D-A237 674 2iIllfII111111111I111111 ~I1 (? ---PL-TR-91- 2063

MAGNETOSPHERIC STRUCTURE AND DYNAMICS:A MULTISATELLITE APPROACH

W. Jeffrey Hughes

Boston UniversityCenter for Space PhysicsBoston, MA 02215

20 March 1991

DTICScientific Report No. 1 9JUL8E C T E

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

91-03946

tit PHILLIPS LABORATORYdh AIR FORCE SYSTEMS COMMAND) HIANSCOM AIR FORCE BASE, MASSACHUSETTS 01731-5000

This technical report has been reviewed and is approved forpublication.

,/ Ut ___ __ _ __ _

IRVING MICH WILLIAM P. SULLI . ChiefContract Ma ager Space Plasmas and Fields BranchSpace Plas as and Fields Branch Space Physics DivisionSpace Physics Division

WILLIAM SWDERDeputy DirectorSpace Physics Division

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1. AGENCY USE ONLY ieivc' blank) 2 REPORT DATE 3 REPORT TYPE AND DATES COVERED

120 March 1991 Scientific Report No. 1

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Magnetospheric Structure and O-vanmics: A PE 61102FMultisatellite Appraoch PR 7hOl TA 18 'JCU I

Contract q9Q -rt

6 AUTHOR(S)

W<. Jeffrey Hughes

7 PERFORMING ORGANIZATION NAME(S) AND ADDRKSS(ES) 8 PERFORMING ORGANIZATIONREPORT NUMBER

Baston UniversityCenter for Space PhysicsBoston, MA 02215

Q SPON4OR!NC ! 10N!TC'R'N' A'-FN""~ %:kr'S) AND ADDRESS(ES) 10. SPONSORING MONTORiNGAGENCY REPORT NUMBER

Phillips Laboratory

Hanscom Air Force Base, MA n1731-5000 PL-TR-91-2-06?-

Contract Manager: Irving Michael/PHG

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Approved for public release; distribution unlimitcA

13. ABSTRACT (Maximumn 200 words)This report reviews progress during the first year of a contract to studymagnetospheric structure and dynamics. Four areas of scientific investigation.are highlighted. Pressure gradients form in the geotail because ions drift ~eferentially toward the dusk flank. These pressure gradients drive field ' ecurrents that close in the ionosphere and which provide a natural explanat~o.C''the Harang discontinuity when the full electrodynamics are modelled. Observationsmade during a passage by DE 2 through the dayside cusp at a time when the =M %'adirected northwards are consistent with magnetic merging occurring on field lin.-sthat map to the poleward cusp boundary. We infer that tail lobe field lines werEmerging with magnetosheath field lines at the magnetopause tailward of theexternal cusp. During the March 1989 magnetic storm, the DMSP F9 spacecraft cbservez'extensive substantial decreases ia uquaLorial Jic-n Iisit ' in the post-du" scz-'-Modelling calculations show that the depletions were cuased by unusually larep:vward flows moving the equatorial F region peak above 850 km. Calculations Of 1,,

cyclotron wave group velocities show that the\, are s3ensitive to both the hict ar.cold plasma populations. Calculated group delays agree with our earlier observat ions.

14. SUBJECT TERMS 15 NUMBER OF PAGES

Magnetosphere, Harang discontinuity, magnetic reconnection, 14

electrodynamic ion cyclotron waves, magnetic storms, 16 PRICE CODEDynamic Explorer, DMSP______________________

17. SECURITY r, '~fJ .~~~ CL; 3 itf.ICATION 19. SECURITY CLASSIFICATION 20 LIMITATION OF ABSTRACTUF k'Lj.~i OF THIS PAGE Of ABSTRACT

Unclassified Unclassified Unclassified SAR

'JSN 7540-0 -280-5500 .- -

I. Introduction

This contract funds a comprehensive five year study of magnetospheric structure anddynamics. There are four major areas of study: waves andt wave particle interactions. mag-netospheric tail and substorm dynamics, ionosphere- magneltosphere coupling, and activeexperiments. The first three areas are all central to our understanding of the geoplasina

environment. Each plays a critical part in deternilnirig tle pattern of plasma flows and

currents and the distribution and properties of the plasina and energetic particles withiil themagnetosphere-ionosphere system. The last topic, active experiments, is an exciting emerg-ing field in space plasmas that holds much potential. The major effort is directed toward,the analysis of existing and newly acquired spacecraft data, with particular emphasis on miil-

tisatellite studies. The data analysis is complemented by theoretical ano simulation st ildies.the development and maintenance of data analysis and display software for use in the dataanalysis, and the design of new innovative plasma and field instruments for use in the nextgeneration of spacecraft. The overall goal of the st;idy is to provide the understanding ofthe magnetosphere-ionosphere systen needed to coiistruct reliable models that will forecastthe future state of the system.

