Cooperation of High- and Low-Latitudes Wave Trains in the Occurrence of Extreme Winter Precipitation over South China

Using the ERA-Interim reanalysis data and daily precipitation observation from 756 stations over China, the extreme winter precipitation over South China during 1979–2015 are identified and classified into five groups according to their spatial distribution via K-means clustering method, i.e., extreme precipitation occurs over the Yangtze River valley, central South China, southeastern South China, Huaihe River valley, and Southwest China. To disclose the causes of the widespread extreme winter precipitation over South China, the extreme precipitation with an eastward migration from Southwest China to coastal Southeast China has been further analyzed by comparing with that occurring locally over Southwest China. Results show that the main differences in the trigger and maintenance mechanisms of the extreme winter precipitation between the local and eastward migrating cases are the conflict between the warm and moist advection by the India–Burma trough and the intensity of cold air activity. For local cases, the active cold air activity inhibits the development of the India–Burma trough, resulting in the constraint of extreme precipitation over Southwest China. On the contrary, the warm and moist advection by the India–Burma trough moves eastward continuously in the eastward migration cases along with the weak cold air activity. The cooperation of the high-latitude wave train and South Asian jet wave train is crucial to the conflict between cold air activity and warm advection. When these two wave trains develop synchronously, the cold air activity over South China will be strong, and the warm advection from the Bay of Bengal will be confined over Southwest China, so does the resulting precipitation. However, when the high-latitude wave train developed ahead of the South Asian jet wave train and the cold air activity is weak when the India–Burma trough is enhanced by the South Asian jet wave train, the warm advection from the Bay of Bengal could move eastward continuously, resulting in the eastward migration of precipitation from Southwest China to coastal Southeast China.