Interannual Variations Of Hadley Circulation In WPWP Region And Its Relationship With SST

Hadley circulation is an important component of atmospheric circulation，it plays ansignificant role in the transportation of heat and angular momentum and massexchanges at low latitudes，besides，it can also influence global or local climate andweather. Warm pool,especially West-Pacific Warm pool(WPWP), is the most activeregion in the world,it’s the main heat producer of Hadley Circulation and WalkerCirculation and key factor of air-sea interactions like ENSO, recently,it has been ahotspot.Up and down iteration method of mass stream function(MSF) combined withempirical orthogonal function(EOF),composite analysis, correlation analysis andharmonic analysis were used to analyse the character of Hadley circulation of WPWPregion and its relationship with SST in this paper.Main conclusions are as follows:(1) It has obvious annual variations of Hadley circulation in WPWP region.Theposition of Hadley circulation is northwardly except for winter,it’s southernmost inwinter but in summer it’s northernmost, definitely,it has close connections withseasonal changes of ITCZ(intertropical convergence zone).It is different from globalHadley circulation that both northern and southern branch of Hadley circulation mustbe taken into consideration in WPWP region.(2) There exists significant interannual variations in Hadley circulation of WPWPregion and they are mainly reflected in intensity and position and it has interdecadalvariations in spring at the same time.(3) PC1in EOF of anomaly Hadley circulation can mainly characterize interannualvariation of each season’s Hadley circulation.PC2s reflect different information ofHadley circulation in each season,in winter,spring and summer,it reflects Hadleycirculation’s non-obvious displacement and in spring interdecadal variation can alsobe reflected, in autumn,it reflects intensity changes of Hadley circulation,as it’svariance contribution is small,it’s influence to intensity of Hadley circulation is small. (4) Interannual variations of Hadley circulation are well connected with ENSO signalsInterdecadal variation in spring is related with tropical SST,especially Indo-Pacificwarm pool’s warming in recent decades.Strengthened years of Hadley circulationmainly correspond with negative SST anomaly in Ni o region and weakened yearscorrespond with positive SST anomaly in winter，spring and autumn,this feature isjust opposite in summer.It is also found that Hadley circulation anomalies areasymmetric in strengthened and weakened years,this is probably related with ENSO’sasymmetry itself.(5) Interannual variations of Hadley circulation are also connected with Indian Ocean,it exhibits a basin-wide mode of Indian Ocean SST anomaly in winter and spring andan IOD mode in summer and autumn.(6) Lead-lag correlation between PC1and three key regions of SST anomaly index intropical ocean is analysed and it has different effects each season.Correlations withNi o region achieve the best over the same period,it reflects that responding ofatmosphere to ocean is a quick-process.Correlations with lead SST anomalies inwinter,spring and autumn are caused by the persistence of ENSO cycles,and as ENSOcycles can not last to summer normally,it has weak correlation with lead SSTanomalies in summer.Correlations with lag SST anomalies may probably due to thepersistence of ENSO cycles or positive feedback to the ocean.Interestingly,correlationbetween PC1and Indian Ocean lag behind that of Ni o region,so it is probably aresponding to ENSO cycles.Overall,ENSO is the strongest signal in interannualvariations of Hadley circulation.