active experiments, magnetospheric modification, and a naturally occuring analogue

7/29/2019 Active Experiments, Magnetospheric Modification, And a Naturally Occuring Analogue

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Radio Science,Volume 8, Number 11, pages1035-1048, November 1973

Active experiments,magnetosphericmodification,and a naturally occurring analogueMargaret G. Kivelson and C. T. Russell

Institute of Geophysics nd Planetary Physics,Universityof California,Los Angeles, California 90024(Received August 6, 1973.)

Active experiments n the magnetospherenclude some intended to be primarily diagnostic(barium release, electron guns) and others designed o perturb the system to generate insta-bilities (VLF or ULF wave injection from ground stations, onosphericheating). Recently, aschemehas been proposedwhich would modify the magnetosphere y injecting plasma nearthe equator beyond the plasmapause and initiating wave-particle instabilities. The expectedeffects have been examined theoretically. Injection of plasma into this region is also a natu-rally occurring phenomenon produced by the cross-tail electric fields which are associatedwithgeomagnetic activity. For further investigation of magnetospheric nstabilities, the advantagesof examining artificially injected plasma (control of time and location of injection and of thevolume of plasma injected) contrast with the advantages of studying natural enhancements(no extra payload, frequent occurrence). Thus, the two types of experiments are comple-mentary. In preliminary studies of natural plasma enhancementsboth ULF and ELF emissionshave been observed. The ELF noise is consistentwith generation by the electron cyclotroninstability.

1. INTRODUCTIONDuring the 1960's the propertiesof the magneto-spherewere investigated rimarily with passive ech-

niques, othground-basednd on satellites.n recentyears, he methods f observation ave been broad-ened to include active experiments n which themagnetospheres locally modifiedand its responseto a well-definedperturbation s examined. n thispaper,we brieflydescribe numberof activeexperi-ments which have been performed or suggested,emphasizinghe differentways in which they con-tribute to an understanding f the magnetosphere.We then concentrate on the proposed light ionseeding xperiments,eviewing he anticipated ffectsof plasma injection in the magnetosphere eyondthe plasmapause. oting that plasma njectionbe-yond the plasmapause an occur naturally, pro-ducing substantiallysimilar phenomena,we reporton preliminary bservationsn suchnaturallyoccur-ring plasma enhancements.2. BRIEF HISTORY OF ACTIVE EXPERIMENTSActive experimentswhich have been performedin the magnetosphere nd the ionosphereor are

Copyright ) 1973 by the American Geophysical Union.

being considered re summarized n Table 1. Theseexperimentsnclude he releaseof heavy on plasmaclouds and the injection of accelerated hargedpar-ticles,as well as the injectionof electro.agneticwave energy at frequencies ranging from ULF(0.001 to 10 Hz) to HF (3 to 30 MHz). Thechargedparticle experiments ave been used o mea-sure ambient electric fields and to verify conjugacy;beamsof chargedparticleshave also nitiated insta-bilities, thus providing information on dynamicalprocesses. he initiation of instabilities an be con-sidered he principalpurposeof mostelectromagneticwave injection experiments,as well as of proposedlight ion plasma seedingexperiments.2.1. Barium clouds. Plasma clouds of heavyions, usually barium, have been released both inthe ionosphere and deep in the magnetosphere[Foppl et al., 1965; Haerendel et al., 1967; Haer-endel and Liist, 1970; Brence et al., 1972]. At lowaltitudes, the drift motion has been used to inferelectric fields [Haerendel, 1971a; Schutz et al.,1971] and to relate the observedelectric fields tothe dynamics f substormsHaerendel,1971a]. Thedevelopmentof striations n the barium clouds[Haerendel, 1971b] has demonstrated he impor-tance of nonlinear process.

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1036 KIVELSON AND RUSSELL

TABLE 1. Active experiments n the magnetosphere nd theionosphere.Principal application

Measurement ofpreexisting ields;

verification of PerturbationExperiment conjugacy of systemHeavy ion plasma clouds

(Barium, Cesium)Injection of acceleratedparticles (shaped Bacharges,acceleratedelectrons)Injection of ULF, VLF,MF and HF waves

Light ion plasma clouds nthe magnetosphere

X X

One of the most ambitious njectionsof a bariumcloud from a rocket was a release at 5 R altitude[Brence et al., 1972]. The motion of this cloud hasbeen used to infer the local magnetospheric lectricfield (0.7 mv m ) [Rieger et al., 1972] while asimultaneous alloon flight measuredboth electricfields and X-ray intensity at the foot of the fieldline in the ionosphereMozer, 1972]. Thesemeasure-ments provided an upper limit on the flux of ener-getic electronsprecipitatedby the cloud. If theparticle accelerationoccurred over regions greaterthan several thousand km in diameter at the bariumcloud, ess han 1% of the trapped lux of electronsgreater than 30 key was precipitated.On the otherhand, if the interaction region was equal to theoptical dimensionof the cloud, of the order of100 km, then the precipitated flux could haveequalled the trapped flux without disagreeingwithX-ray observations. ield lines tracedby the bariumionswere used o testmagnetospheric odels Barishand Roederer, 1972] with resultswhich suggest hata ring current at the magnetic equator is presenteven or moderatelyquiet times.Finally, the develop-ment of striations in the magnetosphericbariumcloud has been interpreted in terms of a flute insta-bility [Haerendel et al., 1972].

The most distant barium release was made fromthe HEOS-1 spacecraft at 12.5 R on March 18,1969 [Haerendel and Liist, 1970]. At such a largeradial distance,where the plasma density is prob-ably below 1 cm 3, the motion of the plasmacloudis largely independent f the motion o.f the ambientmedium. In fact, Haerendel and Liist estimate that

1 to 10 hr would be required o destroydifferentialmotion between he injected and natural plasmas.The barium cloud elongatedalong the directionofthe magnetic field as measuredby the HEOS-1magnetometer nd broke into striations.During theformation of one suchstriation, the development fa weak tail was observed.Using this tail to putlimits o.n he velocityof the ambientplasmaHaer-endel et al. [1971] showed hat the observedmag-netic luctuationsn the polar cap were not consistentwith either Hall or Pedersen currents but could beinterpreted n termsof a field-aligned urrentsystem.

