Impact of La Niña on the Following-Summer East Asian Precipitation through Intermediate SST Anomalies

This study investigates the impact of boreal winter-peaked La Niña on the following summer precipitation in East Asia through intermediate SST (Sea-Surface Temperature) anomalies playing the role of relay, in observation and numerical models. There are widespread dry conditions in both North and South China, and wet conditions in coastal areas of central and eastern China. Such a pattern is mainly attributed to an anomalous low pressure over the western tropical Pacific and an anomalous anticyclone over Northeast Asia. It is found that the delayed impact of La Niña on East Asian climate is operated through intermediate SST anomaliesthe Z-shape cold SST anomalies in the tropical-North Pacific. There might be three ways for the SST anomalies to operate. Firstly, they produce tropical atmospheric perturbations that can penetrate into the subtropical jet through the westerly trough over the northeast subtropical Pacific, the wave train being then excited along the jet. Secondly, perturbations created through the monsoon trough over the western Pacific can directly stimulate northward propagating Rossby waves along the East Asian coast, mainly at low level. And thirdly, perturbations over the tropical Atlantic-Northwest Africa can also trigger downstream propagating waves along the subtropical jet. The observation effects of the intermediate SST anomalies and their possible impact mechanisms on atmospheric circulation are largely reproduced within numerical simulations performed with the Community Earth System Model