Jenkins. "Radio Noise Data f o r the I n t e r n a t i o n a l Geophysical Year, July 1, 1957 - December 31, 1958." NBS Tech. Note No. 18, July 27, 1959. W. Q. Crlchlow, R. T. Disney, and M. A. Jenkins: "Quarterly Radio Noise Data." NBS Tech. Note Nos. 18-2 - 18-19 covering the q u a r t e r l y periods March 1959 through August 1963. W. Q. Crichlow: "Noise I n v e s t i g a t i o n at VLF by the National Bureau of Standards." Proc. IRE, v o l . 45, 6, 778 (1957). 273

IONOSPHERIC PHYSICS W. Q. Crichlow, C. J. Roubique, A. D. Spaulding, and W. M. Beery: "Determina- t i o n of the Amplitude-Probability D i s t r i b u t i o n of Atmospheric Radio Noise from S t a t i s t i c a l Moments." NBS J. Research-D. Radio Propagation, v o l . 64D 1, 49 (1960). W. Q. Crichlow, A. D. Spaulding, C. J. Roubique, and R. T. Disney: "Ampli- tude P r o b a b i l i t y D i s t r i b u t i o n s f o r Atmospheric Radio Noise." NBS Monograph 23, November 4, 1960. W. Q. Crichlow and R. T. Disney: "Predictions of Radio Noise and Systems App l i c a t i o n s . " NBS Course m Radio Propagation, 1961. W. Q. Crichlow, C. J. Roubique, A.' D; Spaulding, and W. M. Beery: " I n t e r - ference P r e d i c t i o n . " January, 1960. W. Q. Crichlow and R. T. Disney: " T e r r e s t r i a l Radio Noise." URSI National Committee Report, XIV General Assembly, Tokyo, September, 1963: Commission 4, Section 3. "World D i s t r i b u t i o n and C h a r a c t e r i s t i c s of Atmospheric Radio Noise." C.C.I.R. Report 322, X Plenary Assembly, Geneva, 1963 ( I n t e r n a t i o n a l Radio Consultative Committee, S e c r e t a r i a t , Geneva, Switzerland). F. F. Fulton, J r . : "The E f f e c t of Receiver Bandwidth on Amplitude D i s t r i b u - t i o n of VLF Atmospheric Noise." National Bureau of Standards, VLF Symposium Paper 37, Boulder, Colorado, 1957. F. F. Fulton, J r . : " E f f e c t of Receiver Bandwidth on the Amplitude D i s t r i b u - t i o n of VLF Atmospheric Noise." J. of Res., v o l . 65D, no. 3, May-June, 1961. C. A. Samson: "E f f e c t s of High-Altitude Nuclear Explosions on Radio Noise." J. of Res, v o l . 64D, no. 1, January-February, 1960. A. D. Spaulding, C. J. Roubique, and W. Q. Crichlow, (November-December, 1962): "Conversion of the Amplitude-Probability D i s t r i b u t i o n Function f o r Atmospheric Radio Noise from One Bandwidth t o Another." J. of Res, v o l . 66D (Radio Pro- pagation) no. 6, pp. 713-720. A. D. Spaulding: "Determination of Error Rates f o r Narrow-Band Communication of Binary-Coded Messages i n Atmospheric Radio Noise." Proceed, of IEEE, v o l . 52, no. 2, February 1964. U. R. S. I . Special Report No. 7- "The Measurement of C h a r a c t e r i s t i c s of T e r r e s t r i a l Radio Noise." Elsevier Publishing Co. (1962.). A. D. Watt, R. M. Coon, E. L. Maxwell, and R. W. Plush: "Performance of Some Radio Systems i n the Presence of Thermal and Atmospheric Noise." Proceed. of IRE, December 1958. 274

IONOSPHERIC PHYSICS Project 6.8 - Ionospheric Absorption-Pulse Method 1. Objectives. This p r o j e c t a t the Ionosphere Research Laboratory, Pennsylvania State U n i v e r s i t y , provided f o r absorption measurements using v e r t i c a l incidence pulse equipment, i n accordance w i t h CSAGI recommendations. 2. Operations. Equipment was i n s t a l l e d a t a f i e l d s t a t i o n near the campus a t Univer- s i t y Park. The t r a n s m i t t e r had a peak power of 10 kw, w i t h a pulse w i d t h of 100 micro- seconds. Two C O - l i n e a r folded d i p o l e antennas, one f o r t r a n s m i t t i n g and one f o r r e - c e i v i n g , were erected, about 80 f e e t above ground l e v e l . They were broad-banded, and quasi-resonant a t 2.6 Mc. Frequency a l l o c a t i o n s of 2.155, 2.600 and 3.208 Mc were ob- tained from FCC and CAA; t h i s allowed compliance w i t h CSAGI recommendations of 2.2 + 0.2 Mc. Observations were made, then, at 2.155 Mc, and also at 2.600 Mc according to time of year. Observations commenced on July 1, 1957, and continued through Decem- ber 31, 1958. An automatic recorder was placed i n t o operation l a t e i n the IGY, but manual recording was also continued to preserve c o n t i n u i t y . Only the r e s u l t s of the manual recordings were included i n the reports d i s t r i b u t e d concerning t h i s work. 3. Personnel. Dr. A. H. Waynick supervised t h i s p r o j e c t . Senior personnel associated w i t h the work were Dr. Sidney S t e i n , Dr. S. A. B o w h i l l , and Dr. R. S. M i t t r a . 4. Data. A l l data from the IGY period have been processed. Six data booklets were prepared, each of which contains the data f o r one quarter. The booklets have been d i s t r i b u t e d to i n t e r e s t e d workers as w e l l as the IGY World Data Centers. 5. Results. Absorption measurements were c a r r i e d out according t o the f o l l o w i n g schedule f o r s i x days of the week: a. Noontime measurements: Six 15-minute samples were obtained on 2.155 Mc s t a r t i n g a t 1130, 1145 and 1200 and continuing to 1245, 1300 and 1315. During days i n which the d i u r n a l v a r i a t i o n of absorption was determined the schedule i n (c) was followed. b. Constant solar zenith-angle measurements: Two consecutive 15-minute samples were obtained f o r Cos x z 0.4 on 2.155 Mc and 2.600 Mc. One frequency was used i n the morning and the other i n the afternoon, the order being reversed on successive days. The timing of the samples was arranged so th a t Cos x s 0.4 occurred w i t h i n the measuring i n t e r v a l while maintaining the s t a r t time on quarter hours E.S.T. c. Diur n a l measurements; On a t l e a s t one day of each week and on a l l r egular world days the d i u r n a l v a r i a t i o n of absorption was obtained on 2,155 Mc and 2.600 Mc, Measurements commenced on the quarter hour preceding the hour and ended on the quarter hour a f t e r the hour. The two frequencies were r o t a t e d each hour. Various exigencies and d i f f i c u l t i e s of a wide v a r i e t y forced a small number of changes from t h i s schedule. A l l such changes may be found I n the tabulated data. No s p e c i f i c analysis of the data were undertaken although they have been used i n other studies such as "The Determination of the World-Wide E f f e c t i v e Recombination C o e f f i c i e n t of the E-Region.", by F. D. P a l l u c o n i , S c i e n t i f i c Report No, 198, Iono- sphere Res. Lab., Penn State U n i v e r s i t y , November 1, 1963. 6. Bibliography. a. Published Papers. S. A. B o w h i l l , G. R. P. Bulman, R. M i t t r a : "Instrumentations f o r the Auto- matic Observation of High Frequency Ionospheric Absorption." S c i e n t i f i c Re- port No. 98, Ionosphere Res. Lab., Penn State U n i v e r s i t y , December 1957. 275

IONOSPHERIC PHYSICS Project 6.9 - True Height Determination 1. Objectives. This p r o j e c t a t the Ionosphere Research Laboratory, Pennsylvania State U n i v e r s i t y was part of a CSAGI recommended program to obtain N(h) ( e l e c t r o n density N as a f u n c t i o n of height h) p r o f i l e s from v e r t i c a l incidence records a t se- lected locations f o r the IGY period. 2. Operations. V e r t i c a l - i n c i d e n c e lonograms give the v i r t u a l heights of r e f l e c t i n g regions versus frequency ( h ' - f curves), and while these contain much inf o r m a t i o n t h a t can be r e a d i l y e x t r a c t e d , they do not a t once supply a l l the d e t a i l s concerning v e r t i - c a l e l e c t r o n d i s t r i b u t i o n t h a t ionospheric p h y s i c i s t s need f o r various areas of r e - search. A method was developed by Budden to e x t r a c t from h'-f curves the e l e c t r o n density N as a f u n c t i o n of true height h(N(h) curves), using the group r e f r a c t i v e index ex- pressed as a matrix. The height h i s then derived by a process of matrix i n v e r s i o n and m u l t i p l i c a t i o n on a d i g i t a l computer. A matrix i s computed f o r each l o c a t i o n i n a way that takes account of the magnetic f i e l d . For the IGY program, t h i s method was modified to improve the r e s u l t s . The matrix was enlarged from a 30-square to a 40- square array. This required extensive receding i n order not to tax the data handling c a p a b i l i t y of the computer. Four s t a t i o n s were chosen from which to reduce data. These were selected to be at a range of l a t i t u d e s , approximately equal i n longitude, and w e l l separated from the sta t i o n s being analyzed by B r i t i s h workers, w i t h whom close contact was maintained, both i n e s t a b l i s h i n g the program and during i t s operation. The s t a t i o n s were the NBS sta t i o n s at Fort B e l v o i r , V i r g i n i a (near Washington, D. C ) , Panama, and Talara and Huancayo, Peru, which were operated by Peruvian s c i e n t i s t s i n cooperation w i t h NBS. For each s t a t i o n , ten magnetically q u i e t days and three World Days were analyzed. Methods were explored to determine the best way of sampling the o r i g i n a l h'-f curves. I t was decided to compute f o r each s t a t i o n three matrices, f o r sampling i n - t e r v a l s of 0.2, 0.33 and 0.5 Mc. I n t h i s way the matrix f o r each h'-f curve could be chosen to make best use of the av a i l a b l e data. Standard 35 mm pro j e c t o r s were tested f o r use i n scaling the records. They were found to have inadequate o p t i c a l systems and a photographic enlarger to which a high- q u a l i t y lens was attached proved to be s a t i s f a c t o r y . A v a i l a b l e computing f a c i l i t i e s , i n c l u d i n g the Pennstac d i g i t a l computer, were used f o r t h i s p r o j e c t . 3. Personnel. The p r o j e c t was supervised by Dr. A. H. Waynick. Dr. Erwin Schmerling was the senior s c i e n t i s t associated w i t h the work. 4. Data. The data were tabulated and p l o t t e d f o r the four s t a t i o n s f o r each month and published i n a series of 18 monthly books, which were d i s t r i b u t e d to i n t e r e s t e d workers as w e l l as the IGY World Data Centers, 5. Results, As indic a t e d above, these tables have been computed from r o u t i n e lono- grams by the matrix method of Budden, The d e t a i l s of the method as used here are more f u l l y discussed by Schmerling (1957), 40 x 40 matrices were used, two matrices being computed f o r each s t a t i o n , to cover the ranges 1.6(0.2)9.6 Mc and 2.0(0.5)22 Mc. For F2 c r i t i c a l frequencies below 10 Mc the former matrices were used, and f o r F2 c r i t i - cals above 10 Mc, the l a t t e r . I n a d d i t i o n , i f s i g n i f i c a n t s t r u c t u r a l d e t a i l s were seen on lonograms w i t h F2 c r i t i c a l s above 10 Mc, the former matrices were used to determine the p r o f i l e s i n greater d e t a i l below 10 Mc. The method takes f u l l account of the earth's magnetic f i e l d , but ignores e l e c t r o n i c c o l l i s i o n s . No assumptions are 276

IONOSPHERIC PHYSICS made as to p r o f i l e shape other than a monotonic v a r i a t i o n of e l e c t r o n density w i t h height. A t t e n t i o n i s drawn to several scaling p r a c t i c e s . On occasions when the E region cusps were not v i s i b l e on the ionograms (due to absorption by sporadic E or from other causes), the E-F t r a n s i t i o n s were sketched i n from the monthly median values of f^E as given by the CRPL i n t h e i r s t a t i o n booklets of F-series p u b l i c a t i o n s . Since the day- to-day v a r i a b i l i t y of f^E i s -small, i t i s not considered t h a t t h i s procedure leads to s i g n i f i c a n t e r r o r s . The i n d i v i d u a l electron-density-height p r o f i l e s were drawn f o r each hour, and the peaks of the p r o f i l e s sketched i n by e x t r a p o l a t i n g t o tangency w i t h the peak e l e c t r o n density, as found from foF2. Errors m t h i s e x t r a p o l a t i o n are very small when e l e c t r o n densites are read at f i x e d heights, since the p r o f i l e s are nearly v e r t i c a l i n t h i s region. The heights a t the e l e c t r o n peaks, on the other hand, are not w e l l defined, and f o r t h i s reason no attempt has been made to measure The p r o f i l e s are not r e l i a b l e a t the lowest heights, due t o the low-frequency cut- o f f on the ionograms. Some discussion of t h i s e f f e c t i s given by Schmerling (1957). For the same reason, the presence of an E-layer below the lowest scaled frequency can also cause appreciable errors a t the lower heights. This e f f e c t occurs a t night and near sunrise and sunset. A discussion of t h i s p o i n t i s given by Thomas, Haselgrove and Robbins m t h e i r i n t r o d u c t i o n to the English Tables of Electron Density. The tables give e l e c t r o n d e n s i t i e s a t i n t e r v a l s of 20 km every hour f o r the Regu- l a r World Days and the 10 magnetically q u i e t e s t days. The f i r s t column gives e l e c t r o n d e n s i t i e s i n u n i t s of 10^ electrons/cc. Times are given i n the top row. These are l o c a l zone times, d i f f e r i n g from UT by an i n t e g r a l number of hours. The symbol NmF denotes the maximum e l e c t r o n density, as obtained from fQF2. Analysis of the N(h) data i s described i n Project 22.9. 6. Bibliography. a. Papers Presented at Meetings. E. R. Schmerling: " I n c l u s i o n of the Earth's F i e l d m a Simple and Rapid Method f o r Reducing h'-f Curves to Electron-Density-Height P r o f i l e s . " URSI Meeting, May 1957, Washington, D. C. E. R. Schmerling- "Electron-Density-Height P r o f i l e s from Routine Ionograms." URSI Meeting, A p r i l 1958, Washington, D. C. E . R. Schmerling: "Electron-Density Height P r o f i l e s from Routine Ionograms." Vth CSAGI Assembly, August 1958, Moscow. S. Chandra, J . J . Gibbons, E . R. Schmerling: "A Study of V e r t i c a l D r i f t i n the F-Region from True Height P r o f i l e s . " URSI Meeting, October 1958, State College. C. A. Ventrice, E. R. Schmerling: " C o e f f i c i e n t s f o r the Rapid Reduction of h'-f Records to N-h P r o f i l e s Without Computing Aids." URSI Meeting, October 1958, State College. D. Grant, E. R. Schmerling: "The Determination of Consistent Ionospheric Parameters f o r Region F from Electron Density Height P r o f i l e s . " URSI Meeting, May 1959, Washington, D. C. S. Chandra, J. J. Gibbons, E. R. Schmerling: "Diurnal V a r i a t i o n of V e r t i c a l D r i f t i n the F-Region." URSI Meeting, May 1959, Washington, D. C. 277

IONOSPHERIC PHYSICS S. Chandra, J. J. Gibbons, E. R. Schmerling: " V e r t i c a l Transport V e l o c i t i e s i n Region F." URSI-IGY Meeting, September 1959, Brussels. D. Grant, E. R. Schmerling: "The Determinations of Consistent Ionospheric Parameters f o r Region F from Electron-Density-Height P r o f i l e s . " URSI-IGY September 1959, Brussels. E. R. Schmerling. "Height and Thickness Changes i n Region F of the Ionosphere." URSI-IGY Meeting, September 1959, Brussels. Y. V. Somayajulu. "Magnetic Storm E f f e c t s on the Electron Density D i s t r i b u t i o n of the F-Region of the Ionosphere." URSI Meeting, May 1960, Washington, D. C. D. Grant, E. R. Schmerling: "The Charge Transfer Mechanism i n Region F of the Ionosphere." URSI Meeting, May 1960, Washington, D. C. b. Published Papers. E. R. Schmerling. Sci. Report 94, 1957, Ionosphere Research Lab., Penn State U n i v e r s i t y . E. R. Schmerling. "An Eas i l y Applied Method f o r the Reduction of h'-f Records to N-h P r o f i l e s I n c l u d i n g the E f f e c t s of the Earth's Magnetic F i e l d . J.A.T.P. v o l . 12, 1957, pp. 8-16. E. R, Schmerling, C. A. Ventrice: " C o e f f i c i e n t s f o r the Rapid Reduction of h'-f Records to H-h P r o f i l e s Without Computing Aids." J.A.T.P., v o l . 14, 1958, pp. 249-261. Y. V. Somayajulu. "Magnetic Storm E f f e c t s on the F Region of the Ionosphere." JGR. v o l . 65, 1960, pp. 893-895. E. R. Schmerling: "Height and Thickness Parameters f o r Region F of the Iono- sphere." JGR. v o l . 65, 1960, pp. 1072-1073. S. Chandra, J. J. Gibbons, E. R. Schmerling: " V e r t i c a l Transport of Electrons i n the F Region of the Ionosphere." JGR, v o l . 65, 1960, pp. 1159-1175. E. R. Schmerling: "The E f f e c t s of V e r t i c a l D i f f u s i o n Near the Magnetic Equa- t o r . " Nature, v o l . 188, no. 4745, pp. 133-134, October 8, 1960. S. A. B o w h i l l , E. R. Schmerling: "The D i s t r i b u t i o n of Electrons i n the Iono- sphere." Electron Physics, v o l . 15, pp. 265-326, 1961, Academic Press. Y. V. Somayajulu: "A Study of the Changes i n F-Region During Severe Magnetic Storms." S c i e n t i f i c Report No. 146, Ionosphere Research Lab., Penn State U n i v e r s i t y , March 1961. E. R. Schmerling, D. Grant: "An Analysis of the Electron Densities i n Region F of the Ionosphere." S c i e n t i f i c Report No. 147, Ionosphere Res. Lab., Penn State U n i v e r s i t y , A p r i l 1961. 278

