钨制灶台

GeophysicalResearchAbstracts,Vol.7,04384,2005SRef-ID:1607-7962/gra/EGU05-A-04384©EuropeanGeosciencesUnion2005ImpactsofcometsontotheSunandcoronalmassejections.I.Nemtchinov(1),I.Kosarev(1),A.Kovalev(1),T.Losseva(1),V.Shuvalov(1),R.Treumann(2)(1)InstituteforDynamicsofGeospheresRAS,Moscow,Russia,([e-mail]),(2)Max-PlanckInstituteforExtraterrestrialPhysics,Garching,GermanyAsmuchas300sun-grazingcometswereobservedbetweenJanuary1996andJune2001bythesensitiveSolarHeliosphericObservatory(SOHO)instrumentationcapa-bleofdetectingfaintobjects.Theaveragenumberofsun-grazersis60peryear.AcometwasdiscoveredthatdidnotreappearafterthetimeofclosestapproachtotheSun.Muchlater,extremelybroaddiffusebrighteningofthecoronaoveronesolarhemispherewasobserved.Thisbrighteningwasinterpretedashavingbeencausedbythecometarydebrisback-scatteredintotheambientsolarwind.OneJune11,1998,twosun-grazingcometsfollowingsimilarbutnotidenticalor-bitswereviewed.Shortlyaftertheydisappearedbehindtheoccultingdisksofthecoronographs,acoronalmassejection(CME)withanenormouseruptingprominenceappearedonthelimboftheSun.Observationsliketheseraisethequestionofwhetherthesehavebeenpurecoincidencesorwhether,ifonlyinsomecases,thereexistsacausallinkbetweencometaryimpactsontheSunandthereleaseofCMEs.HerewepresentthefirstresultsofanattempttoinferwhetherCMEscaninprinciplebecausedbycometaryimpactsontheSun.ThetypicalmassaCMEliftedagainstthesolargravityisofthesameorderofmag-nitudethemassofa1kmicysphere.Theenergyreleasedintheimpactofsuchacometmaybesufficienttoproducea“directlydriven”CME,whenthesuddenre-leaseofthermalenergyinthecorona(“thermalblast”)createsahighlyenhancedgaspressurethatcannotbecontainedbythesolarmagneticfield.Inthiscasethecoronaisliterallyblownopen,intenseshockwavesaregenerated,propagatingouttolargedistancesfromtheSun.Historicevidenceshowsthatamongsun-grazerstherewereseverallargecomets.Ourpreviousinvestigationshaveshownthatlargeimpactorsmaydeeplypenetrateintothesolarphotosphere(e.g.downtoanaltitudeofabout1500kmforacomet30kminradius).Energyoftheseimpactorsissufficientfordirectigni-tionofaCME.Butimpactsoflargebodiesareratherinfrequent,whilethereare270toabout1500CMEsperyear.Itisobviousthatthemainpartoftherelativelyfaintsun-grazersisrathersmallandtheirmassandenergiesaremuchlessthanthoseofatypicalCME.CurrentlythebestacceptedmodelofgenerationofCMEsrefersto“storedandre-leased”coronalmagneticenergy.ThismodelproposesthatCMEsaretriggeredbymicro-instabilitiescausinganomalousresistivity,currentdissipation,andreconnec-tion.TheenergyfuellingtheCMEisstoredinthecorona.Theenergyoftheimpactorswhichmayinitiatetheevolutionofmicro-instabilities,reconnectionofmagneticfieldlinesandultimatelytriggeraCMEmaybesubstantiallylessthanthefinalenergyofCME.Soweshouldinvestigatethepeculiarpropertiesofimpactsofsmallcomets,whichpreviouslyhavenotbeenstudiedthoroughly.SimpleestimatesshowthatneartheSunthemassofanicycometevaporateddur-ingitsapproachtotheSunundertheactionofsolarradiationisequivalenttothemassofanicylayerabout100mthick.Therefore,smallsun-grazersmaybefullyevaporated.Theseestimatesshould,however,becorrectedasthesurfaceofthecometreachestemperaturesmuchhigherthanthetemperatureofvolatileevaporation.Thisclaimissupportedbytheobservationofthelightcurveswhichshowthatthenormal-izedbrightnessdependsonlyontheheliocentricdistanceofthecomet.ThatcanbeunderstoodifweassumethatthemaximumtemperatureisgivenbytheequilibriumblackbodytemperatureTB.Attemperaturesof1600to2700Ktherefractorymaterialbecomesintenselyevaporated,whilevolatilesmayevaporateatsmallerheliocentricdistances.Thedeterminationoftheablationismademoredifficultbythecomplicatedradiationtransferprocessesinthevapourlayer.Detailedspectralabsorptioncoefficientsinawiderangeoftemperatures,densitiesandspectralintervals(intheIR,visibleandUVwavelengthranges)werecalculatedfortypicalvolatile-richcometarysubstancesandforchondriticcomponents,whichmayrepresentacometaftertheevaporationofices.Theanalysisofthesecoefficientsshowsthattheevaporatingsurfaceisatleastpartiallyscreenedbythevapourlayer.Becauseofthemultitudeofmoleculeabsorptionbandsandlinesinvolved,oneneedstointroduceaverylargenumberofspectralintervalsinordertoinferabouttherealra-diationspectrum.Thespectralmethodsforsolvingtheradiationhydrodynamicprob-lemtakingintoaccountthedetailedspectrumandangulardependenceoftheradiationhavebeendevelopedandusedtodeterminethetemperatureprofileinthevapourlayerandthemassablationratetakingintoaccountbothscreeningofthesurfaceandre-radiation.Itisusuallyassumedthatdisruptionofcometsintheatmosphereoccursduetoaero-dynamicloadingduringtheflightthroughthedenselayersoftheatmosphere.Undertheactionoftheseaerodynamicforcesthecometisdeformedintheatmosphereofaplanetinaliquid-likemanner.InthecaseofimpactsontothehotSuninadditiontothetidalforcesandthermalstressestheejectionofvapourstreamsfromtheintenselyevaporatedsurfaceplayanimportantrole.Theseforcesactontothecomet’ssurfacenotonlyduringarathershort(severalseconds)timeintervalwhenthecosmicbodypassesacrossthedenselayersoftheatmosphere.Theybeco