简介：Inthispaper,aWindDirectionChangeIndex(WI),whichcandescribefour-dimensionalspatiotemporalchangesoftheatmosphericcirculationobjectivelyandquantitatively,isdefinedtostudyitsevolutionandseasonalvariation.ThefirstfourmodescanbeobtainedbyEOFexpansionofthezonallyaveragedWI.ThefirstmoderevealsthebasicspatialdistributionoftheannuallyaveragedWI.Thesecondmodereflectsthequasi-harmonicpartsoftheWIdeviations.Tropical,subtropicalandextratropicalmonsoonareascanbeclearlyreflectedbythismode.Thethirdmodereflectsthenon-harmonicpartsoftheWIdeviations.Itshowstheso-calledFebruaryreverseinstratosphericatmosphereaswellastheasymmetricseasonalchangesfromspringtofallandfromfalltospringduetoboththeland-seadistributioncontrastbetweentheNorthernandSouthernHemispheresandthenonlineareffectofatmosphericandoceanfluids.Thefourthmoderevealsthenorthwardadvancingoftheglobalreversedwindfieldsfromspringtosummerandtheirsouthwardwithdrawalfromsummertoautumn.