The Indian Ocean's asymmetric effect on the coupling of the Northwest Pacific SST and anticyclone anomalies during its spring-summer transition after El Nino

摘要

By comparing different climatologies in El Nino decaying summer with regard to the presence of Indian Ocean Basin (IOB) warming, we studied the effect of IOB warming on the Northwest Pacific sea surface temperature (SST) anomalies and the coupling process with the surface wind. Zonal asymmetric coupling feedback in the west and east of the Northwest Pacific were caused by the asymmetric spring-summer transition of the background tropical atmospheric circulation. Although the westward wind anomaly caused by the remote effect of IOB warming is found in the whole Northwest Pacific, reversal of the mean background surface winds in the western part leads to negative wind-evaporation SST (WES), whereas sustained trade winds lead to positive WES in the eastern part. The east-west SST gradient resulting from this zonal asymmetric evolution of SST sets off more positive feedback that strengthens the local anticyclone easterly anomalies.