苏州“7.26”强飑线增强机制分析

Analysis of the Enhancement Mechanism of a Strong Squall Line in July 2022 in Suzhou

关键词:  飑线  后侧入流  冷池  太湖

Key words:  squall line  rear inflow  cold pool  Taihu Lake

摘要:

针对 2022 年 7 月 26 日发生在江苏南部的一次由强飑线引起的大范围极端雷暴大风天气，利用双偏振雷达、再分析数据、探空、地面自动站、风廓线、微波辐射计等资料分析产生飑线的天气形势背景和飑线在移过太湖附近突然增强的原因。(1) 低空急流向下传播形成超低空急流，增强的中层干冷空气卷入，随下沉气流到达地面形成出流，加强了地面辐合，使飑线形成组织化。(2) 飑线东移过程中的强降水导致其冷池不断增强，在飑线内部形成次级环流，加强了后侧入流，使飑线进一步发展。(3) 由于湖面摩擦系数大大减小，强飑线经过光滑的太湖湖面移动速度大幅增加；冷湖效应、湖陆温差等机制使得飑线在经过太湖湖面时对流强度维持和增强；同时飑线过境湖面时水汽得到补充，多种作用叠加造成了地面12级强风。

Abstract:

This study examined the circulation patterns and factors contributing to the sudden intensification of a squall line near Taihu Lake during a large-scale extreme thunderstorm and gale event in southern Jiangsu Province on July 26, 2022. The analysis was based on data from dual-polarization radar, reanalysis data, radiosonde, automatic ground station, wind profile data, and microwave radiometer. The results showed that: (1) The downward propagation of a low-level jet resulted in the formation of an ultra- low-level jet, which enhanced the influx of dry and cold air in the middle layer. This led to the formation of an outflow with sinking airflow reaching the ground, intensifying ground convergence and further developing the squall line. (2) The strong precipitation during the eastward movement of the squall line led to the continuous strengthening of its cold pool, leading to a secondary circulation inside the squall line, strengthening the rear inflow, and further developing the squall line. (3) The reduced friction coefficient of the lake surface significantly increased the speed of the strong squall line passing over the Lake. The cold lake effect and temperature difference between the lake and land maintained and the convective intensity increased as the squall line passed over Taihu Lake. The passage of the squall line over the lake surface replenished water vapor and these effects jointly led to a level 12 strong wind on the ground.