Regulation of the subseasonal variability of winter rainfall in South China by the diversity of El Niño Southern Oscillation

Abstract

Winter precipitation over South China tends to increase with enhancement of the 10–30-day intraseasonal oscillation (ISO) during El Nino Southern Oscillation (ENSO) events from 1981 to 2017. This study shows that, in contrast with central Pacific El Nino and La Nina events, the 10–30-day ISO of rainfall particularly intensify during eastern Pacific (EP) El Nino events. The seasonal evolution of the anomalous circulation, indicated as the annual cycle (AC), bridges the slow-varying ENSO and the transient 10–30-day ISO of winter rainfall over South China. As to the AC component, the EP El Nino events not only enhance the Philippine Sea anticyclone to provide a wetter low-level background over South China, but develop the mid-latitude cyclone and westerly winds in the upper-level over East Asia by changing tropical convection. The moisture over South China further increases due to the low-level wind convergence on a 10–30-day timescale. In the upper troposphere, the AC component of the anomalous westerly redistributes the 10–30-day relative vorticity by modulating the subseasonal mid-latitude wave train to strengthen the positive vorticity advection and ascending motion over South China. Their collaboration amplifies the subseasonal variance of winter precipitation in situ. By contrast, the AC component of the upper level circulation at mid-latitudes is not well organized in other ENSO subsets, corresponding to their lack of influence on the ISO variability of rainfall over South China.