multi-spacecraft observations of solar energetic and energetic storm particle events during...

Adv. SpaceRes.Vol. 13, No.9,pp. (9)355—(9)35$,1993 0273—1177)93$24.00Printedin GreatBritain. Mi rightsreserved. Copyright@ 1993COSPAR

MULTI-SPACECRAFFOBSERVATIONSOFSOLAR ENERGETICAND ENERGETICSTORMPARTICLEEVENTSDURINGNOVEMBER/DECEMBER1982

M.-B. Kallenrode,*G.Wibberenz,*N. Kontor** andV. Stolpovskii~

* Institutfir Kernphysik,UniversirätofKiel, Otto-HahnPlatz1, 2300Kiel,Germany** NuclearPhysicsInstitute,MoscowStateUniversity,Moscow,Russia

ABSTRACT

Multi-spacecraftobservationsby Helios, IMP, and Venerashow that interplanetaryshockscanextendup to more than 900 east of the flare normal and are capableof acceleratingparticles,in particular protons up to energiesof some tens of MeV. At the flanks the shock speedandthe accelerationefficiency decrease;this decreaseis more pronouncedin high than in low energyprotons.Shockspikescanbe observedat energiesup to 50 MeV andshockaccelerationseemstobe very effectiveinside0.5 AU.

INTRODUCTION

During the lastyearsstatisticalstudiesof earthboundobservationshavepointedout the import-anceof interplanetaryshocksfor the accelerationof tensof MeV protons,especiallytheorderingof the intensity profiles by the anglebetweenobserverandflare normal /1/, the mixing of flare-acceleratedand shock-acceleratedparticlesin well-connectedevents/2,3/, and the extensionofproton accelerationat interplanetaryshocksup to energiesof 100 MeV /3/. In this paperwewill useobservationsfrom threespacecraftat differentlongitudesanddifferentradial distancestostudyindividual eventsin moredetail.

OBSERVATIONS

The dataused in this paperwere obtainedby the University of Kiel particleinstrumentE6 onHelios, the MoscowState UniversityKV-77 instrumenton Venera,andthe JHU/APL instrumenton IMP. Fig. 1 gives anoverviewoverthe entiretime period showingprotonswith energiesof afew MeV andabout20 MeV observedby Helios (upperpanel),( Venera,2nd panel),and (IMP, 3rdpanel),togetherwith the flare activity during that time period (bottompanel, smallopencirclesmark flares with soft X-ray classbetweenMl and M4, largeopencircles flares betweenM5 andM9, filled circles flares �X1, starsthe eleven largesteventsmarkedin the abovepanels,for thismethodcompare/6/). The insert in the bottompanelgives the spatialconfigurationof the threespacecraft.The entire time period is markedby strongflare activity on the visible disk, elevenflares seemto dominatethe particleintensityprofiles (numberedcircles in the upperpanels)andinitiate interplanetaryshocks(triangles).Dueto this strongactivity, theintensitystays,especiallyin thelowerenergychannels,abovebackgroundfor mostof the timeforming asuper-event/cf. 5/.

Fig. 2 shows event#3 (26 Nov 1982) in more detail: Around the spatial configuration(upperright) we show the IMP proton intensities (upper left), andfor Veriera (lower left) and Helios(lower right) the anisotropy(bottom),the time evolutionof theproton spectrum(middle) andtheproton intensities(top) in four channels.All threespacecraftarelocatedeastof the flare normalwith anglesto the flare normalup to about90°(IMP). The arrowsin the configurationplot givethemeanshockspeedsdeterminedfrom the traveltimesof the shockin thatdirection. The shockis observedon all threespacecraft,giving an extensionof the shockof at least 90°to the east.Assumingthat theshockis moreor less symmetricalaroundthe flare normalthis would indicatea total extentof the interplanetaryshockof about 180°.The shockis fastestcloseto the flarenormal,the speeddecreasesas onegoesto theeasternflank of the shock.

(9)355

(9)356 M.-B. Kallearodeeta).

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10 t4-25M.V ~ Q ~. 0 0 0 0 0 0 0 0 - 0iø~ ‘ .2~- ~ ..____;—._ ~ 1o..~

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320 325 330 335 340 345 350 355 360 365

TIMEFig. 1. Overview over particle dataand flare activity for the time period Novem-ber/December1982 (cf., text).

On all threespacecrafttheshockhasaninfluenceon theintensityprofilesof protons. Thisinfluenceis strongestcloseto theflare normal (Helios)whereashockspikeis observedevenin energiesup to50 MeV. On Heliosparticlescomefrom the solardirectionbeforethearrival of the shock(indicatedby a‘-F’ signin the anisotropy,which in this exampleis determinedwith respectto the directionofmain particlestreaming),aftershockpassageparticlesstreamtowardsthesun(‘-‘), indicatingthatthe shock is a moving sourceof particlesthat is sweptacrossthe observer.The intensityprofilesin the different energyrangeslook quite similar. Going eastfrom theflare normal,on Veneratheshock spike is observedin the lowest proton channel,in the higherproton energiesonly a smallhumpof shockacceleratedparticlesseemsto be superposedon the intensityprofile. Note that inhigh energiesthe shockacceleratedparticlesseemto havetheir maximumlongbeforethe arrivalof the interplanetaryshock. Theseparticlesprobably are acceleratedrelatively closeto the sunwere the shockis quasi-paralleland thereforemoreeffectivein particleacceleration.Furthereaston IMP the superposedshockparticlesare visible in thelow energyprotons;in thehigherenergiesthereseemto be no or only few shock-acceleratedprotons.Thereforeto theflank of the shocktheaccelerationefficiencyseemsto decrease,especiallyin higherenergies.

