一次飑前降雹超级单体分裂过程的雷达回波及流场特征分析

Analysis on radar echo and airflow fields of a splitting hail-producing supercell ahead of a squall line

  • 摘要: 2019年4月23日浙江南部发生一次明显的超级单体分裂过程,为研究超级单体风暴分裂特征,利用多部雷达构成的双雷达三维风场反演组网技术,结合雷达基本产品、风廓线雷达及探空资料对此次分裂过程做了分析。该超级单体风暴在较强的风垂直切变环境下(地面—500 hPa大于15 m/s)发生,形成于飑线主体弓形回波前端,具有明显的三体散射特征且持续时间较长。分裂从初始风暴的北侧中层开始,然后迅速向上、下伸展,左移超级单体具有明显的中反气旋涡旋结构,呈现由悬垂、强回波柱、强上升气流配合构成的典型超级单体结构,与右移超级单体无论在形态或是流场结构上都形成近似镜像对称的特征。在两者即将分离时,两风暴均发生了降雹,对应强下沉气流。在新风暴分裂形成的发展阶段其垂直廓线中最大垂直速度和最大负散度均在增大,而对应时段原风暴这两个物理量数值减小;整个分裂过程两个风暴正、负涡度数值均一同逐渐增大,气旋—反气旋涡旋的旋转程度变大趋势一致。低层风垂直切变矢量随高度上升逆时针旋转,分裂的左移反气旋超级单体加强发展,右移的气旋式超级单体受到一定抑制,与理论研究结论一致。该个例雷达反演的风场特征与径向速度分布吻合,反演风场基本可靠,为直观理解超级单体风暴分裂的动力学特征提供了进一步参考。

     

    Abstract: An obvious supercell splitting process occurred in southern Zhejiang province on 23 April 2019. To study the splitting characteristics of the supercell storm, the splitting process is analyzed using multiple-group dual-radar three-dimensional wind field retrieval networking technology and the products of radar, wind profile radar and radiosonde data. The supercell storm occurred in an environment of moderate vertical wind shear (more than 15 m/s between the surface and 500 hPa). It formed in front of the bow echo of the squall line, and its obvious three-body scattering signature (TBSS) lasted for a long time. The splitting started from the middle layer on the north side of the original storm, and then extended rapidly both upward and downward. The leftward-moving supercell had an obvious mesoscale anticyclone vortex structure. It showed a typical supercell structure composed of suspension, strong echo column and strong updraft, forming an approximate mirror symmetrical state to the rightward-moving supercell in terms of morphology and airflow structure. When the two storms almost separated, hails fell in both storms, corresponding to strong downdrafts. In the developing stage of the new splitting storm, the maximum vertical velocity and maximum negative divergence in their vertical profiles were increasing, while the two physical quantities of the original storm in the corresponding period were decreasing. The vorticity of the two storms gradually increased simultaneously during the whole splitting process, and the rotation degree of the cyclonic and anticyclonic vortexes increased with the same trend. The vertical wind shear vectors in the lower layer rotated counterclockwise with increasing height, the leftward-moving anticyclonic supercell strengthened and developed, and the rightward-moving cyclonic supercell was suppressed. This is consistent with the theoretical research results. The airflow characteristics of this case retrieved from radar observations are consistent with the radial velocity products, and the retrieved wind field is basically reliable, which provides a further reference for intuitively understanding the dynamic characteristics of supercell storm splitting.

     

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