Influence of the tropical Pacific east-west thermal contrast on the autumn precipitation in South China

Abstract

Analysis of observational and reanalysis data shows that the autumn precipitation in South China is closely related to the east-west sea surface temperature (SST) contrast in the tropical Pacific. An east-west contrast (EWC) index, defined as the difference of the normalized area-averaged SST between the tropical eastern Pacific (150 ∘ W-90 ∘ W, 5 ∘ S-5 ∘ N) and the tropical western Pacific (WP; 110 ∘ E-180 ∘ E, 5 ∘ S-5 ∘ N), is proposed to delineate this feature. When the EWC index is positive, the tropical eastern (western) Pacific is warmer (colder) than normal. It would cause significant southerly wind anomalies from the Indochina Peninsula to eastern China, leading to enhanced water vapour convergence and anomalous ascending motion over South China. Therefore, enhanced autumn precipitation is observed in South China. Further analysis suggests that the SST of the tropical WP dominates the lower-tropospheric meridional wind and the resultant water vapour transport and convergence over subtropical East Asia, and that the SST of both the tropical eastern and the tropical WP contributes to the anomalous ascending motions over South China. These results highlight the combined effects of tropical eastern and WP on the autumn precipitation in South China and specifically emphasize the role of tropical WP SST. Given the performance of the EWC index in describing the autumn precipitation as well as the leading time and the persistence of the EWC index, it could be used as a good indicator in the monitoring and prediction of the autumn precipitation in South China, which is demonstrated by a simple statistical prediction model.