Multi-SpacecraftObservationsin NovemberdDecember1982 (9)357

I ~ -Protons 1-1.8 McV -

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TIME TIME

Fig. 2. Configurationandparticledatafor the 26 Nov 1982event(cf. text).

~ ~: ~ Protons 118 ~ I I

353.6 354 354.4 354.8 . 10- Helios -

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Fig. 3: Configurationand particledatafor the 19 Dec 1982 event(ci. text).

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Fig. 3 showsevent#9 (19 Dcc 1982). The geometricalsituationis similar to theoneshownabove,however,it is importantto note that Helios is locatedat a distanceof only 0.45 AU. On Heliosshock-acceleratedprotonsare visibleup to energiesof at least50 MeV; however,further to theeastof the flare normal on Venerathereis acomparablepromptcomponentof particlesacceleratedonthe sun(in thephotosphereor e.g.by a coronalshock,cf. /2/). Heretheshockacceleratedparticlesare dominantonly in low energyprotons,while in the higherenergiesthereseemto be no or onlyveryfew energeticstormp-~.rticlessuperposed.Furthereaston IMP the shockis not detected,thepromptevent is visible in the high energyprotons,in the low energy protons the backgroundistoo high to detectthis event. This exampleclearly showsthat closeto the sun,where the shockis quasi-parallel,proton accelerationat an interplanetaryshock occurs to a quite large degree.It is interestingthat thereare no or only few shock acceleratedparticlesin the higher energieson Venera. Probably particleaccelerationhas becomeinefficient, at leastfor the high energies,becausedueto the curvatureof the interplanetarymagneticfield line theshockhasbecomemoreperpendicular.Closeto the suntheshockhasbeenquasi-parallelon thefield line Venerais locatedon; if it has acceleratedparticlesthere, theseparticlesseemto vanishin the promptcomponentbecausethey are acceleratedonly arelatively shorttime later (cf., small super-posedhumpin theeventdiscussedabove).

DISCUSSION

Wefind that interplanetaryshockscanextendup to 90°eastof theflare normal,in a symmetricalconfigurationthiswould correspondto atotalangularextendof 180°,muchlarger thanthetypicalspansof the CME which are believedto be thedriver of the shock(ci., /7/ andreferencestherein).In addition, the shockspeeddecreasesconsiderablyas onegoesto the flanks of the shock.

Shockaccelerationis mostefficient closeto theflare normalanddecreasesto theflank, in intensityas well as in maximum energy; however,the low energy (a few MeV) protons are acceleratedup to angulardistancesof 900 from the flare normal. The quasi-parallelshock closeto the sunseemsto be a very efficient particle accelerator;in addition, thereseemsto be someindicationthat shockaccelerationbecomesless efficient as the shockpropagatesoutward,probablybecauseof geometricalreasons(due to the curvatureof the interplanetarymagneticfield line the shockbecomesmoreoblique) and eventuallyalso due to the weakeningof the shock. This would beinterestinginsofaras it would imply that shockaccelerationbecomeslessefficient beyond 1 AU, atleastforprotonswith energiesof sometensof MeV. On theotherhand,shock-acceleratedparticlesare observedbeyond 1 AU (cf., /8,9/); however,it is not clearwhetherall shocksbeyond 1 AU areableto accelerateprotons to energiesof sometensof MeV or whetherthis accelerationis limitedto extremelystrong shocksor systemsof shocksas suggestedin /9/. Suchsystemsof shocksormergedshocksseemalso importantfor theformationof asuper-event,e.g.due to theformationofa closedshell aroundthe sunconfining andacceleratingthe particles/4,5/. The sizes,directions,andspeedsof the shocksobservedin the time periodunderstudyshowevidencefor theformationof at leastsystemsof shocks,possiblyevenfor tile formationof aclosedshell aroundthesun. Fora betterunderstanding,however,the continuationof this preliminarystudyunderconsiderationof spacecraftat larger radial distances,in particularthe study of radial gradientsof promptandshock-acceleratedparticles,seemsto be important.

Acknowledgement:We aregratefulto all membersof the University of Kiel Helios team(principalinvestigatorH. Kunow). This work wassupportedby the DFG undercontractWi-259/8-1.

REFERENCES

/1/ H.V. Cane,D.V. Reames,andT.T. von Rosenvinge,J. Geophys.Res.93,9555 (1988)/2/ D.V. Reames,H.V. Cane,andT.T. von Rosenvinge,Astrophys.J. 373, 259 (1990)/3/ D.V. Reames,Astrophys.J. Lett. 358, L63 (1990)/4/ R. Miiller-Mellin, K. Röhrs, and G. Wibberenz, in: The Sun and the heliospherein threedimensions,ed. R. Marsden,Reidel,Dordrecht1986,p. 349/5/ W. Dröge,R. Müller-Mellin, and E.W. Cliver, Astrophys.J. Lett. 387,L97 (1992)/6/ E.C. Roelof, R.E. Gold, G.M. Simnett,S.J. Tappin, T.P. Armstrong, and L.J. Lanzerotti,Geophys.Res.Lett. 19, 1243 (1992)/7/ H.V. Cane,J. Geophys.Res.93, 1 (1988)/8/ S.M. Krimigis, SpaceSci. Rev. 59, 167 (1992)/9/ G. Wibberenz,H. Kunow, it. Miiller-Mellin, H. Sierks,B. Heber,M.-B. Kallenrode,A. Raviart,P. Ferrando,andR. Ducros, Geophys.Res.Lett. 19, 1279 (1992)