IONOSPHERIC PHYSICS Project 6.10 - Whistler Program - West 1. Objectives. The primary purpose of t h i s p r o j e c t at the Radio Science Laboratory, Stanford U n i v e r s i t y , was to c o l l e c t data on occurrence ( i n space and time) and charac- t e r i s t i c s of w h i s t l e r s and r e l a t e d v l f phenomena, such as dawn chorus, h i s s , e t c . , i n the range of 400 - 30,000 cps. Stations were set up covering a wide range of l a t i t u d e so that northern and southern locations were approximately conjugate w i t h respect to the magnetic f i e l d . 2. Operations. Equipment was developed a t Stanford f o r t h i s p r o j e c t . The t y p i c a l s t a t i o n included: a. antenna• single t u r n v e r t i c a l t r i a n g u l a r loop of 30-foot a l t i t u d e and 60-foot base, located 250 to 1000 fee t from recorder b u i l d i n g and oriented f o r minimum power l i n e i n t e r f e r e n c e . b. p r e a m p l i f i e r : balanced 100-ohm output, 100 db dynamic range, low-noise cas- code input stage, mounted a t base of antenna. c. mixer-monitor: automatic WWV and l o c a l time mark i n j e c t i o n , also providing f o r a u r a l monitoring of incoming signals and microphone input f o r voice announcements. d. tape recorder: h a l f track heads, modified f o r constant current recording c h a r a c t e r i s t i c . Also provided were a c a l i b r a t o r and volt-meter, program clock, WWV- WWVH receiv e r , and power supply. Stations were set up by personnel from the Radio Science Laboratory and operated by l o c a l personnel a t cooperating i n s t i t u t i o n s and agencies. A troublesome problem at some s t a t i o n s was pickup from power l i n e s , which was solved by high-pass f i l t e r s and r e l o c a t i o n of antennas. S t a t i o n Geomag. Lat. St a r t Date Operating Group Kotzebue, Alaska 64°N 11/57 Geophys. I n s t . U. of Alaska College, Alaska 65°N 11/57 Geophys. I n s t . U. of Alaska Anchorage, Alaska 61°N 11/57 N. B, S. Seat t l e , Wash. 54° N 1/58 Contracted to Private Party Unalaska, Alaska 51°N 5/58 Geophys. Ins. Boulder, Colo. 49°N 8/57 N. B. S. Stanford, C a l i f . 44° N 7/57 Stanford Wellington, N. Z. 45°S 8/57 Dom. Phys. Lab., N. Z. Dunedm, N. Z. 51°S 2/58 N. Z. Broadcasting Co. Maquarie I s . 61° S 5/58 Ant. Dlv., A u s t r a l i a n Dept. External A f f a i r s Byrd S t a t i o n , Ant. 10/58 N. B. S. A n t a r c t i c Personnel A recording schedule of two minutes every hour was chosen to provide a reasonable sampling of a c t i v i t y without producing an unmanageable q u a n t i t y of data. Special s t o r i n g f a c i l i t i e s were provided f o r the tapes, which were arranged i n a l i b r a r y to f a c i l i t a t e reference. 3. Personnel. Dr. R, A. H e l l i w e l l supervised t h i s p r o j e c t ; R. L. Smith, J. H, Crary and W. T. Kreiss were the senior personnel associated w i t h Dr. H e l l i w e l l during the i n i t i a l phases of the program. 279

IONOSPHERIC PHYSICS 4. Data. Tapes have been monitored and events logged. Log sheets were submitted to the IGY World Data Centers. The o r i g i n a l tapes are retained at Stanford f o r an a l y s i s . A f t e r tapes were monitored and events logged, spectrograms were obtained f o r de- s i r e d events w i t h a Kay E l e c t r i c Sonagraph. I t was found to take, on the average, f i v e minutes f o r the scanning process f o r each spectrogram. A standard c a l i b r a t i o n was ob- tained by supplying the sonagraph w i t h two t r a i n s of impusles a t r e p e t i t i o n rates of 10 and 500 per second r e s p e c t i v e l y . From the sonagrams, which present a p l o t of f r e - quency (0-8 kc or 0-16, 0-20, 0-32 kc) versus time (2.4 seconds f o r 0-8 kc range) on a sheet of paper about 10 x 30 cm, q u a n t i t a t i v e information could be derived, i n c l u d i n g time delays r e l a t i v e to some f i x e d p o i n t , upper and lower c u t o f f frequencies, r e l a t i v e i n t e n s i t y of various w h i s t l e r components, and slope of w h i s t l e r t r a c e . 5. Results. A d e t a i l e d discussion of a l l phenomena, t h e i r c h a r a c t e r i s t i c s and what may be i n f e r r e d from them i s beyond the scope of t h i s discussion. Only a few examples are taken from the d e t a i l e d Stanford f i n a l r e p o r t . a. C l a s s i f i c a t i o n of Phenomena. One of the f i r s t tasks was to develop a nomen- cl a t u r e f o r the various events, which have c h a r a c t e r i s t i c a u r a l and s p e c t r a l proper- t i e s . Some of these are defined and described below and conform r a t h e r c l o s e l y t o terms used by other workers. ( i ) Atmospherics -- Signals a r i s i n g from v l f energy from a l i g h t n i n g discharge which has propagated between the e a r t h and the lower boundary of the ionosphere. (a) Tweek - a short musical c h i r p , the musical q u a l i t y a r i s i n g from d i s - persion of the energy i n the range j u s t above the tweek c u t o f f f r e - quency. The amount of curvature seen on the spectrogram i s an i n d i - c a t i o n of the distance over which the atmospheric has t r a v e l l e d . (b) Ordinary Impulse - an atmospheric w i t h no s p e c i a l s p e c t r a l character- i s t i c , c o n s t i t u t i n g the bulk of s h o r t - w h i s t l e r sources. (c) Bonk - an atmospheric of unusually long d u r a t i o n but without the d i s - t i n c t l y musical q u a l i t y of a tweek, usually associated w i t h storms i n the hemisphere of the receiver. ( i i ) W h i s tlers. (a) Short Whistler - a w h i s t l e r that has t r a v e l l e d once through the iono- sphere, a "one-hop" w h i s t l e r . (See F i g . 3 ) . (b) Long Whistler - a w h i s t l e r t h a t has t r a v e l l e d twice through the iono- sphere, a "two-hop" w h i s t l e r . (See F i g . 3 ) . (c) Nose Whistler - a w h i s t l e r that e x h i b i t s simultaneous r i s i n g and f a l l i n g tones joined together i n a continuous and smooth manner a t the frequency of mmimxmi time delay -- the nose frequency. Normally t h i s property can be defined only by spectrographic a n a l y s i s . (See Fig . 4 ) . (d) Whistler Echo Tr a i n - a succession of w h i s t l e r s r e s u l t i n g from r e - peated traverses of the o r i g i n a l disturbance through the ionosphere. Usually the time delays of echoes of short w h i s t l e r s are i n the r a t i o s 1.3 5 7 ... and f o r long w h i s t l e r s are i n the r a t i o s 2 4 6.8 ... . (See F i g . 5 ) . 280

IONOSPHERIC PHYSICS Kc 8 S T 9 F E B 1 9 5 9 0 9 3 6 - 2 8 U T A , Kc 8 S T 9 F E B 1 9 5 9 0 9 3 6 ' 3 7 U T B E B4 C, O- lOsec Figure 3. Short and Long Whistlers Kc mi. S E 7 J U N E 1 9 5 9 1 3 3 6 - 2 3 U T - 0 5see- Figure 4. Nose Whistler Kc 8 - 21 DEC 1958 1235 27 UT ' V I I I I' f - 1 0 sec- Figure 5. Whistler Echo Tr a i n 281

IONOSPHERIC PHYSICS ( i i i ) I o n o s p h e r i c Noise - a l l n a t u r a l l y o c c u r r i n g e l e c t r o m a g n e t i c n o i s e o r i g i - n a t i n g i n the atmosphere e x c e p t a t m o s p h e r i c s , w h i s t l e r s , and w h i s t l e r i n t e r a c t i o n s . ( a ) H i s s - n o i s e r e s e m b l i n g b a n d - l i m i t e d w h i t e - n o i s e . (See F i g . 6 ) . ( b ) Dawn Chorus - a s e r i e s o f s h o r t d i s t i n c t m u s i c a l t o n e s , a l m o s t ex- c l u s i v e l y between 1 and 5 k c , e i t h e r r i s i n g o r f a l l i n g i n p i t c h and o f t e n o v e r l a p p i n g m t i m e . (See F i g . 7 ) . ( c ) D i s c r e t e Events - n o i s e s t h a t a r e i s o l a t e d i n t i m e and show w e l l de- f i n e d s p e c t r a may be a s s o c i a t e d w i t h o r a r i s e o u t o f dawn chorus and/ o r h i s s . The hook i s a r e l a t i v e l y pure tone t h a t u s u a l l y f a l l s s l o w l y i n f r e q u e n c y over a p e r i o d o f about 0.5 seconds and t h e n r i s e s r a p i d l y over an o c t a v e o r more. Other d i s c r e t e e v e n t s a r e r i s e r s , f a l l i n g t o n e s , and q u a s i - c o n s t a n t t o n e s . (See F i g . 8 ) . ( i v ) I n t e r a c t i o n s - n o i s e s t h a t appear t o be a s s o c i a t e d w i t h a w h i s t l e r . Pre- c u r s o r s precede and s u i v a n t s f o l l o w t he w h i s t l e r . b. W h i s t l e r Occurrence S t a t i s t i c s . W h i s t l e r s a r e more f r e q u e n t a t n i g h t t h a n d u r - i n g t h e day, presumably as a r e s u l t o f D - l a y e r a b s o r p t i o n . V i r t u a l l y no w h i s t l e r s oc- c u r i n e q u a t o r i a l l a t i t u d e s and t h e o c c u r r e n c e peaks a t about 50° geomagnetic l a t i t u d e ; s t a t i s t i c s a t h i g h e r l a t i t u d e s a r e as y e t u n r e l i a b l e . D u r i n g 1958, a w i n t e r t i m e maxi- mum was n o t e d f o r s t a t i o n s a t geomagnetic l a t i t u d e s lower t h a n a p p r o x i m a t e l y 52° and h i g h e r t h a n 62°, w h i l e summertime maximum was seen f o r s t a t i o n s between 52° and 62°. There appears t o be l i t t l e c o r r e l a t i o n between d a i l y w h i s t l e r r a t e s and magnetic i n d e x . When t h e d i s t a n c e between s t a t i o n s exceeds 1000 km ( e x c e p t f o r c o n j u g a t e p a i r s ) t h e oc- c u r r e n c e s t e n d t o be independent f o r w h i s t l e r s e x c e p t f o r the v e r y s t r o n g s i g n a l s w h i c h are o f t e n d e t e c t e d a t s t a t i o n s many thousands o f k i l o m e t e r s i n s e p a r a t i o n . Spaced s t a - t i o n e x p e r i m e n t s i n d i c a t e t h a t a w h i s t l e r component o f average s t r e n g t h spreads over an area about 500 km m r a d i u s b e f o r e d i s a p p e a r i n g i n t o t h e background n o i s e . The s i m i - l a r i t y o f e f f e c t i v e areas f o r b o t h d i s c r e t e VLF e m i s s i o n s and i n d i v i d u a l w h i s t l e r com- ponents suggests t h a t b o t h types o f event propagate i n the same way. ( i ) W h i s t l e r D i s p e r s i o n . D i s p e r s i o n (frequency-dependent time d e l a y ) p a r a - meters were c a l c u l a t e d f r o m the sonagram t r a c e s , a f t e r some e x p e r i m e n t a t i o n and t e s t - i n g d i f f e r e n t methods. A f t e r a s t u d y o f some t e n s t a t i o n - m o n t h s o f d a t a , i t was de- t e r m i n e d t h a t t h e s a m p l i n g , f o r t h e purpose o f c a l c u l a t i n g t h e m o n t h l y a v e r a g e s , c o u l d be reduced t o one w h i s t l e r , r e c o r d e d near l o c a l m i d n i g h t , per day. W h i l e t h i s s a m p l i n g p r e c l u d e d s t u d y o f d i u r n a l v a r i a t i o n , i t g r e a t l y f a c i l i t a t e d t h e d e r i v a t i o n o f m o n t h l y s t a t i s t i c s . For S t a n f o r d , S e a t t l e , W e l l i n g t o n , and Unalaska, a l a r g e a n n u a l v a r i a t i o n was found i n m o n t h l y average d i s p e r s i o n f o r 1958, w i t h a minimum i n J u n e - J u l y and a maximum i n November-January. The w i d e s t v a r i a t i o n was found f o r S t a n f o r d . The 1959 p a t t e r n , f o r S t a n f o r d , r e p e a t e d a p p r o x i m a t e l y , a l t h o u g h t h e November-December v a l u e s were s u b s t a n t i a l l y lower and the summer minimum i s m August. ( i i ) Nose W h i s t l e r s . T h i s phenomenon, d i s c o v e r e d b e f o r e t h e IGY, has a low occurrence r a t e , b u t n e v e r t h e l e s s i s capable o f y i e l d i n g i m p o r t a n t i n f o r m a t i o n . The two parameters, nose f r e q u e n c y and nose t i m e d e l a y , have been a n a l y z e d i n some d e t a i l , l e a d i n g t o t h e i n f e r e n c e t h a t near sunspot maximum t h e r e i s an a n n u a l v a r i a t i o n o f about 2:1 i n e l e c t r o n d e n s i t y i n the o u t e r atmosphere. On t h e b a s i s o f a model, i t i s c a l c u l a t e d t h a t t h e r e a r e about 100 e l e c t r o n s / c c a t 5 e a r t h r a d i i , a bout 200 a t 4R, 500 a t 3R, and 2000 a t 2R. 282

IONOSPHERIC PHYSICS Kc BO 13 FEB 1958 0735 UT I — l O s e c F i g u r e 6. Hi s s Kc 8 - SE 2 JUNE 1958 1835'11 UT fc—i= — •lOsec- F i g u r e 7. Dawn Chorus UN 12 SEPT 1958 0535 65 UT I lOsec J Kc 16- 0 — I 05 sec 1 F i g u r e 8. D i s c r e t e Events 283

IONOSPHERIC PHYSICS 6. B i b l i o g r a p h y . a. Papers Presented a t M e e t i n g s . R. A. H e l l i w e l l , L. N. M a r t i n , K. Marks: "Very Low Frequency O b s e r v a t i o n s i n the A n t a r c t i c . " F o r t y - F i r s t Annual M e e t i n g , Am. Geophysics Union, A p r i l 27-30 1960, Washington, D. C. b. P u b l i s h e d Papers. R. A. H e l l i w e l l , J. H. C r a r y , J. H. Pope, R. L. Smith: "The 'Nose' W h i s t l e r - - A New Hi g h L a t i t u d e Phenomenon." JGR, v o l . 6 1 , no. 1, pp. 139-142, March 1956. R. A. H e l l i w e l l - "ICY W h i s t l e r O b s e r v a t i o n s . " Science, v o l . 123, no. 3201, p. 788, May 1956. R. A. H e l l i w e l l , E. G e h r e l s : " O b s e r v a t i o n s o f Magneto-Ionic Duct P r o p a g a t i o n Using Man-Made S i g n a l s o f Very Low Frequency." PIRE. v o l . 46, no. 4, pp. 785- 787, June 1958. R. A, H e l l i w e l l : " W h i s t l e r s and VLF Emissions--Geophys. and IGY." Geophys. Monograph No. 2. AGU, Washington, D. C, pp. 35-44, J u l y 1958. R. A. H e l l i w e l l , A. G Jean, W. L. T a y l o r . "Some P r o p e r t i e s o f L i g h t n i n g Impulses w h i c h Produce W h i s t l e r s . " PIRE, v o l . 46, no. 10, pp. 1760-1762, October 1958. R. A. H e l l i w e l l , M. G. Morgan: "Atmospheric W h i s t l e r s . " PIRE. v o l . 47, no. 2, pp. 200-208, F e b r u a r y 1959. R. M. G a l l e t , R. A. H e l l i w e l l : " O r i g i n o f Very Low Frequency E m i s s i o n s . " J. Res. NBS. v o l . 63D, no. 1, pp. 21-27, J u l y - A u g u s t 1959. R. A. H e l l i w e l l : " W h i s t l e r Paths and E l e c t r o n D e n s i t i e s i n t h e Outer I o n o - sphere." P r o c . o f t h e Symp. on Phys. Processes i n the Sun-Earth Environment, Defence Res. Bd., Ottawa, No. 1025, pp. 165-175, March 1960. T. F. B e l l , R. A. H e l l i w e l l : "Traveling-Wave A m p l i f i c a t i o n i n t h e Io n o s p h e r e . " Proc. Symp. on Phys. Processes i n the Sun-Earth Environment, J u l y 20-21, 1959 Defence Res. Bd., Dept. o f N a t ' l Def., Ottawa, No. 1025, pp. 215-22, March 1960. D. L. C a r p e n t e r : " I d e n t i f i c a t i o n o f W h i s t l e r Sources on V i s u a l Records and a Method o f Routine W h i s t l e r A n a l y s i s . " Tech, Rept. No. 5, AF18(603)-126, Radioscience L a b o r a t o r y , S t a n f o r d E l e c t r o n i c s Labs., S t a n f o r d U n i v e r s i t y , S t a n f o r d , C a l i f o r n i a , March 1960. R. L. Smith, R. A. H e l l i w e l l , I . W. Y a b r o f f - "A Theory o f T r a p p i n g o f W h i s t l e r s i n F i e l d - A l i g n e d Columns o f Enhanced I o n i z a t i o n . " JGR, v o l . 65, no. 3, pp. 805-823, March 1960. R. A. H e l l i w e l l , T. F. B e l l : "A New Mechanism f o r A c c e l e r a t i n g E l e c t r o n s i n the Outer Ionosphere." JGR, v o l . 65, no. 6, pp. 1839-1842, June 1960. R. L. Smith: "The Use o f Nose W h i s t l e r s i n the Study o f t h e Outer I o n o s p h e r e . " Tech. Rept. No. 6, AFOSR-TN-60-861, Radioscience L a b o r a t o r y , S t a n f o r d E l e c - t r o n i c s Labs., S t a n f o r d U n i v e r s i t y , S t a n f o r d , C a l i f o r n i a , J u l y 1960. 284

