“21·7”河南特大暴雨过程的维持机制

Maintenance Mechanism of the Extremely Severe Torrential Rain Process in Henan Province in July 2021

利用地面观测站降水观测数据、CRA再分析数据、NCEP再分析数据,采用天气分析与诊断的方法,研究了“21·7”河南特大暴雨过程的维持机制。研究结果表明:本次过程有暴雨持续时间长、累积雨量大的特点。在过程期间,河南省对流层中、低层受低压系统控制和切变线的影响。台风稳定少动,环流形式难以调整,过程得以维持。在副高南侧和“烟花”北侧有一条强东南风速带,将西北太平洋上的水汽不断输送至内陆,为“21·7”河南特大暴雨过程提供了充沛的水汽;河南省上空低层辐合、高层辐散,在大气的“抽吸”作用下产生了强烈的上升运动,为此次过程提供了有利的动力条件;河南省西部山地丘陵地形的抬升作用,对强降水起到促进作用;对流层低层为上冷下暖的不稳定层结,为暴雨的发生、发展提供了有利的对流不稳定条件。湿位涡的分析表明,925 hPa上湿位涡对降水的落区和层结状况有指示作用。“列车效应”对此次强降水过程具有重要的影响。

By adopting the synoptic analysis and diagnosis methods as well as the precipitation data from meteorological observation stations,the CRA reanalysis data and the NCEP reanalysis data,we investigate the maintenance mechanism of the extremely severe torrential rain that happened in Henan Province in July 2021.The results show that this process was characterized by a long duration and high amount of accumulated precipitation.During the process,the middle and lower layers of troposphere over Henan Province were controlled by the low-pressure system and the cold and warm shear lines.The Typhoon“IN-FA”was stable and less moving,resulting in the less adjustment of circulation and the maintenance of the process.Between the south edge of the subtropical high and the north edge of Typhoon“IN-FA”,there was a strong southeasterly wind belt,which continuously transported the water vapor from Northwest Pacific to the inland areas,providing sufficient moisture to the extremely severe torrential rain in Henan Province in July 2021.The convergence at the lower level and divergence at the upper level over Henan Province produced a strong upward movement under the“suction”action of the atmosphere,which offered favorable dynamic conditions for this process.In addition,the topographic lifting effect of the hills and mountains in western Henan promoted the extremely severe rainfall.In the lower troposphere,the pseudo-equivalent potential temperature was high at low level but low at high level,becoming favorable convectional instability conditions for the occurrence of the severe rainstorm.The analysis of moist potential vorticity(MPV) shows that the MPV at 925 hPa had a good indicative significance for the rain falling area and unstable stratification.Meanwhile,the train effect also had an important impact on the occurrence and maintenance of this severe precipitation process.