TheNCEP/NCARreanalysisdatasetsandClimatePredictionCenter(CPC)MergedAnalysisofPrecipitation(CMAP)raindataareusedtoinvestigatethelargescaleseasonaltransitionofEastAsiansubtropicalmonsoon(EASM)anditspossiblemechanism.ThekeyregionofEASMisdefinedaccordingtotheseasonaltransitionfeatureofmeridionalwind.Bycombiningthe’thermalwind’formulaandthe’thermaladaptation’equation,anew’thermal-wind-precipitation’relationisdeduced.Theareameanwinddirectionsandthermaladvectionsindifferentseasonsareanalyzedanditisshownthatinsummer(winter)monsoonperiod,theaveragedwinddirectionintheEASMregionvariesclockwise(anticlockwise)withaltitude,andtheEASMregionisdominatedbywarm(cold)advection.TheseasonaltransitionofthewinddirectionatdifferentlevelsandthecorrespondingmeridionalcirculationconsistentlyindicatesthatthesubtropicalsummermonsoonisestablishedbetweentheendofMarchandthebeginningofApril.Finally,aconceptualschematicexplanationforthemechanismofseasonaltransitionofEASMisproposed.