IONOSPHERIC PHYSICS R. L. S m i t h , R. A. H e l l i w e l l - " E l e c t r o n D e n s i t i e s t o 5 E a r t h R a d i i Deduced f r o m Nose W h i s t l e r s . " JGR. v o l . 65, no. 9, p. 2583, September 1960. R. L. Smith. " G u i d i n g o f W h i s t l e r s i n a Homogeneous Medium." J. Res NBS, v o l . 64D, no. 5, pp. 505-508, September-October 1960. N. M. B r i c e : " T r a v e l i n g Wave A m p l i f i c a t i o n o f W h i s t l e r s , " JGR, v o l . 68, no. 1 1 , pp. 3840-3842, November 1960. R. A. H e l l i w e l l : "Summary o f Research on W h i s t l e r s and R e l a t e d Phenomena," J. Res. NBS, v o l . 64D, no. 6, pp. 642-644, December 1960. R, A. H e l l i w e l l . "Whistler-Mode P r o p a g a t i o n . " The Radio Noise Spectrum, Chap. 6, pp. 93-100, Harvard U n i v e r s i t y P r e s s , Donald H. Menzel, Ed., 1960. R. A. H e l l i w e l l . " E x o s pheric E l e c t r o n D e n s i t y V a r i a t i o n s Deduced f r o m W h i s t l e r s . " E x t r a i t des Annales de G^ophysique, v o l . 17, no. 1, pp. 76-81, January-March 1961. R. A. H e l l i w e l l , D. L. C a r p e n t e r . " W h i s t l e r s - W e s t IGY-IGC S j m o p t i c Program," F i n a l Rept, NSF IGY 6,10/20 and G8839, Radioscience L a b o r a t o r y , S t a n f o r d E l e c t r o n i c s Labs., S t a n f o r d U n i v e r s i t y , S t a n f o r d , C a l i f o r n i a , March 1961, J. H. C r a r y : "The E f f e c t o f the E a r t h - I o n o s p h e r e Waveguide on W h i s t l e r s . " Tech. Rept. No. 9, AF18 (603)-126, Radioscience L a b o r a t o r y , S t a n f o r d E l e c - t r o n i c s Labs., S t a n f o r d U n i v e r s i t y , S t a n f o r d , C a l i f o r n i a , J u l y 17, 1961, R. A. H e l l i w e l l - " W h i s t l e r s Radio Probes f o r E x p l o r i n g t h e Outer Atmo- sphere." New S c i e n t i s t , v o l . I I , pp. 458-460, August 1961. R. L. S m i t h , D. L. C a r p e n t e r " E x t e n s i o n o f Nose W h i s t l e r A n a l y s i s . " JGR, v o l . 66, no. 8, pp. 2582-2586, August 1961. R, L. Smith: " E l e c t r o n D e n s i t i e s i n the Outer Ionosphere Deduced f r o m Nose W h i s t l e r s . " JGR, v o l . 66, no. 8, pp. 2578-2579, August 1961, Lokken, J E., J, A, Shand, S i r S. C. W r i g h t , KCB, OBE, and L. H. M a r t i n , N. M. B r i c e , R. A. H e l l i w e l l : " S t a n f o r d - P a c i f i c Naval L a b o r a t o r y Conjugate P o i n t Experiment," N a t u r e , v o l . 192, no. 4800, pp. 319-320, October 1961. I . W. Y a b r o f f "Computation o f W h i s t l e r Ray Paths." J , Res. NBS, v o l . 65D, no. 5, pp. 485-505, October 1961. R. L. Smith* " P r o p a g a t i o n C h a r a c t e r i s t i c s o f W h i s t l e r s Trapped i n F i e l d - A l i g n e d Columns o f Enhanced I o n i z a t i o n . " JGR, v o l . 66, no. 1 1 , pp. 3699-3707, November 1961. R. L. Smith- " P r o p e r t i e s o f t h e Outer Ionosphere Deduced f r o m Nose W h i s t l e r s . " JGR, v o l . 66, no. 1 1 , pp. 3709-3716, November 1961. D. L. C a r p e n t e r . "New E x p e r i m e n t a l Evidence o f t h e E f f e c t o f Magnetic Storms on the Magnetosphere." JGR, v o l . 67, no. 1, pp. 135-145, January 1962. R. A. H e l l i w e l l , D. L. C a r p e n t e r : " W h i s t l e r - W e s t R e s u l t s f r o m the IGY-IGC-59 S y n o p t i c Program." T r a n s . AGU, v o l . 43, no. 1, pp. 125-133, March 1962. D. L. C a r p e n t e r : "The Magnetosphere d u r i n g Magnetic Storms. "A W h i s t l e r A n a l y s i s . " Tech. Rept. No. 12, AF18(603)-126, NSF G17037, Radioscience L a b o r a t o r y , S t a n f o r d E l e c t r o n i c s Labs., S t a n f o r d U n i v e r s i t y , S t a n f o r d , C a l i f . , June 1962. 285

IONOSPHERIC PHYSICS D. L. C a r p e n t e r : " E l e c t r o n - D e n s i t y V a r i a t i o n s i n the Magnetosphere Deduced f r o m W h i s t l e r Data." JGR, v o l , 67, no. 9, pp. 3345-3360, August 1962. D. L. C a r p e n t e r : " W h i s t l e r Evidence o f a 'Knee' i n t h e Magnetospheric I o n i - z a t i o n D e n s i t y P r o f i l e . " JGR, v o l . 68, no. 6, pp. 1675-1682, March 1963. D. L. C a r p e n t e r : " W h i s t l e r Measurements o f E l e c t r o n D e n s i t y and Magnetic F i e l d S t r e n g t h i n the Remote Magnetosphere." JGR, v o l . 68, no. 12, pp. 3727- 3770, June 1963. N. M. B r i c e , E. Ungstrup: "Use o f ' L o c a l Mean A u r a l Time' f o r Very Low Frequency E m i s s i o n s . " N a t u r e , v o l , 198, no. 4883, p. 874, June 1963. N. M. B r i c e : "An E x p l a n a t i o n o f T r i g g e r e d Very Low Frequency E m i s s i o n s , " JGR. v o l . 68, no. 15, pp. 4626-4628, 1963. R. A. H e l l i w e l l , D. L. Carpenter* " W h i s t l e r s E x c i t e d by N u c l e a r E x p l o s i o n s . " JGR, v o l . 68, no. 15, pp. 4409-4420, August 1963. H. M. Morozurai: " S e m i - D i u r n a l A u r o r a l Peak and VLF Emissions Observed a t t h e South P o l e , 1960." Trans. AGU, v o l . 44, no. 3, pp. 798-806, September 1963. R. A. H e l l i w e l l : " W h i s t l e r - T r i g g e r e d P e r i o d i c VLF E m i s s i o n s . " JGR, v o l . 68, no. 19, pp. 5387-5395, October 1, 1963. R. A. H e l l i w e l l " C o u p l i n g Between t h e Ionosphere and the E a r t h - I o n o s p h e r e Waveguide a t Very Low F r e q u e n c i e s . " Proc. o f I n t ' l Conf. on t h e I o n o s p h e r e , London. J u l y 1962. Bartholomew Press, D o r k i n g , England, pp. 452-460, 1963. R. A. H e l l i w e l l : " W h i s t l e r s . " P r o p a g a t i o n and I n s t a b i l i t i e s i n Plasmas. W a l t e r I . F l u t t e r m a n , Ed., S t a n f o r d U n i v e r s i t y Press, S t a n f o r d , C a l i f o r n i a , 1963. D, L. C a r p e n t e r . " W h i s t l e r Research i n the U. S Since t h e X l l l t h URSI Assembly i n 1960." R a d i o s c i e n c e , v o l . 68D, no. 5, pp. 609-615, 1964. T. F. B e l l : "Time R e v e r s a l o f the G e o c y c l o t r o n Mechanism." JGR. v o l . 69, no. 1, pp. 177-179, January 1, 1964. T. F. B e l l , 0. Buneman. "Plasma I n s t a b i l i t y i n the Whistler-Mode Caused by a G y r a t i n g E l e c t r o n Stream" Phys. Rev., v o l . 133, no. 5A, pp. A1300-1302, March 2, 1964. R. A. H e l l i w e l l , J . K a t s u f r a k i s , M. T r i m p i , N. B r i c e . " A r t i f i c i a l l y - S t i m u l a t e d VLF R a d i a t i o n f r o m the Ionosphere." JGR, v o l . 69, no. 1 1 , pp. 2391-2394, June 1, 1964. R. A. H e l l i w e l l : W h i s t l e r s and R e l a t e d I o n o s p h e r i c Phenomena, S t a n f o r d U n i v e r s i t y P r e s s , S t a n f o r d , C a l i f o r n i a , 1964. R. A. H e l l i w e l l . " W h i s t l e r s and VLF Emissions." Research i n Geophysics, V o l . 1 , Sun. Upper Atmosphere and Space, MIT Press, Cambridge, Mass., 1964. D. L. C a r p e n t e r , R. L. Smith- " W h i s t l e r Measurements o f E l e c t r o n D e n s i t y i n t h e Magnetosphere." Rev, o f Geophysics, v o l . 2, no. 3, pp. 415-441, August 1964. 286

IONOSPHERIC PHYSICS P r o j e c t 6.11 - W h i s t l e r Program - East 1, O b j e c t i v e s . T h i s p r o j e c t , c a r r i e d o u t a t the Thayer School o f E n g i n e e r i n g , D a r t - mouth C o l l e g e , p r o v i d e d f o r the r e c o r d i n g o f w h i s t l e r s and r e l a t e d phenomena a t many l o c a t i o n s a p p r o x i m a t e l y a l o n g t h e l o n g i t u d e band W 65°-75° i n a s i m i l a r f a s h i o n as f o r p r o j e c t 6.10. 2. O p e r a t i o n s . S p e c i a l a m p l i f i e r s f o r r e c e i v i n g w h i s t l e r s , and t i m i n g and program- ming a p p a r a t u s , were desig n e d and c o n s t r u c t e d a t Dartmouth f o r t h e o b s e r v i n g s t a t i o n s . T i m i n g was based upon a l o c a l 1 kc t u n i n g - f o r k f r e q u e n c y s t a n d a r d . Pulses r e c u r r i n g a t 1 cps by s c a l i n g f r o m t h i s s t a n d a r d were phased t o r a d i o t i m e s i g n a l s and used t o s t a r t t he r e c o r d i n g programs s i m u l t a n e o u s l y a t a l l o f t h e s t a t i o n s and t o p r o v i d e time marks a t 8 kc on the r e c o r d s . A 1 kc s i g n a l was i n t r o d u c e d i n t o t he a m p l i f i e r i n p u t b r i e f l y f o r c a l i b r a t i o n a t t h e s t a r t o f each r e c o r d i n g . Recordings were made a t Hanover, N. H. and Knob Lake, Que. (Canada), by Dartmouth p e r s o n n e l , b u t a t most l o c a t i o n s o p e r a t i o n was s u p p l i e d by c o o p e r a t i n g l o c a l p e r s o n n e l . E x p l o r a t o r y r e c o r d i n g s were made b e f o r e the s t a r t o f the IGY a t g e o m a g n e t i c a l l y c o n j u - gate l o c a t i o n s i n the A l e u t i a n I s l a n d s and i n New Zealand t o see whether the t h e o r y o f w h i s t l e r s as completed by S t o r e y was c o r r e c t and w a r r a n t e d a f u l l - s c a l e program o f s y n o p t i c o b s e r v a t i o n s . The s t a t i o n s connected a t one time or a n o t h e r w i t h t h i s p r o j e c t were. a. T h u l e , Greenland. H i g h hum i n d u c t i o n f r o m l o c a l power d i s t r i b u t i o n systems made d e t e c t i o n o f a n y t h i n g o t h e r t h a n s f e r i c s i m p o s s i b l e . P o r t a b l e equipment on t h e i c e cap away f r o m the main base showed some dawn chorus a c t i v i t y , A r e c e i v e r was l e f t w i t h S i g n a l Corps p e r s o n n e l f o r o c c a s i o n a l a u r a l m o n i t o r i n g b u t d i d n o t produce u s e f u l r e s u l t s because o f t h e u n s a t i s f a c t o r y l o c a l i n t e r f e r e n c e s i t u a t i o n . b. F r o b i s h e r Bay, N. W. T. (Canada). The Hudson's Bay Company c o o p e r a t e d m p r o - v i d i n g f a c i l i t i e s f o r i n s t a l l a t i o n . P r i v a t e arrangements were made w i t h t h e l o c a l manager f o r o p e r a t i o n s , b u t o n l y a v e r y l i m i t e d amount o f d a t a were o b t a i n e d . c. Godhavn. Greenland. A Danish g r a d u a t e s t u d e n t w o r k i n g f o r P r o f e s s o r J. Rybner o f t h e T e c h n i c a l U n i v e r s i t y , Copenhagen, b u i l t equipment and o p e r a t e d i t a t t h e God- havn O b s e r v a t o r y . The s t a t i o n o p e r a t e d s u c c e s s f u l l y t h r o u g h o u t the IGY. A l t h o u g h no equipment or funds were p r o v i d e d by t h i s p r o j e c t , t he s t a t i o n was c r e a t e d a t the sug- g e s t i o n o f P r o f . Morgan o f Dartmouth and c o o p e r a t e d as a member o f t h e " W h i s t l e r s - E a s t " program. d. Knob Lake, Canada. Dartmouth w o r k e r s have i n the p a s t c o o p e r a t e d w i t h w o r k e r s a t M c G i l l U n i v e r s i t y i n m a i n t a i n i n g a f i e l d s t a t i o n a t Knob Lake. Power l i n e p i c k - u p was troublesome a t the M c G i l l l a b o r a t o r y and a s i t e was l o c a t e d s e v e r a l m i l e s away where power was a v a i l a b l e and p o w e r - l i n e i n t e r f e r e n c e t o l e r a b l e , a telephone c a b l e w i t h spare p a i r s e x i s t e d between t h i s f a c i l i t y and the M c G i l l l a b o r a t o r y , a d d i n g t o the u s e f u l n e s s o f t h i s l o c a t i o n , e. Mont J o l i , Que. (Canada). I t had been planned t o observe a t F a t h e r P o i n t on the Gasp^ P e n i n s u l a , b u t e x p l o r a t i o n showed p r o h i b i t i v e i n t e r f e r i n g hum l e v e l s . Mont J o l i , a few m i l e s e a s t , proved s a t i s f a c t o r y and arrangements were made w i t h t h e Mete- o r o l o g i c a l Branch o f the Canadian Department o f T r a n s p o r t f o r f a c i l i t i e s and o p e r a t i o n . The s t a t i o n o p e r a t e d s u c c e s s f u l l y t h r o u g h o u t the IGY. f . B a t t l e Creek, M i c h i g a n . Arrangements were made w i t h Mr. E. T. B u r t o n , r e t i r e d f r o m B e l l L a b o r a t o r i e s and a w e l l - k n o w n w h i s t l e r i n v e s t i g a t o r o f the 1930's, t o i n s t a l l and o p e r a t e equipment a t h i s home. Power l i n e hum was h i g h b u t w h i s t l e r s were observed 287

