Influence of annual cycle on the local air-sea processes during El Nino events is investigated based on the Hadley Centre(HadISST1)sea surface temperature(SST)analysis data,10mwind data from the European Centre for Medium-Range Weather Forecasts(ECMWF)ERA-40reanalysis and the CMAP precipitation data.In the observation,SST anomalies associated with El Nino over the equatorial eastern Pacific are meridionally quasi-symmetric about the equator.However,corresponding atmospheric responses display a strong southward movement during the El Nino decaying phase.During the El Nino developing phase(largely before November),almost meridionally symmetric zonal wind and precipitation anomalies are observed over the equatorial central Pacific.After the El Nino peak month(about December),the equatorial westerly and precipitation anomalies shift rapidly southward with a center at about 5°S.Then the zonal wind anomalies stay there till the El Ninos termination.Meanwhile, negative precipitation and anticyclonic anomalies over the western Pacific shift northward.The inconsistence of the meridional movements of the El Nino SST anomalies and the associated atmospheric responses is mainly due to seasonally southward displacement of background warm SSTs along with the seasonal march of solar insolation.There is nonlinear relationship between convection and overall SST.That is,convective precipitation will be rapidly enhanced when total SST exceeds a certain threshold.Thus the corresponding convection anomalies are also displaced southward along with the southward shift of the SST and the zonal wind anomaly also appears south of the equator. In addition,the precipitation over northern hemisphere will be further suppressed due to the enhanced convection in southern hemisphere trough the meridional circulation,which can enhance the negative rainfall and anticyclone anomalies in the western Pacific and move northward.These observed analyses are supported by two experiments with and without considering the annual cycle.Southward shifts of the westerly anomalies and anticyclonic anomalies over the western North Pacific during the El Nino decaying phase are well simulated by the experiment with the annual cycle.However,these observed phenomena are not reproduced by the experiment without consideration of the annual cycle.Therefore,the annual cycle of climatological warm SSTs over the central Pacific plays a crucial role on the local atmospheric responses during the El Nino events.