一次飑线初始阶段的极端大风成因分析

Analysis of the causes of extreme strong winds in the initial stage of a squall line

利用常规天气图、多普勒天气雷达、风廓线雷达、自动气象站等多源气象观测资料和现场勘查情况,对2022年7月26日发生在江苏中南部一次飑线初始阶段的极端大风成因进行了初步分析。结果表明:此次过程发生在冷涡天气背景下,前倾槽东移和西太平洋副热带高压减弱南退,显著的上下层温差、中层异常干的层结、大的环境温度直减率,加上前期积聚较大的不稳定能量,为雷暴大风强对流的发生提供了有利的对流环境。随着近地层冷空气侵入,低空急流范围扩大下移,边界层垂直风切变陡增,对流回波进入江苏后由地面中小尺度辐合线触发的初始对流在扬州—镇江加强为组织化的飑线。飑线顶端出现强烈的辐合旋转,12级极端大风处于超级单体风暴核心区前侧的暖湿上升入流区,风向由暖区指向强回波,中气旋表现出强烈旋转和向上拉伸,并伴随龙卷涡旋特征(Tornado Vortex Signature,TVS),大量水汽和能量也随入流气流向对流系统输入,风暴的垂直环流倾斜和拉伸涡度进一步加大,预示着飑线将强烈发展。

A preliminary analysis was conducted on the causes of an extreme strong wind that occurred on July 26,2022 in the initial stage of a squall line in central and southern Jiangsu Province,using multi-source meteorological observation data such as conventional weather maps,Doppler weather radar,wind profile radar and automatic weather stations,as well as on-site investigations.The results show that this process occurred under the background of cold vortex weather,with the eastward movement of the forward leaning trough and the weakening of the subtropical high pressure southward retreat.The significant temperature differences between the upper and lower layers,the abnormally dry layer structure in the middle layer,the large direct decrease rate of environmental temperature,and the large accumulation of unstable energy in the early stage provided a favorable convective environment for the occurrence of thunder⁃storms,strong winds,and strong convection.With the invasion of cold air in the near surface layer,the range of low-level jets expands and moves downwards,and the vertical wind shear in the boundary layer increases sharply.After the convective echo enters Jiangsu,the initial convection was triggered by the surface small-scale convergence line,and it strengthens into organized squall lines in Yangzhou-Zhenjiang.There is a strong convergence and rotation at the top of the squall line,with extreme winds of level 12 located in the warm and humid upwelling area in front of the core area of the supercell storm.The wind direction points from the warm area to the strong echo,and the mesocyclone shows strong rotation and upward stretching,accompanied by Tornado Vortex Signature(TVS).A large amount of water vapor and energy are also input into the convective system with the incoming flow.The vertical circulation tilt and stretching vorticity of the storm further increase,indicating that the squall line will develop strongly.