IONOSPHERIC PHYSICS and t h e s t a t i o n o p e r a t e d t h r o u g h o u t t h e IGY, g, Hanover, New Hampshire. Equipment had been i n o p e r a t i o n f o r some tim e a t the c o u n t r y r e s i d e n c e o f M. G. Morgan, t he p r o j e c t d i r e c t o r . However, a change by t h e power company i n the c o n n e c t i o n o f t h e i r d i s t r i b u t i o n system f r o m d e l t a t o wye, i n c r e a s e d the hum l e v e l and a second s e t o f equipment was o p e r a t e d a t t h e r u r a l r e s i d e n c e o f a n o t h e r one o f the s c i e n t i s t s o f the p r o j e c t , where power l i n e p i c k - u p was l e s s t r o u b l e s o m e . The a l t e r n a t e l o c a t i o n was i n No r w i c h , Vermont, w h i c h i s c o n t i g u o u s w i t h Hanover, New Hampshire, h. Washington, D. C. Arrangements were made w i t h H. E. D i n g e r , o f NRL, who had been o p e r a t i n g h i s own equipment i n Washington f o r some t i m e , t o i n s t a l l and o p e r a t e a s t a n d a r d " W h i s t l e r s - E a s t " s t a t i o n , 1. Bermuda, Equipment was i n s t a l l e d by Mr, Dinger a t t h e USAF A i r Weather Ser- v i c e s f e r i c s s t a t i o n i n Bermuda and was o p e r a t e d by the s t a t i o n p e r s o n n e l . The hum l e v e l was h i g h and the d a t a were t h e r e f o r e l i m i t e d . J. Huancayo, Arrangements were made w i t h t h e I n s t i t u t o G e o f f s i c o de Huancayo f o r i n s t a l l a t i o n and o p e r a t i o n and a v e r y s a t i s f a c t o r y program was c a r r i e d o u t . k. Ibadan, N i g e r i a . A w h i s t l e r r e c e i v e r was s u p p l i e d t o N. S. Alexander o f U n i v e r s i t y C o l l e g e , Ibadan, f o r e x p l o r a t o r y l i s t e n i n g . 1. Ushuaia, A r g e n t i n a . A program i n c o o p e r a t i o n w i t h S t a n f o r d U n i v e r s i t y was a r - ranged w i t h t h e A r g e n t i n e Navy. The S t a n f o r d e x p e r i m e n t was t o r e c o r d s p e c i a l s i g n a l s f r o m the low f r e q u e n c y s t a t i o n NSS and t h e Dartmouth program was t o r e c o r d n a t u r a l s i g - n a l s . S t a n f o r d p e r s o n n e l i n s t a l l e d equipment and made arrangements w i t h A r g e n t i n e p e r - s o n n e l t o o p e r a t e i t . U n f o r t u n a t e l y , v e r y l i t t l e d a t a were o b t a i n e d . m. P o r t L o c k r o y , A n t a r c t i c a . W i t h t h e c o o p e r a t i o n o f the F a l k l a n d I s l a n d s Depen- dency Survey, equipment was s u p p l i e d t o P o r t L o c k r o y and o p e r a t e d by them. O p e r a t i o n was c o m p l e t e l y s a t i s f a c t o r y t h r o u g h o u t t h e IGY. n. G a i n e s v i l l e , F l o r i d a . C o n t i n u i n g a c o o p e r a t i v e program w i t h Dartmouth begun i n 1954, equipment was o p e r a t e d by U n i v e r s i t y o f F l o r i d a s c i e n t i s t s a t G a i n e s v i l l e . The hum l e v e l was never s a t i s f a c t o r i l y low. o. E l l s w o r t h S t a t i o n , A n t a r c t i c a . The ion o s p h e r e o b s e r v e r s a t E l l s w o r t h o p e r a t e d the w h i s t l e r equipment as p a r t o f t h e U. S, a n t a r c t i c program and t h e o p e r a t i o n was c o m p l e t e l y s u c c e s s f u l , p, Unalaska, A l a s k a . O b s e r v a t i o n s begun b e f o r e t h e IGY were c o n t i n u e d u n t i l t h e S t a n f o r d equipment was i n s t a l l e d and o p e r a t i n g . B o t h equipments were o p e r a t e d by t h e r e s i d e n t ACS o p e r a t o r , 3. P e r s o n n e l . The p r o j e c t was under t h e d i r e c t i o n o f P r o f , M. G. Morgan; Dr, H. W. C u r t i s was the p r i n c i p a l s e n i o r s c i e n t i s t a s s o c i a t e d w i t h Dr. Morgan. 4. Data. A l l tape r e c o r d i n g s have been m o n i t o r e d and events logged. Summary l o g sheets have been s u b m i t t e d t o the World Data Centers and t h e tapes a r e r e t a i n e d a t Dartmouth f o r a n a l y s i s . A complete summary, m o n t h l y , was pre p a r e d o f a l l t h e IGY w h i s t l e r d a t a f o r p u b l i c a t i o n i n the Annals o f the IGY. 5. R e s u l t s . a. W h i s t l e r s . I n the N o r t h e r n Hemisphere, m the l o n g i t u d e under s t u d y , v e r y n e a r l y a l l w h i s t l e r s observed a r e found t o be " l o n g , " and i n the Southern Hemisphere, 288

IONOSPHERIC PHYSICS v e r y n e a r l y a l l t o be " s h o r t . " There i s a pronounced seasonal v a r i a t i o n i n a c t i v i t y w i t h a l a r g e maximum m J u l y and August and a s m a l l e r maximum i n January and F e b r u a r y . These maxima a r e found m the d a t a f r o m b o t h hemispheres. I n the n o r t h e r n w i n t e r months, t h e n o r t h e r n s t a t i o n s r e p o r t more a c t i v i t y i n l o n g w h i s t l e r s t h a n do t h e s o u t h e r n s t a t i o n s i n s h o r t w h i s t l e r s . The n o r t h e r n s t a t i o n s Knob Lake (66° geomagnetic l a t i t u d e ) , Mont J o l i (60°), and Dartmouth (55°), e x h i b i t S i m i l a r and c o n s i s t e n t p a t t e r n s o f w h i s t l e r a c t i v i t y , whereas, f o r reasons unknown, Washington (50°) and Bermuda (44°) a r e n o t a b l y d i f f e r e n t . (A p o i n t t o c o n s i d e r i s t h a t these two s t a t i o n s used l o n g - w i r e antennas whereas a l l o t h e r s used l o o p s . ) I n t h e N o r t h e r n Hemisphere, w h i s t l e r a c t i v i t y reaches a peak a t about 55° and f a l l s o f f r a p i d l y above and below t h a t l a t i t u d e . I n t h e Southern Hemisphere, i t can be s a i d t h a t a c t i v i t y a t P o r t L o c k r o y (53.4°) i s s i g n i f i c a n t l y g r e a t e r t h a n a t E l l s - w o r t h (67°) or a t Ushuaia (43.3°). G e n e r a l l y s p e a k i n g , t h e r e i s a b r o a d d i u r n a l maximum o f a c t i v i t y a t each s t a - t i o n d u r i n g the n i g h t t i m e h o u r s , and a d i s t i n c t minimum j u s t b e f o r e l o c a l noon. The r a t i o o f maximum a c t i v i t y t o minimum v a r i e s w i d e l y f r o m s t a t i o n t o s t a t i o n and season- a l l y . A t B a t t l e Creek, 13° west o f Dartmouth and 2° s o u t h , t h e p a t t e r n o f b e h a v i o r has been f o u n d t o be s i m i l a r t o t h a t a t Dartmouth b u t a t a much lower l e v e l . A t Huancayo on the geomagnetic e q u a t o r , no w h i s t l e r s were r e p o r t e d , though the s t a t i o n was w e l l r u n t h r o u g h o u t 1958 and a l l o f the tapes c a r e f u l l y m o n i t o r e d . T a k i n g a time o f v e r y h i g h w h i s t l e r a c t i v i t y a t Dartmouth and l i s t e n i n g t o the c o r r e s p o n d i n g r e c o r d i n g s f r o m Huancayo, i t appears t h a t e x c e e d i n g l y f a i n t w h i s t l e r s can o c c a s i o n a l l y be heard. They would never be d e t e c t e d w i t h o u t c o n c e n t r a t i n g a t t e n t i o n on a p a r t i c u l a r moment as d i r e c t e d by o b s e r v a t i o n s f r o m h i g h e r l a t i t u d e s . The n o i s e l e v e l a t Hxiancayo I S , o f c o u r s e , u n i f o r m l y h i g h . A t Knob Lake (66°) o n l y weak, l o n g w h i s t l e r s have been heard. A t F r o b i s h e r Bay (75°), t h e y a r e a l s o heard b u t l e s s o f t e n and even more weakly. They have n o t been heard a t Godhavn (80°). S h o r t w h i s t l e r - l i k e s i g n a l s h a v i n g d i s p e r s i o n s i n the range 40-60 and a h i g h minimum f r e q u e n c y have been heard a t F r o b i s h e r Bay and Godhavn b u t i t i s an unanswered q u e s t i o n whether these a r e o r d i n a r y w h i s t l e r s o r some o t h e r f o r m o f e m i s s i o n . A s t u d y has been made o f m e t e o r o l o g i c a l c o n d i t i o n s a t 06h Z f o r 1957 October, November, December m an e f f o r t t o d i s c e r n a g e o g r a p h i c a l p a t t e r n o f storms a s s o c i a t e d w i t h l o n g w h i s t l e r s observed a t Dartmouth. Of the 92 days i n v o l v e d , w h i s t l e r s were observed a t Dartmouth on 66 and none on 26. Storms w i t h e l e c t r i c a l d i s c h a r g e s r e p o r t e d were l o c a t e d i n the g e n e r a l area o f E a s t e r n U n i t e d S t a t e s and the N o r t h A t l a n t i c on 89 days. I t I S i n t e r e s t i n g t o note t h a t on the t h r e e days when no storms were r e p o r t e d , l o n g w h i s t l e r s were observed. The i n c i d e n c e o f w h i s t l e r echoes has been s t u d i e d . A l t h o u g h i t shows a l a r g e and smooth d i u r n a l v a r i a t i o n , v e r y c l o s e l y r e p e a t e d f r o m one y e a r t o the n e x t , r a n g i n g f r o m 5 periods/month a t 01 h Z t o 0.3/month a t 14 h Z ( r e s p e c t i v e l y 20 h and 09 h W 75° t i m e ) , t he d i u r n a l v a r i a t i o n o f the p r o b a b i l i t y t h a t echoes w i l l occur when w h i s t l e r s a r e p r e s e n t i s o n l y about two-to-one. The maximum and minimum o f t h e p r o b a b i l i t y curve occur a t a p p r o x i m a t e l y t h e same time as those o f the echo curves themselves. b. l o n o s p h e r i c s . D u r i n g the IGY, n a t u r a l l y o c c u r r i n g v l f phenomena o t h e r t h a n w h i s t l e r s were grouped i n t o t h r e e i l l - d e f i n e d c a t e g o r i e s , " c h o r u s , " " h i s s , " and " o t h e r . " Together these were c a l l e d " v l f e m i s s i o n s . " The Dartmouth group has now adopted the 289

IONOSPHERIC PHYSICS te r m " l o n o s p h e r i c s " f o r t h e s e , as c o n t r a s t e d w i t h " t r o p o s p h e r i c s " ( l i g h t n i n g ) . As de- f i n e d f o r t h e IGY, " h i s s " was t a k e n t o mean a broa d band o f n o i s e o f no s p e c i a l band- w i d t h o r f r e q u e n c y , phenomena w h i c h o c c u r r e d as i s o l a t e d e v e n t s o r " u n u s u a l " sounds were c a l l e d " o t h e r " , and most e v e r y t h i n g e l s e , " c h o r u s . " On the b a s i s o f these d e f i n i - t i o n s , t h e f o l l o w i n g f a c t s have been d e t e r m i n e d c o n c e r n i n g c h o r u s . I n t h e N o r t h e r n Hemisphere, s t a t i o n s a t 55-60° show t h e most a c t i v i t y . The a c t i v i t y has a sharp maximum i n A p r i l and May and a minimum i n November and December. I n t h e Southern Hemisphere, E l l s w o r t h (67°) shows c o n s i s t e n t l y g r e a t e r a c t i v i t y t h a n P o r t L o c k r o y (53.4°) and, r e m a r k a b l y , b o t h show a p a t t e r n l a r g e l y independent o f the time o f y e a r . Chorus i s r a r e l y heard a t Ushuaia (43.3°). A t E l l s w o r t h i t i s p r e - sent about f o r t y p e r c e n t o f the t i m e . The d i u r n a l v a r i a t i o n o f chorus a c t i v i t y i s s h a r p l y d e f i n e d a t 11 h Z (6 h W 75° t i m e ) a t Mont J o l i (N 60°) and a t Dartmouth (N 55°), whereas a t Washington (N50°) and Bermuda (N 44°), t h e r e i s a maximum near 08 h Z (03 h W 75° t i m e ) . E l l s w o r t h (S 67°) and Mont J o l i (N 60°) show almo s t i d e n t i c a l a c t i v i t y b u t P o r t L o c k r o y (S 53.4°) shows h a r d l y any n o t a b l e d i u r n a l v a r i a t i o n . The d i u r n a l v a r i a t i o n seems t o d i f f e r b u t s l i g h t l y w i t h t h e season. A t D a r t - mouth, t h e s t a t i o n f o r w h i c h most d a t a a r e a v a i l a b l e , a c t i v i t y f o r May-July and f o r August-October, have about the same d i u r n a l v a r i a t i o n w i t h a peak a t 10 h Z. The d i u r - n a l v a r i a t i o n s o f the a c t i v i t y i n t h e p e r i o d s F e b r u a r y - A p r i l and November-June a r e s i m i l a r t o each o t h e r b u t have a b r o a d maximum a t 09-12 h Z. The l e v e l o f a c t i v i t y f o r the s p r i n g months i s about t w i c e t h a t f o r the w i n t e r months. As w i t h w h i s t l e r s , the p a t t e r n o f chorus a c t i v i t y a t B a t t l e Creek has been found t o be v e r y s i m i l a r t o t h a t a t Dartmouth b u t the l e v e l much l o w e r . No l o n o s p h e r i c s were r e p o r t e d f r o m Huancayo, b u t chorus i s heard up t o the v e r y h i g h e s t l a t i t u d e s , i n c l u d i n g Thule (N 88°). Very l i t t l e a n a l y s i s o f " h i s s " and " o t h e r " has been c a r r i e d o u t so f a r . I t can be s a i d t h a t more " h i s s " has been observed a t Dartmouth t h a n a t any o t h e r s t a t i o n . 6. B i b l i o g r a p h y . a. Papers Presented a t M e e t i n g s . M. G. Morgan: "Review o f Past Work on W h i s t l e r s and Summary o f C u r r e n t I n - v e s t i g a t i o n s . " URSI G e n e r a l Assembly, August 22-September 5, 1957, B o u l d e r , Colorado. M. G. Morgan "Path Combinations i n W h i s t l e r Echoes," URSI G e n e r a l Assembly, August 22-September 5, 1957, B o u l d e r , Colorado. M, G, Morgan- "Coincidence o f 'Hook-Type' VLF Emissions w i t h A u r o r a l Flames." August 22-September 5, 1957, B o u l d e r , Colorado. M. G. Morgan- " W h i s t l e r s and VLF Em i s s i o n s . " M c G i l l U n i v e r s i t y P h y s i c a l S o c i e t y , November 22, 1957, M o n t r e a l , Que., Canada. M. G. Morgan and R. A. H e l l i w e l l : "Progress i n W h i s t l e r and VLF Emission S t u d i e s . " CSAGI, F i f t h M e e t i n g , August 1-9, 1958, Moscow, USSR. M. G. Morgan and W. C. Johnson " P r e l i m i n a r y R e s u l t s f r o m US-IGY W h i s t l e r s - East Program." URSI-AGI Comm., Sept. 1-3, 1959, B r u s s e l s , Belgium. 290

IONOSPHERIC PHYSICS M. G. Morgan and W. C. Johnson " W h i s t l e r s - E a s t D u r i n g t h e IGY." URSI-IRE M e e t i n g s , October 19-21, 1959, San Diego, C a l i f o r n i a . M. G. Morgan and W. C. Johnson- " W h i s t l e r s A l o n g W 65° L o n g i t u d e ( W h i s t l e r s - E a s t ) D u r i n g t h e IGY and IGC 1959, URSI-IRE M e e t i n g s , May 2-5, 1960, Washington, D. C. M. G. Morgan and W. C. Johnson: "The Dawn Chorus and R e l a t e d Phenomena Along W 65° L o n g i t u d e ( W h i s t l e r s - E a s t ) D u r i n g t h e IGY and IGC 1959, URSI-IRE Meetings May 2-5, 1960, Washington, D. C. M. G. Morgan* " I o n o s p h e r i c Research a t Dartmouth C o l l e g e . " C o r n e l l U n i v e r s i t y Center f o r Radio and Space Research, May 16, 1960, I t h a c a , New York. M. G. Morgan: " W h i s t l e r s - - A Remarkable T e r r e s t r i a l - S p a c e Phenomenon." Hayden P l a n e t a r i u m , J u l y 29, 1960, New York. M. G. Morgan. " W h i s t l e r A n g l e - o f - A r r i v a l Measurements Using Three W i d e l y Spaced S t a t i o n s . " URSI General Assembly, September 5-15, 1960, London. M. G. Morgan. "A P r o p o s a l t o Use D e c e p t i o n I s l a n d as a S l o t Antenna f o r t h e G e n e r a t i o n o f W h i s t l e r s . " URSI General Assembly, September 5-15, 1960, London. b. P u b l i s h e d Papers. R. A. H e l l i w e l l and M. G. Morgan- "IGY W h i s t l e r O b s e r v a t i o n s . " S c i e n c e , p. 788, May 4, 1956. M. G. Morgan. " W h i s t l e r S t u d i e s a t Dartmouth C o l l e g e . " Geophysics and the IGY, G e o p h y s i c a l Mono. No. 2, AGU, Washington, D. C , pp. 31-34, 1958. M. G. Morgan and H. E. D i n g e r , M. G. Morgan and G. McK. A l l c o c k . " O b s e r v a t i o n s o f W h i s t l i n g A tmospherics a t G e o m a g n e t i c a l l y Conjugate P o i n t s . " N a t u r e , v o l . 177, pp. 29-31, January 7, 1956, M. G. Morgan. " W h i s t l e r s and Dawn Chorus." Annals o f the IGY, v o l . I l l , P a r t I V , pp. 315-336, Pergamon Pres s , 1957. M. G. Morgan: " C o r r e l a t i o n o f W h i s t l e r s and L i g h t n i n g Flashes by D i r e c t A u r a l and V i s u a l O b s e r v a t i o n . " N a t u r e , v o l . 182, August 2, 1958, pp. 332-333. G. McK. A l l c o c k , M. G. Morgan- " S o l a r A c t i v i t y and W h i s t l e r D i s p e r s i o n . " JGR, v o l . 63, no. 3, September 1958, pp. 573-575. M. G. Morgan, H. W. C u r t i s , W. C. Johnson: "Path Combinations i n W h i s t l e r Echoes." Proc. IRE, v o l . 47, no. 2, February 1959, pp. 328-329. R. A. H e l l i w e l l , M. G. Morgan "Atmospheric W h i s t l e r s . " Proc. IRE, v o l . 47, no. 2, February 1959, pp. 200-208. M. G. Morgan " W h i s t l e r s . " J. Atmos. T e r r . Phys,, v o l . 15, 1959, pp. 54-57. M. G. Morgan: " W h i s t l e r S t u d i e s Undertaken or I n s t i g a t e d by Dartmouth C o l l e g e Since t h e X l l t h G e n e r a l Assembly URSI." Report t o t h e X l l l t h G e n e r a l Assembly URSI September 1960. (To be p u b l i s h e d m NBS J. o f Res.) 291