2.2. Particle acceleration experiments. Accel-erated chargedparticles njected along the directionof the magnetic field have been used to trace fieldlinesover thousands f km and to identifyconjugatepoints with great accuracy. Zhulin et al. [1972]have reviewed the experimentsof this type. Near-equatorial injection of accelerated electrons aimedupward along the magnetic ield from Hawaii [Daviset al., 1973] produced an artificial aurora at theconjugate point. In analogous experiments withbarium shaped-charge enerated plasma jets, ionvelocities of several km sec (to be contrastedwithvelocitiesof approximately10 m sec in isotropicbarium releases) made it possible to track ionsoptically fo.r 7000 km [Fu et al., 1973]. Differentdrift velocitieswere observed t conjugate oints nthe northern nd southernemisphereuggestingthat magnetic ield lines are not always equipoten-rials [Westott et al., 1972, 1973].

At midlatitudes, accelerated electrons have beeninjecteddownwards long he magnetic ield towardthe near conjugate oint to produceartificialauroras[Hess et al., 1971]. Pulsed electron beams reflectedfrom mirror points n both hemispheres ave beenstudied as a controlled population from which thebehavior of naturally injected, trapped energeticelectrons can be infered [Winckler et al., 1970].In these experimen.s, whistler mode and otherplasma waves were generatedby the injected ener-getic electrons Cartwright and Kellogg, 1970]. Noevidencehas been found for large instabilities ffect-ing beam propagation [Hendrickson et al., 1970]though the beam intensity decreasedafter multiplereflections.

From auroral zone injection points (L - 6.5)barium shaped-charge enerated plasma jets havetraced ield linesdeep nto the magnetosphereuringquiet and disturbed imes [Westcottet al., 1973].Here, too, acceleratedelectrons have been injected


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MAGNETOSPHERIC MODIFICATION 1037both to studyparticle behavior Hendrickson t al.,1973] and to probe the boundary of closed fieldlines [Hess et al., 1971].

2.3. Wave injection. Electromagneticwaves ndifferent frequency ranges have been beamed intothe ionosphereo investigateransmission,ropaga-tion, and instabilities. In transmissionof VLF waves(10 to 25 kHz) between conjugatepoints, pulsa-tions have been observedor signalsof long duration[Helliwell and Bell, 1971]. Signalsof less than 200msec duration are not observed at the conjugatepoint [Do.wdenet al., 1973]. This finite wave traineffect is not describedby current theoreticalmodelsof whistler amplification.The observation hat VLFsignals ransmitted rom the conjugatehemisphereare abruptly cut off as a polar orbiter enters theplasmaspherehas led to the suggestion hat rela-tively simple narrow band VLF receiverson polarorbiting satellitescould monitor the plasmapauseand other density structures n the magnetosphereand the ionosphere Katsufrakis et al., 1973]. Pro-posals to build large, ground-based urrent loopsto produceULF hydromagnetic avesof observableamplitude in the ionospherehave not yet beenimplementedFraser-Smith,973]. Or the otherhand, radar heating of the ionosphere has beenused to produce parametric plasma instabilitieswhose growth and saturation have been analyzedtheoretically Goldman .and DuBois, 1971].2.4. Light ion injectio.n. The active experi-ments which have been carried out in the pastdemonstrate hat perturbationof the magnetosphereis an effectiveexperimentalapproach.As a logicalextensiono.f previous nvestigations,ight ion injec-tion into the outer radiation belt could significantlysupplement resentexperimentalmethods.The con-sequences f sucha plasma-seedingxperimentwerefirst discussed y Brice [1970, 1971a, 1971b, 1972]and have been further exploredby Cornwall [1972]and Cornwall and Schulz, [1973]. These authorshave concluded hat an increase n the cold plasmadensity at synchronous rbit from the normal valueof 1 cm a to 3 cm a would permit both electronand proton cyclotron nstabilities o develop n theouter radiation zone as schematicallydepicted inFigure 1. Their predictions re basedo.n he observa-tion that cyclotron resonancecan occur only forparticles whose energy exceeds a resonant energyproportional to B2/8'rN, the magnetic energy perparticle. An enhancement f plasma density owersthe minimum resonant energy permitting lower

PATCHFAURORA,IONIZATIONN,TMOSPHERICH EATING TRAPPEDNERGETL //_ .............. " PARTICLES 'PRECIPITATING ENERGETICXX / / RELEASEDY

Fig. 1. Schematic view of a plasma injection experiment.(From Cornwall [1972].)

energy particles to become unstable.Cornwall andSchulz 1973] have estimated hat a 50 kg payloadwill providea sufficientlyarge ithium plasmacloudto produceobservable ffects, hough he precipitatedflux will increase with the dimension of the seededvolume.A light ion plasma s preferable o a heavyion plasma both because he payload required issmaller and becausea light ion is necessary or theproton cyclotron nstability to develop. The effectsanticipated nclude enhancedwhistler-mode urbu-lence (VLF) and ion-cyclotron-mode urbulence(ULF), as well as the accompanying recipitationof energetic (greater than approximately20 kev)electrons rom the outer zone of trapped radiationand the precipitationof ring current protons (ap-proximately20 key). Brice has suggestedhat thethe plasma seedingmay initiate a substorm Brice,1970] or speedup the recoveryphase Brice, 1971a].Light ion plasma-seeding xperimentswould, as anadditional dividend, extend the observationsalreadymade with barium plasma clouds. Field-line geom-etry couldbe investigatedn such nteresting egionsas the nighttimecusp. Plasma diffusion ates alongand across ield lines could be measured and mag-netospheric lectric ields nferred.

