长江中下游一次暖区极端致洪暴雨特征及天气学成因分析

基于多源观测资料和再分析资料,采用天气学诊断分析方法研究了2019年5月长江中下游地区发生的一次致洪暴雨的特征及主要成因。结果表明:该次极端致洪暴雨过程是在稳定的“西低东高”天气形势下,由持续时间长的短时强降水累积而成,具有明显的中尺度和阶段性特征。直接造成极端暴雨的中尺度对流系统在低空急流前沿不断新生东移,表现出明显的“列车效应”和准静止特点。过程中低空急流和超低空急流异常强盛,为极端暴雨提供了持续有利的水汽和对流不稳定条件,特别是整层高湿、较低的抬升凝结高度和较大暖云层厚度有利于提高降水效率,产生雨强较大的短时强降水;高低空急流耦合是强降水发生发展的重要动力机制,强垂直风切变区与暴雨落区有较好的对应。

Characteristics and synoptic causes of the extreme warm-region flood-causing rainfall over the middle-lower reaches of the Yangtze River

Based on the multi-source observation and reanalysis data, the characteristics and main causes of the flood-causing rainstorm in May, 2019 in the middle-lower reaches of the Yangtze River were studied by using the synoptic diagnostic analysis method. The results indicated that the extreme rainstorm with the characteristics of mesoscale and stage was formed by the accumulation of continuously short-time heavy precipitation under the stable "low in the west and high in the east" weather background. The mesoscale convective system directly causing the extreme rainstorm was constantly regenerated and moved eastward in the front of the low-level jet with obvious "train effect" and quasi-static features. Continuously favorable water vapor and convective instability were provided by theextremely strong low-level jet and ultra-low-level jet. In particular, the high humidity of the whole layer, low lifting condensation height and large warm cloud thickness were conducive to improving theprecipitation efficiency and producing the short-term heavy precipitation with high rain intensity. The high- and low-level jet coupling was an important dynamic mechanism for the occurrence and development of heavy rainfall, and the strong vertical wind shear area has a good correspondence with the heavy rainfall area.