IONOSPHERIC PHYSICS P r o j e c t 6.12 - F i x e d Frequency B a c k s c a t t e r Measurements 1. O b j e c t i v e s . T h i s p r o j e c t a t the Radio P r o p a g a t i o n L a b o r a t o r y , S t a n f o r d U n i v e r s i t y , was designed f o r a widespread s t u d y o f the r e g u l a r ionosphere l a y e r s and o f a v a r i e t y of i r r e g u l a r i t i e s o c c u r r i n g w i t h i n them. The b a c k s c a t t e r soundings a t o b l i q u e i n c i - dence are u s e f u l f o r two c a t e g o r i e s o f i n v e s t i g a t i o n . a. S t u d i e s r e q u i r i n g l a r g e - r e g i o n c o n t i n u o u s s u r v e i l l a n c e . ( i ) Sporadic E, i t s o c c u r r e n c e and motions ( i i ) L a r g e - s c a l e t r a v e l l i n g d i s t u r b a n c e s i n the F - r e g i o n b. S t u d i e s o f phenomena ob s e r v a b l e o n l y a t o b l i q u e i n c i d e n c e ( i ) A u r o r a l d i s p l a y s and a s s o c i a t e d r a d i o p r o p a g a t i o n phenomena ( i i ) Magnetic f i e l d - d e s i g n e d i r r e g u l a r i t i e s a t low and m i d d l e l a t i t u d e s ( i l l ) I o n o s p h e r i c t i l t s and t h e i r i n f l u e n c e on l o n g d i s t a n c e p r o p a g a t i o n ( i v ) Meteor i o n i z a t i o n t r a i l s 2. O p e r a t i o n s . P r i o r t o the IGY, b a c k s c a t t e r equipment was developed and o p e r a t e d a t S t a n f o r d . T h i s e x p e r i e n c e formed t h e b a s i s f o r t h e d e s i g n o f the IGY sounders, w h i c h was c a r r i e d o u t m the Radio P r o p a g a t i o n L a b o r a t o r y . The r a d a r o p e r a t e d on t h r e e f r e - quencies near 12 Mc, 18 Mc, and 30 Mc w i t h 2 k i l o w a t t , 2 m i l l i s e c o n d p u l s e s w i t h s h o r t e r p ulses a l s o a v a i l a b l e a t 30 Mc. Three Yagi antennas were mounted on a mast and r o t a - t e d a t a r a t e o f one r e v o l u t i o n per m i n u t e . The s c a t t e r r e t u r n s were d i s p l a y e d on a p o l a r p l o t (PPI p r e s e n t a t i o n ) and photographed w i t h a 16 mm camera a l o n g w i t h i d e n t i - f y i n g i n f o r m a t i o n . An "A" t r a c e scope was a l s o a v a i l a b l e t o s t u d y i n d i v i d u a l p u l s e r e t u r n s . Some o f the equipment was c o n s t r u c t e d a t S t a n f o r d and some c o n t r a c t e d t o commercial f a b r i c a t o r s . T h i r t e e n l o c a t i o n s were chosen f o r i n s t a l l a t i o n o f the b a c k s c a t t e r r a d a r s . Stan- f o r d p e r s o n n e l a s s i s t e d i n the i n s t a l l a t i o n and arrangements were made w i t h the l o c a l i n s t i t u t i o n or agency f o r o p e r a t i o n o f the equipment. I n a d d i t i o n t o S t a n f o r d (44° Geomagnetic N) where p e r s o n n e l o f the RPL o p e r a t e d t h e equipment, t h e l o c a t i o n s were as f o l l o w s a. T h u l e , Greenland (88°N), F o r t Monmouth. N.J. (66°N). Okinawa (15.5°N), and Grand Bahama, F e d e r a t i o n o f West I n d i e s (38°N). O p e r a t i o n s a t these l o c a t i o n s were by p e r s o n n e l o f the U. S. Army S i g n a l Radio P r o p a g a t i o n Agency, w h i c h had f i e l d s t a t i o n s i n o p e r a t i o n t h e r e . b. B o u l d e r , Colorado (49°N). F o r t R a n d o l f . Canal Zone (20.5°N). These were f i e l d s t a t i o n s o f the C e n t r a l Radio P r o p a g a t i o n L a b o r a t o r y , N a t i o n a l Bureau o f Stan- d a r d s , p e r s o n n e l o f w h i c h o p e r a t e d t h e b a c k s c a t t e r equipment. c. Meanook. A l b e r t a (62°N) and Knob Lake(66°N), Quebec, Canada. These were op- e r a t e d c o o p e r a t i v e l y w i t h t h e Canadian IGY Committee. A t Meanook, the i n s t r u - ment was i n s t a l l e d a t the Magnetic O b s e r v a t o r y o f the D i v i s i o n o f Geomagnetism, Department o f Mines and T e c h n i c a l Surveys, and a t Knob Lake a t the M c G i l l U n i - v e r s i t y S u b - A r c t i c Research Center. d. C o l l e g e , A l a s k a (65°N). Equipment was o p e r a t e d by p e r s o n n e l o f the G e o p h y s i c a l I n s t i t u t e , U n i v e r s i t y o f A l a s k a , e. Huancayo. Peru (0.5°S). O p e r a t i o n o f t h e equipment was by p e r s o n n e l o f the I n s t i t u t e G e o f f s i c o de Huancayo. 292

IONOSPHERIC PHYSICS f . P ullman, Washington (53.5°N). T h i s s t a t i o n was o p e r a t e d by p e r s o n n e l o f the D i v i s i o n o f I n d u s t r i a l Research o f the Washington S t a t e U n i v e r s i t y . g. Camden, New South Wales, A u s t r a l i a (42.5°S). Equipment was o p e r a t e d i n coop- e r a t i o n w i t h the Radio Research L a b o r a t o r y , Commonwealth S c i e n t i f i c and I n d u s - t r i a l Research O r g a n i z a t i o n . 3. P e r s o n n e l . A. M. P e t e r s o n s u p e r v i s e d t h i s p r o j e c t , R. P. Egan and D. S. P r a t t were the s e n i o r s c i e n t i f i c p e r s o n n e l a s s o c i a t e d w i t h Dr. P e t e r s o n . 4. Data. S t a n f o r d p e r s o n n e l v i s i t e d s t a t i o n s d u r i n g t h e IGY as a d a t a q u a l i t y c o n t r o l measure. F i l m s were i n s p e c t e d and s c a l e d a t S t a n f o r d . Data were punched on c a r d s m such f o r m t h a t m u l t i l i t h mats c o u l d be prepared a u t o m a t i c a l l y f o r p u b l i s h i n g the d a t a . Data summaries were i s s u e d by the Radio P r o p a g a t i o n L a b o r a t o r y and a l l IGY d a t a have been made a v a i l a b l e i n these books t o i n t e r e s t e d w o r k e r s and t o the IGY World Data Cen- t e r s . The books i n d u c e F - l a y e r , Eg, and f i e l d - a l i g n e d d a t a , and c h a r t s showing major i n s t r u m e n t a l outage. 5. R e s u l t s . T h i s r e s e a r c h a t S t a n f o r d based on b a c k - s c a t t e r soundings has produced new i n f o r m a t i o n on l a r g e s c a l e t r a v e l l i n g d i s t u r b a n c e s i n the F - r e g i o n and on t h e r o l e o f i o n o s p h e r i c t i l t s ( h o r i z o n t a l g r a d i e n t s ) i n the p r o p a g a t i o n o f r a d i o s i g n a l s over l o n g d i s t a n c e s . I t has proven p o s s i b l e t o t r a c k the m o t i o n o f F - r e g i o n t r a v e l l i n g d i s - t u rbances over d i s t a n c e s o f s e v e r a l thousand k i l o m e t e r s and t o e s t a b l i s h t h a t t h e d i s - turbances o f t e n e x t e n d s e v e r a l thousand k i l o m e t e r s i n d i r e c t i o n s p e r p e n d i c u l a r t o t h a t o f the m o t i o n . They appear t o be a k i n d o f g i g a n t i c wave m o t i o n t r a v e l l i n g i n t h e i o n o - sphere. I t has a l s o been e s t a b l i s h e d t h r o u g h the s t u d y o f s c a t t e r sounding data t h a t t i l t s i n t h e F - l a y e r can r e s u l t m p r o p a g a t i o n o f r a d i o s i g n a l s t o g r e a t d i s t a n c e s w i t h o u t i n t e r v e n i n g r e f l e c t i o n s a t the e a r t h ' s s u r f a c e . The presence o f a t i l t o r h o r i z o n t a l g r a d i e n t i n t h e ionosphere makes i t p o s s i b l e t o launch a r a d i o wave m such a manner t h a t i t can t r a v e l by s u c c e s s i v e r e f l e c t i o n s a t the F - l a y e r u n t i l i t s t r i k e s a n o t h e r t i l t and r e t u r n s t o e a r t h . P r o p a g a t i o n over d i s t a n c e s i n excess o f 10,000 km i s com- monly observed. From a s t u d y o f f i e l d - a l i g n e d i r r e g u l a r i t i e s near t h e magnetic e q u a t o r , R. D. Egan has r e p o r t e d t h a t the r a d a r echoes produced by s c a t t e r i n g w i t h i n t he ionosphere have been observed w i t h g r e a t r e g u l a r i t y t h r o u g h o u t the e n t i r e p e r i o d o f o b s e r v a t i o n s . These e x p e r i m e n t a l o b s e r v a t i o n s are c o n s i s t e n t w i t h the Booker t h e o r y o f s c a t t e r i n g f r o m non- i s o t r o p i c f i e l d - a l i g n e d i o n i z a t i o n i r r e g u l a r i t e s . Through a c o m b i n a t i o n o f t h e o r y and e x p e r i m e n t a l o b s e r v a t i o n , the s c a t t e r i n g r e g i o n has been d e f i n e d m b o t h v e r t i c a l and h o r i z o n t a l e x t e n t . S i m i l a r l y , t h e s i z e o f the i r r e g u l a r i t i e s has been e s t i m a t e d , as w e l l as t h e magnitude o f the i o n i z a t i o n v a r i a t i o n s . The e q u a t o r i a l s c a t t e r echoes have been observed m two d i s t i n c t , b u t sometimes o v e r l a p p i n g , groups. The f i r s t , observed n e a r l y e v e r y day, o r i g i n a t e s f r o m i o n i z a t i o n i r r e g u l a r i t i e s b e g i n n i n g a t 100 k i l o m e t e r s and e x t e n d i n g upward o c c a s i o n a l l y as h i g h as 200 k i l o m e t e r s . The second has been observed much l e s s f r e q u e n t l y and appears t o o r i g i n a t e near t h e maximum o f the F - l a y e r where the r e l a t i v e l y h i g h plasma d e n s i t i e s and l a r g e volume t e n d t o enhance the EqS echo. The t r u e - h e i g h t p r o f i l e s p u b l i s h e d by Schmerling i n d i c a t e t h a t the maximum o f the F - r e g i o n v a r i e s s e a s o n a l l y between about 350 and 500 k i l o m e t e r s i n h e i g h t . The f a c t t h a t the s c a t t e r i n g r e g i o n i s s t r o n g l y s o l a r - i n f l u e n c e d i s i n d i c a t e d by the appearance of EqS echo e a r l i e r m the e a s t t h a n i n the west and disappearance l a t e r i n the west than i n the e a s t . There i s a l s o c o n s i d e r a b l y more echo m the e a s t i n the morning and, s i m i l a r l y , t h e r e i s more echo m the west tha n m the e a s t m the a f t e r - noon. Thus, I t appears t h a t the s t r o n g e s t b a c k s c a t t e r e d s i g n a l i s f r o m the s u b s o l a r r e g i o n where the E - r e g i o n plasma d e n s i t y i s g r e a t e s t . 293

IONOSPHERIC PHYSICS The s i z e o f the i r r e g u l a r i t i e s r e q u i r e d t o produce the observed echoes has been es- t i m a t e d by assuming a Gaussian c r o s s s e c t i o n f o r the i r r e g u l a r i t y . I n the r e l a t i v e l y r e s t r i c t e d f r e q u e n c y range used, the e f f e c t i v e t r a n s v e r s e c o r r e l a t i o n - d i s t a n c e must be on the o r d e r o f one meter and the l o n g i t u d i n a l c o r r e l a t i o n - d i s t a n c e g r e a t e r t h a n t h i r t y m e t e r s . I t was concluded t h a t the t r a n s v e r s e c o r r e l a t i o n - d i s t a n c e must be a t l e a s t as s m a l l as one meter, b u t may be s m a l l e r . The l o n g i t u d i n a l c o r r e l a t i o n - d i s t a n c e must be a t l e a s t 30 meters i n l e n g t h , b u t p r o b a b l y i s g r e a t e r -- on the o r d e r o f 100 t o 300 m e t e r s . E s t i m a t e s o f the s t r e n g t h o f the r e t u r n e d b a c k s c a t t e r s i g n a l s t r e n g t h have produced a v a l u e o f the mean-square v a r i a t i o n o f e l e c t r o n d e n s i t y o f about 10"^. Values o f ap- p r o x i m a t e l y t h i s o r d e r o f magnitude have been e s t i m a t e d f o r a u r o r a l - t y p e f i e l d - a l i g n e d i r r e g u l a r i t i e s by o t h e r w o r k e r s . By f i x i n g the v a l u e o f the t r a n s v e r s e c o r r e l a t i o n - d i s t a n c e o f the i r r e g u l a r i t i e s a t about one meter, the optimum s i z e f o r the f r e q u e n c y range observed, a t h e o r e t i c a l v a l u e o f w a v e l e n g t h dependence o f \ i s d e r i v e d , t h i s v a l u e appears t o agree w i t h the ob- s e r v a t i o n s on 10 and 17 meters r e a s o n a b l y w e l l . The w a v e l e n g t h dependence over a wide f r e q u e n c y range, e s p e c i a l l y toward h i g h e r f r e q u e n c i e s , i s p r o b a b l y b e s t d e s c r i b e d by l e t t i n g t h e t r a n s v e r s e c o r r e l a t i o n - d i s t a n c e T be e q u a l t o the optimum s i z e f o r t h a t f r e q u e n c y , about \/y/Sn^ . T h i s a s sumption would be v a l i d u n t i l t h e f r e q u e n c y i s i n c r e a s e d t o the p o i n t a t w h i c h T reaches a v a l u e c o r r e s p o n d i n g t o the minimum-sized i r r e g u l a r i t i e s , a f t e r w h i c h the u s u a l sharp e x p o n e n t i a l - c u t o f f - w i t h - f r e q u e n c y would be observed. There appears t o be l i t t l e or no c o r r e l a t i o n between the o c c u r r e n c e o f EqS echoes and magnetic d i s t u r b a n c e s . However, t h e o b s e r v a t i o n s suggest t h a t f o r a few days f o l - l o w i n g an u n u s u a l l y s t r o n g magnetic d i s t u r b a n c e the amount o f EqS echo decreases--but t h e r e a r e many o t h e r i o n o s p h e r i c parameters t h a t a r e a f f e c t e d m a s i m i l a r manner, and c o n s e q u e n t l y i t i s v e r y d i f f i c u l t t o e s t a b l i s h t h a t t h i s i s a d i r e c t e f f e c t . The e q u a t o r i a l e l e c t r o j e t i s u n d o u b t e d l y an i m p o r t a n t f a c t o r i n the mechanism o f the f o r m a t i o n o f the E - r e g i o n i r r e g u l a r i t i e s . The d i u r n a l v a r i a t i o n o f the H component o f the magnetic f i e l d , w h i c h has been ta k e n t o be r e p r e s e n t a t i v e o f the s t r e n g t h o f the e l e c t r o j e t , i s markedly s i m i l a r t o the d i u r n a l o c c u r r e n c e o f the EqS echo. I t would be e x t r e m e l y i n t e r e s t i n g t o make b a c k s c a t t e r o b s e r v a t i o n s w i t h a p o r t a b l e sounder a t c l o s e l y spaced i n t e r v a l s o f l a t i t u d e m o r d e r t o e s t a b l i s h the l a t i t u d e v a r i a t i o n o f the EqS echo. A s i m i l a r type o f e x p e r i m e n t has been done during the IGY w i t h the v e r - t i c a l - i n c i d e n c e sounders, a l t h o u g h they were f i x e d i n s t a l l a t i o n s a t spacings o f 300 t o 900 km. I t would be d e s i r a b l e f o r the o b l i q u e - i n c i d e n c e sounding t o use spacings a t l a t i t u d e s c o r r e s p o n d i n g t o 2-degree d i p i n t e r v a l s ( a p p r o x i m a t e l y 1-degree l a t i t u d e i n - t e r v a l s ) . T h i s would r e q u i r e n o t more t h a n t e n o b s e r v i n g l o c a t i o n s , w h i c h c o u l d e a s i l y be reached by r o a d t o the n o r t h o f the magnetic e q u a t o r . The p u l s e d p o r t a b l e sounder need n o t consume much p r i m a r y power and a s m a l l p o r t a b l e g e n e r a t o r c o u l d be used. The l a r g e d i u r n a l v a r i a t i o n s o f the i o n o s p h e r i c c h a r a c t e r i s t i c s d i d n o t mask the s t r o n g l u n a r i n f l u e n c e on the e a r l y disappearance o f the EqS echo. M a t s u s h i t a ' s ex- p l a n a t i o n o f the l u n a r i n f l u e n c e on e q u a t o r i a l Es, as a p a r t i a l c a n c e l l a t i o n o f the s o l a r - i n d u c e d upward d r i f t f o r c e , a l s o a p p l i e s t o the l u n a r i n f l u e n c e on the EqS echoes. R e c e n t l y , Knecht has shown t h a t t h e r e i s a l s o a s t r o n g l u n a r i n f l u e n c e on the t i m e o f appearance o f Eg-q a t Huancayo, w h i c h f u r t h e r s u p p o r t s M a t s u s h i t a ' s h y p o t h e s i s on t h e r e l a t i o n o f Eg t o the e l e c t r i c c u r r e n t system. The upward d r i f t f o r c e i s a consequence o f the H a l l e f f e c t . I t i s p e r p e n d i c u l a r t o b o t h E and H f i e l d s and has a d i r e c t i o n g i v e n by (E x H ) , w h i c h i s upward f o r t h e eastward f l o w i n g e l e c t r o j e t and c o n s e q u e n t l y I S the same d i r e c t i o n f o r changes o f b o t h s i g n s . M a r t yn has shown how p e r t u r b a t i o n s may be enhanced w i t h i n a v e r t i c a l l y d r i f t i n g r e g i o n and suggested t h a t much o f the e q u a t o r i a l Eg and spread-F may be due t o f i e l d - 294