3. NATURAL PLASMA SEEDINGLight ion injection into the outer radiation zoneis also a naturally occurringphenomenon. n thiscase, the plasma consistsmainly of hydrogen onsand the source of the plasma is detachment romthe outer plasmasphere y time-varying electricfields.The proposed ffectsof plasmaseeding houldbe independent f whether he sourceof the plasma


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is natural or artificial. Furthermore, wave and par-ticle measurements lready exist for such regions.3.1. The injection mechanism. The detachmentprocess asbeendescribed y Chapphil, 1972] andwe only briefly review t here. Figure 2, representingthe equatorialplane, shows chematicallyquipoten-tials along which plasma flows in the presenceof adawn-duskcross-tailelectric field superimposed nthe corotation field of the earth [Kava,nagh et al.,1968]. Inside the boundary ndicatedwith a heavyline the streamlines close on themselves and theplasmadensitycan build up over many days.Out-side of this boundary he plasma s swept away tothe magnetopause.hus, at the boundarywhichrepresentshe plasmapausehere is a sharpdecreasein plasma density.Figures 3 and 4, similar sche-matic representations,.ndicate the effect of anincrease in the cross-tail electric field [Chappellet al., 1971 . The boundarybetweenclosedand openstreamlines, abelled b in Figure 3, moves earth-

DAWN

SUN bDUSK

Fig. 3. Schematic representation ofthe formation of detached plasma:prestorm. The plasma within contourb is on closed streamlines as in

Figure 2.

ward o a positionabelled in Figure whenhe chronousrbit hedriftvelocityt the equatorfcross-tailield s increased.lasma riginallye- such plasmanhancements about .1 Rs mintweenboundaries and a now is found on open in a field of 1 mv m . Plasmaenhancementsrestreamlinesnd, n theafternoonector,eginso observedooccureyondheplasmapause,rimarilyflow toward the magnetopause,nto regions n in the afternoon,onsistentith this model.How-which he plasma ensitys very ow.Nearsyn- ever,t is mportanto recognizehat f time aria-tions in the cross-tail electric field occur on time

SUN 12

DAWN

DUSK

scalesof tens of minutes to hours, the same mech-anism can produce solatedpatchesof enhancedplasma density beyond the plasmapause n thenightside as well.Although he plasmaof the plasmasphericulgealso extends nto the outer radiation zone near dusk,we emphasize he isolatedplasma enhancementsbecause hey more nearly simulate he conditionsfor an artificial ight ion seeding xperiment.Ener-getic electrons an traverse he plasmabulgesuffi-cientlyoften o produce steady tate.On the otherhand, plasma-seedingxperiments mphasize on-equilibriumconditions. he plasma enhancementsare encounteredmainly at larger L than the averagebulgeposition Chappell, 972] and the energeticelectron flux in this region is not in equilibriumwithin the enhancedplasma. Furthermore,phe-nomena observedwithin the spatially imited en-hanced lasmamay be assumedo havea localizedorigin.For example,t-is probablehat wave urbu-lence observed n detachedplasma enhancementsFig. 2. Equipotentials or streamlines or thermal plasmain thepresencef a cross-taillectricield. utsidehe has eenroducedithinhe nhancements,hereasheavy ontour,he low s openo themagnetopause,he waves bservedn theplasma ulgemayhavepropa-plasmasphereieswithin.FromKavanaght al. [1968]. gated rom the distantplasmasphere.


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MAGNETOSPHERIC MODIFICATION 1039

DAWN

/

DUSK;Fig. 4. The formation of detachedplasma: during the storm. The cross-tail field has been enhanced; closedflow lines are found within contour a.Plasma initially between a and b isnow on open streamlines and movesinto the afternoon quadrant. (FromChappell [1972].)

3.2. Natural or artificial seeding. Though thephenomenawhich should occur in regionsof en-hancedplasmadensitybeyond he plasmapauseresimilar for similar conditionswhether he injectionmechanism e natural or artificial,both techniqueshave advantages nd disadvantages.rtificially in-jectedplasmacan be placedat any desired ocationin the magnetosphere t a selectedtime, whereasnatural injectionoccursprimarily in the afternoonquadrantand at random imes.The artificialplasmacloudswill have small spatial dimensions,and suchinjectionswill probably not be numerous,argelybecause f the payload equired.Naturallyoccurringdetached plasma enhancementswill have variedspatial extension, hough their sizeswill be inaccu-rately known. However, they can be observedwith-out any extra payload, and since they occur fre-quently, they can be observedon many occasions.In other words, the two types of experiments recomplementary.

4. OBSERVATIONS OF THE EFFECTSOF NATURAL SEEDING

The most extensivestudy of the region of de-tachedplasma n the outer magnetosphereas beenmade using the OGO-5 Lockheed on Mass Spec-trometer [Chappell, 1972]. OGO-5 carried a com-prehensive ayloadof field and particleexperiments

and we report here the measurementsmade bysome of these nstruments the UCLA/JPL SearchCoil Magnetometer, he TRW Electric Field Experi-ment, the UCLA Energetic Electron Spectrometer,and the UCLA Fluxgate Magnetometer) duringtraversalsof someof the regionsof detachedplasmainvestigatedby Chappell. _4.1. ELF magnetic fluctuations. The effect ofnaturally occurring plasma enhancements n theouter radiation zone on energetic electrons andelectromagneticwaves has been examined in a pre-liminary study usingdata from a number of experi-ments on OGO-5 [Kivelsonet al., 1972]. Figure 5shows the ion density observedby the LockheedLight Ion Mass Spectrometer n an outboundpassof OGO-5 on September 13, 1968. The measure-

102.96.506.027.358.48t t I I3.31 4.05 4.76 5.43103

10.

