Radar observations of two dimensional turbulence in the equatorial electrojet, 2

Transcription

1 Utah State Unversty From the SelectedWorks of Bela G. Fejer January 1, 1976 Radar observatons of two dmensonal turbulence n the equatoral electrojet, 2 Bela G. Fejer, Utah State Unversty D. T. Farley B. B. Balsley R. F. Woodman Avalable at:

2 VOL. 81, NO. I JOURNAL OF GEOPHYSICAL RESEARCH JANUARY 1, 1976 Radar Observatons of Two-Dmensonal Turbulence n the Equatoral Electrojet, 2 B. G. F EJER 1 AND D. T. FARLEY School of Electrcal Engneerng, Cornell Unversty, hhaca, New York B. B. BALSLEY NOAA Envronmental Research Laboratores, Boulder, Colorado R. F. WOODMAN Rado Observatoro de Jcamarca, Lma, Peru Observatons wth an alttude resoluton of about I km were made wth the large, vertcally drected 50- MHz radar system at the Jcamarca Radar Observatory durng the day, when the electrojet was strong. Type I ('two stream') echoes were seen n a lmted range of alttudes, wth Doppler shfts correspondng to upward and downward moton at the acoustc velocty. Most of the radar returns were due to type 2 echoes, however. The drecton of moton of the type I waves sometmes reversed n as lttle as I s, supportng a turbulent model of the electrojet regon. Durng the day the upgong type I waves were observed to be somewhat more easly excted than the downgong waves, an effect smlar to an east-west asymmetry noted n earler studes. The correspondence between the Jcamarca radar observatons and rocket measurements n Inda s dscussed. INTRODUCTION The propertes of the plasma rregulartes generated n the equatoral electrojet have been and are beng studed ntensvely at the Jcamarca Radar Observatory n Peru by usng mproved radar technques. Recent work has been descrbed n several publcatons [e.g., Balsley and Farley, 1973; Fejer et al., 1975a, b]. The results presented here are a contnuaton of ths seres. Most of the recent Jcamarca observatons have been made wth alttude resolutons of 1-3 km, n contrast to earler studes n the 1960's whch, wth a few exceptons, used long pulses drected normal to the magnetc feld and had a beam wdth for backscatter of about 0.8 ø, gvng a horzontal resoluton of about 1.5 km at the alttude of the electrojet. The receved sgnal was tape-recorded by usng a drect record (rather than an FM) channel wth a bandwdth of about 300 khz. The vertcal resoluton ( < 1 km) was determned by the pulse length ( 5 us) and the bandwdth of the tape recorder. By replayng the tape and samplng the sgnal at dfferent tme delays after the transmtter pulse, smultaneous spectral measurements could be made at any desred alttudes. Some measurements at a sngle alttude were also made n real tme wthout usng the and/or wde beam wdths and hence could only determne tape recorder. The power spectra n both cases were computed average propertes of the entrelectrojet echong regon. The. by usng a 64-pont fast Fourer transform program. Several present paper deals wth daytme spectral observatons made spectra were averaged to smooth out statstcal fluctuatons. wth the large, vertcally drected 50-MHz antennat ca- marca and wth short transmtter pulses yeldng an alttude resoluton of about 1 km. The results extend and confrm smlar studes of Balsley and Farley [1973], whch were made wth an alttude resoluton of 3 km at a tme when the electro- The pulse repetton frequency was 400 s -x, and thus the data were of poor qualty for ntegraton tmes shorter than a few seconds. Further detals of the spectral analyss procedure are gven by Balsley and Ecklund [1972]. RESULTS jet