IONOSPHERIC PHYSICS a l i g n e d i o n i z a t i o n . I n order to m a i n t a i n these p e r t u r b a t i o n s , to e x p l a i n r a d i o - s t a r s c i n t i l l a t i o n as w e l l as Eg and spread-F, Martyn only r e q u i r e d that t h e i r r a d i u s be much l e s s than the s c a l e height of the r e g i o n . Such a requirement i s w e l l met here where the t r a n s v e r s e c o r r e l a t i o n - d i s t a n c e has been found to be on the order of one meter or l e s s . From the above c o n s i d e r a t i o n s i t may be hypothesized that the o b l i q u e - i n c i d e n c e EqS echo i s the r e s u l t of i r r e g u l a r i t i e s i n i o n i z a t i o n which are a l i g n e d w i t h the mag- n e t i c f i e l d and are present throughout the region i n which the e q u a t o r i a l e l e c t r o j e t i s flowing. As a r e s u l t of the v e r t i c a l - d r i f t motion of the Ionosphere during the day, the f i e l d - a l i g n e d i r r e g u l a r i t i e s , which are observed d i r e c t l y by the obllque-mcidence sounder, are f u r t h e r enhanced as a r e s u l t of the i n s t a b i l i t y of these i r r e g u l a r i t i e s on the lower s i d e of the v e r t i c a l l y d r i f t i n g r e g i o n . These enhanced i r r e g u l a r i t i e s a re seen on the v e r t i c a l - i n c i d e n c e sounder and have been c a l l e d e q u a t o r i a l sporadic-E (Eg-q) i n the p a s t . The v e r t i c a l - i n c i d e n c e Es-q echoes are g e n e r a l l y observed up to about 8 Mc. Applying a secant f a c t o r of about three to t h i s frequency would imply that the enhanced i r r e g u l a r i t i e s would support the propagation of ground-backscattered s i g n a l s a t 17.7 Mc, Such ground-backscattered s i g n a l s have not been r e g u l a r l y observed and the c o n c l u s i o n must be drawn that the i r r e g u l a r i t i e s are not s u f f i c i e n t l y numerous or dense to produce a d e t e c t a b l e ground-backscattered s i g n a l . The IGY e q u a t o r i a l s c a t t e r experiment conducted i n South America by Bowles and Cohen has shown nighttime enhancements of s i g n a l s b e l i e v e d to be the r e s u l t of s c a t - t e r i n g w i t h i n the F-region. They have not, as y e t , reported daytime F-region s c a t t e r - ing or d i s c u s s e d the r e s u l t s of t h e i r E-region o b s e r v a t i o n s . C a l c u l a t i o n s , based on the present study, have i n d i c a t e d that over an east-west path a t 50 Mc w i t h 10 kw peak power and a 50 microsecond p u l s e , s i g n a l s a t l e a s t 20 db above noise should be produced. Most of Bowles' and Cohen's paths were north-south, and i t i s d i f f i c u l t to estimate the s i g n a l that might be expected f o r t h i s c a s e . T h e i r east-west paths were a t a magnetic- dip l a t i t u d e of about 20° South and consequently were probably beyond the e q u a t o r i a l anomaly region. I t i s extremely i n t e r e s t i n g to note t h a t the EqS s i g n a l s have a l r e a d y been used i n a r o u t i n e communications c i r c u i t . The I n s t i t u t o Geof£slco de Huancayo i s only 180 km e a s t of i t s Lima o f f i c e s , but Huancayo i s a t an e l e v a t i o n of about 3400 meters, and the mountains between Huancayo and Lima are over 4900 meters high. Under these circum- stances i t would be normal to use frequencies below the v e r t i c a l i ncidence c r i t i c a l frequency for communications. However, s i g n a l s a t these lower frequencies were weak, g i v i n g poor communications g e n e r a l l y . At present, Huancayo and Lima are using f r e - quencies of about 30 Mc, c o n s i d e r a b l y above the v e r t i c a l i ncidence c r i t i c a l frequency, obtaining completely acceptable communications by means of the E-region f i e l d - a l i g n e d i r r e g u l a r i t y s c a t t e r s i g n a l . 6. Bibliography. a. Papers Presented a t Meetings. R. 0. Egan: "Radar I n v e s t i g a t i o n of F i e l d - A l i g n e d I r r e g u l a r i t i e s Located Within the Ionosphere a t the Magnetic Equator." URSI Meeting, October 1959, San Diego, C a l i f o r n i a . b. Published Papers. A. M. Peterson: " I o n o s p h e r i c B a c k s c a t t e r . " Annals of the IGY. v o l . 3, pp. 361-381, 1957, Pergamon P r e s s . A. M. Peterson, R, D, Egan, D, S. P r a t t : "The IGY Three-Frequency B a c k s c a t t e r Sounder," Proc, IRE, v o l . 47, p, 300, February 1959. 295

IONOSPHERIC PHYSICS R. D. Egan "Anisotropic Field-Aligned Ionization I r r e g u l a r i t i e s Within the Ionosphere Near the Magnetic Equator." Tech. Report No. 1, December 30, 1959, Stanford Electronic Laboratory, Stanford University. R. D. Egan: "Anisotropic F i e l d Aligned Ionization I r r e g u l a r i t i e s i n the Ionosphere Near the Magnetic Equator." JGR, vol. 65, pp. 2343-2358, August 1960. 296

IONOSPHERIC PHYSICS P r o j e c t 6.14 - O b l i q u e I n c i d e n c e Sporadic-E (Eg) Measurements 1. O b j e c t i v e s . T h i s p r o j e c t a t CRPL, N a t i o n a l Bureau o f Standards, was s e t up t o ex- p l o r e a s i g n i f i c a n t l o n g i t u d e e f f e c t o f E^ o c c u r r e n c e t h a t had been i n d i c a t e d by e a r - l i e r CRPL exp e r i m e n t s i n t h e U n i t e d S t a t e s and Japan. There was a l s o evidence f r o m l o n g t e r m a n a l y s i s o f v e r t i c a l i n c i d e n c e d a t a t h a t tended t o suggest a l o n g i t u d e e f - f e c t i n Eg. 2. O p e r a t i o n s . Two c i r c u i t s were a r r a n g e d , each t o have e s s e n t i a l l y t h e same l e n g t h (1300 km) and geometry w i t h r e s p e c t t o t h e e a r t h ' s magnetic f i e l d . One c i r c u i t was f r o m Panama t o Guantanamo Bay, Cuba, s i g n a l s were a l s o t r a n s m i t t e d f r o m Panama i n the d i r e c t i o n o f G u a y a q u i l , Ecuador, f o r r e c o r d i n g o p e r a t i o n s under p r o j e c t 6.6. A c i r - c u i t m e a s t P a c i f i c l o n g i t u d e s was e s t a b l i s h e d between the P h i l i p p i n e s and Okinawa, s i g n a l s were a l s o beamed f r o m Okinawa t o Japan f o r r e c o r d i n g by Japanese s c i e n t i s t s . T r a n s m i t t e r s were f r e q u e n c y s t a b i l i z e d and o p e r a t e d a t 50 Mc a t a power o f 2 kw; r e c e i v e r s were a l s o f r e q u e n c y s t a b i l i z e d . F i v e - e l e m e n t Y a g i antennas were used. The system was d e s i g n e d t o r e c o r d s i g n a l l e v e l s r a n g i n g between 20 and 110 db below t h e i n v e r s e - d i s t a n c e l e v e l . I o n o s p h e r i c s c a t t e r s i g n a l l e v e l s and g a l a c t i c n o i s e l e v e l s were r e c o r d e d as w e l l as Eg l e v e l s . The a s s i s t a n c e o f the P h i l i p p i n e IGY Committee and the Voice o f America h e l p e d make p o s s i b l e t h e e a s t e r n c i r c u i t . O p e r a t i o n s a t Guantanamo were conducted by navy p e r s o n n e l . Under a c o o p e r a t i v e agreement, t r a n s m i t t e r power r e c o r d s were s u p p l i e d t o the Japanese s c i e n t i s t s who i n t u r n s e nt r e c o r d s o f s c a l i n g s t o CRPL f r o m t h e i r two r e c o r d i n g s t a t i o n s . The main ex p e r i m e n t was conducted i n the p e r i o d October 1957 t h r o u g h September 1958, however, t h e Far East c i r c u i t s were c o n t i n u e d u n t i l November 1959. 3. P e r s o n n e l . E. K. S m i t h , CRPL, s u p e r v i s e d t h i s p r o j e c t ; J. W. F i n n e y was the s e n i o r s c i e n t i s t a s s o c i a t e d w i t h Dr. Smith. 4. Data. A l l d a t a have been s c a l e d and t a b u l a t e d i n v a r i o u s f o r m s . They were pub- l i s h e d i n NBS T e c h n i c a l Note No. 48, PB 151407, March 1960, and a l s o s u b m i t t e d t o IGY WDC-A. Ionosphere (CRPL). 5. R e s u l t s , From p a s t e x p e r i e n c e i t was expected t h a t t he f o r w a r d - s c a t t e r s i g n a l would always be p r e s e n t and t h a t t he m e t e o r i c mode r a t h e r t h a n the s o l a r mode would dominate due t o t h e w i de beamwidth o f t h e Y a g i antennas. The r e c o r d s , t h e r e f o r e were expected t o be v e r y s p i k e y i n appearance and t o e x h i b i t a maximum s i g n a l l e v e l a t about 0600 hours and a minimum a t about 1800 hours l o c a l time i n t h e absence o f spora- d i c - E enhancements. The r e c o r d s f r o m t h e Panama-to-Cuba c i r c u i t d i d prove t o be as e x p e c t e d ; however, on the Poro-to-Onna r e c o r d s the s i g n a l showed an enhancement i n t h e e a r l y e v e n i n g hours o f a t y p e n o t a s s o c i a t e d w i t h E^. The g e n e r a l appearance o f t h e s i g n a l t r a c e changed f r o m a wide s p i k e y one t o a narrow t r a c e more or l e s s d e v o i d o f s p i k e s . T h i s type o f t r a c e i s h e r e a f t e r r e f e r r e d t o as the " e v e n i n g s i g n a l anomaly" ( t h e t e r m "Far E a s t e r n Anomaly" has a l s o been used t o r e f e r t o the phenomenon, w h i c h i s much more i n - tense over t h e Poro-to-Onna c i r c u i t t h a n e l s e w h e r e ) . I n F i g u r e 9 p a r t ( a ) i s a day's r e c o r d f r o m Cuba showing the type e x p e c t e d when no Egis p r e s e n t . I n p a r t ( b ) i s shown a sample r e c o r d f r o m each c i r c u i t c o n t a i n i n g an Eg enhancement, and ( c ) shows t h e c h a r a c t e r o f the evening s i g n a l anomaly i n the Far East and what appears t o be t h e same phenomenon i n the Caribbean. 297

IONOSPHERIC PHYSICS Figure 10 i s the d i u r n a l chart of monthly median s i g n a l and noise le v e l s f o r Octo- ber 1957 from Onna^ Okinawa and Guantanamo Bay^ Cuba. The noise le v e l s appear to be s l i g h t l y out of phase but t h i s i s not a r e a l e f f e c t . I t i s due to the f a c t t h a t l o c a l time i s used^ which r e s u l t s i n a d i f f e r e n c e i n s i d e r e a l time of some f o r t y minutes. The Guantanamo curve shows the t y p i c a l 6 am meteor peak observed whenever broad-beam antennas are used on s c a t t e r c i r c u i t s . The median s i g n a l l e v e l a t Onna shows the evening s i g n a l anomaly and i s also c o n s i s t e n t l y higher throughout the day than the Guantanamo s i g n a l . Pulse experiments and measurement of delay times have shown th a t the anomaly i s F region s c a t t e r . Figure 11 shows the comparison of between the two c i r c u i t s . The d i f f e r e n t char- acter of Eg occurrence i s c l e a r , w i t h a marked seasonal dependence i n the Far East as compared to the Caribbean. The s i g n a l l e v e l t h a t was exceeded one percent of the time was 37 db higher i n the Far East than i n the Caribbean. For any given transmission loss, the general conclusion i s drawn th a t Eg was three to f i v e times more prevalent i n the Far East. There i s a suggestion t h a t a meteorological e f f e c t , possibly i n asso- c i a t i o n w i t h the Indian and East Asian Monsoon, would generate the abnormally high Eg. A suggestion by D. F. Martyn r e l a t i n g t o E^ i o n i z a t i o n appears t o lend support t o the idea t h a t E^ i n t e n s i f i c a t i o n can r e s u l t from v e r t i c a l c i r c u l a t i o n alone and makes the meteorological explanation more acceptable than previously. 6. Bibliography. a. Papers Presented a t Meetings. E, K. Smith and J. W. Finney: " P e c u l i a r i t i e s of the Ionosphere i n the Far East: Sporadic-E and F-Scatter." URSI-AGI Meeting, September 1959, Brussels. b. Published Papers. R. Bateman, J. W. Finney, E. K. Smith, L. H. Tveten, and J. M. Watts: " I n t e r - n a t i o n a l Geophysical Year Observation of F-Layer Scatter i n the Far East." JGR, v o l . 64, no. 4, pp. 403-406, A p r i l 1959. E. K. Smith, J r . , and J, W. Finney: " P e c u l i a r i t i e s of the Ionosphere i n the Far East: Sporadic-E and F-Region Scatter." JGR, v o l . 65, no. 3, pp. 885-92, March 1960. J. W. Finney and E. K. Smith: "Report on the IGY Oblique-Incidence Sporadic- E and F-Scatter Program." • NBS Technical Note No. 48, March 1960. "Ionospheric Sporadic E", Edited by E. K. Smith and S. Matsushita, Pergamon Press, 1962. 298

ro vo 2 0 19 18 17 16 15 14 13 12 I I 10 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 01 (a) EXAMPLE OF SIGNAL LEVEL DURING A "QUIET DAY AS RECEIVED AT 6UANTANAM0 BAY GTMO- » U 6 21 1958 > 2 0 - J - > (D 0 - r - r - c : > i 2 0 ^ 0 N N i - A U G 9 ^ 9 5 8 j p _ - 1 6 0 20 19 18 17 16 15 (b) EXAMPLES OF SPORADIC-E PROPAGATION AS RECEIVED AT ONNA AND GUANTANAMO BAY - 1 6 0 in O N N A - S E P T 24 I 9 5 B 2 4 2 3 22 21 2 0 19 IB (c) EXAMPLES OF THE EVENING SIGNAL ANOMALY AS RECEIVED AT ONNA AND GUANTANAMO BAY TIMES SHOWN ARE LOCAL STANDARD TIMES AT RECEIVING LOCATIONS Figure 9. Transmission Loss Records Made w i t h 12-Second Time Constant o o