10-:02:00

L: 3.71, m:28.4L-T =1358

L: 5.58, Xm:34.7L.T =1512

i

03:00Universel Time

03:40

Fig. 5. Example of detached plasma density be-yond the plasmapause; he diagram shows hydro-gen ions measured by the Lockheed Light IonMass Spectrometer plotted with respect to uni-versal time, September 13, 1968, OGO-5 out-bound. The upper scale gives L-value and radialdistance. L-values, magnetic latitude, X,,, andlocal time are given for the plasmapause and the

first enhancement.


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ments were made at magnetic atitudes near 35 UCLA/JPL Search Coil Magnetometerhave beenin the local time regionbetween1400 and 1600 hr. describedby Burton et al. [1972] and Chan et al.The plasmapause ppearsas a steep gradient n [1972] from which Figure 6 showingELF powerthe numberdensityat L = 3.7, indicated y the versus requencys reproduced. he dashed race,first arrow. The enhanced plasma density was labelledB, is the spectrummeasured t 0200 UT,encounteredlmost alf an hour ater n the region within the plasmasphere.his plasmasphericissfromL = 5.6 to L = 8. Peakplasma ensitiesell terminatedt theplasmapause,here qualitativelyoff approximately s L -4. The ragged appearance differentspectrum, ere abelledC, with substantialof the density nhancementsay give evidence f power above 400 Hz was found. Burton et al.instabilitiesnalogouso those.causingtriationsn [1972]call hisspectrumhighatitude iss."nsidebarium clouds Chappell,1973]. the detachedplasma enhancements spectrumThe ELF spectraor this orbit measuredy the labelledA with peak powerof order 10 4 y2 Hz-

[0-4

]0-5

10-6

IO-e

i

X .j

IO '1oo '1oo9FREUEOY

Fig. 6. Power spectra rom 1-min averagesofmeasurements of the UCLA/JPL Search CoilMagnetometeron OGO-5 for September13, 1968.Curve B (0200 UT) was measured within theplasmaspherewhere peaks are observednear 100and 500 Hz. Curve C (0230 UT) was measuredin the region of low plasma density beyondthe plasmapause.This characteristic high lati-tude hisshas a peak just below 1000 Hz and littlepower near 100 Hz. Curve A (0236 UT), mea-sured within a density enhancement, has peakpower near 100 Hz and falls off at high frequency.(From Chan et al. [1972].)

near 100 Hz, quite narrow banded in the range50 to 150 Hz, was observed.Figure 7 showsELF measurementsor the sameday on an expanded time scale for the intervalduring which plasma density enhancementswere

encountered.On the bottom panel the density ofhydrogenons s plottedversus niversalime, withshading mphasizinghose egionsn which he iondensityexceeds cm 3. On the upper panel thespectrum hannelsrom 10 to 999 Hz of a singleaxis of the UCLA/JPL SearchCoil Magnetometerare plotted. Shadingo.f the peaks n the 100 Hzchannel mphasizeshe highcorrelation etweenhepresence f thermalplasmaand of ELF signals t100 Hz. This closecorrelationsupports he sugges-tion of Burton et al. [1972] that this low frequencyband is generated y the cyclotron esonance fenergetic lectrons ear the equatorand is ductedthrough nhanced ensity egionso high atitudes.Measurements f the propagationdirectionshowthat the wave vector lies within less than 30 of B.Note that at 0233 and 0256 UT, the plasma en-hancements do not correlate with the 100-Hz hiss.Note also hat the high atitudehisspresent n the467 and 999 Hz channels is anticorrelated withthe densityenhancements,ven in the narrow en-hancement at 0233 UT.

One possiblecauseof the absenceof 100-Hznoise in these two enhancementss that the signalshave leaked out because the enhancements weretoo narrow to trap the radiation. n particular, henarrowest enhancement at 0233 UT was traversedin 20 sec.A stationary nhancementf less han84 km thicknesswould have been traversed in thistime at the satellite velocity of 4.2 km sec.Although he enhancementightbe moving, tsvelocity hould e ess han hatof thesatellite. orexample,he velocity orrespondingo an electricfield of 1 mv m is 1.2 km sec, in the observed


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X999N x467--- x216

E X100 X47

X22

i I i i i i i i i i i i i i i i i i i i i i i i i iI

I I

I : II I

I II Ii I

II IXI0i0 i I

t0-1 ..... _ , , ...... i , , _02:25 02:40 02:55 03'1014:48 15:26 15:56 16:02

04.89 06.02 07.04 07.9433.10 35.50 36.80 37.30

l0>" 0T o 10

UTLTLXM

Fig.7. CorrelatedLF-hissnd lasmaensityrdaancementsbservedyOGO-5 nSeptember3,1968. hebottompanel isplayshemeasurementsf heLockheedightonMass pectrometernanexpandedime cale.heupperpanelsisplayhe msmagneticoise easuredlonghe pacecraftaxis y heUCLA/JPL earchoilMagnetometerat sevenrequenciesrom 0 o 999Hz.The ntervalsuring hichheplasmaensityxceededcma have een hadedin the 100-Hz hannel nd n the on density lots o emphasizehestrong orrelation.he noisen the467-and999-Hzchannelsasat saturationrior o 0236UT exceptor a brief nterval ndwas nitially nticorrelatedith hedensityenhancements.