was relatvely weak and no type I ('two stream') echoes were present. The type 2 echoes seen then showed a very The data to be presented here were all obtaned between 'turbulent' structure; the shape of the spectrum of the scattered 1056 and 1104 local tme (75øW, or EST) on January 15, sgnal and the mean Doppler shft changed rapdly wth both Ths perod was typcal of tmes when the electrojet s strong alttude and tme. The present measurements were made when and vertcally propagatng type 1 rregulartes can be detected the electrojet was strong and are partcularly concerned wth at a dscrete Doppler shft correspondng approxmately to the the type I echoes whch were seen n a narrow range of altacoustc velocty. The sgnal-to-nose rato was hgh, as t.usutudes. The same turbulent character of the medum s apparally s n electrojet measurements usng the large ncoherent ent. The type 1 rregulartes appear, dsappear, and reverse scatter system at Jcamarca. Fgure I shows a small segment n drecton rapdly. tme (26 s) of the data, sampled n steps of 750 m n alttude, except for the lowest alttudes. Fgures 2 and 3 show a porton EXPERIMENTAL PROCEDURE of the data of Fgure 1 (labeled A, B, and C) at 106 km The measurement echnques were very smlar to those de- expanded n tme (shorter ntegratons) by factors of 2 and 4, scrbed by Balsley and Farley [ 1973]. The 50-MHz antenna was respectvely, to reveal the temporal behavor n more detal. The spectra n Fgure 3 have large statstcal fluctuatons bex Now a,t Unversty of Calforna at S n Dego, La Jolla, Calforna cause of the short ntegraton tme (only eght samples of the spectrum were averaged). Fgure 4 shows the results of much Copyrght 1976 by the Amercan Geophyscal Unon. longer (42 s) ntegratons at about the same tme. The spectra 130

3 FEJER ET AL.' OBSERVATIONS OF ELECTROJET TURBULENCE, JtCAMARCA oh56m26 s / t = 52 sec 0 h 56m52 s K m,.- ',,., IO9 I - 1',,.--,e-' "'"'",-.,,. -'"'?""" --,...<,"1",',?"I ',---.,...'/':'"I;,"..,,..,...,.,'..,...,.:.,:.,... ",,? ;.,.+.:.....:/'...:...,.,...:..:.:...,. :..:...,,....,.','.,....,. /,' "', 7".'" ':.":'...',".,:.,"".?'.,.;,:':?'"". "' '... '." ':?.¾ o 06,....,.,....,,...,.?:,, -, :-...:..,,.,:.,. :..,/..:.'.T:,...'.,, V- øø,.:.':,..,,:", "?':?.,/,'", '-,, -'"/ /,-":'.%.,.'\.;,,>....,.',.'....- "' :.., :,.,....;,..:.'...' :. :, '-'" " -I: O I: O -I: O I O -I: O I O -I O I: O, /,..7.-'%.:,.,...,...?./,.: : "' '"',o./.....,: ',,,.',..o..,.. '"' I.L. ' ;L :,:"I,.. "',."'c l.,, ' DOPPLER SHIFT (HZ) 15 JAN HEIGHT = 106 Km At = 1.3 sec '...'... A. rr ' ', I *' uj B 0 '...: :..,.,.,... o o. ' '..... "' '" ": '...'... '.'. ' Fg. 3. Further expanson of part of Fgure 1. The four spectra labeled A, for example, correspond to the sngle spectrum labeled A n Fgure 1, wth tme progressng from left to rght The large scatter n the spectra s due to the small ntegraton tme. of about Hz) can be detected n many of the spectra, due to a stronger electrojet current. Alttude dependence. Fgures I and 4 show that the type 1 echoes are observed only n the central porton of the echong regons, between about 103 and 107 km. The downgong type l Fg. 1. Power spectra from vertcally propagatng 3-m electrojet waves (postve Doppler shft) are lmted to an even narrower rregulartes. The ntegraton tme (At) for each spectrum s 5.2 s, regon. At the bottom and the top of the echong regon, only correspondng to an average of 32 spectral samples. type 2 echoes are seen, and the spectrum becomes narrow, symmetrcal, and peaked at zero Doppler shft. The seres of spectra correspondng to 10h 56m 3 