This report focuses on four areas of scientific investigation iII which significant progresshas been made in the first. year of the contract: the electrodynamics of the ilara,,g disntiit y and geotail convection; signatures of magnetic merging observed on the polewardboundary of the cusp; understanding the causes of the extreme equatorial densily depletionsobserved bv DMSP F9 during the March 1989 magnelic storm: and modelling electroniag-netic ion cyclotron wave group delays. Each of these topics is ilrade tle subject of orlesection of this report and has or will result in tle pibliation of a scientific paper. IlIre wesurrniarize tle main scientific resllls and refer tire reader to one or Iimore of the plrblicatIO1Sarising out of our research for filler delails. A collpete list of )Iiblicalions arini I, of

this research is contained in the last section of this report.

As this contract has been ill effect for only one year. allt Iio~t of tlie researcllers wo ill

on this project have been supported iby this conlract for less t han a year. all of i lie work(escribed here was begun under otlher contracts, at lHoston (niversilv and elewhrere. ili

substantial work was (loni( and tle work was cornpl)lc t I nder 1}iis coltrat.

11. The Physics of the Ilarang Disconti1mity

W\e have developed a niatuiiral explaniat ion (,,' illl-eha rang dis(mlinulIit\' t hat arises frontthe asv ma~tr','of lonl (ilt pat us inl the l ad. ' Ilarallg (1i(oii ii is tie locus of pointSill file nightside aiuroral zonle acioss whlich the 111cr idlonl compllonent of the io!!~osphlric

electric field reverses fromi a lmasiallV JIlewar(I fOld on the equatorward side to a basicallyequat orwardl field on the poleward side. In other words the H aranrg (1iscJlit ili n V rprsntsa convergence of ionlosphderic electric fHeld. 'll- o)verall st riot re of tN 1 fatulre is evil'h-u

ill h igl-at itude radar obsevrvations, anid in satell itei nicasue intof hoth Ii letc Hvels aw~lionospheric plasmi flows.

loris in the ph snta AMee dh riftwstward or (Iusk wan i acros 16 litil dAiv to the Ill iltic

gmrad1iet and cii rat ne drifts. Tile west ward cuni rvatni and grad (lt drift deplets (Ia xvnsitdefilix tubes of energetic ions beca use there is rio st-rnig soir rc of enieget i plasmia ini thedawriside rnagnetopause lhotiri y hvlyr to1 replace- those thIlt haue drifted westward . This

dawrisi de depletion effet incanis that . on average. th le d isksi le of t lie plasniasheet xwill havehigher ion termperatulres, pressuires aiid fi x ti he(ndit 'Iis. andl lieice st roniger xvst xai'd( ross-t ail drift cuirrent , t han t hie dawriside, Thli deficit of (lalx'rsidle current (or surphus of

diiskside current ) i!st be1 (onwil(isaireId tyuvlpwxard(l cuii'iit s fromi t he ionosphere (list rihiiteda( ross lie tail toe(lisilre cirrnit cont1inuiity. In t he ioiiosIplei', ('lo-iii'(of Ihis current requireis

ai 'onivergenlce of ioi)..,ieric lPe(Irs('ii current s, anid Iieni(e at conivergenice of elctrc field.dIirect ed towardls the center of th linipxvaid cuirrent . Tliis is exactly the formn of the I lararig

Th'i requirement that Oh i's lawv he satisfied in thle ionosphere creates an ionospheric

electric field that miaps b~ack to tlie tal and rniolifes the p~lasm~a flow there. Ihe lregion

lpocxxa rd of thle II ara ng (lisconti or ut maps wvellI out into the plasnma; sheet 'het( eqiiatonxvard

elect iic field iii this region of Ilie ioniosphere Inaps inito all earlhlivardl elect rc field ill thlilplasinashe(t that drives a daxvniwar' I E x B floxw thIiat opposes lie dulskwxard gradient aridlcuvu"Ire (rI ts. This helps keep the flow of ios ini I he lpsnuiasllcet dIirected towards thle

earth arid reduces the loss of ions from th ltail at the (lllk flank. The poleward electricfield observed eqllatorward of the Ilararig (liscont iniitv inaps to a tailward electric field atthe inner edge of tlie plasnia she. I'his dries a westward E x B flow that reinforces thewestwxard cuirvatunre and gradient drift of ions arouinid thle dursk si~le of th iecart h toxwards thle

davside mla gnet opause.