780-y magneticield.For this ieldstrength nd anaverageon density f 10 cm 3 in the enhancement,we obtain a wavelength f 160 km at a frequencyof 100 Hz for a parallelpropagating ave.Whilethewavelengthouldbe somewhatess or off-anglepropagationndsomewhatess t thepeakof theenhancementwhere the density s about 20 cm 3,we cannot scapeheconclusionhat hewavelengthis comparable ith the hicknessf the enhancementand hence eakage s possible.This conclusion is consistent with the observationthat the enhancementat 0239 UT, which is abouttwice the dimension of the 0233 UT feature, con-tains some 100 Hz noise but much less than the0237 UT enhancementwhich is three times as bigagain.On the otherhand, he 0256 UT enhance-ment,which s evenwider han he one at 0239 UT,containsno detectableELF noise. Thus, while someof the behaviorof the ELF signals an be explained

in termsof the ability of the enhancementso ductthe waves, not all the properties can.The attenuation f the high latitude hiss in thedensity nhancementss notreadily xplained. hilethe owerhybrid esonancerequencyieswellbelowthe 467-Hz channel, and thus the 467- and 999-Hzwavescan propagate nly within a broadconeofdirectionsabout the directionof the magnetic ield,this limitation does not seem to us sufficient toexplain he observed ttenuation.Finally,wenote hat hisclose ssociationetweennarrow band ELF noise at 100 Hz and plasmaenhancements as been found on many orbits. Infact, on some orbits where the ELF data havebeen examined irst, the plasma enhancements erelocated rom .the ELF data (K. W. Chan, personalcommunication, 1973).4.2. Energetic electron observations. The pos-sibilitythat the ELF signals re produced y


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Doppler-shifted lectroncyclotron esonance an befurther testedby reference o the flux of energetic(greter than 50 kev) electronsmeasuredby theUCLA Energetic Electron Spectrometer. Beforeexamining the flux of these energetic electrons, tis well to note that the presenceof densityenhance-ments beyond the plasmapauseeads to resonanceconditions which can be somewhat surprising. InFigures 8 and 9, the minimum resonant energy atthe dipole equator, labelled L, is plotted for bothprotonsand electrons or different assumed lasmadensitiesand for 00/.r= 1/6. Beyond the plasma-pause, or example n the region 3.5 < L < 7.5,40 key electrons are stable to the electron resonancefor a plasmadensityof 1.0 cm 3, but if the densityrises to 10 cm a, the same 40 kev electrons can beunstablebeyondL - 5, while a densityof 100 cm 3is sufficient for these electrons to exceed the mini-

1.0m5 20 evrotonsunstable f= N>00 m3 .I0 m:t 20evrotons ' unstablef -

x [>lOcm5 I00 m- X, 20 evrotons! unstablef .[>l'Ocnf3- '1000

l0

0 2 4 6 8 10 12 'LFig. 8. Resonant nergiesor protoncyclotron nstabilitiesat densities 1, 10, and 100 cm a at the dipole equator

IOOO

IOO

IO

i I i i i i i , i i i i Il40 kev electrons' conbe unsf(]bleorN>100m5: I 40 evlectrons _1.0m-5(]nensf(]bleor0cm5

I0 cm- 40 key electronscan be unstable orN>I.O m3' I00m-5 I -

0 2 4 6 8 10 12L

Fig. 9. Same as Figure 8 for electron cyclotroninstabilities, calculated for a wave frequency equalto 1/6 of the equatorial electron gyrofrequency.

mum resonanceenergy beyond L = 3.5. Similarstatementsapply to ring current protons: 20 kevprotons at L = 6.6 fail to meet the resonancecriterion for densities of 10 cm -a but can be resonantif the density is 100 cm a.On September 13, 1968, plasma enhancementswith densities from 10 to 30 cm -a were encounterednear L - 6. From Figure 9 it is apparent thatelectronsof energy near 50 kev lie just above theminimum energy required for resonancenear theequator.Figure 10 shows, or the same time interval, theintegraldirectional lux of locally mirroringelectronsof energyexceeding 0 kev measured y the UCLAEnergeticElectron Spectrometer.Resonantenergiesfor the whistler-modenstabilityhave been evaluatedfrom the cold plasma theory:

Ell = (Be/87rN)(e/Co)[l- (C0/-e)]plotted gainst . Wavegrowth anoccur nly f there where C2es the electroncyclotron requency. heexists sufficientlyargenumber f chargedarticles ith magnetic ield, B, at the equatorhas been obtainedenergiesbovehe esonantnergyndicatedy he pplica- rom he ocallymeasuredagneticieldby assum-ble curve. The curves have been calculated for a wave ing the ratio applicable or a dipole field line. Thefrequency equal to 1/6 of the equatorial proton gyro-frequency.his orrespondsoa criticalnisotropyf0.2. equatoriallasmaensity,, hasbeen stimatedFor largeranisotropyhe instabilityanoccur t a lower assuming iffusiveequilibriumof the plasma n aenergy. flux tube, an assumptionwhich is appropriate f


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the plasmawas detachedrom the plasmasphere, hereA is the anisotropyf the energeticlectronwhere t was n diffusive quilibrium, y the mech- distribution, ositive or a distribution eaked atanism described reviously.For such equilibrium, 90. Although he valuesestimated or the aniso-the dependencef densityon magneticatitude s tropy from the energetic articlemeasurementsx-weak, so the locally measured alueswere used ceeded1/4, the valueA = 1/6 was used n thefor equatorial ensities. calculationo provide conservativestimate,.e.,For the electron yclotronmode o be unstable, an overestimate,f the maximum tably rappedthe flux of electrons bove he resonant nergymust flux. The measuredlux above he resonant nergybe sufficientlyarge hat wavegrowth an exceed exceededhe calculatedtably rappedlux n eachloss, a criterionwhich reduces o the requirement of the intervalsduring which 100-Hz noise wasthat the flux must exceed the maximum stably present. he diagramshowshecalculated* (>En)trapped lux, J* (>ER). This flux has beenesti- and the observedlux above he resonant nergymated rom an approximationf Kenneland Pet- for severalimesduring he interval.At 0233 UT,shek [1966] as: during he first isolated pike,' he resonant nergywas 108 kev, and the measured flux above thatJ*(> ER)= [(1 -- w/fe)/(A -- W/fe)] energywas oocloseo theestimatedtably rapped 3B/4rL)10M m 2 sec ster flux to draw clearconclusions.n the density n-100

.

