资源环境科技发展态势分析平台

This study investigates the transition from East Asian winter monsoon (EAWM) to following summer monsoon (EASM) under two types of El Nino and La Nina events. A robust out-of-phase transition from weak EAWM to strong EASM is related to El Nino events, which is more distinct in eastern Pacific (EP) El Nino than that in central Pacific (CP) El Nino due to the stronger and wider western North Pacific (WNP) anticyclone (WNPAC) as a persistent atmospheric bridge. The WNPAC differences result from the combined impacts of the warming over northern Indian Ocean (NIO) remotely, the dipolar sea surface temperature (SST) anomalies and the anomalous sinking motion over WNP locally. In terms of La Nina, the out-of-phase strong EAWM to weak EASM transition exists only for CP La Nina. Moreover, this connection is weaker compared to that for El Nino events because of a weaker WNP cyclone (WNPC). Conversely, when EP La Nina occurs, an in-phase transition is detected with a strong EAWM evolving into a strong EASM due to the emergence of WNPAC in summer. For CP and EP La Nina, the cooling SST anomalies over NIO and WNP play opposite roles in affecting WNP summertime circulation anomalies. Observational and model results suggest that the WNPC (WNPAC) is dominated by remote (local) cooling in NIO (WNP) in the summer following CP (EP) La Nina. In addition, the local rising (sinking) flow also contributes to the WNPC (WNPAC) associated with CP (EP) La Nina.