Intensified impact of the central Pacific warming on the monsoon trough over the western North Pacific since 1984

Abstract

The present study investigates the impact of the central Pacific warming (CPW) on the monsoon trough (MT) over the western North Pacific (WNP) during July–November of 1948–2015. It is shown that the relationship of the CPW with the MT experienced a remarkable change around 1984. Compared with 1948–1983, the MT was significantly stronger and extended eastward during the CPW events from 1984 to 2015. This relationship can be explained by the increase in the sea surface temperature (SST) in the tropical Pacific around 1984, especially over the central Pacific. Before 1984, the significantly cool ocean in the tropical western Pacific with the weakly warm ocean in the tropical central Pacific reduced the MT development and the eastward shift over the WNP during the CPW events. However, the enhanced low‐level westerlies and cyclonic vorticity induced by the warmer ocean surface in the tropical central Pacific led to the strengthening and further eastward extension of the MT during the CPW events after 1984. Following the eastward extension of the MT, the enhanced 850‐hPa positive vorticity, intensified 200‐hPa divergence, increased relative humidity, and reduced vertical wind shear tend to shift eastward during the CPW events after 1984, which favor tropical cyclone (TC) genesis. The results show more TCs after 1984 over the WNP during the CPW events than before 1984.