20-

0 .,io

io-Iu T 02:50L T 15:02L 05.28XM 34.!0

j*(>69),40j(>69)=65IIIIII

_.l_j*(>40).,35j(>40)>50IIIIII I i I i '

i i i i02'55

I

I, I , , I , , , I ' 'I iII i

02 40 02'50 02:55 05:002 45

05.65 06.02 06.57 06.71 07.04 07.5554.90 55.50 56.10 :.'56.50 56.80 57.00

Fig. 10. Hydrogen on densitymeasured y the LockheedLight Ion Mass Spectrom-eter and integraldirectional lux of >50 key locally mirroringelectronsmeasured ythe UCLA energeticelectronspectrometer n September 3, 1968. The minimumresonant nergies avebeendeterminedor the density eaks ust to the right of thevertical dashed ines at 0236.5, 0243, and 0256 UT, and estimatesof the theoreticalmaximumstably rapped lux and the measuredlux above heseenergiess shown.Although he observed nergetic lectrons atisfy he instability onditions,heirdistributionhas not been visibly affected.

15:14 15:26 15:37 15:47 15:56 16:04


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hancement t 0256 UT, the resonant nergyhad Furtherevidencehat the onsetof cyclotroneso-droppedo 17 kev and the availablemeasurements ance affects he energetic lectrons ery little iswere nsufficiento provide n explanationor the obtainedrom an examinationf the pitch-angleabsence f noise. distributionof the particlesbefore and after theNote that although he energetic lectronswhose plasmaenhancement as encountered t 0236 UT.flux is shownare unstableo whistler urbulence, Figure 11 shows itch-angle istributions easuredthey have not been significantlyaffected.No holes half a minute before and half a minute after thein theirdistributionevelopn the plasma nhance- plasma nhancementasencountered.hetop racementsas a resultof the precipitation f a large displayshe integral lux of electrons f energy>fractionof the resonant lectrons. comparison 50 kev plottedversus itch angle.Note that theof time scales or spatialdrift and for pitch-angle flux peakedat 90 as required or unstablewavediffusionmakes t clear hat holescannotdevelop. growth. n the lower races, he pitch-angle istri-Plasmaenhancementsxtend or 1 to 2 R at the bution of differential lux at selected nergiessequator.Gradientdrift causes lectrons f 50 kev displayed. lux measurementsutside he plasmato traverse R in less han 12 min for L between are marked , andmeasurementsnsideheplasma5 and 10. Pitch-anglediffusion ifetimescan be cal- are marked as dots, but have been shifted 3 toculated or the observed LF powerand are found the left to increase isibility.Experimental ncer-to exceedone hr. Therefore, he plasmaenhance- tainty s indicated y the separationf a pair of X'smentaffectshe electronlux very ittle. This argu- or of dots near 90, and within this uncertaintyment is furthersupported y the observationhat there s no differencen the pitch-angleistributionsthe energydensityn the whistlerwaves s less han or the energyspectra nside and outsideof the1% of the particleenergydensity. densityenhancements.

__= Infegrallux o .,, (>50kev) IO6c-

- o GOev - 160 ey. 104 480 ey

i

200 ,400,' ,0 200 60 00Pifch ngleFig. 11. Integral (top panel), anddifferential directional flux of ener-getetic electrons versus pitch angle,September 13, 1968. The measure-ments outside the plasma enhance-ment (0235.5 UT) are plotted as x,while those inside (0236.5 UT) areplotted as , and these points havebeen shifted 3 towards smallerangles for greater clarity. Experi-mental uncertainty can be estimatedfrom the spread in a pair of dots orcrosses,which are measuredby a pairof back-to-back detectors at the same

pitch angle.

4.3. ELF electric fluctuations. The electronplasma frequency emission s sometimesdetectedin this region by the TRW Electric Field Experi-ment and in thesecases onfirms he plasmadensityreportedby the Light Ion Mass Spectrometer. owfrequency electric fields are also measured, and at200 Hz the electric ield from this experiment or-related closely n intensitywith the plasma densityenhancements. he data of this experiment areshown n the centralportion of Figure 12 with theplasma density shown below and the search coilamplitude above. The electric fields are measuredevery 9 sec over a narrow range of frequencies(-+20 Hz) about 200 Hz. The ratio of the electricto the magnetic ield at 200 Hz was highly variableand the questionof whether, in some regions, hefields are componentsof whistlers s being investi-gated. n other regions he electric ield may repre-sent purely electrostaticwaves associatedwith thelower hybrid resonance requencywhich increasedand decreased, rossing hrough the pass band ofthe 200-Hz channel as the density enhancementswere traversed.

4.4. ULF magnetic fluctuations. For five orbitson which plasma enhancements ere present out-side the plasmapause,he magnetic ield measuredby the UCLA Fluxgate Magnetometer has beenexamined for evidence of ULF waves. The waveswould have been identified if their peak-to-peak


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X999

467,-"' X216E x100 x47

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i i i i i [ i i i i i i i i i i i iI,I

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i 'I II II II I II II II I: I -

I11 II,.Ah///j.,i i i i i i I i i i i i i I i i i i i i i,, ,UT 02'25 02,40 0255L T 14:48 15:26 15'56L 04.89 06.02 07.04

33.10 35.50 36.80Fig. 12. Electricieldamplitudef the200-Hz hannelf theTRW Electric ieldExperimentn OGO-5 s shownn thesecondanelrom hebottom. ther anelsrepeatdata of Figure7 for comparison.

amplitude xceededy and had periods f 0.5 secto 1 min. A rangeof periodsbetween and 4 secis obscured y the presence f boom vibrations.ULF waveswere observed n only two of the fiveorbits,and were present ntermittentlyor a totalof 12 min most requentlywith a periodof about20 sec.Figure13 shows xamplesf theULF wavesobserved n the outbound assof August10, 1968,for which the thermal on density s shownat thebottom.The densityenhancementeakedbetweenL = 7 and L = 8.5, near 1900 LT. At the top o.fthe diagram n the fight an example f the 20-secwaves is shown. This wave was observed at L = 8.3and at 1913 LT. The diagram s 2 min across ndthe arrows re separatedy 19 sec.The coordinatesystems field-aligned,ith the z axisalong heaverage agneticield.Theperturbationsrepurely

transverse, nd the wave is left-handcircularlypolarized.orproton yclotronesonance,heesti-mated resonant nergyof a proton at the equatoris about50 kev, but no measurementsre availableto indicatewhat fluxes of protonsof this energywere present.