Is n the second column of were measured out to Doppler shfts of +200 Hz, but only the Fgure I llustrates well the varablty of the spectral features sgnfcant portons are shown n the fgures. At the operatng wth alttude. At km there s no sgn of type 1 echoes, frequency of 50 MHz a Doppler shft of -4-1 Hz corresponds to but at km both upgong and downgong type I waves can a downward phase velocty of 3 m/s. The areas under the be clearly seen. The upgong type I waves are slghtly stronger curves n Fgures 1-4 are only approxmately proportonal to than the downgong waves at 107.5, , and km and the echo power, due to varatons n the gan of the tape recorder amplfers from one run to the next. Fgure 5 shows an accurate plot of total echo power as a functon of alttude for ths perod. At =42 $ec The data shown n Fgures 1-4 are qute smlar to the I O h 56 m 00 s I O h 56 m 42 s earler results gven by Balsley and Farley [1973], excepthat n the present case the alttude resoluton s consderably better.. IO9 o and the presence of type I echoes (the peaks at Doppler shfts.'"...'" N,. ""......'"'" "...e.. F'"'"' ':"" o 15,JAN 1973 HEIGHT=106 Km At =2.6 sec DOPPLER SHIFT (HZ) Fg. 2. Expanded verson of part of Fgure I at 106 km wth mproved tme resoluton. Tme progresses from left to rght and downward. oo I.'.. '" '... '...".'.' n- Lk,I ' "...'"'""... I 0.''" '"" " ; ".'" o '""'..'.'..'" tn...' '. 0 "" I! '" t.). Lk,I. '. UJ '.",1 _.1.'.. ;...'.".. Lk,I ' ". '. :'"""' I ' ".N.;. "... "' I I " I00...'"".. r "... '" '"" "'"" ';' '""%! "' DOPPLER SHIFT {HZ) Fg. 4. Electrojet spectra smlar to those of Fgure 1 but correspondng to a much longer ntegraton tme of 42 s. The type 2 spectra can be seen to be practcally symmetrcal around the zero Doppler shft.

4 132 FEJER ET AL..' OBSERVATIONS OF ELECTROJET TURBULENCE, I10 oh56m45 s _ oh57m50 s Hz, but there s no correspondng feature on the postve sde. Further examples of ths asymmetry are shown n Fgures 6 and 7. The strength of the downgong waves may equal or exceed that of the upgong waves for short perods of a few seconds, but, on the average, the upgong waves always predomnate durng the day. Prelmnary analyss of comparable nghttme measurements made n January 1974 shows tl at ths asymmetry reverses at nght. Note that the phase velocty of the upgong and downgong type 1 waves s the same even though the ampltudes are dfferent. DISCUSSION are much stronger at 106 km, km, and below. Comparng Fgures 1 and 5, we see that the type 1 echoes are present at the heght of maxmum echo strength and somewhat above t but are not present below t. Temporal varatons. Obvous rapd varatons n the shape of the spectrum at a partcular alttude can be seen n Fgure 1 and n even more detal n Fgures 2 and 3, whch correspond to only 16 s of the data at 106 km. (In successve reprocessng of the tape-recorded data the startng tme of the ntegratons may vary by a few tenths of a second, and so, for example, the sum of the two curves n part B of Fgure 2 does not exactly reproduce the curve labeled B n Fgure 1.) We see from these fgures that the upward and downward travelng type 1 waves, both of whch appear n the curve labeled B n Fgure 1, can be resolved nto separate tme perods f a short enough ntegraton tme s used. Although Fgure 3 s of poor qualty because of the short ntegraton tmes, t ndcates that a complete reversal of the observed drecton of propagaton of the type I waves can take place n a tme as short as 1.3 s (mddle two spectra of row B of Fgure 3). Relatve echo strengths. Although we have been emphaszng here the