Thiis argumrlent was stOie (flialititat ively by irncudirig thlese effects iii the Rice C on-xvect ion Model ( RCM). 'Thiis was done by' ext end i g t Qmhm i tii sp~ mu'ea ch fNOtWer downthe tail arid including a re'alist ic plasmna soinrmIe lOiiidal' condit ion onl the dawn flank ofThe tail. T]his reslted in a sign i fica t dawn deplct on efet hxiich caused a large ban d ofupward Wlreland e-rrer!it o a drawn out. of the (('nt r;l aurioral /,one( onl lhe night side. Theresultg ;.Oitudinal dist ilmint i of l~irkel currnt ds mat dies t hose oblserved l iinch bet ten

han those calculatedl inl PROW.'I nwI J.a 1h AN V~'~ 'in Ic .~j -'~(qdt'

was modlr fed to produ~ce a strorig con x'egence of el('ct in' field similar to t hat observed in thle

1-arang discontinuity. The dawn side (lepletion effect, also results lin a reduicionl of plasmlasheet pressure in the near- Earth mnidn ighit sector of tHec plastria sheet du le to the loss of io1nsthrough the dusk flank of the( tail. H oweve'r the( flows diven in thle tail 1I v the elect nc( fichk"associated with the Hlarang discontinuity tcid to reduce tice losses, which mecans h lal pres-sure can still build up to unstable levels in the inner plasmia sheet even during magnet icalvcalm intervals of slow convection. This latter effect. will be explored ]ni fuitutre work.

Principal Reference

Eri( kson, C .M . 11 .'v. Spiro and] 1 .A. WVolf, Thle I'hYsics of t lie I a ranig lDiscontimit i . ..Gcophys. JBcs.. 96, 1633, 1991.

6

XTrS O;RA&IDT IC TABJUrantioumced Q

An iI ability Codas

0ist special

31

111. Cusp Electyrodynaiies witth Nortiwaurd IMF

Thie Df)-2 satellite ofteni psm-, t liroirgl t ie( regili of tI ho tospli(ric (1151 /cleft t hat

are are characterized l)v Hite(is( Iiiglily-variille (piastl) electri iici ed. colocated wit I

miagrieloslieath-like parties, Ili additioni, duriing iterval> ot st roig soulthIwaid (lirlcdei

[Llarge spu ke- like elect rit field s a re occasiial liv seeni mear th lieeq at orward boui nidla r ofhe cusp. These are t hought to be thre iortoslheriC' Si 1nti e fiaiti merig at thle

ctaysid nngiieto[, aus, Thi- hy,,pot lies's was tested arid tonifirri ed iii earlier case study

during the large mnagnet iC stormn Of September 6 1982, wheni DE- I anl- _ )[-- were conijugate

ali(l D1) crossed the mnagnet opar ise. A plow~ardl-(lrect ed elect ric hield spik e was (detected at

the etuiatorward boundary, of t Ite cuIsp. This was iiit eriireted ats I lie ioniospheric signat iire of

lie iii it al mnot ion of the neiwly-miierged flux tube III thre direct lion of the local mnagnet osliat il

flow. However mnagnietic t ensioti forces soon become (1011 iuawit in let ernmi nig flux t ilt)(-uio-

ion. reversing the senlse of flow. ThIe electric fieldl spike corrcsi or is to a iiarrow regin of

plasmia convectioni at the hom idar rv of crisp preci pit d ioll ilIi t(-e dii loll of' nagiietoslieat It

flow arid Is alr iriditalt i that tlie satmellille crossed iel low-alt it ide foot prit of thre mlerg-

ing lie. Anothler featunre associatecl with Ii ragrretoparrse irertgi rig a chIiaract erist ic energy.

(lispersionl Observed inl tie( eriergetic ioll fluxes near tie( eqiiatorwitird huidar 'vof the cuisp.

Thle hiighest eniergy ion)s are observed closest to t lie eq at orwa rd lior midarv- of t lie cusp, aiid

, tittessivel V lower enlergies with Ii icreasinig lat iturde.

