Association analysis of synchronous events of summer extreme precipitation in area south of Yangtze River

Based on the daily precipitation data of meteorological stations and NCEP/NCAR reanalysis data from 1970 to 2019, the spatial characteristics of synchronous extreme precipitation events in summer and their correlation with atmosheric circulation were analyzed by aid of the event synchronization method, Louvain algorithm and SOM-K clustering method. The results show that :(1) the synchronous extreme precipitation events in Region Jiangnan have a large correlation range in the central region, and play a major role in the event propagation, that is, providing a channel for water vapor transport from the Indian Ocean and the south China sea. (2) Except for the coastal type, the sites with high spatial consistency showed zonal arrangement and distribution, which could be subdivided into southern type, central type and northern type. (3) the regional extreme precipitation formation of the low-level geopotential height field is divided into six categories, which shows a possible existence of visible approximate of dipole substructure; in terms of 500 hPa geopotential height in the east Asian continent at the middle and high latitude exists a large amplitude groove ridge; in area south of the Yangtze River more frequent low trough activities are observed; the western Pacific subtropical high is on average tilting towards west and south, making the east Asian summer monsoon a lot weaker; the convergence of airflow stays stably in the study area, forming regional extreme precipitation.