propertes of the type 1 echoes, t s clear from Fgures 1-4 that most of the echo power at all alttudes and almost all tmes corresponds to type 2 echoes, wth ther relatvely unstructured spectrum centered (on the average) at zero Doppler shft. Ths s true even near 106 km, where the type 1 echoes are strongest, except perhaps for occasonal very bref perods (Fgures 2 and 3). For longer ntegratons, such as those shown n Fgure 4, the type 2 echoes always predomnate. When all alttudes are averaged together, as was done n most of the older vertcal ncdence studes [e.g., Cohen and Bowles, 1967], the presence of the type 1 echoes s even more obscured by the type 2 echoes. Ths behavor for a vertcally drected radar s n sharp contrast to the stuaton for large radar zenth angles (e.g., 60 ø from the vertcal), for whch the type 1 echoes are much stronger thap the type 2 echoes when the electrojet s strong. Up-down asymmetry. Fgure 1 suggests that upgong type 1 waves are more commonly observed durng the day than are downgong waves. The upgong waves are detected over a wder range of alttudes and are generally stronger, on the average, than are type 1 downgong waves at alttudes at whch' both are seen. Ths behavor s somewhat more obvous l 'the longer ntegratons shown n Fgure 4. At 106 km the negatve peak s certanly stronger than the postve 'bump' on the spectral curve, and at 103 km a bump can be seen at about Alttude dependence. Hgh-resoluton, oblque spectral measurements dscussed by Fejer et al. [1975a] made wth an eastward drected antenna ndcated that the strongest type 1 echoes occur at about 107 km, whch s slghtly hgher than the correspondng alttude for the vertcal measurements descrbed here. Snce the heght of maxmum drft velocty' may change wth tme, however, smultaneous oblque and vertcal spectral measurements would be necessary to determne whether or not the heght of the two-stream regon really depends on zenth angle, and even then the measurements would not be completely defntve, snce the scatterng volumes would be dfferent for the two observatons. Turbulent structure. Earler hgh-resoluton, vertca. l spectral measurements by Balsley and Farley [1973] showed that the phase velocty of the type 2 waves vared rapdly wth tme and heght and thus provded support for the two-dmensonal turbulent model suggested by Farley and Balsley [1973] and Sudan et al. [1973]. The data presented here refer to a perod of apprecably stronger echoes, and ther general aspects also agree wth those n the two-dmensonal turbulent model. The dea here s that the type 1 echoes are observed only when the mean (averaged over, say, a few hundred meters) vertcal elec- tron velocty exceeds values of the order of the acoustc velocty. If the scatterng volume were smaller than the large scale structure, type 1 echoes wth both postve and negatve Doppler shfts could never be observed smultaneously (.e., usng t = 42 sec 103 Km 106 Km 'l'* Ioh 59m30s.'.' %.....'.'".... "'""" I "'. '"'" I """ ".0 * 0,%. '"* I I [ I l" ' ** I I I I I ' ; *l*"* hoom 12 s n 0 % *.,,... %0*** [AJ eeeeee e eeee 0.. '*****. '.**. - eee e I 0 : I I I I ' 000 I [AJ '[' o ", I-- ' '"..'.', ee e,,,....'-..'-"" I h 00m54 s ** I ' '%".'...'. '"';' I I I.eee I I '"'%'"" I '... ' _> **** <[ IJ.J" I I I " n 'l'. Ilh 01m36' J '.. 'e e. '...'""""%,....' %¾.. '" I I I ' ""I I I I';' DOPPLER SHIFT (HZ) Fg. 6. Spectra at two dfferent heghts at whch type I echoes are observed. For type I waves the backscattered power from upgong waves s usually greater than that from downgong waves durng daytme.

