河南“21·7”特大暴雨过程中尺度低空急流和低涡的演变特征及成因分析

Evolution Characteristics and Formation Analysis of Mesoscale Low-Level Jet and Vortex in Henan Province During the July 2021 Severe Torrential Rain

利用地面常规气象资料、区域气象站逐小时观测数据、ERA5再分析资料,分析了2021年7月19—20日河南省特大暴雨过程中尺度低空急流以及中尺度低涡的发展演变特征及其形成机理。研究表明:此次特大暴雨天气过程发生在弱天气尺度系统强迫的背景下,中尺度低空急流以及中尺度低涡是其直接影响系统。低空急流的建立和发展与降水的发生和增强同步,而中尺度低涡出现在低空急流建立后约10 h,随着低涡发展增强,低空急流强烈发展;西太平洋副热带高压的增强西伸与河套弱低压东移造成的地转风加大是低空急流形成的重要原因;偏北变压风的贡献主要是对风向的改变,使得低空急流以偏东急流为主;低空急流引起的对流层低层水平辐合及扭转是对流层中低层低涡发展的主要原因,对流层中层垂直上升运动造成的涡度垂直平流是对流层中层涡度增强的主要原因。降雨引起的对流层中层凝结潜热加热是低涡发展增强的又一重要原因。

Based on surface conventional meteorological data,hourly observation data from regional meteorological stations and ERA5 reanalysis data,the evolution characteristics and formation mechanism of mesoscale low-level jet and mesoscale vortex during the severe torrential rain process in Henan Province from 19 to 20 July 2021 are analyzed.The results show that the process of this extreme precipitation was directly related to the formation and development of the low-level jet and mesoscale vortex.The establishment and development of low-level jet was synchronized with the occurrence and enhancement of precipitation,while the mesoscale vortex appeared about 10 hours later than the establishment of low-level jet,and the low-level jet developed strongly with the enhancement of low-level vortex development.The strengthening and westward extension of the western Pacific subtropical high and eastward movement of the low pressure on the southeast of the Hetao Area increased the geostrophic wind,which was the main reason for the formation of the low-level jet.The existence of allobaric wind was the main reason for the easterly jet.The horizontal convergence and torsion in the lower troposphere caused by low-level jet were the main reasons for the development of mesoscale vortex in the middle and lower troposphere.The vertical vorticity advection caused by the vertical motion was the main reason for the enhancement of the voriticy in the middle troposphere.The condensation latent heat in the middle troposphere was another important reason for the vortex development.