If thle electric field spikes seeii at tie( ecliat orwarul bounldary. of thei clisp dunring timeIS,

of sou t hward IIF are i ideed low-altituide sign atuties of rirergi rig, tien onle might ex pect o

observe s' i 1i electric field signatures near the polewa rd cuisp 1)OrlIrdal- ry ilring periodls of

niorthwv.ard directed INIF if merging t heni takes place betweeni the MPand( oppositely, directed

iiagiietospheric field lines at the magnetoparise tailward of the cusp. We have studlied ill

detail a single I) -2 cuisp crossing that took place aromnd 1900 F T oil 1 7 'bruar *rv 9,'2

dirriirug a periodl of iiorthiward I Ni F. Ill the polar cap lplolew\a rd of thle clisI). Plasma Was

flowi rig su nward towards t !ie (cusp1. At the poleward bour idanY of tie( t151 preci pi tat ion, we

observed anl- eqiratorwa rd dIirect ed electc itfielid spike. mi(l icat inrg a r iarrow region of duskward

flow. fol lowedl by a mirch b~roadler region of iioie mnoderat e lawniwa rd flow. The( electric

field spike was accompainied by ant ion dispersin even t, but ]i tie( opp~osite senise to t hat

usual ly observed duiri rig souithIward ! NJff . That is t ie( Ii igliest (ilergy- lolls were ohsei-ved at

the polewardl ciusp boundary, arrd suiccessivly lower eniergy, lolls w%]it I increasing dist ance

from the boundary. Threse observa tions are consist ('lt with mii ergi ig occur ri rig oin thle hiigh

lan't ride magnetopause tail ward of t ie( cuisp biet weeni I NI I anrd tail lobe field li nes. The global

con vect ion pat tern has plasma flowi ig out, of t ie( polar cap, orI ]it Ilie t all lobe towards thle

nuagietopaurse, where field linies reconnect withi tie I NF. Immirediately after reconnlectil.

magiietoshea th flow drags ft(e iiwwIv reconnect ed flu x t ri ies rap idIly lusk ward. !ut( magnet (it

tensioni rapidlly comes inrto play. reversi rig tie( flow so tIi at t t tibes cou \ect t ai ward p~ast

the (lawn~ flank. This gives rise tol thle lct nric field spike arid subsequent opp~ositely directed

electric fieldl as well as thie associrtc elmragriet ic sigriat res of field aligiil curreit s.

fIn add~itioni to these larger scale featunires. a traini of abiiut thiree qniasi-siruisoidal. ele tilt

and magnetic field oscillations was observed just equ atorward, or dov, ;,itrearn, of the electricfield spike. The oscillations had a period of about 2 s in the spacecraft frame, and therewas an approximately 40' i)hase shift between the electric al magnetic variation,. \Veput forward two alternative explanations for these waves which appear to be the result ofthe partial reflection off the ionosphere of hydrornagnetic waves incident from above thespacecraft. One possibility is that what DE 2 observes is primary temporal in nature, thatthe waves have a period of 2 s in the plasma frame. This is near the ion cyclotron frequency.so the waves might, well have been generated by the ions observed in the ion dispersion eventbeing unstable to electromagnetic ion cyclotron wave growth. Ii this scenario the wave aregenerated higher tip the field line and propagate down the field line to the ionosphere. Herethey are partially reflected, so that DE 2 observes the interfering upgoing and downgoingwaves, which explains the phase shift The three cycles observed represent the spatial extentof the source region, which is about 50 km at the DE 2 altitude of 850 kin.

The second scenario links the oscillations more (lir,-ctlv to the electric field spike at thepolar boundary of the cusp. If this is an electric field experienced by each field line as itreconnects at the magnetopause and is dragged duskward by the flow in the magnetosheath.this electric field signature propagates down the field line as a shear mode Alfven wave. Asthe Alfven wave travels down the field line, the field line is convecting equatorwards at 10)or 200 m/s. On reaching the ionosphere, a few hundred kilometers below I)E 2, the ;\lfvenwave partially reflects and travels back tip the field line which has in the meantime movedequatorward. The electric fields of the incident and reflected waves will tend to cancel.while their magnetic fields will tend to add, thus suhstant iallv changing the ratio of theelectric and magnetic perturbations of the initial spike and the subsequent oscillations. Themagnetopause, where field lines bend sharply and tih Alfven speed changes abruptly, willalso act as a partial Alfven wave reflector, so the wave will tenid to bounce a few timesbetween the ionosphere and magnetosphere before its energy is dissipated. This explainsthe train of three oscillations. The oscillation period is about 2 s in the spacecraft data.similar to the time scale associated wit Ih tie spike. lit 2 s the spacecraft mlioves about I I kin.The plasma, moving at 100-200 in/s along the spacecraft patlli. takes on the order of 100 sto move this distance. At typical magnetospheric Alfven speeds ( 1000-2000 ki/s), a wavewould travel 10-20 RE in this time, not unreasonable for a 1 ri) from the I aguiet opal Ise tothe ionosphere and back again. Flux tube area increases by about a factor of 1000 between,DE 2 altitude and the magnetopause where the field streligt h Iliglit be a factor of 1000lower, so the 1H km distance along the spacecraft path increases to .500 kin normal to tiemagnetopause at the magnetopatise, or even iore if flu x tulbe shape is not preserved. wvh hhis probable. This is not an unreasonable thickness for a reconnect ion region.

