2021年10月山西一次罕见持续性强降水过程物理机制分析

利用气象观测资料、NCEP/NCAR 1°×1°再分析资料以及GDAS资料,对2021年10月2-7日山西持续性强降水天气过程进行分析。结果表明：稳定的乌拉尔山低槽后部冷空气扩散,中纬度短波槽东移,与副热带高压外围西南暖湿气流持续交汇,同时高低空急流耦合形成强烈上升运动,低层切变线和地面辐合线稳定维持,及低层水汽不断输送并形成辐合,为持续性强降水的发生发展提供有利动力和水汽条件。此次强降水过程分为对流性降水和稳定性降水2个阶段,2阶段水汽输送通道的源地、路径、高度均有明显差异,但水汽输送贡献率均以对流层中低层山西南侧的水汽输送占主导地位。降水开始前,对流层中上层存在对称不稳定,大气可降水量明显跃增；对流性降水阶段,干空气不断入侵,对流不稳定快速建立与释放,对流层中低层水汽辐合区与强上升气流配合,导致山西出现强对流天气。地形的阻挡、抬升及地形收缩作用,对局地极端强降水具有增幅作用。

Analysis of the Physical Mechanism of a Persistent Heavy Rain Event in Shanxi Province in October 2021

A persistent heavy rainstorm occurred in Shanxi Province during 2- 7 October 2021 was analyzed based on the meteorological observation data, NCEP/NCAR 1°×1° reanalysis data and GDAS data. The results show that the cold air behind the stable Ural low trough and mid-latitude short wave trough diffused southward, and met with the southwest warm moist air outside the subtropical high. At the same time, the high and low jet coupled to a strong upward movement, the low-level shear line and the surface convergence line are maintained stably, and the low-level water vapor is transported continuously and forms convergence, providing favorable driving force and water vapor conditions for the occurrence and development of persistent heavy rainstorm. The heavy precipitation process was divided into two stages: convective precipitation and stable precipitation. The source, path and height of water vapor transport channels in the two stages were significantly different, but the contribution rate of water vapor transport was dominated by water vapor transport in the middle and lower troposphere from the southern side of Shanxi Province. Before the onset of precipitation, there was symmetric instability in the upper troposphere, and precipitable water jumped significantly. In the convective precipitation stage, dry air constantly invaded, convective instability was rapidly established and released, and the convergence area of water vapor in the middle and lower troposphere cooperated with strong updraft, resulting in strong convective weather in Shanxi Province. The blocking, uplift and contraction of the terrain have an increasing effect on the local extreme heavy precipitation.