A possible mechanism for the occurrence of wintertime extreme precipitation events over South China

Abstract

This study examines the formation of circulation patterns favorable to wintertime extreme precipitation events over South China between 1979 and 2013. During these extreme precipitation events, a barotropic wave train having seven centers of action was observed to extend from the Arabian Sea to the west coast of the North American continent with a maximum amplitude at 300 hPa. A center of action located over South China, comprised of cyclonic anomalies, favored powerful updrafts and large-scale moisture convergence over South China. About 77% of wintertime extreme precipitation events in South China were preceded by European blocking events. The formation mechanism for the 141 precipitation events with pre-existing European blocking highs is presented. Rossby wave energy propagation associated with the positive phase of circumglobal teleconnection enabled the European blocking event with a lead time of $\sim$10 days to generate cyclonic anomalies over South China. Moreover, significant warm anomalies were present over South China before the onset of these blocking-related extreme precipitation events. Increases in atmospheric moisture holding capacity associated with these warm anomalies enabled a buildup of precipitable water via moisture fluxes into South China through the western and southern boundaries. Onset of the extreme precipitation events was then triggered by the intrusion of cold temperature anomalies from the north, which lifted warm moist air upward from the surface and lowered the moisture holding capacity, producing large amounts of precipitation.