Models of solar energetic particle fluxes- the main requirements and development prospects(8)

航天,航天器,航天器环境,空间辐射

2010N.V.Kuznetsovetal./AdvancesinSpaceResearch36(2005)2003–2011

uncontrollablesensitivityvariationsoftheinstrumentchannels.

Themethodologicalmeasurementerrorsareverydangerousandcaptiousandarisemainlyfromtheaddedparticlecountsinthedetectorsthatmeasurethehighest-energyparticle uxes.Asaresult,themeasuredSEPeventprotonenergyspectrabecomespuriouslyri-gid.Themagnitudeoftheresultantdistortionsisdis-cussedin(MottlandNymmik,2003a).

Besidetheengineeringprinciplesofeventdetermina-tion,theSEPeventcataloguessu ermainlyfromtheuncertaintiesthatarisewhencalculatingtheintegralpar-ticle uxesfromthemeasureddi erential uxes.Theuncertaintiesareproducedbydi erentapproximationsthatmustbeusedtogooverfromthe uxesmeasuredbydi erentialchannelsofinstrumentstotheintegralSEP uxes.Di erentauthorsmakeuseofdi erenttech-niques,sothereliabilityoftheresultantdatabasesandtheirassociatemodelsisdi culttodetermine.4.Themodeloutputrequirements

Theimperativerequirementofthelatestcomputa-tionalmethodsisthattheSEPmodeloutputshouldbedescribedintermsofdi erentialSEPenergyspectra,permittingtheradiatione ectstobecalculatedas

EF¼CZEmax

rðEÞ

dF

dE;ð5ÞEmindEwherer(E)designatestheenergydependenceoftheef-fect(theenergylossincluded).

5.Discussion

Ourviewsonthepresent-daysituationwithcon-structingSEP uxmodelshavebeenstatedabove.Bas-ingonthemodelrequirements,whichwebelievetobequiteobvious,westrivedtoexposesomeofthemaindrawbacksoftherecentmodelsandto ndoutthewaysofeliminatingthem.

The rststepmustbetodenythemechanicalexperi-mentaldatadescription,whichisregardingthedetectionthresholde ectsandthedistortionsthatarisewhenmea-suringtheSEP uxesduetothegalacticbackgroundandbecauseofthearti cialeventselectioncriteria.

Anattemptwasmadeabovetosingleoutthedistor-tionsoftheSEP uxcharacteristics(theeventdistribu-tionfunction,nparticular)thatarisefromdisregardingthedetectionthresholde ects.Obviously,theparame-tersoflognormaleventdistributions,whichariseessen-tiallyfromdistortionoftheinputpower-lawdistributionfunctions,arenottheparametersoftheSEPdistributions,whilethevaluesoftheparameterseitherre ectthearbitraryselectioncriteriaintroduced

bydi erentauthors,ordependonthegalacticback-groundde nedbythevaryingsolaractivity.Ithasbe-comeclearthatallthreeparametersusedtodescribe

theSEP uxesintermsofthecumulative uencedistri-butions,namely,themeanofthelognormaldistribu-tion,thestandarddeviation,andtheaveragedSEPeventoccurrencefrequency(see,forexample,Feynmanetal.,1993),arearbitraryandessentiallyirrelevanttothenaturalphenomenonproper.Allthreeparametersvary,givendi erentenergythresholdusedtodeterminethecumulativeSEPevent uencedistribution.

WeclaimthatanySEP uxmodelshouldbedevel-opedbasingontheknownregularfeaturesandonthefeaturestobefoundbystudyingtheSEP uxesandtheirrelationshipstosolaractivityandtoothersolar areactivitydisplays.

Toreachthesaidlevelofdevelopingthemodels,wemust

rejecttheengineeringideaofeventandgoovertophys-icaldeterminationofSEPeventtobeaparticle uxgeneratedinasingleeventofaccelerationand/orejec-tionofaSEP uxfromthesolarchromosphere;

makeuseofthemethodsandvaluesthatwouldbeadequatetothevariationrateofthegeneralsolaractivitylevel;themean-yearlycharacteristicsofsolaractivityandSEP uxesarenottobeusedintheanal-ysisbecausetheyaretooroughandcamou agethetruecharacterofthespectraldependencesinherenttothestudiedphenomenon;

rejectsuchvisualsemi-quantitativesolaractivityparametersastheyearscountedfromsolarmaximumorminimum;instead,wemustusetherealsolaractiv-itycharacteristics(sunspotnumbers,radioemissionintensity,etc.).

However,theseproposalswouldbebutpalliativeun-lesswefullyrevisealltheSEPeventdatabasesbecausetheyhavebeencompiledmainlyintermsofthe‘‘engi-neering’’determinationoftheeventswithoutdetermin-ingthereliabilityandmethodologicalerrorsforthevariousinstruments ownondi erentspacecraft,whosereadingsareusedtodeterminetheSEPeventsandtheirphysicalparameters.

ItistheaboveprinciplesthatunderlieourdevelopingtheSEP uxmodel,whoseintermediateversionispre-sentedin(Nymmik,1999a).Themodelisbeingspeci edcontinuallyastheprinciplesandthefoundrelevantreg-ularfeaturesofSEPeventsareusedmoreandmoreextensively.

6.Conclusion

Wehavereportedourviewsofthepresent-daystatusofmodelingSEP uxesandoutlinedthewaysofover-