Possible role of Southern Hemispheric sea ice in the variability of West China autumn rain

Abstract

West China Autumn Rain (WCAR), the last rainy season in China associated with the East Asian summer monsoon, is prone to flooding and secondary disasters and has profound impacts on the economic society. Thus, it is of great interest to understand its variability. Through an analysis with gridded rainfall data and reanalysis data, this study reveals that the variability of WCAR is positively correlated to the boreal summer (austral winter) sea ice concentration (SIC) in the Southern Indian and Pacific Ocean basins. Such a relationship is supported by the SIC-related changes in atmospheric circulations and water vapor transport. Corresponding to a high summer SIC, both the Lake Balkhash trough and the Asian low pressure are deepened, the East Asian jet shifts northward, and the water vapor transport to West China is enhanced during the boreal autumn, providing a favorable background for the increase of WCAR, and vice versa. The potential mechanism of how the boreal summer SIC affects the autumn atmospheric situation is further investigated. Results show that the atmospheric circulation in the high latitudes of the Southern Hemisphere possesses a seasonal persistence from the boreal summer to autumn due to the sea ice persistence. Thus, the boreal summer SIC-related anomalies in the upper-tropospheric winds over the Southern Indian and Pacific Ocean basins can persist to the following autumn and subsequently exert substantial influences on the Eurasian atmospheric circulations via two meridional teleconnections. The counterpart in the lower troposphere contributes to the water vapor transport toward West China. Certainly, this candidate mechanism is a preliminary explanation, and other processes may also act in their linkage.