The intensified impact of El Nino on late-summer precipitation over East Asia since the early 1990s

摘要

This study reveals a pronounced enhancement of the relationship between the winter El Nino and the following late-summer precipitation over East Asia since the early 1990s. Before the early 1990s, precipitation anomalies over East Asia were weak during the decaying phase of El Nino. In contrast, after the early 1990s, an evident dipole pattern of precipitation anomalies was observed, with centers of action over the central and southern parts of East Asia. The El Nino-induced atmospheric convection and anticyclonic anomalies over the western North Pacific (WNP) moved to the west after the early 1990s. Correspondingly, a Pacific-Japan-like atmospheric meridional wave pattern excited by the WNP anomalous convection shifted westward toward East Asia after the early 1990s. This resulted in an increased impact of the winter El Nino on the subsequent East Asian summer precipitation. The westward movement of WNP convection was related to the change in the El Nino decay time, which became shorter after the early 1990s. Specifically, sea surface temperature (SST) warming was still apparent in the equatorial eastern Pacific (EEP) before the early 1990s, while after the 1990s, the EEP was dominated by SST cooling, and significant SST warming could be observed in the maritime continent. The prominent SST warming in the maritime continent was accompanied by marked upward motion and excessive rainfall anomalies, which further contributed to the westward shift of the WNP convective center by modulating the local Hadley circulation. Further analysis indicated that the strengthening of El Nino-induced SST anomalies in the Indian Ocean might have partly contributed to the rapid decline of the El Nino events after the early 1990s.