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两次冬季罕见大冰雹超级单体风暴对比分析

Comparative Analysis of Two Rare Large Hail Supercells in Winter

  • 摘要: 利用再分析资料、自动站观测、闪电定位以及S波段双偏振雷达资料,对2024年2月21日(简称“24·2·21”)和2025年3月3日(简称“25·3·3”)两次浙江入春前发生的大冰雹超级单体进行分析,结果表明:两次对流均发生在寒潮冷锋后,为高架对流,逆温层顶之上存在条件不稳定层结和正的对流有效位能,深厚垂直对流在850 hPa切变线作用下迅速触发。强深层风垂直切变有利于超级单体发展。“25·3·3”干层较“24·2·21”更深厚。降雹过程均伴随着风暴质心和中气旋最大切变高度的下降,降大冰雹区在风暴后侧下沉气流中。“24·2·21”超级单体维持时间长,中层有双涡旋结构,差分反射率(ZDR)柱和差分相移率(KDP)柱高于6 km,悬垂回波内ZDRKDP小,相关系数(CC)随高度下降而减小,包含融化的小冰相粒子,有利于冰雹湿增长;而“25·3·3”超级单体维持时间较短,有深厚单涡旋(中气旋)结构,并有明显后侧入流,ZDR柱和KDP柱在5 km之下,高层ZDRKDP小,CC大,干的冰相粒子较多,表现为云闪频次增多,可能与后侧干冷空气流入加速冻结有关,有助于冰雹在高层冷云中干增长。

     

    Abstract: Two large-hail supercells that occurred before spring in Zhejiang, on February 21, 2024 (“24·2·21”), and March 3, 2025 (“25·3·3”), were analyzed using the reanalysis data, automatic weather station observations, lightning location data, and S-band dual-polarization radar data. The results indicate that both convection events occurred after the passage of a cold wave front and were elevated convection systems. Above the inversion layer, conditionally unstable stratification and positive convective available potential energy were present. Deep convection was rapidly triggered under the influence of the 850 hPa shear line. Strong, deep-layer vertical wind shear favored the development of supercells. The dry layer in the “25·3·3” case was deeper than that in the “24·2·21” case. In both supercell hail processes, hailfall was accompanied by a decrease in storm centroid height and in the maximum shear height of the mesocyclone. The “24·2·21” supercell exhibited a long maintenance time, a mid-level double vortex structure, and differential reflectivity (ZDR) and specific differential phase (KDP) columns extending above 6 km. The ZDR and KDP values within the overhanging echo were small, and the cross-correlation coefficient (CC) decreased with decreasing height, indicating the presence of melting small ice phase particles, which favored moist hail growth. In contrast, the “25·3·3” supercell had a shorter maintenance time, a deep single vortex (mesocyclone) structure, and a pronounced rear inflow. The ZDR and KDP columns were confined below 5 km. Small ZDR and KDP values accompanied by large CC values at upper levels indicated a greater abundance of dry ice phase particles. This was manifested by an increased frequency of intracloud lightning flashes, which may be associated with accelerated freezing caused by rear-inflow dry cold air and was conducive to dry hail growth in the upper cold cloud region.

     

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