Basin shift of tropical convection impact on the Western China Autumn Rainfall interannual variability

The Western China Autumn Rainfall (WCAR) is a special and important climate phenomenon in China during September and October. This study elucidated a notable decadal change in the influence of the tropical convection across different basins on the interannual variation of WCAR around the late 1980s. Prior to the late 1980s, WCAR exhibited a robust connection with tropical convection over the Indian and Pacific Oceans, with a significant correlation coefficient of 0.43 (p < 0.05). However, this robust linkage subsequently broken down. Instead, a significant correlation materialized between WCAR and the tropical North Atlantic convection post the late 1980s, featuring a substantial correlation coefficient of 0.47 (p < 0.01). Further analysis uncovered that the shift in tropical convection influencing WCAR circa the late 1980s was predominantly attributed to a shift in the mean state of tropical sea surface temperature (SST). The tropical inhomogeneous warming SST pattern led to a decrease in low-level specific humidity within the central Pacific Ocean and an elevation in middle-level specific humidity in the Indian Ocean, due to vertical motion induced by SST anomalies. This alteration results in a more stable atmosphere within these two regions. Conversely, SST warming in the tropical North Atlantic increased local low-level specific humidity, fostering atmospheric instability. These changes in the tropical mean state intensified (diminished) the convection response in the tropical North Atlantic Ocean (central Pacific and Indian Oceans) to the SST in the tropical eastern Pacific. As a result, tropical convection in the North Atlantic overshadowed that in the central Pacific and Indian Oceans after the late 1980s, ultimately prompting a basin shift in the driving force of tropical convection for the WCAR from the Indo-Pacific to the Atlantic region.