2021年5月14日武汉龙卷风暴的环流背景和涡度来源分析

Analysis of the circulation background and vorticity source for the Wuhan tornado storm on 14 May, 2021

摘要

2021 年 5 月 14 日 20:39 (北京时)，武汉发生了一次罕见的 EF3 级龙卷，造成严重人员伤亡和财产损失。中国地质大学 (武汉) 的 X 波段双偏振天气雷达和武汉市观象台的 S 波段天气雷达均显示，此次龙卷的母体风暴为一个具有钩状回波的超级单体。利用探空数据、ERA5 再分析数据，并结合中尺度数值模式，首先对此次龙卷风暴的雷达回波特征、环流背景和环境条件进行分析，并与湖北 1977 年 4 月 16 日的 EF3 级龙卷过程的环流背景进行对比，最后研究了此次过程的涡度来源。结果表明：(1) 此次龙卷风暴发生在西北太平洋副热带高压 (以下简称副高) 外围的南支气流中。青藏高原东侧低压系统的发展加强了其与副高之间的气压梯度，一方面有利于形成低空急流，另一方面也有利于低空垂直风切变的增强，为龙卷风暴的发生提供了有利的水汽和动力条件。高、低空急流的耦合为深对流的充分发展提供了有利的“低层辐合、高层辐散”条件，而江淮倒槽为风暴的形成提供了触发条件。(2) 此次龙卷风暴与 1977 年 4 月 16 日湖北另一次 EF3 级龙卷过程的环流背景有相似之处，主要体现在高低空急流的耦合、江淮倒槽的影响、以及强的西南—东北向低空垂直风切变。(3) 此次龙卷风暴产生过程中，低层风暴相对速度与环境水平涡度均为东南—西北向，环境水平涡度在风暴相对速度方向有着较大的投影分量，风暴相对螺旋度大值区由东南向西北伸入风暴内部，为中气旋的发展提供了涡度来源。这凸显了在龙卷风暴短时临近预报预警中，高时空分辨率垂直风廓线观测资料的重要性。

Abstract

At 20:39 BT on 14 May 2021, a rare EF3 tornado struck Wuhan, causing severe casualties and significant property damage. Both the X-band dual-polarization weather radar at China University of Geosciences (Wuhan) and the S-band weather radar at Wuhan Observatory indicated that the parent storm of this tornado was a supercell with a hook echo. Using ERA5 reanalysis data combined with a mesoscale numerical model, the radar echo characteristics, circulation background, and environmental conditions of this tornado event were analyzed. And the tornado’s circulation background was compared with that of another EF3 tornado which occurred in Hubei Province on 16 April 1977. The vorticity source during this event was analyzed at last. The results are as follows. (1) The tornado occurred within the southern branch flow on the periphery of the Western North Pacific Subtropical High (WNPSH). The development of a lowpressure system east of the Tibetan Plateau enhanced the pressure gradient between the low-pressure system and the WNPSH, which favored the formation of a low-level jet and strengthened low-level vertical wind shear, providing favorable moisture and dynamic conditions for the tornado storm. The coupling of upper- and low-level jets created an excellent environment for deep convection with low-level convergence and upper-level divergence, while the Jianghuai inverted trough served as a triggering mechanism for the convective storm. (2) The circulation background of this Wuhan tornado shares similarities with that of another EF3 tornado that occurred in Hubei on 16 April 1977, particularly in terms of the coupling of upper- and low-level jets, the influence of the Jianghuai inverted trough, and strong southwest-northeast oriented low-level vertical wind shear. (3) During the tornado storm genesis, both the low-level stormrelative velocity and the environmental horizontal vorticity were oriented southeast-northwest. The environmental horizontal vorticity had a large projection component along the storm-relative velocity direction, and a high-value area of storm-relative helicity extended from the southeast into the storm interior, providing a vorticity source for mesocyclone development. This underscores the importance of high spatiotemporal resolution vertical wind profile observations in the nowcasting and warning of tornadoes.

关键词

龙卷风暴 / 环流背景 / 涡度来源 / WRF 模式模拟

Key words

tornado storm / circulation background / source of vorticity / WRF model simulation

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基金资助

中国气象局流域强降水重点开放实验室(2023BHR-Y28)

国家自然科学基金项目(42075055)

中央高校基本科研业务费专项资金资助项目(G1323521141)

山东省气象局面上课题(2020sdqxm20)

山东省气象局预报员专项(SDYBY2021-04)

全国暴雨研究开放项目(BYKJ2025Q04)