简介：Weanalyzethedecadalvariationofthestratospheretropospherecoupledsystemaroundtheyear2000byusingtheNCEPreanalysis-2data.Specifically,therelationshipbetweentheNorthernHemisphereAnnularMode(NAM)andthetroposphericEastAsiantroughisinvestigatedinordertofindtheeffectivestratosphericsignalsduringcoldairoutbreaksinChina.Statisticalanalysesanddynamicdiagnosesbothindicatethatafter2000,increasedstratosphericpolarvortexdisturbancesoccurandtheNAMismainlyinnegativephase.Thetroposphericpolarareasaredirectlyaffectedbythepolarvortex,andinthemidlatitudes,theUralblockinghighandEastAsiantrougharemoreactive,whichleadtoenhancedcoldairactivitiesineasternandnorthernChina.Furtherinvestigationrevealsthatunderthiscirculationpattern,downwardpropagationsofnegativeNAMindexarecloselyrelatedtotheintensityvariationoftheEastAsiantrough.WhennegativeNAManomaliespropagatedowntotheuppertroposphereandreachacertainintensity(standardizedNAMindexlessthan1),theyresultinapparentreinforcementoftheEastAsiantrough,whichreachesitsmaximumintensityaboutoneweeklater.Thenortherlywindbehindthetroughtransportscoldairsouthwardandeastward,andtherangeofinfluenceandtheintensityarecloselyassociatedwiththetroughlocation.Therefore,theNAMindexcanbeusedasameasureofthesignalsfromthedisturbedstratospheretogivesomeindicationofcoldairactivitiesinChina.