Analysis of Summer Extreme Precipitation Typology and Associated Circulation Anomalies in the Jianghuai Region

Enhancing the understanding of the characteristics and causes of extreme precipitation anomalies in the Jianghuai region is crucial for comprehending regional climate change patterns and improving disaster prevention and mitigation capabilities. Based on gauged precipitation data by China Meteorological Administration and NCEP/NCAR reanalysis data, this study analyzes the circulation configuration and evolutionary characteristics during different types of extreme precipitation events through percentile and K-means clustering methods,atmospheric dynamic-thermodynamic diagnostics technique.. The research indicates that extreme precipitation in the Jianghuai region can be categorized into four types according to the location of precipitation center: C-Type, N-Type, S-Type, and E-Type. The first three types concentrate during periods associated with the seasonal northward shift of the rain belt, while the fourth type is more scattered. During the occurrence of the four types of extreme precipitation, the main precipitation zones are located below the divergence area in the upper troposphere where is between the strong South Asian High and the westerly jet stream, with increased vertical velocity, enhanced temperature gradients in the upper and middle troposphere, greater meridional circulation in mid-high latitudes, intensified subtropical high, and enhanced water vapor transport from oceanic regions. The first three types of precipitation are different from the fourth type in East Asian teleconnection pattern (EAP), low-level jet, and water vapor transport. During the first three types, EAP is more typical, and low-level jet is obvious. The water vapor transport mainly comes from the Western Pacific and South China Sea. The temperature gradient in the upper troposphere is a dipole anomaly structure with colder temperatures to the north and warmer temperatures to the south. When E-type occurs, there is atypical EAP, no obvious low-level jet, obvious easterly water vapor transport along the East Asian coast, and only a unipolar warm center in the upper troposphere. The low-frequency evolution of thermal-dynamic conditions for the four extreme precipitation types differs as follows: C-Type precipitation occurs during the northeastward movement of subtropical high and the downward propagation of the EAP wave train; in the N-type case, the warm center of the near-surface temperature moves southward from the Yangtze-Yellow River to the south of the Yangtze River, and the temperature over the Jianghuai region is cold up and warm down; S-Type occurs during the southwestward movement of subtropical high, with the temperature gradient at 300hPa transitioning from cold north and warm south to warm north and cold south, and positive height values dominating throughout the entire troposphere; E-Type occurs during the northeastward movement followed by the southwestward movement of subtropical high, with convective activity strengthening from low to middle latitudes, and almost entirely warm areas at 200hPa and below. Further analysis demonstrates that changes of subtropical high and thermal effects have better indicative significance for low-frequency prediction of extreme precipitation events.