IONOSPHERIC PHYSICS G U A N T A N A M O B A T S I O U L L E V E L S NOISE L E V E L S I I I • I I I I . I , 0 0 « 0 4 Oa 10 12 ( 4 16 18 2 0 2 4 0 0 L O U L T g t f Figure 10. Diurnal Chart of Monthly Median Signal and Noise Levels as Received a t Onna and Guantanamo Bay, October 1957. 1957-1958 10 11. o 5db 50 db GTMO 1957-1958 Figure 11. Seasonal V a r i a t i o n of Sporadic-E Occurrence f o r Reference Levels of 5 and 50 db. Above 1 f o r Onna and Guantanamo Bay. 300

IONOSPHERIC PHYSICS Project 6.19 - A r c t i c D r i f t i n g S t a t i o n Sounder 1. Objectives. This p r o j e c t , c a r r i e d out a t the Central Radio Propagation Laboratory, provided f o r supplies f o r v e r t i c a l - i n c i d e n c e ionosphere soundings from S t a t i o n B, F l e t - cher's Ice I s l a n d , a tabular mass of ice f l o a t i n g i n the A r c t i c Ocean. 2. Operations. The basic equipment was supplied through a cooperative arrangement between CRPL and the U. S. Army Signal Corps Radio Propagation Laboratory, which sup- p l i e d personnel to operate the sounder. 3. Personnel. B. A. Benway, CRPL, supervised the purchase of supplies and t h e i r d e l i v e r y to A i r Force u n i t s f o r transport to S t a t i o n B. 4. Data. F i l m records were sent to SCRPA f o r processing and the scaled values were submitted to IGY World Data Center A. Project 6.20 - Ionospheric Absorption, Cosmic Noise Method 1. Objectives. This p r o j e c t at the Geophysical I n s t i t u t e , U n i v e r s i t y of Alaska, pro- vided f o r four riometers, i n a d d i t i o n to those supported under pr o j e c t 1.43. These a d d i t i o n a l u n i t s were i n s t a l l e d at Farewell, College, Fort Yukon and Point Barrow, Alaska. For a l l other d e t a i l s see p r o j e c t 1.43. 301

IONOSPHERIC PHYSICS Project 6.21 - Ionospheric Absorption, Cosmic Noise Method 1. Objectives. This p r o j e c t c a r r i e d out a t the Thayer School of Engineering, Dart- mouth College, provided f o r the continuous measurement of the amplitude of cosmic r a - dio noise by a total-power radiometer operating m the 20-30 Mc region. The reduction of the sig n a l s , under d i f f e r e n t ionospheric conditions, from the unattenuated s i g n a l associated w i t h each s i d e r e a l hour makes possible a determination of changing absorp- t i o n conditions i n the ionosphere. Observations were made i n the aur o r a l zone a t Knob Lake, Quebec (Canada), and at Hanover, New Hampshire. The observations obtained a t Knob Lake w i l l be es p e c i a l l y use- f u l f o r the study of a u r o r a l zone blackout e f f e c t s and these w i l l be compared w i t h s i m i l a r observations made i n the au r o r a l zone (at College, Alaska, and at Kiruna, Swe- den). The r e s u l t s from Hanover, N. H. w i l l permit conclusions regarding the r a t e and extent of the expansion to lower l a t i t u d e s of absorption events noted a t Knob Lake. 2. Operations. Cosmic noise on 27 Mc has been measured a t Hanover and Knob Lake since July 1958. Operation a t Hanover has been continuous, but a t Knob Lake there have been some lapses due to l o c a l radio interference and equipment f a i l u r e . The equipment a t both locations consisted of a receiver and a noise diode c o n t r o l - led by a servo system which adjusts the noise output of the diode to match the incoming noise sig n a l developed i n the antenna. The current input to the noise diode was r e - corded on a s t r i p c hart. This system, developed by C. G. L i t t l e (when a t the Univer- s i t y of Alaska), avoids the necessity of maintaining constant receiver gain. The an- tenna was a three-element Yagi array aimed v e r t i c a l l y . 3. Personnel. This p r o j e c t was supervised by Blanchard P r a t t assisted by Prof. Morgan at Hanover and E. W. Bentley a t Knob Lake. 4. Data and Results. The data were tabulated i n three d i f f e r e n t ways according to the procedures adopted by CSAGI: a) the r e l a t i v e noise i n t e n s i t y a t the beginning of each hour; b) the amplitude and time of rapid changes of noise i n t e n s i t y occurring i n less than one hour, c) the r e l a t i v e noise i n t e n s i t y a t the beginning of each hour of a side- r e a l day. The t h i r d t a b u l a t i o n made possible a p l o t of the magnitude of the received noise i n the absence of absorption, versus time of a s i d e r e a l day (quiet-day curve), i f the data selected are taken from undisturbed nighttime periods. The amount of absorption at any time may be found by comparison of the amount of noise received a t t h a t time w i t h the value read from the q u i e t day curve a f t e r making the appropriate conversion from c i v i l time t o si d e r e a l time. The f i r s t year's data from Hanover have been used to prepare a q u i e t day curve f o r that s t a t i o n . However, the curve i s not defined s u f f i c i e n t l y c l e a r l y t o permit the scaling of absorption i n amounts of less than two or three db and various methods are being t r i e d to obtain an improved quiet-day curve. Study of the Knob Lake data awaits f u r t h e r experience w i t h the reduction of the Hanover records. 302

IONOSPHERIC PHYSICS Project 6.22 - Radio Amateur Reports on Unusual Propagation 1. Objectives. This p r o j e c t , administered by the Geophysics Research D i r e c t o r a t e , AFCRL, and c a r r i e d out by the American Radio Relay League (ARRL), u t i l i z e d the a c t i v i - t i e s of amateur radio operators, taking advantage of the v a r i e t y and widespread geo- graphical d i s t r i b u t i o n of av a i l a b l e propagation c i r c u i t s . Propagation i n the 50 Mc bands was p a r t i c u l a r l y i n t e r e s t i n g and r e l a t e d to studies of tr a n s e q u a t o r i a l s c a t t e r propagation and propagation v i a E„. 2. Operations. Through the p u b l i c a t i o n s of the ARRL and a special newsletter created f o r the p r o j e c t , r adio amateurs were informed of the pr o j e c t and i n v i t e d to p a r t i c i p a t e by noting unusual radio contacts, f i l l i n g out logs, describing them, and sending them to ARRL f o r c o l l a t i o n and study. A series of awards and endorsements were made as i n - centives to increase r e p o r t i n g . At the end of the IGY, there were nearly 600 active observers, 128 of whom were i n other c o u n t r i e s , and 11 of whom were short-wave l i s t e n e r s . 3. Personnel. The s c i e n t i f i c supervisor of the pr o j e c t was Wolfgang P f i s t e r , GRD. Mason P. Southworth, ARRL, was responsible f o r the operation of the p r o j e c t . 4. Data. The r e p o r t i n g was done on special forms which give c a l l sign and l o c a t i o n of the r e p o r t e r , the frequency band, dates and times, c a l l and l o c a t i o n of s t a t i o n s worked w i t h or heard, a s i g n a l q u a l i t y code w i t h c h a r a c t e r i z i n g l e t t e r s f o r bursts or rapid fading, the antenna bearing and a code f o r the estimated type of propagation l i k e a u r o r a l , backscatter. Eg, F laye r , meteor s c a t t e r , or tr a n s e q u a t o r i a l s c a t t e r . The incoming reports were checked f o r obvious e r r o r s , omissions and s i g n i f i c a n t events, and then f i l e d according to frequency band, r e p o r t i n g period, and geographical area of the repo r t e r . When a l l the reports were i n , they were cross-checked and analyzed and transcribed i n a new form which was used f o r typing punch cards. I n t h i s analysis a f i n a l d ecision on the mode of propagation was made, d o u b t f u l cases being marked w i t h special symbols. A special job was the a d d i t i o n of the geographical coordinates to the c a l l signs. For that purpose a catalog f o r the l o c a t i o n of amateur s t a t i o n s was prepared, which con- tained considerably more s t a t i o n s than were r e p o r t i n g . About 3,000 st a t i o n s were l i s t e d i n t h i s catalog. Each reported contact and each unsuccessful t r i a l was punched on a separate card. A t o t a l of nearly 300,000 cards was prepared. The cards were l i s t e d , the l i s t i n g s bound i n t o volumes, and supplied to the IGY World Data Centers. 5. Results. The analysis of amateur data so f a r has been concentrated on two classes of data, one i d e n t i f i e d as single hop sporadic E propagation, the other one as trans- e q u a t o r i a l scatter propagation. a. Ea. Analysis of Eg amateur data was performed a t A i r Force Cambridge Research Laboratories where the f o l l o w i n g r e s u l t s were obtained. Eg a c t i v i t y i n the c o n t i n e n t a l United States has a pronounced peak i n the sum- mer months May, June, J u l y , and August, so t h a t during 20% of the time a t least one E cloud r e f l e c t i n g 50 Mc over a distance between 200 and 2000 km can be reported. The percentage f o r the winter months December and January i s only 4% and even lower (2%) f o r the r e s t of the months. The fi g u r e s are average f o r the two IGY years 1957 and 1958. The a c t i v i t y measured i n percentage of time i s somewhat higher i n 1957. There i s also a d i u r n a l d i s t r i b u t i o n of Eg a c t i v i t y w i t h a broad maximum i n the evening hours amounting t o 40% of the time between 18 and 23 hours, i f taken over 303

IONOSPHERIC PHYSICS the whole United States i n the summer months. The minimum was found between 03 and 06 o'clock w i t h a value around 1% of the time i n siiramer. I t might be somewhat influenced by the working habit of the amateurs. A second maximum w i t h 407. i s i n the noon hours between 9 and 14 hours. I t I S i n t e r e s t i n g to note t h a t the geographical d i s t r i b u t i o n of E clouds over the United States i s f a r from uniform. The highest l o c a l a c t i v i t y has bein found to occur i n Missouri and Arkansas 1.25% of the time during the summer season. I n general the l o c a l a c t i v i t y i s below 0.5% except i n the area covering the State of I l l i n o i s and the surrounding states. This r e s u l t i s not believed to be caused by lack of coverage by radio amateur s t a t i o n s . Such a lack, however, i s evident near the boundaries of the c o n t i n e n t a l United States. The size of the Eg patches as seen by the amateurs i s about 600 km m diameter. They usually l a s t f o r several hours and move somewhat i r r e g u l a r l y w i t h an average velo- c i t y of 100 m/sec predominantly toward the west. There i s no tendency f o r a growth i n size. However, i t i s possible t h a t two patches come i n close contact and separate again. b. Transequatorial Scatter. From an analysis of the amateur data, M. P. South- worth, while a t Radioscience Laboratory, Stanford U n i v e r s i t y , reported as f o l l o w s : ( i ) E quatorial Propagation Paths. For convenience, the nocturnal 50 Mc pro- pagation reported from South America, and more re c e n t l y from the Far East, has been separated i n t o three main categories on the basis of path length. The longest are the t r a n s e q u a t o r i a l paths, ranging from 4000 to nearly 9000 kilometers i n length. These paths are roughly bisected by the magnetic equator and t h e i r end points generally have magnetic dip angles between 20° and 60°. I n a d d i t i o n , t r a n s e q u a t o r i a l propagation bet- ween A f r i c a and Europe was reported. Medium-range paths are from 2500 to 4000 km i n length; paths between 200 and 2500 km long are i n the short-range category. Transequa- t o r i a l propagation was also reported c o n s i s t e n t l y between Southern Rhodesia and Cyprus. No short- or medium-range paths were reported i n t h i s area, almost c e r t a i n l y because of l i m i t e d amateur a c t i v i t y . ( i i ) D a i ly V a r i a t i o n s . Data f o r paths from Japan to various parts of A u s t r a l i a show maxima a t two times, roughly 18-19 (the time t r a n s e q u a t o r i a l echoes were observed by B. Dueno, Un i v e r s i t y of Puerto Rico), and 20-21 (the time the 50 Mc amateur contacts are reported i n South America). During the e a r l i e r period, signals were us u a l l y steady; during the l a t e r one, f l u t t e r fading was almost always present. Two shorter Far East- ern t r a n s e q u a t o r i a l paths -- Japan to Queensland and to Papua — were more consistent than the ones shown, and only the l a t e r , f l u t t e r i n g k i n d of propagation was observed. Medium-range propagation was observed i n both South America and the Far East. Short-range propagation was reported most f r e q u e n t l y south of the equator i n South America and n o r t h of the equator i n the Far East. Both types tended to occur a t the same midpoint time as the l a t e t r a n s e q u a t o r i a l mode, and both o f t e n showed f l u t t e r fading c h a r a c t e r i s t i c s . Some of the medium-range paths n o r t h of the equator i n South America appeared connected i n time and midpoint w i t h the patch of high e l e c t r o n den- s i t y observed over Bogota (magnetic d i p angle 32 degrees) a t about 22 hours. ( i i i ) Seasonal V a r i a t i o n s . I n order to observe the v a r i a t i o n patterns of equa- t o r i a l modes throughout the year, p l o t s of the number of nights per month on which t r a n s e q u a t o r i a l signals were received were made f o r the Americas and the Far East f o r the period January 1957 through July 1959. Seasonal graphs f o r medium- and short-range propagation and f o r i n d i v i d u a l t r a n s e q u a t o r i a l paths look much the same. (For about the f i r s t nine months of 1957, A u s t r a l i a n amateurs were not able t o use the 50 Mc band. Hence, there were fewer t r a n s e q u a t o r i a l i n t e r c e p t s than would otherwise have been made, and the curve representing t h i s i n t e r v a l cannot, t h e r e f o r e , be accepted a t face value.) 304

IONOSPHERIC PHYSICS Past references to t r a n s e q u a t o r i a l propagation have mentioned maxima at the equinoxes and minima at the s o l s t i c e s . I n the present data, however, i t appears th a t the s i t u a t i o n i s not q u i t e so simple. While the e q u i n o c t i a l months of March- A p r i l and September-October o f t e n had maxima, the s o l s t i c e periods of December-January 1958 and 1959, i n South America, had even higher maxima, and June and July 1959 i n the Far East were not f a r below the equinox peak. A c r i t i c a l review of the data f o r the s o l s t i c e s showed that the November- through-February period i s almost always higher i n a c t i v i t y than May through August i n the Americas, whereas the opposite i s true f o r Australia-Japan paths. An obvious geo- physical f a c t o r w i t h which t h i s d i f f e r e n c e between the Western Hemisphere and the Far East may be r e l a t e d i s the change i n r e l a t i v e p o s i t i o n of the magnetic equator w i t h change m longitude. On t h i s side of the world the magnetic equator i s south of the geographic equator, while i n the Far East t h e i r p o s i t i o n s are reversed. Perhaps the s o l s t i c e when tr a n s e q u a t o r i a l s c a t t e r i s l i k e l y to be high i s the one t h a t occurs when i t i s summer along the magnetic equator. H. W. Wells has reported the same r e l a t i o n - ship w i t h respect to the e q u a t o r i a l spread-F mode of propagation during the period 1938-1954. Dueno's 40 Mc data f o r 1958 and 1959, on the other hand, do not reveal a s o l s t i t i a l preference. ( i v ) Relationship to Geomagnetic A c t i v i t y and Layer Height. Sudden magnetic disturbances are almost always followed by a dearth of t r a n s e q u a t o r i a l propagation, while good propagation usually comes during periods of low magnetic a c t i v i t y . I t ap- pears t h a t t r a n s e q u a t o r i a l propagation, l i k e spread F, i s i n v e r s e l y r e l a t e d to magne- t i c a c t i v i t y . From a study of ionospheric data a t Huancayo, i t i s evident t h a t the higher the F layer r i s e s at 19, the b e t t e r the f l u t t e r i n g type of t r a n s e q u a t o r i a l pro- pagation l a t e r on. Furthermore, magnetic a c t i v i t y during t h i s period appeared to be a f a c t o r i n how high the layer r i s e s . Every major d i p i n magnetic index was accom- panied by a r i s e i n h'F, and layer height was low f o r nearly a l l magnetic peaks. (v) Other C h a r a c t e r i s t i c s . The upper frequency l i m i t of these e q u a t o r i a l modes was much above 50 Mc. Police signals from Cyprus a t 70 to 72 Mc, f o r example, were received i n the Rhodesias j u s t about as o f t e n as were 50 Mc amateur transmissions. T e l e v i s i o n signals as high as 72 Mc (channel 4) are f r e q u e n t l y propagated from Caracas, Venezuela, to Argentina. B r a z i l i a n TV channels 3, 4 and 5 (60-82 Mc) are o f t e n r e - ceived by Argentine s t a t i o n s over medium- and short-range paths. The l a t e evening t r a n s e q u a t o r i a l s i g n a l s , and very o f t e n those of medium and short range, have a c h a r a c t e r i s t i c r a p i d f l u t t e r f a ding, which was measured, i n one instance, to be 5 to 15 cycles per second. This fading was usually very deep and capable of modulating a strong s i g n a l completely i n t o the noise l e v e l . Evening t r a n s e q u a t o r i a l propagation i s apparently a low-angle phenomenon, but shows a greater time delay than ordinary 2-hop F2 propagation. Two amateurs, i n Southern Rhodesia and Cyprus, measured the angle of a r r i v a l on t h e i r path a t 2-4 de- grees. They also made pulse tes t s which indicated a time delay of around 45 m i l l i s e c ( e a r l y type propagation) and 55 m i l l i s e c ( l a t e type) compared w i t h 40 m i l l i s e c f o r daytime propagation over the same path. ( v i ) Conclusions. There are two types of evening t r a n s e q u a t o r i a l propagation; one mode provides steady signals and i s best between 18 and 19 l o c a l time; the other gives signals w i t h deep f l u t t e r fading and maximizes between 20 and 22. Paths which are geographically and magnetically symmetrical to the magnetic equator and roughly 6000 km long have both types. Very long paths are apt to see only the e a r l y mode, while l o c a t i o n w i t h magnetic l a t i t u d e s around 30 degrees or less usually see only the l a t e r mode. The l a t e r mode i s also more t o l e r a n t of paths which are not symmetrical 305