At. this stage we are not Fble to distilnguish between Ihiese alterniative scenarios oil tilebasis of the data we'veanalysed. lHopefully analysis of fi rt her spacecraft passes through tIlecusp will allow us to decide which lescript ion is beller alhle to explain tlie ( obsrvations.

5

Principal References

IBasins'ka, FEM.. WI.Ili-keand N.C. Ia\'iia:'I, leIiKt-6 and' .\l;.giri H.eld Fliic.1tiothu I lthe Cusp/Cleft Region", i /I Phi~sWs of Spacu IPu.s ma.' 1.99J( Si '1 (oi11l .en e ~oeuIand] Reprint Series. Nunii l 10, J I. Chalmig, G. B. Cew and J. R . 1 asperse. e(1s.Scientific- Publisher-s. Cam1uIidgc, Mass., I99i I. (imn press)

Basinska. E.M , W.J. Bur-ke, N.(C. Nlaynard, W.J. flughes, J.A. Slaviii. and Ji..umighamn, Cusp Elect rod vfamtics withI Nor-thwa ui INI 1MV pi Iit .o bOle Subm1tit ted toi .Ceophys. Rcs.

6

IV. Equatorial Plasmia Density Depletions during a Magnetic Stormi

Early on 14 March, 1989, duiring a major, nagnetic storm, the Henrna I plasm a prohe on

the DMSP F9 spacecra ft. detected extenisivye ait( draiici decreases Ii the ion deii sit v at I"1(0

kin, near 2130 LT, duirin tigIwo coiisectiiv( t rs.isequtat orial passes over Southi Anmen ~a. 'I'lie

order of magnitude decreases iii ion dlensity extentded1 more tfan .1000 kill along thle satellite

track. The depict ions were accomp janied by upward an 111westwardl plasmia drifts. buth ItIn

excess of 100 rn/s. Their onsets awl terminations were marked by extremely sharp) ulenisit

gradients. The satell i te observed no simnilar depict ions over the At lant ic d urinrg Ow hepricefili

orbits. A partial (depletion was detected over the eastern Pacific (luring I lie followliiq orbit.

The satellite ground track passedl slightly west of a B~razilian TEC st at ion and t wo Brazilian

ionosonides during the orbit on which the first depict ion was observed. Thel( TF' felIl far

below normal during thle night of 1 3- 11 March. 'Ilie, loiosonide mieasuremnent s inid icat e that.

in the hour aft ter suinset, before 1) NISP pased tltrot igh the (leplet ion s. the F2 layerve ro~c

rapidlly and disappeared, but at Ihle tinte of thle first IiSl) pass thIirou gh the deplet ion.

hmF2 was decreasing over one of thec st at Ionts.

A sister spacecraft, DNISI [8, orbits iii the (lawn-(l tsk meridian. When thi s:pare, raft

passed over South America at, dusk on 1:3 March, sorte t hree hours before D)NIS FI) 11tf. lterd

he depletions, it detected externely large ion derisi ties andl upward and w('st w i d drifts .

Twelve hours later, during two (lawn passes over thle eastern Pacific. l)NISI FS8 Jul (let etdepletions ~~~~somewhat siniilar tothose bee )M NSP [9, accomtpaniled bY alrewta~

dlrift . These morning side, deplet ions could well1 be( t he~ ret 111a t s of t hose (let e,(tI (1 earl ier. in

he premidnight sector, by l)MSP [F9.

