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

This study investigates the impact of boreal winter-peaked La Nina on the following-summer precipitation in East Asia through intermediate sea surface temperature (SST) anomalies playing the role of relay in observation and nu-merical 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 andan anomalous anticyclone over northeast Asia. It is found that the delayed impact of La Nina on the East Asian climate is operated through intermediate SST anomalies}the Z-shape cold SST anomalies in the tropical North Pacific. There might be three ways for the SST anomalies to operate. First, they produce tropical atmospheric perturbations that can penetrate into the subtropical jet through the westerly trough over the northeast subtropical Pacific, the wave train be-ing then excited along the jet. Second, 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 third, 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.

Automated summary

This study investigates the influence of boreal winter-peaked La Nina on the precipitation in East Asia during the following summer. It is found that the impact is mediated through intermediate sea surface temperature (SST) anomalies, particularly Z-shaped cold SST anomalies in the tropical North Pacific. The SST anomalies can operate through three main mechanisms: tropical atmospheric perturbations, perturbations created through the monsoon trough, and perturbations over the tropical Atlantic-northwest Africa.