IONOSPHERIC PHYSICS or normal t o the magnetic equator. The l a t e r mode p a r t i c u l a r l y tends to show a s o l s t i - t i a l preference, the b e t t e r s o l s t i c e being the one when i t i s summer along the magne- t i c equator. Both modes are best during the equinoxes. I t i s believed t h a t the ear l y type of tr a n s e q u a t o r i a l propagation involves the mode proposed by V i l l a r d , S t e i n , and Yeh which employs two successive r e f l e c t i o n s from the F region without intermediate ground r e f l e c t i o n . The f l u t t e r i n g mode tends to accompany spread-F, a s u b s t a n t i a l r i s e i n the F2 layer over the magnetic equator around 19 hours, and low magnetic a c t i v i t y . Perhaps the f l u t t e r i n g mode r e s u l t s from a s c a t t e r i n g region formed by the breakup of the e q u a t o r i a l bulge. Similar s c a t t e r i n g may be responsible f o r the medium- and short-range propagation. 6. Bibliography. , a. Papers Presented a t Meetings. M. P. Southworth: "Night-Time Equato r i a l Propagation a t 50 Mc/s: F i r s t Results from an IGY Amateur Observing Program." F a l l Meeting URSI, San Diego, 1959. b. Published Papers. M. P. Southworth. "Night-Time Equato r i a l Propagation a t 50 Mc/s: F i r s t Results from an IGY Amateur Observing Program." JGR, v o l . 65, no. 2, pp. 601-607, February 1960. T. J. Keneshea: "Sporadic E", Handbook of Geophysics, McMillan and Co. Revised E d i t i o n . 306

IONOSPHERIC PHYSICS Project 6.23 - Radio Star S c i n t i l l a t i o n 1. Objectives. This p r o j e c t at the U n i v e r s i t y of V i r g i n i a provided f o r the observa- t i o n of the s c i n t i l l a t i o n s of radio stars w i t h a view to studying the d r i f t rates of the ion-clouds i n the earth's upper ionosphere responsible f o r the s c i n t i l l a t i o n s . 2. Operations. Three r e c e i v i n g s t a t i o n s were established a t the v e r t i c e s of a r i g h t t r i a n g l e having legs approximately two miles long east-west and one mile long n o r t h - south. Low noise, f i x e d frequency, high gain superheterodyne receivers operating a t 39 Mc w i t h a bandwidth of 75 kc were designed and constructed. The antenna system a t each s i t e was a switched lobe, two-element interferometer (element separation - 10 wavelengths). I n i t i a l l y , s i n g le half-wave dipoles over ground planes were used, but these were l a t e r replaced w i t h Yagi antennas capable of being pointed i n any d i r e c t i o n . Signals from the two o u t l y i n g s t a t i o n s were c a r r i e d by co a x i a l cables to the c e n t r a l s t a t i o n where three ink-pen traces were made simultaneously on a si n g l e c h a r t . An e l e c t r o n i c d i g i t a l i z e r was designed and constructed w i t h which selected lengths of the records could be transcribed i n t o a form s u i t a b l e f o r c a l c u l a t i o n of auto- and cross- c o r r e l a t i o n functions by computer. Late i n the IGY, i t became evident t h a t no simple, r e l i a b l e method of d r i f t velo- c i t y c a l c u l a t i o n was applicable to the interferometer data. Plans were made to con- tinue s c i n t i l l a t i o n studies a f t e r the IGY w i t h the experimental techniques modified and improved i n accordance w i t h the d i c t a t e s of the experience obtained from the IGY pr o j e c t . 3. Personnel. E. C. Stevenson supervised the work, aided by graduate and undergra- duate students. 4. Data. No d r i f t data were submitted to the data centers, o r i g i n a l records have been retained f o r f u t u r e study. 5. Results. Attempted analyses of the IGY records showed that the v a r i a b l e gain inherent i n the interferometer made d r i f t v e l o c i t y c a l c u l a t i o n s by c o r r e l a t i o n methods u n r e l i a b l e . The Ryle-Vonberg m o d i f i c a t i o n of the Dicke radiometer should give more su i t a b l e s c i n t i l l a t i o n records. Subsequent work showed the presence of systematic accelerations i n the ground pat- terns. The model of a d r i f t i n g ionospheric layer i s m question and i t i s d o u b t f u l t h a t r e l i a b l e d r i f t rates can ever be sys t e m a t i c a l l y obtained from s t a r s c i n t i l l a t i o n data. Also, i n the process of proving t h a t the o r i g i n a l proposal was premature, a great deal was learned about the c o r r e l a t i o n method of a n a l y s i s , and some exce l l e n t t r a i n i n g was given to e i g h t graduate students. Seven Masters theses and two Ph.D. di s s e r t a t i o n s were completed by June 1961. Two students have gone i n t o radio a s t r o - nomy, one i s working toward a Ph.D. i n astrophysics, and a f o u r t h i s s t a r t i n g h i s own research program on s a t e l l i t e s c i n t i l l a t i o n s under a new NSF grant. 6. Bibliography. Reports 1-8, Study of S t e l l e r S c i n t i l l a t i o n , Contract No. DA-36-039-SC-85150, U. S. Army Signal Supply Agency, 307

IONOSPHERIC PHYSICS Project 6.24 - Ionospheric Data Processing and P u b l i c a t i o n 1. Objectives. This p r o j e c t a t CRPL, National Bureau of Standards, covered prepara- t i o n and e d i t i n g of hourly values and monthly median values by hours of some 12 iono- spheric parameters being observed and scaled a t 36 v e r t i c a l incidence ionospheric sounding s t a t i o n s during the I n t e r n a t i o n a l Geophysical Year. E d i t i n g of 1 " f - p l o t " of the d a i l y v a r i a t i o n of the frequency parameters received from most (25) of the sta - t i o n s f o r each day throughout the 18 months of the IGY was included. These data were entered on punch cards and these cards used f o r c a l c u l a t i o n s and p r i n t i n g - o u t of the required values f o r p u b l i c a t i o n i n s t a t i o n booklets. Data p u b l i c a t i o n consisted of d u p l i c a t i n g 300 copies each of s t a t i o n booklets of data. 2. Operations. The s t a t i o n s w i t h which the U. S. e f f o r t was concerned were divided i n t o three groups. a. P r i n c i p a l s t a t i o n s operated by the United States. b. Secondary U. S. sponsored s t a t i o n s . c. Stations i n other countries w i t h which the United States cooperated but where r e s p o n s i b i l i t y f o r p u b l i c a t i o n was presumed to be w i t h the n a t i o n a l organizations i n the countries concerned. 3. Personnel. This work was supervised by W. B. Chadwick. 4. Results. During IGY 233 booklets of Detailed Values of Ionospheric Data and F- Plots were published covering 447 s t a t i o n months of data from 25 s t a t i o n s . 300 copies of each booklet were made. I n a d d i t i o n the data from 11 other ionosphere s t a t i o n s were processed. These data covered 198 s t a t i o n months. Tabulations were made by e l e c t r o n i c computer and the r e - s u l t s furnished to IGY World Data Center A f o r Airglow and Ionosphere, where photostats were made and sent to other World Data Centers. Thus, a t o t a l of 645 s t a t i o n months of IGY data were processed. 5. Biblioaraphy. F i r s t Report of the Special Committee on World-Wide Ionospheric Soundings (URSI/AGI), Brussels, September 1956. Second Report of the Special Committee on World-Wide Ionospheric Soundings (URSI/AGI), Brussels, May 1957. 308

IONOSPHERIC PHYSICS Project 6.26 - Signal Corps Ionospheric Sounder Stations 1. Objectives. This p r o j e c t of the U, S. Army Signal Corps Radio Propagation Agency provided f o r the operation of four v e r t i c a l incidence ionosphere sounders as a Signal Corps c o n t r i b u t i o n to the IGY program. 2. Operations. Equipment, furnished under p r o j e c t 6.1, was i n s t a l l e d at Signal Corps sta t i o n s a t Thule, Greenland, and Grand Bahama I s l a n d , FWI. Parts and supplies were also provided f o r operation of a C-2 on A r c t i c D r i f t i n g S t a t i o n B (Fletcher's Ice I s l a n d ) . E x i s t i n g equipment was operated a t St. Johns, Newfoundland, Canada. 3. Personnel. F. H Dickson and Harry F, Busch supervised the operations under t h i s p r o j e c t . 4. Data. A l l IGY data have been scaled and processed, and were submitted to the IGY World Data Centers. 309

IONOSPHERIC PHYSICS Project 6.27 - Whistler Stations - Alaska 1. Objectives. This p r o j e c t a t the Geophysical I n s t i t u t e , U n i v e r s i t y of Alaska, pro- vided f o r operation of three s t a t i o n s of the Stanford Whistler Network. For d e t a i l s see p r o j e c t 6.10. 2. Operations. I t was o r i g i n a l l y intended to operate, under t h i s p r o j e c t , equipment at Unalaska. Problems, however, required t h a t operations a t t h i s l o c a t i o n be taken over by Stanford. The equipment at College was put i n t o operation i n January 1958, and that a t Kotzebue i n December 1957. 3. Personnel. This work was under the supervision of C. T. Elvey; J. H. Pope was the senior s c i e n t i s t associated w i t h the operation. 4. Data. A l l tapes from the IGY have been scanned. Logs of events were prepared and sent to Stanford to be incorporated w i t h the r e s t of the w h i s t l e r data. 5. Results. a. Whistlers. I t had been suggested t h a t there might be a small p o s i t i v e corre- l a t i o n between w h i s t l e r s and magnetic a c t i v i t y . Using d a i l y indices of w h i s t l e r a c t i - v i t y and d a i l y K-index sums f o r College, the c o r r e l a t i o n c o e f f i c i e n t was found to be too small to be s i g n i f i c a n t . On the other hand, the c o r r e l a t i o n c o e f f i c i e n t showed some behavior which may t u r n out to be s t a t i s t i c a l l y s i g n i f i c a n t . Only f u r t h e r study w i l l resolve t h i s question. I t was also found t h a t the occurrence of w h i s t l e r s a t high and low l a t i t u d e s i s d i f f e r e n t . I n high l a t i t u d e s the annual v a r i a t i o n peaks during the w i n t e r months. The d i u r n a l v a r i a t i o n ( F i g . 12 ) i s s i m i l a r f o r high and low l a t i t u d e s except t h a t i t has a maximum during the e a r l y morning hours i n high l a t i t u d e s rather than the e a r l y evening hours at lower l a t i t u d e s . The d i u r n a l v a r i a - t i o n i s much less pronounced i n summer than i n w i n t e r . Propagation conditions i n high l a t i t u d e s may account f o r p a r t of these d i f f e r e n c e s . b. Chorus. As received a t College between December 1955 and December 1959, chorus shows annual and d i u r n a l v a r i a t i o n s of occurrence. The d i u r n a l v a r i a t i o n i s s i g n i f i - c a n t l y d i f f e r e n t from those obtained i n lower l a t i t u d e s a t i t s time of maximum. The annual v a r i a t i o n shows a maximum i n the w i n t e r . These r e s u l t s appear t o d i f f e r from those obtained a t low l a t i t u d e s i n t h a t the maxima at the lower l a t i t u d e s t a t i o n s tend to occur during the summer. The d i f f e r e n c e between w h i s t l e r and chorus d i u r n a l curves makes i t u n l i k e l y that propagation conditions of low frequency radio waves between the e a r t h and iono- sphere can be the cause of the chorus d i u r n a l v a r i a t i o n . The time of maximum i s seen to be a f u n c t i o n of l a t i t u d e . Thus, i t appears th a t the observed d i u r n a l v a r i a t i o n i s e s s e n t i a l l y a c h a r a c t e r i s t i c of the phenomenon of chorus i t s e l f , r ather than one of some other phenomenon. The annual v a r i a t i o n observed might be a t t r i b u t a b l e to other phenomena such as ionospheric absorption. The c o r r e l a t i o n between chorus and magnetic a c t i v i t y ( F i g , 13) has a seasonal v a r i a t i o n . This v a r i a t i o n might be due to a complex i n t e r a c t i o n between three or more phenomena. I t appears t h a t the generation of chorus i s r e l a t e d i n a p o s i t i v e manner to magnetic a c t i v i t y and hence, possibly, solar corpuscular r a d i a t i o n . Neither theory nor analysis of chorus has progressed to a p o i n t where one theory or another can be considered more l i k e l y . For the time being the various theories proposed must be considered e s s e n t i a l l y conjectures. There i s some evidence, however, i n d i c a t i n g t h a t chorus might be generated by solar p a r t i c l e s . Further i n - v e s t i g a t i o n i n t h i s d i r e c t i o n may lead to conclusive r e s u l t s . 310

IONOSPHERIC PHYSICS CLO I - 10 I—Lr-rU 150 ' WMT Figure 12. Diurnal V a r i a t i o n of Whistler Occurrence at College, Alaska, Data from December 1955-March 1958. I95S I i s s e Figure 13. C o r r e l a t i o n C o e f f i c i e n t s f o r (A) Daily Chorus Indexes f o r College vs. Daily K-index Sums f o r College, and (B) Da i l y Chorus Indexes f o r Washing- ton, D.C. vs. Daily K-index Sums f o r Fredericksburg, V i r g i n i a . 311

IONOSPHERIC PHYSICS 6. Bibliography. a. Papers Presented a t Meetings. J. H. Pope. "The Determination of Electron Densities m the Outer Atmosphere by the Use of Nose Wh i s t l e r s . " Alaska Science Conference, Juneau, 1959. W. B. Murcray, J. H. Pope. "Radiation from Protons of Auroral Energy i n the V i c i n i t y of the Earth." AAAS, Anchorage, Alaska, 1960. J. H. Pope: "A High L a t i t u d e Study of Chorus." AGU, Los Angeles, Dec. 1961 b. Published Papers. J. H. Pope: "An I n v e s t i g a t i o n of Whistlers and Chorus a t High L a t i t u d e s . " Sc. Report 4, A p r i l 1959, Geophysical I n s t i t u t e , U n i v e r s i t y of Alaska. J. H. Pope: " E f f e c t of La t i t u d e on the Diurn a l Maximum of Dawn Chorus." Nature, v o l . 185, p. 87, 1960. J. H. Pope: "Whistlers and Chorus Observations." F i n a l Report, A r c t i c Pro- pagation Studies of Troposheric and Ionospheric Modes of Propagation. A i r Force Contract AF19(604)-1859, Geophysical I n s t i t u t e , U n i v e r s i t y of Alaska, October 1959, pp. 51-67. E. M. Wescott, J. H. Pope, D. Dyer, W. H. Campbell- "Rare Hiss, Earth Cur- rents and Micropulsations on November 27, 1959." Nature, v o l . 185, 1960, p. 231. J. H. Pope, W. H. Campbell. "Observation of a Unique VLF Emission." JGR, v o l . 65, no. 8, 1960, pp. 2543-2544. W. B, Murcray, J. H. Pope "Doppler Shifted Cyclotron Frequency Radiations from Protons i n the Exosphere." Phys. Rev. L e t t e r s , v o l . 4, 1960, p. 5. W. B, Murcray, J. H. Pope: "Radiation from Protons of Auroral Energy i n the V i c i n i t y of the Earth." JGR, v o l . 63, no. 11, 1960, pp. 3569-3574. W. B. Murcray, J. H. Pope: "Comment on Energy Fluxes from the Cyclotron Radiation Model of VLF Emissions." Proc. IRE ( I n press). J. H. Pope: "An Estimate of Electron Densities i n the Exosphere by Means of Nose-Whistlers." JGR, v o l . 66, no. 1, 1961, pp. 67-76. J. H. Pope: "A Correction to the Exospheric Electron Density Estimate Using the Nose-Whistlers of March 19, 1959." JGR, v o l . 67, 1962, p. 412. J. H. Pope: "A High L a t i t u d e I n v e s t i g a t i o n of the Natural Very Low Frequency Electromagnetic Radiation Known as Chorus." JGR, v o l . 68, 1963, pp. 83-99. 312

IONOSPHERIC PHYSICS Project 6.28 - Fixed Frequency Backscatter - Alaska 1. Objectives. This p r o j e c t a t the Geophysical I n s t i t u t e , U n i v e r s i t y of Alaska, pro- vided f o r the operation of a backscatter radar, as part of the Stanford network of s t a t i o n s . 2. Operations. The equipment was put i n t o operation i n September 1957 and operated through the IGY. Some problems t h a t were encountered w i t h f a i l u r e of e l e c t r o n i c and mechanical components reduced operating time to about 60%. The t r a n s m i t t e r was not a f f e c t e d , however, and these outages d i d not a f f e c t a propagation experiment arranged between College and Kiruna, Sweden, where an i d e n t i c a l radar was i n operation. The j o i n t observational m a t e r i a l from the Kirtma Geophysical Observatory and College has been made the subject of a special study a t the Geophysical I n s t i t u t e under A i r Force sponsorship. 3. Personnel. This p r o j e c t was under the supervision of C. T. Elvey. L e i f Owren was the senior s c i e n t i s t associated w i t h the work. 4. Data. The f i l m s f o r the IGY period were processed and sent to Stanford f o r copy- i n g ; the o r i g i n a l f i l m s were returned to College f o r analysis. 313