2020年夏季长江流域异常暴雨洪涝气象特征分析

Analysis of Meteorological Characteristics of Abnormal Rainstorm and Flood in the Yangtze River Basin during the Summer of 2020

摘要: 2020年夏季长江中下游经历了超级暴力梅和8月上游极端强降雨，造成长江流域降水异常偏多，发生了全流域性洪水。本文利用NCEP/NCAR再分析资料和常规气象水文观测资料，分析了2020年夏季长江流域严重洪涝期间的气象特征，大尺度的环流形势分析表明：西太平洋副热带高压、中高纬阻塞高压、孟加拉湾越赤道气流均较历史同期异常偏强，西太平洋副热带高压北跳早，长时间稳定维持在20˚~25˚N，且强度偏强，造成长江中下游梅雨期异常。中高纬度经向环流发展，阻高形势稳定强盛，冷涡活跃，有利于冷暖空气持续在长江流域交汇，雨带位置相对稳定。孟加拉湾越赤道气流较常年爆发早、强度强，造成南海夏季风爆发略偏早，强度偏强，为向长江流域发生致洪暴雨提供充足的水汽输送。另外由于大尺度环流经向性增大，大气斜压性增强，多低空急流、气旋性低涡系统以及切变系统的产生，也是2020年夏季降雨极端强的重要原因。

Abstract: The summer precipitation in the Yangtze River Basin in 2020 is more than normal; it experienced the super violent Meiyu period and the extreme rainfall process in the upper reaches of the Yangtze River in August. It caused the disaster flood of the whole Yangtze River Basin. Based on the NCEP-NCAR reanalysis data and the conventional meteorological and hydrological observation data, we analyzed the meteorological characteristics of severe rain and flood disasters in the Yangtze River Basin in the summer of 2020. The analysis of large-scale circulation patterns showed that the Western Pacific subtropical high, the blocking high covering the middle-high latitude and the cross-equatorial flow in the bay of Bengal were stronger than those in the same period in history. The Western Pacific subtropical high was jumped earlier to the north and maintains at 20˚~25˚N for a long time, and the intensity of subtropical high was stronger, causing the abnormal Meiyu period in the middle and lower reaches of the Yangtze River in 2020. With the development of meridional circulation in middle and high latitudes, the situation of blocking high was stable and strong, and the cold vortex was active, which was conducive to the continuous intersection of cold and warm air in the Yangtze River Basin, and the position of rain belt was relatively stable. The cross-equatorial flow in the Bay of Bengal broke out earlier and stronger than usual, which caused the South China Sea summer monsoon to break out earlier and stronger, and provided sufficient water vapor transport for the flood causing rainstorm in the Yangtze River Basin. In addition, due to the increase of meridional characteristics of large-scale circulation, baroclinic characteristics of atmosphere, and the production of low-level jet, cyclonic vortex system and shear system, it was also an important reason for the extremely strong rainfall in summer 2020.