On the top of the figure o the eft, an exampleof an rregular urstof approximately-sec eriodat L = 7.7 is shown.The diagram s 70 sec acrossand hearrows reseparatedy 5 sec.Theperturba-tion, again n the field-alignedoordinate ystem,is transverse ut almost inearly polarized.4.5. Summary. This introductory xaminationof phenomenabservedn andnearnaturally ccur-ring plasma nhancementsaisesmanyquestionsthat shouldbe examined urther. For example,doescoldplasmaheory orrectlyredicthe minimum


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T

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206.0

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RZ 210.0

I 07470

os:3o o13o16150

2'I',0 18:50 19:00'o ilo ;.5 1, [5 '1

19 sec

075830 F759:00 F759;30

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3bO0:00 0600:30 080L:00 OEO s30

of the ELF electric noise observed?What are theconditions ecessaryor the formationof thesede-tached lasmaegionsndwhat s their elationshipto substorms?s there an identifiablenstabilitywhichproducestriations ithin he cold plasma?

flux of energetic articleswhich must be exceededfor ELF wavegrowth? oes t correctly redictthe requiredpitch-anle nisotropy? hat is thecritical ize or ELF waveducting? hy are ULFwavesonly occasionallyresent?What is the nature

Fig. 3. Hydrogenon ensityeasurednOGO-5nAugust0, 968splottedn heowerortionf his iagram.he pperpanelshowxamplesf he pproximately0-seceriodavesright-handide)ndhe pproximately-secrregularurstsb-servedn his ass.oth pperanelsre lottedna field-alignedoordinateystemnwhichhe verageield irectionsz.


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We feel many of thesequestions an be answeredby examining ata we have already n our datalibraries, nd we hope o do so n futurestudies.5. CONCLUSION

Active experiments ill continueo contributenimportantways to our understandingf the mag-netosphere. hile the decadeof the 1960's wasdominated y passiveexperiments,he most sig-nificant contributions n the 1970's may result froman increasedmphasisn activeexperiments.tudiespresentlyunderway or utilizationof the SpaceShuttle indicate that the trend toward active experi-mentationmay continuewell into the 1980's.Theinjection f light on plasmanto the outer adiationzone is one of the most promising of presentlyproposedxperiments.owever,manyof the phys-ical phenomena f interest n a plasma-seedingexperiment an be studied n naturallyoccurringregions f enhanced lasmadensity. hese egionsshouldbe probedextensivelyo that their propertiesare fully understood. he emphasisn planning rti-ficial plasma-seedingxperiments hould hen beplacedon investigatinghoseproblemsor whichactive experimentations the unique availableapproach.

Acknowledgments. We are deeply indebted to C. R.Chappell, R. E. Holzer and F. L. Scarf who have freelyprovided us with their data and advice throughout thecourse of this study, and to P. J. Coleman, Jr., andT. A. Farley for their efforts in designingand buildingthe OGO-5 experimentsand their subsequent ssistancenthe analysis of the data. We are also. grateful to W. H.Campbell and H. I. West for providing us with data inadvanceof publicationbut which we did not have occasionto use in the events studied here. We also wish to thankR. K. Burton, and K. W. Chan for many stimulating dis-cussionsabout the search coil data, and A. C. Fraser-Smithfor pointing out that some enhancementsmay be too narrowto duct ELF signalseffectively. This work was supportedby the National Aeronauticsand Space Administrationunder contracts NAS 5-9097 and NAS 5-9098 and grantNGR 05-007-305, and by the Office of Naval Researchunder contract N00014-73-C-0130.

REFERENCESBarish, F. D., and J. G. Roederer (1972), Experimentaltest of magnetospheric models (abstract), EOS Trans.

AGU, 53, 484.Brence, W. A., H. Neuss, R. E. Carr, and J. C. Gerlach(1972), An overviewof the NASA/Max Planck InstituteProject to study a barium release at five earth radii(abstract), EOS Trans. AGU, 53, 482.Brice, N. (1970), Artificial enhancementof energetic par-ticle precipitation hrough cold plasma injection: a tech-

nique for seeding substorms?, J. Geophys. Res., 75,4890-4892.

Brice, N. (1971a), Space weather modification (abstract),EOS Trans. AG U, 52, 330.

Brice, N. (1971b), Harnessing the energy in the radiationbelts, J. Geophys. Res., 76, 4698-4701.Brice, N.M. (1972), Magnetospheres (abstract), EOSTrans. A G U, 53, 1106.Burton, R. K., R. E. Holzer, and E. J. Smith (1972), ELFhiss in the magnetosphere (abstract), EOS Trans. AGU,53, 490.

Cartwright, D. G., and P. J. Kellogg (1970), Observationsof plasma waves from the electron echo experiment (ab-stract), EOS Trans. AGU, 51, 805.Chan. K. W., R. E. Holzer, and R. K. Burton (19'72), ELFhiss associated with detached ion density enhancements(abstract), EOS Trans. A G U, 53, 1094.Chappell, C. R. (1972), Recent satellite measurementsofthe morphology and dynamics of the plasmasphere,Rev.Geophys. Space Phys., 10, 951-979.Chappell, C. R. (1973), Morphology of detached coldplasma regions in the magnetosphere, paper presented atChapman Memorial Symposium on MagnetosphericMo-tions, American Geophysical Union, Boulder, Colo., June1973.

Chappell, C. R., K. K. Harris, and G. W. Sharp (1971).The dayside of the plasmasphere, . Geophys. Res., 76,7632-7647

Cornwall, J. M. (1972), Precipitation of auroral and ring-current particles by artificial plasma injection, Rev.Geophys. Space Phys., 10, 993-1002.Cornwall, J. M., and M. Schulz (1973), Theoretical aspectsof artificial plasma injection, Aerospace Rep. ATR-73(72 79)-1, 118 pp., The Aerospace Corporation, E1 Se-gundo, Calif.

