Circulation Pattern and Moisture Transport for Summertime Persistent Heavy Precipitation in Eastern China

Based on daily precipitation data collected at 502 gauge stations in China during 1957-2011, regional-persistent heavy precipitation is defined to be the precipitation with regional mean precipitation larger than one standard deviation for five consecutive days. In total there are 74 regional-persistent heavy precipitation events in the Yangtze River basin, North China, and Northeast China in the summer (June to August). The main circulation pattern and moisture transport corresponding to the regional-persistent heavy precipitation events in the Yangtze River basin and North China are analyzed. The results show that the blocking high in the middle and high latitudes of Eurasia is the main circulation pattern for the regional-persistent heavy precipitation. The blocking high in the 500-hPa geopotential height field appeared in 86% of the heavy precipitation events. The main blocking patterns for heavy precipitation in the Yangtze River basin are central-blocking (there is a ridge near the Baikal Lake) and double-blocking (there are ridges near the Ural Mountains and the Okhotsk Sea at the same time). For heavy precipitation in North China, the main circulation pattern is central-blocking. The moisture transport from the tropical ocean to the regions of heavy precipitation is vital. For the Yangtze River basin, the moisture is largely from the Indian Ocean-Bay of Bangal-South China Sea. For North China, in addition to the moisture transport from the Indian Ocean-Bay of Bangal-South China Sea, moisture from the western North Pacific is also important. There is an anticyclonic center in the region to the north of the Philippines, which is favorable for abnormal moisture transport from the South China Sea to the Yangtze River basin. Corresponding to the anticyclonic center, the western North Pacific subtropical high at the 500 hPa strengthens. For the heavy precipitation in North China, the anticyclonic center favorable for abnormal moisture transport is located at the Bohai Sea-Korean Peninsula, and more moisture is pulled from the South China Sea and the western North Pacific. The positive geopotential height anomalies in the Bohai Sea-Korean Peninsula at 500 hPa are important for persistent heavy precipitation in North China. One common feature for the heavy precipitation in the Yangtze River basin and North China is the deep upward movement or divergence at upper levels and convergence at lower levels. There is no obvious difference in the moisture transport between central-blocking and double-blocking circulation patterns for heavy precipitation over the Yangtze River basin. However, the difference in upward movement determines the difference in precipitation location.