Impact of Atlantic sea surface temperature anomalies on the summer climate in the western North Pacific during 1997-1998

Abstract

The summers of 1997 and 1998 were characterized by large anomalous atmospheric circulations in the tropical western Pacific, which in turn were associated with anomalous atmospheric circulation and precipitation in the adjacent areas. We use an atmospheric general circulation model to investigate the role of sea surface temperatures (SSTs) on the anomalous atmospheric circulations and associated precipitation in the tropics in these two summers. It is found that the circulation and rainfall anomalies are well reproduced when the model is forced with the observed global SSTs. A further experiment is performed to investigate the role of the SST anomalies in the Atlantic. In summer 1997, the Atlantic SST anomalies, compared with the SST anomalies outside the Atlantic, play a secondary role in influencing the circulation and rainfall anomalies in the tropical Indian Ocean and Pacific. By contrast, it shows that the SST anomalies in the Atlantic play a comparable role to those outside the Atlantic in influencing the circulation and rainfall anomalies in the remote tropics in summer 1998. In this summer, equatorial stationary waves, similar to a Kelvin wave and a Rossby wave, are clearly illustrated by the results implied by the Atlantic SST anomalies. The eastward equatorial stationary wave extends into the tropical western Pacific, and suppresses the atmospheric convection in the intertropical convergence zone in the Indian Ocean and Pacific. The evidence presented here for the role of Atlantic Ocean conditions on summer climates suggests that attention should be paid to accurate simulation of the Atlantic Ocean state as well as the states of the Pacific and Indian oceans in developing a seasonal forecasting system.