Large east ward electric fields will (Irive large up~wardl drifts at low lat it ides. As thle PMIS P

orbit is normally well above the alt itutde of the F2 peak dlensity, uplwardl di if? S ota

give rise to Increased not (decreased (densit ies. H owever, we argue that on this ight lieelectric fields and hence the drift~s were so st rong t hat lie [2 peak w as lifted above thle

WI)S P altitude. placinrg the spacecra ft in thle very low densityv plasmna below t he iii glttilt1 l(

F2 peak. When an eqtiatorial flux tube Is raised, lplasnia tends to fall down t lie, flux tithe

uinder the force of gravity, raising p~lasmiia denlsities at lower a It . tires oil ihe e(1 tat it. Miodel

calculations of the effect, of large suistalied upward dift at lie e(Iltttor coiillied wit It gravity

(iv en field aligned flows reproduc lft'lte sorts of (lellet ]oiin I hat were seti Lv ) NI 1\P F". Tlhc

sharp boundaries to thle dheplet ion areI created itatirlally bY aI convergencfe of I )iastila dr1ift

paths.

T he cause of the Intense uipwardI drifts that p)roduicedl thle plasia leplet ions' fail nh d

be unambiguously determined. I lowever there are two processes that (-alt giv~e rise toal

east ward electric field at. the ((1 ator duinug a large miagnet ic stonrm. l)tiriig large iiiagneltic

storms the normal uippe'r atniospliere cirteulat ion patht ( ms arme hist ii rhed by Ihle add itiotial

thermal inputs. 'Ilie, new circuhat iou drives aut at tiosplirric 'hynaunlo t hat (.ati reer'v the

electric field that, is tiorniall v west ward Ini thlis local t uric spi't or. whichi resitlts I ittupard

dlrifts. Under normal cotiditiotis. utfttc slinf(le icidli are siieled fron 1mid and low

7

lat it uides h-, the act ion oft lie ion w diere it self. I lowever dum ig large (list u rltances. especial lYif tI lie regIin of sum na rd convectI loll comies c lose to thle ca rthi I Is s I I Iell d I g can b reak down.

If thlns occirt-d. t ho maignet usieric convectin ('Vctric field could halve penietrated to 11wequator. It is UIWI\' ' thalt ;I ( oli)litj;it loll of these i wo effects p~roduccd the laIrge lipwar'l tl-Ift,

observed l) 'v hot h l)MS1T simaccr;ii't aiiil heli(( (.tIlscl the ols. rved dep)Ict loll.'. [hat;1 tilt

leltois were ohlservedl shortl 'v al~ter thle ring ciurrellt reachcd~ Its niaxiuniiuitn v11.1,1 antI1nea ri va day afterthe first ssc of t11e st ormi nieaiis t hattleStrii Inanicx rendiHelvImportant iii their format ion. '['lie, lole'3 locat ion hn'tween Ille eveiiug teriniiator mid Hite

So i I tlantic Anromnaly ( where intiiense particle p)re:i pit ation raises ion iza tion levels) ii dia role for condluict ivi ty gradinen ts iii enhlanicinig thle electrnc fields.

Principal Reference

(ireens[ari. M. ['., C. E. Ranritsser. VV. .1. 'Iiiike aiid Ml..Abdu. Fti-'atoria! (heiisitv(h1 )ie ioiis okbserveth at 810 kill durinig the great i',agiet( ucstom1 of Mlch.l St 1

(b nphyi ys. . in p~res-s. I1100.

V. Ion Cyclotron Group Delay near the Plasmapause

Flectroinagnet ic ion c (l( tron waves are genlerat ed near t he in agilt tic eq 118 or irwlolI

anl inst ability drIn ei v enlerg t i ioln eperatulre alIs;ot ropv. 'Fie waves propagate a lolignmilet ic flux t u hes, an 11( ria ii are observed oni cegrollil~d as pci magnet ic pilsatlins II e-t

oft en exhibit a (list i nct ye wave p~acket sI ruct tirc b~elieved to be the reslt, of wave packets

bouincing back and forthI along a fluix ti he prod tic ing thle repetitive st ructuiire that gives rl(

t.o the name pearl pilsat ions. In 81n earlier report we comnpared ion cyclot ron waves oh servedbV tl~ I) I spacecraft iiear lie equnatorial planec near 1.=l with ground1( based obscrva I (plls

of pci pulsations observed near thle foot. of the I) F I field Ii lie by the A F(AI Magnet on et erNet work. For thIiree of the six events observed si ii ilt aneoiisly In space and onl t h groui id,we were able to estimate 11'he (ela 'v time for thle signal to propagate fromt thle eqtiat or to thegrouind. The est imat es foi the di frcrent events ranged between 35j aiid] 10 I)s.

