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一次深秋高架雷暴形成的对流活动特征分析

Analysis of convective activity characteristics formed by a late-autumn elevated thunderstorm

  • 摘要: 利用ERA5再分析资料、闪电定位仪、双偏振雷达以及微波辐射计等资料,对2022年11月28日浙北地区一次深秋高架雷暴的环境背景,动力条件,不稳定机制及雷电、雷暴大风等对流活动特征进行了分析。结果表明:(1) 这是一次发生在暖锋前部的高架对流,500 hPa高空槽和低空西南急流是主要的影响系统。高空短波槽前涡度平流随高度增加引起强烈 的上升运动,低空急流前部深厚的辐合,强垂直风切变等为对流发展提供了有利的动力条件。(2) 中层干空气和较强的下沉对流有效位能(DCAPE)有利于形成强下沉气流。条件不稳定和条件对称不稳定共同作用为对流发展提供了充足的能量条件,其中条件不稳定起主要作用。(3) 双偏振雷达分析显示,强盛阶段50 dBz强回波可以达到−20 ℃层,零度层以上存在差分反射率因子(ZDR)柱和差分传播相移率(KDP)柱;强上升气流以及大量冰相粒子的存在,有利于出现密集雷电。(4) 随着反射率因子核心的快速下降,风暴后侧入流急流经由风暴强反射率因子核心下方下降到近地面,表明对流产生的强下沉气流能够冲破逆温层并带动中层高动量空气到达地面。对流发生前后地面温度变化很小,表明在低层负浮力作用较小;水凝物分类结果显示大量冰雹粒子下落到低层,等效水凝物负载估算结果表明冰雹等降水粒子的拖曳对下沉气流有较强的增强作用。

     

    Abstract: Using data from ERA5 reanalysis, lightning locators, dual-polarization radars, and microwave radiometers, this study analyzed the environmental background, dynamic conditions, instability mechanisms, and characteristics of lightning and thunderstorm gale of an elevated severe thunderstorm in the northern Zhejiang region on November 28, 2022. The results are as follow. (1) this was an elevated convective event occurring ahead of a warm front, which was mainly influenced by the 500 hPa upper-level trough and low-level southwesterly jet stream. The vorticity advection increasing with height in front of the shortwave trough caused strong upward motion. The strong and deep convergence in the front of the low-level jet stream, and the strong vertical wind shear provided favorable dynamic conditions for the development of convection. (2) Mid-level dry air and strong downdraft convective available potential energy (DCAPE) contributed to the formation of intense downdrafts. The joint action of conditional instability and conditional symmetry instability provided sufficient energy conditions for the development of convection, among which conditional instability played a major role. (3) Dual-polarization radar data analysis showed that, during the peak stage, the 50 dBz strong echoes reached the −20 ℃ layer, and above the 0 ℃ layer, ZDR columns and KDP columns existed. The coexistence of strong updrafts and a large number of graupel particles was conducive to the frequent occurrence of lightning. (4) With the rapid descending of the reflectivity core, the rear inflow jet formed and dropped to the surface through the reflectivity core of the storm, indicating that the strong downdraft generated by convection could penetrate through the inversion layer and bring the high momentum air to the ground. Little changes in the ground temperature were observed before and after the convection, indicating that the negative buoyancy effect of the downdraft at low levels was small. The equivalent hydrometeor load estimation showed that the drag effect of large particles, like hail, could have a strong enhancement effect on the downdrafts.

     

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