Spatiotemporal characteristics of summer rainstorm days in eastern China and their relationships with the atmospheric circulation and SST

By using the NCEP/NCAR reanalysis datasets, the NOAA SST datasets and Chinese 387-station daily precipitation data over eastern China for the period of 1961-2010, the spatiotemporal characteristics of rainstorm days during summer and their relationships with the atmospheric circulation and SST are studied. It is found that the summer rainstorm days over eastern China experience three interdecadal variation processes in the recent 50 years. According to the EOF and cluster analysis, the summer rainstorm days over eastern China are divided into six distribution patterns, namely the Bohai Sea pattern, north pattern, Huaihe River pattern, Yangtze River pattern, south pattern, and both branches pattern. The relationships between the six distribution patterns and the atmospheric circulation show that the summer rainstorm days are closely related to the East Asian summer monsoon. The Bohai Sea pattern and the north pattern correspond to the monsoon with its position by north, while the Huaihe River pattern and Yangtze River pattern correspond to the monsoon with its position by south, and the south pattern corresponds to a weak monsoon with its pisition even souther. When the both branches pattern occurs, the monsoon is strong, and affects most parts of eastern China. The relationships of the different distribution patterns with water vapor transport characteristics show that moisture transport is closely related to an anticyclonic circulation anomaly in the western Pacific with more available moisture. The relationships of the different distribution patterns with SST show that the Bohai Sea pattern and the north pattern occur more likely in the La Nia development or maintenance period, the Huaihe River pattern and Yangtze River pattern occur more likely in the El Nio maintenance or decay period, the south pattern occurs in the El Nio development period. While the both branches pattern occurs, the Pacific and most of the northern Indian Ocean show a cold state and a significant land-sea thermal difference.