5 FEJER ET AL.: OBSERVATIONS OF ELECTROJET TURBULENCE, JANUARY 1973 HEIGHT = KM Ih02 m 33 s,,,]... Iho2m40 s,, tu u,;,, "...: Ih m09... s II h 03ml7 s..,..-' IIho3m23 '... s > "'.".:.,J IZ: "%... "' ;:..:... ';'. :(...,.,.-.:'. "'.:.':'." ':....,,, :':...,' -120 O O DOPPLER SHIFT {HZ}.....,,.. : ':.',..,.:,:..., Fg. 7. Examples of spectra observed wth good alttude and temporal resoluton at 106 km durng a perod of pronounced type 1 asymmetry. Tme ncreases from left to rght and downward. The ntegraton tme was 5.2 s n each case. These spectra were calculated on lne wthout usng a tape recorder. very short ntegratons), but both types of type 1 echoes could be seen wth longer ntegratons due to horzontal convecton of the turbulent structure through the scatterng volume. Our scatterng volume s probably not qute ths small, but nevertheless, the turbulent structure seems to be nearly resolved wth the shortest ntegratons. If we take the characterstc electron velocty here to be of the order of 400 m/s and the characterstc tme of the large scale structure to be about 1 s (snce sgnfcant changes n the spectrum are sometmes observed n tmes as short as ths; see Fgure 3), we arrve at a characterstc scale sze of about 400 m, whch s about half that of the scatterng volume. On the other hand, the spectral shape sometmes perssts for 10 s or more (see Fgure 1), correspondng to a horzontal scale sze of several klometers. These numbers are of course very rough, but they do lead to a selfconsstent model whch seems to ft the data reasonably well. Theores based on lamnar electrojet models [e.g., Rogster and D'Angelo, 1970; Whtehead, 1971; Lee et al., 1974] are unable to explan the generaton of any vertcally propagatng waves, let along the type 1 waves travelng vertcally, sometmes upward and sometmes downward, that we have descrbed here. In an attempt to deal wth ths problem, Lee et al. [1974, see note added n proof] and Rogster and Jamn [ 1975, Appendx B] menton an unpublshed suggeston of P. Waldteufel that perhaps-the type 1 echoes seen when the antenna s drected vertcally are not really travelng vertcally but correspond to oblque sde lobes of the antenna pattern. Ths explanaton fals for at least two reasons. Frst, the sde lobes of the antenna pattern are very small ndeed; the frst sde lobe s less than 2 ø off axs and yet s about 27 db weaker than the man lobe for backscatter measurements. For 10 ø off axs the re- sponse s down by db. Second, even f the sde lobes II a.k wc,c.,ut mm, u, cutt pondng echoes would be cjlrnlnateu " ' ' ': by the range-gatng process for all but small off-axs angles. Echoes comng from, say, an alttude of 106 km at a zenth angle of 30 ø would appear at an apparent alttude of 122 km, not 106 km. Comparsons wth rocket observatons. Prakash et al. [1972, 1973] studed electrojet rregulartes over a large range of scale szes and showed that durng strong electrojet condtons, rregulartes wth vertcal scale szes n the range 1-15 m, whch were observed prmarly near 105 km, have a spectral ndex of zero (no wavelength dependence). The suggeston was made that these rregulartes were smlar to type 1 rregulartes, snce ther spectral ndex was dfferent from that of other rregulartes attrbuted to the gradent drft nstablty. The data presented here have shown, however, that the vertcally propagatng type 2 waves are always stronger than the type 1 waves durng the day, at least for 3-m wavelengths. How can we explan ths apparent contradcton? Frst, as Ott and Farley [1974] ponted out, n any comparson between rocket and radar data t must be kept n mnd that the 'wavelengths' referred to n the rocket measurements are 2;r/ks, where ks s the component of the plasma wave vector k parallel to the rocket trajectory, the other components of k beng arbtrary; hence the true wavelength wll always be less than or equal to the quoted value. Radar measurements do not have ths ambguty; the