StormsthatoccurattheBayofBengal(BoB)areofabimodalpattern,whichisdifferentfromthatoftheotherseaareas.ByusingtheNCEP,SSTandJTWCdata,thecausesofthebimodalpatternstormactivityoftheBoBarediagnosedandanalyzedinthispaper.TheresultshowsthattheseasonalvariationofgeneralatmospherecirculationinEastAsiahasaregulatingandcontrollingimpactontheBoBstormactivity,andthe'bimodalperiod'ofthestormactivitycorrespondsexactlytotheseasonalconversionperiodofatmosphericcirculation.Theminorwindspeedofshearspringandautumncontributedtothestorm,whichwasacrucialfactorforthegenerationandoccurrenceofthe'bimodalpattern'stormactivityintheBoB.Theanalysisonseasurfacetemperature(SST)showsthattheSSTsofalltheyeararoundintheBoBareameettheconditionsrequiredforthegenerationoftropicalcyclones(TCs).However,theSSTsinthecentralareaofthebayarehigherthanthatofthesurroundingareasinspringandautumn,whichfacilitatestheoccurrenceofa'two-peak'stormactivitypattern.Thegenesispotentialindex(GPI)quantifiesandreflectstheenvironmentalconditionsforthegenerationoftheBoBstorms.ForGPI,theintenselow-levelvortexdisturbanceinthetroposphereandhigh-humidityatmospherearethesufficientconditionsforstorms,whilelargemaximumwindvelocityofthegroundvortexradiusandsmallverticalwindsheararethenecessaryconditionsofstorms.
