山东地区一次夏季极端暴雨中尺度系统发展演变过程及机理分析

对2020年7月22日山东半岛一次极端暴雨天气过程开展观测分析,并利用中尺度模式WRF对此次局地降水过程进行了高分辨率数值模拟,对暴雨过程进行了天气背景和中尺度降雨的诊断。WRF模式较好地再现了此次极端暴雨过程,结果表明：此次极端暴雨过程短时降水强度大且局地性强,在时空上具有明显中尺度特征。降水发生在北抬副热带高压与华北低涡底部之间的西南气流中,强低涡与低空急流是影响此次降水的重要天气系统。西南急流为本次暴雨过程极端水汽的主要输送载体;在弱高空辐散场下,从地表延伸至500 hPa高空的深厚低涡是造成本次暴雨的主要影响因子,其时空演变特征与中尺度云团变化一致,与暴雨的发生直接相关。低涡、低空急流和副高之间的相互作用使低涡加强发展,低涡南部有暖湿气流入流,北部有干冷气流流入,比湿梯度基本呈现为自南向北递减分布,是典型的伴有低空急流的中尺度低涡流场分布;低涡辐合及其与副热带高压边缘强风速带的共同作用,导致强垂直运动发展并维持,是造成本次山东半岛极端暴雨的重要原因。

Evolution Process and Mechanism Analysis of the Mesoscale System of an Extreme Summer Rainstorm in Shandong Province;

The synoptic circulation pattern and mesoscale systems associated with the extreme torrential rain occurring in the Shandong Peninsula on 22 July 2020, are analyzed with conventional observational data and a high-resolution numerical simulation using the mesoscale model WRF. The simulation agreed well with the precipitation process. The results show that the rainstorm process is characterized by mesoscale features spatially and temporally, represented in its high intensity of short-term rainfall, severe locality, etc. Precipitation occurs in the southwest airflow between the subtropical north elevation and the bottom of a low vortex. Strong vortices and low-level jets are important weather systems that affect this precipitation. The southwest jet stream is the main carrier of extreme water vapor during this heavy precipitation. Under a high-level weak divergent field, the main influence of this rainstorm is the deep low vortex extending from the surface to the 500-hPa high altitude. Its temporal and spatial evolution characteristics are consistent with the mesoscale cloud cluster changes shown by the FY-2E hourly TBB data. This consistency is directly related to the occurrence of heavy rain. The interaction between the vortex, low-level jet, and subtropical high strengthens the development of the low vortex. There are warm, wet airflows from the north and cold, dry airflows from the south of the low vortex. The specific humidity gradient is roughly distributed from south to north, which is a typical flow field distribution of a vortex accompanied by a low-level jet. The convergence of the low vortex and its interaction with the strong wind speed belt at the edge of the subtropical high lead to the development and maintenance of strong vertical motion, thereby contributing to the persistence of extreme rainstorms. © 2023 Science Press. All rights reserved.