BasedontheCMAtropicalcyclone(TC)besttrackdataaswellasthereanalysisdatasetsfromtheNCEP/NCARandNOAA,thevariationcharacteristicsofTCnumberfrom1949to2013overthewesternNorthPacific(includingtheSouthChinaSea)areexamined.Notably,thetimeseriesofTCnumberexhibitsasignificantabruptchangefrommoretolessaround1995.ComparativeanalysisindicatesthattheenvironmentalfactorsnecessarytoTCformationalsochangesignificantlyaroundthemid-1990s.After1995,accompanyingwithanomalouswarmseasurfacetemperature(SST)inwesternequatorialPacific,aLaNia-likepatternintropicalPacificappearsobviously.However,comparedwiththeperiodbefore1995,theverticalupwardmovementdecreases,verticalshearoftroposphericzonalwindincreases,andsealevelpressure(SLP)rises,allofwhichareunfavorabletoTCformationandworktogethertomakeTCnumberreducemarkedlyafter1995.Furthermore,whenthetypicalinterannualmoreandlessTCsyearsareselectedinthetwoseparatestagesbeforeandafter1995,therelativeimportanceofoceanicandatmosphericenvironmentsininterannualTCgenerationisalsoinvestigatedrespectively.TheresultsimplythattheSSToverthetropicalPacificexertsrelativelyimportantinfluenceonTCformationbefore1995whereastheatmosphericcirculationplaysamoreprominentroleinthegenerationofTCafter1995.