k vector and wavelength are unquely determned. We have just seen that for vertcal k the type 2 waves always domnate at 3-m wavelengths durng the day, and the results of Balsley and Farley [1971] suggesthat ths would be even more true at ncreasng wavelengths but perhaps less true at decreasng wavelengths. At oblque angles, however, the type 1 echoes can domnate at 3 m. From these consderatons we conclude that the suggeston of Prakash et al. [1972, 1973] s probably correct, but t s undoubtedly the oblquely and not the vertcally propagatng type 1 waves that are responsble for the rocket effects, and furthermore, the true wavelengths are shorter than the values quoted. Asymmetres. The up-down and east-west spectral asymmetres have been mentoned n earler Jcamarca studes [e.g., Cohen and Bowles, 1967, Fgure 1; Balsley, 1970]. Balsley [1970] found from oblque spectral measurements that the electron drft veloctes (deduced from the Doppler shft of the type 2 echoes) to the west of Jcamarca were consstently equal to or larger than the correspondng veloctes to the east durng both day and nght. He suggested that ths velocty asymmetry mght be due to geographcal factors such as the land-sea boundary to the west of the observatory or the Andes mountan range to the east. On the other hand, durng the day the electrons move from east to west, and so a radar ponted oblquely westward responds to waves whch have an upward as well as a westward velocty component. At nght, after the electrojet reverses, the waves seen from the west have a partally downward velocty. As a result, one mght suspecthat the small vertcal current n the electrojet plays a role n the asymmetres, but Balsley [1970] argued that on the bass of lnear theory at least, ths current s far too small to account for the observed east-west velocty dfferences. Perhaps the nonlnear lmtng processes act somewhat dfferently on the upgong and downgong waves, dependng upon the drecton of current flow. Rognlen and Wenstock [1975] have made suggestons along the latter lnes. In any case, t s obvous that geographcal factors cannot explan the asymmetry seen at vertcal ncdence (upward movng type 1 waves beng most easly excted durng the day and downward movng waves at,, gnt), snce u,,y a sngle scatterng volume s nvolved. In consderng the east-west asymmetry, one must be careful to dstngush between the type 1 and the type 2 waves. Durng both day and nght the type 2 mean Doppler shft (and hence the wave phase velocty) and the total echo power are normally slghtly larger to the west of Jcamarca than to the east. Type 1 waves are sometmes seen to the west when they are not

6 134 FEJER ET AL.: OBSERVATIONS OF ELECTROJETURBULENCE, 2 seen to the east, but the reverse s seldom true. When the type 1 waves are seen smultaneously n both drectons, they usually have the same phase velocty, although small dfferences can occur, presumably due to dfferences n the parameters (e.g., temperature, wnd velocty) of the medum n the two scatterng volumes, whch may be separated by several hundred klometers. For example, Fejer et al. [1975a] dscuss a case n whch the type 1 phase velocty s larger n the east for some tme. We reterate that ths observaton should not be confused wth the type 2 data n whch the veloctes are almost always larger n the west. CONCLUSIONS The data presented here add further support to earler theoretcal and expermental work [Farley and Balsley, 1973; Sudan et al., 1973; Balsley and Farley, 1973] and computer smulatons [McDonald et al., 1975], all of whch ndcate that the structure of the electrojet scatterng regon s hghly turbulent. Sato [1973] has also made somewhat smlar suggestons. Most of the echoes receved by a vertcally drected radar are from slow-movng type 2 rregulartes, but when the electrojet s strong, hghly varable type 1 echoes wth postve and negatve Doppler shfts are also observed between about 103 and 