Anomalous circulation patterns in association with two types of regional daily precipitation extremes over South China from July to October

Using daily precipitation data collected at 753 stations in China and from the Meteorological Information Comprehensive Analysis and Process System (MICAPS), the Southwest Pacific Ocean Tropical Cyclone (TC) optimal path data from the Tokyo Typhoon Center in Japan, and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis, the statistical characteristics of regional mean daily precipitation extreme (RDPE) events and circulation anomalies in South China were studied. Depending on whether the occurrence of a given RDPE event is affected by TC, the RDPEs are classified into two categories, i.e., TCfree-RDPE and TCaff-RDPE events. The TCaff-RDPE events account for about 42% of the total RDPEs and mainly occur in late August, while the TCfree-RDPE events frequently occur in July. When TCfree-RDPE events occur, South China is controlled by abnormal cyclonic circulations, and the warm and moist airflow from the western Pacific region and the South China Sea merge with the cold air from the north in this region, inducing a long narrow zone of water vapor convergence and significant and strong ascending motion, which are responsible for the occurrence and maintenance of TCfree-RDPE events. Simultaneously, the wave energy propagates from the northeastern side of the Tibetan Plateau and the Hexi Corridor region to South China and converges in this area, which favors the development and maintenance of perturbation over South China. When TCaff-RDPE events occur, the southern part of China is dominated by TC-related strong anomalous cyclonic circulations. The warm, moist air mass is transported into this area from the Bay of Bengal, the western Pacific and the South China Sea, leading to large amounts of latent heat release and strong ascending motion over South China. These results are helpful for better understanding and predicting the occurrence of regional extreme precipitation events in South China.