航天,航天器,航天器环境,空间辐射

2004N.V.Kuznetsovetal./AdvancesinSpaceResearch36(2005)2003–2011

sincetheSEPimpactisafunctionoftheparticleenergy(theenergytransfertomatterandthecross-sectionsforinelasticinteractionsareenergy-depen-dent),theparticle ux,asamodeloutput,mustbeknownforanyenergy,i.e.,wemustdeterminethecontinuousdi erentialSEPenergyspectrathatsuitanyfurtheron-lineanalysis;

sincemanyoftheradiatione ectsdependontheheavyparticle ux,theSEPmodelsmustincludenotonlyprotons,butalsoallsolarheavyions;

sincethesolarheavyion uxesarerelativelysmall(likethehigh-energyproton uxes),anysu cientlycomprehensiveSEPmodelcannotbedevelopedbas-ingonlyonthemeasuredion uxdistributionbecauseofthescantystatistics,butshouldbebasedonthefoundfeaturesoftheSEPion uxes,theenergydependenceoftherelativeparticlecompositionincluded(see,forinstance,Nymmik,1998,1999b); sincethedatabasesofSEP uxesmeasuredbysepa-rateinstrumentsaredi erentenough,thusindicatingsigni cantsystematicandmethodologicalerrorsoftheSEPmeasurements(MottlandNymmik,2003a),anySEPmodelcannotbedevelopedwithoutcheckingonthefullreliabilityoftheinputexperimentaldata.Atthesametime,theoutputofthemodelsmustper-mititson-lineusagetocalculatetheimpactofchargedparticle uxesonmaterials,equipment,andbiologicalobjects.

Mostofthepresent-daySEPmodelsfailtomeettheaboverequirements.Weshallattempttodrawattentiontothedi erencesintheconceptsandtodi erentwaysofdesigningtheSEPmodels.

Theapproach(Feynmanetal.,1993,2002;Xapsosetal.,1998,1999)usedmostextensivelyelsewhereistosimulatethemeasuredsolarproton uencesbasingontheSEPdatabasesthatdisregardthedistortionsfromthemeasurementdataobtainedwithdi erentinstru-ments(MottlandNymmik,2003a)andfromthethresh-olde ects(KurtandNymmik,1997)andalsomakeuseofthephysicallyincorrectSEPeventconcept(seethispa-perbelow).Wewillshowthattheapproachislittlepromisingbecauseitislimitedtodescribingthoseparti-clespecies(protons)andthoseparticleenergies(<100MeV)thatcanonlybemeasuredwithinthestatis-ticalaccuracythatwouldbehighenoughtosu cethesimulation.

Anotherapproach(Nymmik,1998,1999b)istosim-ulateanaturalphenomenonbasingonthebehavioralfeaturesinherenttosingleSEPevents(accordingtotheSEPdatabasesbyBazilevskayaetal.,1986,1990andSladkovaetal.,1998)andtoSEP uxesandinclud-ingtheexperimentaldatasetdistortionsintroducedbythethresholde ectsandbythemeasurementmethods.Theapproachhasmadeitpossibletodevelopthemodel(Nymmik,1998,1999b),whichcoverstheparticlespe-

cies(16Z628)andenergies(10MeV6E610GeV)thatcannotbedeterminedinanywayreliablybecauseoftheirinsu cientstatisticalsupport.

2.Thesep uxesinquietsunyears

Mostofthepresent-daymodelsdisregardtheSEP uxesinthequietSunyears(4yearof11-yearcycle)anddescribetheSEP uxesintheactiveSunyears(7yearsof11-yearcycle)only(Feynmanetal.,1990b,1993,2002;Xapsosetal.,1998,1999).Thisapproachdoesnotseemtobesu cientlyaccuratebecauseofthefollowing.

Ifthemodelsareappliedtoperiodsthatareclosetothe7-yearactiveSunperiod,theinaccuracyarisingfromusingthesameSEPeventoccurrencefrequencyforsuchsolarcyclesas19and20doesnotexceed35%.Incasethemodelsareappliedseparatelytoeachofseven1-yearactiveSunperiods,whensolaractivitymayvarybyafactorofupto5fromyeartoyear(theWolfnumbersvaryfrom40to200)andthemeanSEPeventoccur-rencefrequencyvariesaccordingly(Nymmik,1999c),theinaccuraciesintheparticle uxmodelestimationscanalsoreachfactor5ontheaverage.

Meanwhile,thequestionarisesastowhetherthequietSunSEP uxescanbedisregarded.

WeshallshowwhatarethemeasuredSEP uencesofthequietSunperiods(Nymmik,2001)ascomparedwiththeSEP uxesduringsolarmaximum.Forthatpurpose,wedeterminedthesmoothedsunspotnumbersÆWæonthecommencementdayofeachSEPeventandsepa-ratedtheeventsthatoccurredatÆWæ<40,i.e.,duringquietSunperiods.Since1965,22eventswithP30MeVproton uences(U30)inexcessof106pro-tons/cm2havebeenrecordedinquietsunperiods.Ofthem,18eventswererecordedbefore1985(Feynmanetal.,1990b)and4eventsof1994–1997werefoundbyourIMP-8database(INTERNET:IMP-8)analysis.TheseSEPeventsareasfollows(theyearsandthedaysofayearoftheSEPeventcommencementsareindi-cated):1965(36),1973(210,250,307),1974(159,184,254,309),1975(232),1976(83,121,235),1977(203,251),1985(21,114,185,198),1994(51),1995(293),1997(308,310).

Table1

Thetotal(upper3lines)andmean-annual(lower3lines)proton uencesmeasuredduringtimeT(months)atdi erentsolaractivitylevelsin1965–1997WperiodW640;period1W640;period21456W6155RUEP107.82·1081.24·1098.6109

RUEP301.36·1084.0·1081.63·109RUEP60–1.3·1083.89·108T

101

85

24

ÆUEP10æ8.9·1071.74·1084.3·109ÆUEP30æ1.6·1075.68·1078.6·108ÆUEP60æ

–

1.84·107

1.95·108