107 km; however, even here the type 2 echoes stll predomnate. Reversals n the observed phase velocty of the type 1 waves can occur n tme ntervals at least as short as 1.3 s. These rapd changes are probably due to convecton of the turbulent structure through the radar beam. On the average, the upgong type I waves grow to a larger ampltude and are observed over a wder range of alttudes durng the day than are the downgong waves. Ths up-down asymmetry n the vertcally propagatng waves may be related to the east-west asymmetry observed n prevous oblque spectral measurements. Fnally, we note that consderable care must be exercsed n comparng rocket and radar studes of electrojet echoes, snce the wavelengths referred to n rocket 'measurements are not true wavelengths and the drecton of the k vector s not determned. Acknowledgments. The data presented here could not have been obtaned wthout the consderable help and cooperaton provded by the staff of the Jcamarca Radar Observatory. Support for ths work was provded by Natonal Oceanc and Atmospherc Admnstraton grant and Natonal Scence Foundaton grant GA The Jcamarca Radar Observatory receves partal support from the Natonal Scence Foundaton, the Natonal Aeronautcs and Space Admnstraton, and the Natonal Oceanc and Atmospherc Admnstraton. The Edtor thanks M. K. Hudson and P. Waldteufel for ther assstance n evaluatng ths paper. REFERENCES Balsley, B. B., A longtudnal varaton of electron drft velocty n the equatoral electrojet, J. Geophys. Res., 75, , Balsley, B. B., and W. L. Ecklund, VHF power spectra of the radar aurora, J. Geophys. Res., 77, , Balsley, B. B., and D. T. Farley, Radar studes of the equatoral electrojet at three frequences, J. Geophys. Res., 76, , Balsley, B. B., and D. T. Farley, Radar observatons of two-dmensonal turbulence n the equatoral electrojet, J. Geophys. Res., 78, , Cohen, R., and K. L. Bowles, Secondary rregulartes n the equatoral electrojet, J. Geophys. Res., 72, , Farley, D. T., and B. B. Balsley, Instabltes n the equatoral electro- jet, J. Geophys. Res., 78, , Fejer, 13. G., D. T. Farley, alsley, and R. F. Woodman, Oblque VHF radar spectral studes of the equatoral electrojet, J. Geophys. Res., 80, , 1975a. Fejer, 13. G., D. T. Farley, alsley, and R. F. Woodman, Vertcal structure of the VHF backscatterng regon n the equatoral electrojet and the gradent drft nstablty, J. Geophys. Res., 80, , 1975b. Lee, K., C. F. Kennel, and F. V. Coront, On the margnally stable saturaton spectrum of unstable type I equatoral electrojet rregulartes, J. Geophys. Res., 79, , McDonald, 13. E., T. P. Coffey, S. L. Ossakow, and R. N. Sudan, Numercal studes of type 2 equatoral electrojet rregularty development, Rado Sc., I0, , Ott, E., and D. T. Farley, The k spectrum of onospherc rregulartes, J. Geophys. Res., 79, , Prakash, S., 13. H. Subbaraya, and S. P. Gupta, Rocket measurements of onzaton rregulartes n the equatoral onosphere at Thumba and dentfcaton of plasma rregulartes, Indan J. Rado Space Phys., 1, 72-80, Prakash, S., S. P. Gupta, 13. H. Subbaraya, H. S.S. Snha, and C. L. Jan, A revew of the n-stu measurements of E-regon rregulartes, report, Phys. Res. Lab., Ahmedabad, Inda, Rogster, A., and N. D'Angelo, Type 2 rregulartes n the equatoral electrojet, J. Geophys. Res., 75, , Rogster, A., and E. Jamn, Two-dmensonal nonlnear processes assocated wth 'type 1' rregulartes n the equatoral electrojet, J. Geophys. Res., 80, , Rognlen, T. D., and J. Wenstock, Theoretcal propertes of twodmensonal electrojet turbulence, Rado Sc., 10, , Sato, T., Unfed theory of type I and 2 rregulartes n the equatoral electrojet, J. Geophys. Res., 78, , Sudan, R. N., J. Aknrms, and D. T. Farley, Generaton of smallscale rregulartes n the equatoral electrojet, J. Geophys. Res., 78, , Whtehead, J. D., The equatoral electrojet and the gradent nstablty, J. Geophys. Res., 76, , (Receved February 3, 1975; accepted July 25, 1975.)