Abstract:Based on the ERA-Interim reanalysis data from the European Center and CN05.1 gridded Precipitation observation data from the National Climate Center during the summer from June to August during 1979-2015, the Self-Organizing Maps (SOM) method is introduced to classify objectively sea level pressure fields over the Yangtze River Bain, and 25 surface synoptic patterns and their characteristics of evolution in the area is obtained. It's found that the stability and shift of synoptic patterns are related to the strength of the weather systems. The stronger high and low pressure system, the higher stagnation frequency of synoptic patterns, and the more stable synoptic patterns. On the contrary, the synoptic pattern is more unstable. Three systematic evolution paths associated with local precipitation are found on the basis of the SOM synoptic patterns transition probability. Among them, warm air force on the first path is strong and push the front northward with subtropical pacific high pressure northward, which brings Northern Yangtze River Rainfall Pattern (NYRP) mostly occurring in July. The second path reflects that the cold air forces spurs the southward of the front, resulting in Yangtze River Rainfall Pattern (YRP), which is likely to occur in June and July. Path three represents the influence of the typhoon movement to the precipitation in the Jiangnan region of lower reaches of the Yangtze River, which forms Southern Yangtze River Rainfall Pattern (SYRP) concentrated in August. In this study, the SOM method is used to classify the daily atmospheric circulation and capture the movement characteristics of the weather system related to the precipitation from the climate state, which reflects the advantages of the SOM method in simulating the evolution of the weather system.