Cross-seasonal Connection of Convection over the Western Tropical Indian Ocean with Winter Climate in Southern China and the Bridging Role of the Tibetan Plateau

Abstract Concurrent cold and wet winter conditions in southern China may cause human discomfort and give rise to freezing rain and snow disasters. This work examines the cross-seasonal connection of autumn convection over the western tropical Indian Ocean (WTIO) with the winter climate in southern China based on both statistical analysis and numerical experiments. Result shows that the anomalous WTIO convection in autumn can persist into winter, which continuously excites a wave train propagating northeastward from the Arabian Sea to southern China. The subtropical westerlies are strengthened to the north of the anomalous Arabian Sea anticyclone and are conducive to the widespread cooling in subtropical Eurasia, including the Tibetan Plateau (TP). The anomalous cyclone over the TP and southern China favors enhanced precipitation in situ. Accordingly, the TP snow cover increases significantly since early winter and persists into the following winter and spring due to the snow-albedo effect. The cooling effect of the TP snow cover helps to intensify the cyclone over southern China and the anticyclone over the western North Pacific. Combined with the deepened India-Myanmar trough induced by WTIO convection, the anomalous southerly wind transports more water vapor from the ocean to southern China, leading to wetter winter in the region. Result of the linear baroclinic model experiments further verifies that the WTIO heating can trigger a wave train propagating to the TP, and the cooling effect of the TP helps to maintain and extend the influence of WTIO convection from autumn to winter, affecting southern China.