Fateofsub-keVringcurrentionsobservedbyVikingViking20子keV的環(huán)電流離子的維京海盜20觀察到的

Fateofsub-keVringcurrentionsobservedbyViking

Viking20years

YamauchiandLundin*Superposedepochanalyses*VikingIondata+AE(andDst)Eastwardmotionofsub-keVionsaftersubstorms :///EGU/annales/24/1/355.htm Yamauchi,M.andLundin,R.(2006), Ann.Geophys.,355-366. SRef-ID:1432-0576/ag/2006-24-355 XY0868(EGU06-A-05964)2006-4-6PreviousWorksReversed(Type2)Ordinary(Type1)Both(island)sub-keVionprecipitation@subauroralregion):*Aureol1(400~2500km):Sauvaudetal.,1981 00-06MLT: increasessomehoursaftersubstorms.*DMSPF6/F7(800km):NewellandMeng,1986 0830MLT:correlatedwithKpwithsome hoursdelay,andeventmaylastaday.*Viking(2~3RE):Yamauchietal.,1996a,b "Wedge-likedispersedstructures" modulationbypc-5pulsation*Simulation:Ebiharaetal.,2001

driftmodel(ExB,grad|B|,andcurvature)

manyhoursafternightsideinjection

dispersionpatterns+MLTdependence*Freja/Viking/Cluster:Yamauchietal.,2005 05-19MLT:morningpeak altitudecomparison:O+/H+ratiochange*Others:Shelleyetal.,1972;Chappeletal.,1982Reversed(Type2)Both(island)VikingObservationEbiharaetal.,2001PresentWork

(1)simplestatistics(2)casestudy(3)advancedstatisticsSimulationindicates:*Driftslowlyeastward*Originatedfrompastsubstorm-relatedinjectionsintotheringcurrentregion5~20hoursbefore.However,nosoliddataanalyseshasbeendonetoconfirmthedynamicpartofthemodel.Aretheydrifting?Ifso,velocity?fromwhere?Relatedtosubstorms? Ifso,timelag?SimpleAEcorrelation?TmisleadingAfternoonsectorshownegativecorrelation.Thus,onemaynottakedirectcorrelation.SimpleDstcorrelation?TmisleadingBeforeall,only58outof700areduringDst<-30nT.Magneticstormactivityisnotthedirectcause.159 209 280 58#traversals80 198 192 15977#traversals(2)CasestudyItrequiresisolatedsubstormactivity+consecutivetraversals=rare.Eventhebestcase(860912)showsuperficialanti-correlation(3)BackwardSuperposedEpochAnalyses*Probabilitieswith/without“wedge〞signatureatvariousMLTindaysideisobtainedfordifferenttime-lagsfromlatestAEincrease.(a)IdealAEprofilegives3characteristictimes(b)&(c)ButwemustfightagainstrealityHopestatisticshelps,WhyViking?*AEindexisavailablefromall12stations.*IdealorbitandinstrumentationTotalonly700sortedbyLT&time-lags.*3-hourMLTbins*3-hourwindows(runningsummation)forthetime-lagexceptfor0thand1sthour*addalltypesofdispersions*divideintoonlythreecategories:"clearstructure","marginal",and"quiet.Result:1Probabilitiesofobservingthewedge-likestructureaftertheendofAEactivity.(cf.(2)inexplanation)Quietprobabilitycorrespondstothelastinjection

Lowestquietprobabilitystartincrease(=lastwedgepassingthrough)starttoincreaseatlatertime-lagatlargerMLT,itmoveseastward,whilethevalueitselfincreaseeastward.Time-lag(hours)6MLT9MLT12MLT15MLT18MLTResult:2Probabilitiesofobservingthewedge-likestructureafterthestartofAEactivity(cf(1)inexplanation)Thepeakprobabilityisfoundatlatertime-lagatlargerMLT,i.e.,peakmoveseastward,whilethepeakvalueoftheprobabilitydecreaseasthepeakmoveseastward.6MLT9MLT12MLT15MLT18MLTTime-lag(hours)Evacuationisseen(theprobabilityisevenlowerthanasymptoticone)SummaryMLTMinimumQuietcaseAfterendof300nTactivityAsymptoticQuietcaseAfterendof300nTactivityMaximumClearcaseAfterstartof400nTactivity5~71~3h(0%)8~9h(30%)0~3h(85%)8~102~3h(5%)9~10h(50%)2~4h(75%)11~133~5h(10%)10~11h(70%)4~6h(70%)14~164~6h(35%)12~13h(80%)6~7h(50%)17~196~8h(50%)14~16h(100%)10h(25%)?=?corot+?model·sin(LT)?model/?corot

Kp=2 Kp=3 Kp=4L=4 0.08 0.13 0.25L=6 0.25 0.4 0.8Observed?model/?corotfrom6MLTto15MLT>0.5:Thisisfasterthanprediction.1.Thewedge-likestructuredriftseastward(modelisright!).2.Thestructureisafossilofsubstormactivity(modelisright!).3.Decaytimeisconsistentlyseveralhours(modelisright!).4.However,itappearsmuchearlierthanprediction!Conclusions:wedge-likestructures1.ThestructureisrelatedtothepastAEactivitybutnotdirectlytoDst2.AfterhourlyAE>400nT,themajorityofthestructurereachesthenoon,andnearlyhalfofthemreachestheearlyafternoonsector.3.Thestructuresintheeveningsectormostlikelyhavetraveledbyeastwarddriftratherthandirectlyfromthenightsidebywestwarddrift.4.Theresponseat6MLTisnearlyimmediateafterhighAEactivities.Sourceofwedgeshiftsorextendstotheearlymorning,e.g.,4-5MLT.5.ThedriftspeedforhourlyAE>400nTissomewhatfasterthanmodelpredictioneventakingintoaccountofthemorning-shiftofsource.6.ThedecaytimeofseveralhoursatallMLTisconsistwiththechargeexchangelifetime.7.Sub-keVionsaresometimesevacuatedrightaftertheonsetofsubstormorstorm.Morestatistics(∑3h)PeakprobabilitiesvsAEthresholdOptimumtime-lagvsAEthresholdFordifferentAEthresholdvaluesBestthresholdvaluevaluesare400nTforstartofactivityand300nTforendofactivityResultofsuperposedepochanalyses(∑3h)Fromendofactivity(cf(2)inexplanation)

Fromstartofactivit