关键词: 暴雨特征； 降水异常； 梅雨期； 大气环流； 2020年长江洪水； 长江流域

Abstract: Precipitation anomalies occurred in the Yangtze River Basin during major flood season (from June to August) in 2020. We collected daily precipitation data of 701 national stations in the Yangtze River from June to August of many years, conventional sounding data and the NCEP/NCAR reanalysis data to analyze characteristics and causes of this phenomenon. The results showed that: ① There were two obvious precipitation periods and three precipitation centers. The precipitation periods were from mid-June to mid-July and in mid-August. The precipitation centers were the middle and lower reaches of the Yangtze River, Poyang Lake basin，Jialing River and Minjiang River basin. ② During the major flood season, Meiyu period began early, ended late, and precipitation was heavy in the Yangtze River Basin. The rainstorms were characterized by high intensity, wide range and strong extreme, significant rainstorm stage distribution, and high overlapping degree of heavy rain areas in each stage. ③ From June to July, the middle and high latitudes of Eurasia were in a stable double-resistance pattern with two ridges and one trough. The position of the ridge of the Western Pacific Subtropical High (WPSH) had been abnormal for a long time, and failed to northward jump for many times. As a result, the shear line and Meiyu front remained near the Yangtze River for a long time. The southeast current from the South China Sea and the Pacific Ocean was extremely strong, in addition, the polar cold vortex and the upper air cold trough were active, which led to frequent rainstorms in the middle and lower reaches of the Yangtze River. ④ In August, the circulation situation of the middle and high latitudes in Eurasia transformed into two troughs and one ridge line. The Sichuan Basin was near the edge of WPSH. The warm and wet air that flowed from the bay of Bengal and the South China Sea was relatively strong. The influence of several southwest vortices and cold air, together with the help of topography and typhoon, led to the long duration and stable location of extreme heavy precipitation in Jialing River and Minjiang River basin in mid-August.

Key words: rainstorm characteristic; precipitation anomalies; Meiyu period; atmospheric circulation; Changjiang River Flood in 2020; Yangtze River Basin