Role of off-equatorial SST in El Nino teleconnection to East Asia during El Nino decaying spring

摘要

Observational evidences are presented to show significant differences in Pacific-East Asian (PEA) teleconnections during the El Nino decaying period depending on the northern off-equatorial sea surface temperature (SST) conditions. On the basis of the northern off-equatorial central Pacific SST (NOCP) index, we separate El Nino events into two groups. Distinctive differences are observed between the two groups not only in tropical features but also in mid-latitude teleconnections. In particular, the NOCP index is closely related to the strength of the local feedback between the SST anomalies and the anticyclonic flow over the western North Pacific (WNP) during the ensuing spring of the El Nino events. Because the WNP anticyclone tends to persist until boreal spring in the case of negative NOCP, diabatic cooling due to the reduced precipitation over the WNP induces anticyclonic flow over the Kuroshio extension region via a Rossby wave response, which leads to warm and wet conditions over East Asia. However, because the WNP anticyclone decays early in the case of positive NOCP, cyclonic circulation exists over the North Pacific, which leads to cold and dry conditions over East Asia. Consequently, the maintenance of the WNP anticyclone during the El Nino decaying period may explain the discrepancy in the PEA teleconnections in various types of El Nino. Accordingly, the NOCP index could be a possible predictor for boreal spring climate conditions over East Asia.