The South China Sea (SCS) serves as a medium in the influence of tropical Indo-Pacific on East Asian climate. The tropical Indo-Pacific sea surface temperature anomaly (SSTA) can modulate circulation and climate over the SCS and Philippine Sea, and then affect climate of continental China. The onset of SCS summer monsoon usually occurs in mid-May, which signifies the transition from spring to summer in East Asia. It also indicates the beginning of rainy season in eastern China, which is a key factor in summer short-term climate prediction. Therefore, an improved understanding of precipitation and circulation variability over the SCS during spring-to-summer transition and influences of SSTAs in key regions may greatly help raise the skill of short term climate prediction in China.

The studies of Drs. HU Wenting, WU Renguang and LIU Yong from the Institute of Atmospheric Physics (IAP) showed that SCS rainfall anomalies are influenced by SST anomalies in the equatorial Pacific (EP), tropical Indian Ocean (TIO), and western North Pacific (WNP) during spring-to-summer transition (April-May-June; AMJ).

Their research revealed the importance of the configuration of SSTAs among the above three regions. Both cross equatorial flows induced by negative SSTA in the southwestern TIO and Walker circulation forced by negative EP SSTA contribute to enhanced convection over the SCS and the surrounding regions, with additional contribution from positive WNP SSTA via a Rossby wave-type response.

Through model sensitivity tests of different configurations of SSTAs, they confirmed the importance of combined influences of SSTAs on SCS precipitation variability, which is different from the previous studies that only consider individual region SSTA's impact.

On the basis of this, HU and WU also evaluated the capacity of 23 IPCC CMIP5 model in the relationship between SCS precipitation variability and tropical Indo-Pacific SSTAs during spring-to-summer transition. They found that the tropical Indo-Pacific SST anomaly pattern is important to produce the SCS precipitation variability properly by models. Furthermore, excessive local/regional SST anomaly forcing may disrupt the relation of the SCS precipitation variability to the tropical Indo-Pacific SST anomaly.

This series of research is published in Journal of Climate and Advances in Atmospheric Sciences.

Distributions of correlation coefficient of SST (shading) with respect to the time series of the leading mode of precipitation anomalies in April-May-June. The three rectangular boxes denote the key SST regions. (Image by IAP)