Davis, T. N., W. N. Ness, M. C. Trichel, and E. M. Wescott(1973), Initial results of a recent electron acceleratorexperiment (abstract), EOS Trans. AGU, 54, 436.Dowden, R. L., N. R. Thomson, L. E. S. Amon, D. A.McPherson, H. C. Koons, and M. H. Dazey (1973),Experimentally observeddependence f whistler propaga-tion on pulse length (abstract), EOS Trans. AGU, 54,

423.Foppl, H., G. Haerendel, J. Loidl, R. Last, F. Melzner,B. Meyer, H. Neuss, and E. Rieger (1965), Preliminaryexperiments or the study of the interplanetarymediumby the releaseof metal vapour in the upper atmosphere,Planet. Space Sci., 13, 95-114.Fraser-Smith, A. F. (1973), Generation of micropulsationswith a large ground-based urrent loop (abstract), EOS

Trans. AGU, 54, 419.Fu, J. H. M., H. Mo Peek, and E. P. Marram (1973),Payload performanceof the shaped-charge arium injec-tion experiment'OOSIK (abstract), EOS Trans. AGU,

54, 432.Goldman, M. V., and D. F. DuBois (1971), Theory ofparametric instability in the ionosphere abstract), EOS

Trans. AGU, 52, 883.Haerendel, G. (1971a), Observation of plasma convectionin a westward traveling surge (abstract), EOS Trans.

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1048 KIVELSON AND RUSSELLHaerendel, G. (1971b), Interaction of barium cloudswiththe ionosphere abstract), EOS Trans. A G U, 52, 881.Haerendel, G., and R. Liist (1970), Electric fields in theionosphere nd magnetosphere,n Particles and Fieldsin the Magnetosphere, edited by B. M. McCormac,pp. 213-228, Springer,New York.Haerendel, G., R. L[ist, and E. Rieger (1967), Motion ofartificial ion clouds in the upper atmosphere, Planet.

Space Sci., 15, 1-18.Haerendel, G., P. C. Hedgecock,and S.-I. Akasofu (1971),Evidence for magnetic field-aligned currents during thesubstorms of March 18, 1969, J. Geophys. Res., 76,2382-2395.

Haerendel, G., H. Kappler, R. List, E. Rieger, and H. Vflk(1972), Momentum transfer from ambient magneto-spheric to the seeded barium plasma (abstract), EOSTrans. AGU, 53,483.

Helliwell, R. A., and T. F. Bell (1971), Pulsation phe-nomena observed in long duration VLF whistler-modesignals,J. Geophys. Res., 76, 8414-8419.

Hendrickson, R. A., R. W. McEntire, and J. R. Winckler(1970), Electron echo data interpretation (abstract),EOS Trans. AGU, 51, 805.

Hendrickson, R. A., J. R. Winckler, and R. L. Arnoldy(1973), Preliminary report on artificial magnetosphericelectron injections at Fort Churchill (abstract), EOSTrans. AGU, 54, 436.Hess, W. N., M. C. Trichel, T. N. Davis, W. C. Beggs,

G. E. Kraft, E. Stassinopoulos, nd E. J. R. Maier (1971 ),Artificial auroral experiment: experiment and principalresults. J. Geo?hys. Res., 76, 6067-6081.

Katsufrakis, J.P., C. G. Park, and D. L. Carpenter (1973),Detection of the plasmapause using VLF transmitter sig-nals observed on polar orbiting satellites (abstract),EOS Trans. A GU, 54, 416.

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(1968), Plasma flow in the magnetosphere, J. Geophys.Res., 73, 5511-5519.Kennel, C. F., and H. E. Petschek (1966). Limit on stablytrapped particle fluxes, J. Geophys. Res., 71, 1-28.Kivelson, M. G., C. T. Russell, K. W. Chan, and C. R.Chappell (1972), An investigation of regions of highdensity cold plasma in the outer magnetosphere (ab-stract), EOS Trans. AGU, 53, 1103.Mozer, F. S. (1972), Balloon measurements of ionosphericelectric fields and precipitating particles during a bariumcloud release in the magnetosphere (abstract), EOSTrans. AGU, 53, 483.

Rieger, E., G. Haerendel, H. Kappler, J. Loidl, R. Liist,and H. Neuss (1972), Magnetospheric convection de-rived from barium cloud motions at 5 Rs altitude (ab-stract), EOS Trans. AGU, 53, 482.Schutz, S. R., F. S. Mozer, and G. Adams (1971), Electricfield measurements n and near large barium releases nthe ionosphere (abstract), EOS Trans. A GU, 52, 880.Wescott, E. M., H. M. Peek, H. C. S. Nielsen, W. B. Mur-cray, R. J. Jensen, and T. N. Davis (1972), Two suc-cessful geomagnetic field-line tracing experiments, J. Geo-phys. Res., 77, 2982-2986.

Wescott, E. M., H. M. Peek, P. Bottoms, E. R. Rieger,H. C. Stenbaek-Nielsen, W. B. Murcracy, and T. N. Davis(1973), Results of 5 successfulmagnetosphericprobingswith barium shaped-charge generated plasma jets (ab-stract), EOS Trans. A G U, 54, 435.

Winckler, J. R., R. A. Hendrickson, and R. W. McEntire(1970), Electron echo experimentbjectives of instru-mental configuration (abstract), EOS Trans. AGU, 51,805.

Zhulin, I. A., V. I. Karpman, and R. Z. Sagdeev (1972),Controlled experiments in the earth's magnetosphere, nCritical Problems of Magnetospheric Physics, edited byE. R. Dyer, pp. 245-260, IUCSTP Secretariat, NationalAcademy of Sciences, Washington, DC.

active experiments, magnetospheric modification, and a naturally occuring analogue

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