InI this work we compare thlese ii iasiiremteiit. wit Ii calelilat ions of thle group del a 'vmade

Using the fill] hot p~lasmla. (islpersioi i rela tioil Integra tedl a long a dIip1 ole field lin e froi n theeqnia tor to the ground. The lalisma pa ra meters uised in thle calclllatiots are b~asetd on t li

plasma and~ particle measurements miadle by IM7 1 a thle t ilne of the wave events. As the

p~aramueters are not always nieasii re I precisel . we conl dlicted a variatiolt aal-l s to dtlterit iehow sensitive the grouip delay is to thle various plasma parameters. and also 'omnparedl oir

resti 1ts to the resi Its obt a ined earlier uising only the co, p~lasma dispersion relatjont.

We fon nd t hat tie deiisi t v otf 1hot Ii th lhot and (c1(1 species affect the wave groil p veloci t v

significantly. especially tva r t'lie eqniia t rial plane where thle grotilp veloci v. is smaIlest. andr M

where it has thle largest effect on I lie total groupI delay. Iitelidiiig thle flull disperISIOn1 rtlat iOu

ais opposed to t lie cold l)!11.,lll d ispelioli rehi t Ion prod1 littt (llauges Ii I lie grt Iip) delay onl

the oi-ler of lt)X . I siing ilteasillrvllttlit s froml thle F~trigetc lu (olilpos It onl S)pec rilieter.

the P~lasmra Wave Ilist Ilincilt aliid thle lktiildiiig lou lls LS ,pcclt ioitlI l t'" 111( h

and~ cold plasma eiiviroiiiiieiit s we ohl~tieditt good iigit( Ilicli t eiiel our1 cal( Illaltei griotip

delayvs and tit se we obt ainied earlier fo nii a cros corlait oil oif thle wave, leaslretI Lv 1)11 and oil the groundt.

Principal Reference

1.1idow, ( .f?.,W .J. 111"les ald 111'. CirilliTll I' )eldml i IV Soti r t

lgis rear thle P~lmiltls(, piImjtI t.ltt tll ili t to) ku.1)II~d 1J. (H!ItI. ?

V1. Publications

(a) Primary Publications

Erickson. G.ALI, H .W. Spiro and~ R. A. Wolf, Thel( PhlYsIcs of thle llaraiig Discontinuity. .1.Gcophys. Rhs., 96, 16:33, 1991.

hulghes. W.J .. Waves Oil tilie Niagnetopauisc andl t 11(11 Sigiiat lire onl thet Grouind, in BRcportof Ilit (cospac( En ni'on,,u'rt Modeling Workshop on lonosplf ric Signaturcs, of Cutsp.Mfagnudopazisr and Boindary Layer- Proccsstes, (TiJ. Rosenb~erg. Ed.), p.0 3 . Univ. Mar\'-land,1 College P'ark, MD, 1990.

Ba-sinska. E.M., l)E-2 Electric Fields in the Cuisp/Cleft Regions. in Gcospace Enrironment.1foddzing Workshop IReport on Inlcralibraliriq Cuisp SI'gnature-s. (N.IT. (7rooker. Ed.)p. 12. Nat ionial Scien'e Found~ation. Washingt on DC(. 1900.

Basinsika , E.MN.. W .J. B iiirkc anid N .C . MIaynardl, Electric and( NMagneticr Field Fluctunations in]thfe ( '1sp/(ieft Regions, InI 1Physics of Space IMasrnas 1 990, SIl~ I on ference Proceedligsai(I Reprn t Series. N iinlwer 10. ( T. Clialig. G. 13. (rew, anrd .1. R. .Jas perse. e'ds.)Scientific Publishiers. Cambridge, Nlass., 199)]1. (iii press)

(Grteenspan. NM. E., C. E. Rasnitssen, WV. J. Burke, and NM. A. Abdui, Equtatorial densitydlepletions observed at 8.10 kml duii-ng the great miagnetic stormi of March, 1989, J.GCrohym-. Rb s., in press. l99)0.

(b) Other Publications

Baker. K'i. .1..A. G~reeunwald, .JAL NI nolioniemi, ..H?. Dtudney. M. 1'innock, P.1. Newell.NI.F 1K.( enspan . and C. M Neng. Sitntilt anieous IIF- Radar and D)NI SP Observations ofhe Cuisp. (;(ophi.Us. Rts. /Aft. 11, 1869-1872, 1990.

Newell. P).'., W.J. Buirke, (X-l. Mieng, E.R. Sanchiez, and NI .E. Greenspan. Id(ent ificat in andObservat ions of thfe Plasma Mlant le at low alt it tides, J. (ophy. IRcs. 96. 35-16. 1991.

