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简介：Theactivitiesofgeomagneticstormsaregenerallycontrolledbysolaractivities.Thecurrentsolarcycle(SC)24isfoundtobemild;comparedtoSCs19–23,thestormoccurrenceandsizederivedbyaveragingtheoccurrencenumberandDstaroundthesolarmaximumarereducedbyabout50–82%and36–61%,respectively.Weestimateseparately,forSC19to24,therepeatintervalsbetweengeomagneticstormsofspecificDst,basedonfitsofpower-lawandlog-normaldistributionstothestormdataforeachSC.RepeatintervalsbetweensupergeomagneticstormswithDst≤–250nTarefoundtobe0.36–2.95year(s)forSCs19–23,butabout20yearsbasedonthedataforSC24.Wealsoestimatetherepeatintervalsbetweencoronalmassejections(CMEs)ofspecificspeed(VCME)sinceCMEsareknowntobethemaindriversofintensestormsandtherelatedstatisticsmayprovideinformationaboutthepotentialoccurrenceofsupergeomagneticstormsfromthelocationoftheSun.OuranalysisfindsthataCMEwithVCME≥1860km/smayoccuronceper3and5monthsinSC23and24,respectively.BasedonaVCME-Dstrelationship,suchafastCMEmaycauseastormwithDst=–250nTifarrivingattheEarth.BycomparingtheobservedgeomagneticstormstostormsexpectedtobecausedbyCMEs,wederivetheprobabilityofCMEcausedstorms,whichisdependentonVCME.ForaCMEfasterthan1860km/s,theprobabilityofaCMEcausedstormwithDst≤–250nTisabout1/5forSC23or1/25forSC24.AlloftheaboveresultssuggestthatthelikelihoodoftheoccurrenceofsupergeomagneticstormsissignificantlyreducedinamildSC.

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