Mayniard, N. C'.. 'L L. Aggson. E- NM. Basinska. W. Ji. Butrke. 1). ( raven, '. N\. I~etersoui.NI. Suigitura. and 1). R. %Veiintl, NIagnet osplieric Botiin lar- 1) 'viainlics": )E- 1 and( 1)1-?Ohstrvat ions n',ar tilet Nagnetopaiise and Cuisp, J1. (op/iys. [?s.. 3 :505. 1991.

liat ,t a. 1. S.. 1E. R. dc P'anila. Ni. A. U diu, N. BI. Fri vedl iand M1. I". (4re'rspan. Ionosphericeffects tof the 1:3 March' 1989 inagnet ic st orni at low andi(l pia torial )a I tid~es, suibmittedto .1. (;eojph!/s. lbs., 1990.

10

(c) Papers Presented at Meetings

Baker, K.B., H .A. Greenwald, J .M. Ruohonieri, 1I.l. Newell, $.R. IDuderv.ncy .. I'irinock

and M.E. Greenspan, Simultaneous Observat ions of thle Cusp with D,%ISP and~ thePACE Radars, present ed at the A merican Geophyisi cal Ujnion Sprinrg MIeet irg. Bali-

more, May 1990. (Abstract: EOS, 71, 581, 1990.)

Erickson, G.M., Onl the Deterininat ion of the Polyt ropic Index in the Plasina Sheet. presenltedlat the American Geophysical Union Spring Mleeting. Balt imore, Max' 1990. (.*\ bst ract:

EOS, 71, 606, 1990.)

Basinska, E.M., W.J. Burke, and N.C. Maynard, Electric andl Magnetic Field Iluctuat ionsObserved in the Low-altitude Dayside Cusps, presented at 1990 Cambridge Wrsoon Geoplasma Physics, MIT, June 1990.

Hughes, W.J., Observations of Magnetospheric ULF WVaves: A Tutorial Review. pr-esenitedat 1990 Cambridge Workshop on Ceoplasma Phyrsics, MIT, Julne 1990.

Singer, H .J. and W..J. Hughes, Srrbstorru Detection: A Comparison 1et weeni P12 and] Al.indices, presented at tire Chapmnan Conference on Niagriet osphieric Srrbst orrrr . I lakone..Japan, September 1990.

Greenspan, V. E. , F.1. R ich, anrd [?. A. I eelis, DI) SP F8 M\easurremnrts of Tori Cornposit iolland Drift: Low- Alt it rlde Boundary Conditions for Plasniasplieric Mlodels. p~resenited( atthe Workshop onl Plasmaspliere Refilling, Huntsville, October i 990.

Basinska, F.M., 1)E-2 Electric Field Signatures of the (risp. present ed at lie G.FEM Workshopon Intercalibrat ing Crusp Signati res, Weston. MIa. Oct ober 1990.

Basinska, E.MN., W..J. Burrke, N.C . Mlaynard. .J .A. Slav Iii a r iI ..D. Winin irglia rrr. Flcct Pornag-

netic Signatures of Mlerging at thle Poleward 'isp Boinr r y "v presented at AniericailG'eophiysical U nion Fall Meet inrg. Sari Francso (1(. ecenri lETI990. (A.\bst ract: [' 71.i54.-, ;iqq0)

Erickson, C.MN., Mgeoprri-lrsperc (ou 1 ling and( thel pre-sirc hal ice Inrcorisilieric v

presented at A ircr eolviaIErilorr Fall Ni ecti rig Sari F'rancisco . [)eceril icr I 9 )().(Abstract: F'0,5 71, 15.15. 11090)

(reenspan, M.E ., C.F. Hasimism-rr \\.J. lBrrke, arid \ A. Ahdiri. Iriteiricat rol of ar

storrui-in(lrrced holes iii lie eqriatorial iorrosplnrev. picsclited at Amiririrri f pi]i

Union Fall %lectinig. Sari Francisco. lDeceiher. l 9. (A.lst ract: 1-,';. 71. I S1 I99) tt

Lrrdlow.Gj.R.,\V..J. lhuglesarid IIl. (ollirr,'I'lieioricc11ri groij)i~iYr for' sllv irrce rgiori1

near the plasinaparise. present ed ait Ai iericani ( eophdrsicailI i,1oll Val Icitl iiiu. SariF'rancisco, D~ecemrb er 1 990. (A.\l,)t ract: 1,,'S, 71. 1).33. 1 990)