一次贵阳冰雹过程数值模拟及冰雹形成微物理机制研究

Numerical Simulations of a Hailstorm in Guiyang and Study on the Microphysical Mechanisms of Hail Formation

本文采用WRF4.2模式对2020年5月19日发生在贵阳的一次冰雹过程进行数值模拟,再现了冰雹云在贵阳市的移动路径和发展演变过程。通过对冰雹云不同发展阶段的动力、热力和云微物理特征的分析,以及冰雹混合比源汇项的收支分析,得到了冰雹形成的微物理机制及概念模型。研究结果表明:(1)模拟的冰雹云在成熟阶段呈现典型的超级单体结构,存在悬垂回波和回波空洞。云内最大上升速度可达20 m s^(−1),上升气流从地面延伸至12 km,在高空西风的作用下向东流出,形成宽广的高空云砧。在上升气流后部中低层为强下沉气流。(2)雹胚粒子通过云冰碰冻雨滴形成,通过收集过冷云滴和雨滴增长,雹粒子的最大汇项是融化成雨水。(3)在冰雹云的成熟阶段,雹收集过冷云滴的效率增大,主要发生在强上升运动区中高层(6~10 km高度),大量雹粒子分布在上升运动区中高层以及悬垂回波区,最大混合比可达11 g kg^(−1)。(4)在冰雹云的消散阶段,云内上升速度减弱,高空云砧的范围扩大。雹粒子净转化效率降低,雹混合比减少。雹融化为雨水的效率增大,雨水分布质心降低,在近地面产生大量雨水。

Herein,numerical simulations of a hailstorm that took place in Guiyang,Guizhou Province,on May 19,2020,were conducted based on the Weather Research and Forecasting model version 4.2.It was found that the numerical simulations generally reproduced the moving path of the hailstorm in Guiyang.By analyzing the dynamic,thermodynamic,and microphysical structures of the hailstorm during the different developing stages and diagnosing the tendencies of the hail mixing ratio,the microphysical mechanism of hail formation was examined,and a conceptual model was developed.It was concluded that(1)the simulated hailstorm in the mature stage was characterized by a super-cell storm,existing free-echo,and overhang region.The updrafts reached up to 12 km with a maximum vertical velocity of about 20 m s^(−1) and then flew out eastward because of the westerly wind in the upper troposphere,forming wide anvil clouds.Strong downdrafts were found at lower levels in the rear of the updraft region.(2)Hail embryos were formed through the collection of raindrops by cloud ice,occurring at 6–7 km,and then grew by collecting supercooled cloud droplets and raindrops.The main sink term of hail was melting to rain.(3)During the mature stage of the hailstorm,the collecting rates of supercooled cloud droplets by hail,which mainly occurred at the upper levels of the strong updrafts(6–10 km),increased significantly and produced large mass content of hail with a maximum at 11 g kg^(−1) in the region of overhang echo and the upper levels of updrafts.(4)During the dissipating stage of the hailstorm,the vertical velocity decreased,and the anvil clouds in the upper troposphere expanded.The net production rate of hail decreased and resulted in a decrease in the hail mixing ratio,while the melting rate of hail into rainwater increased and produced a large amount of rainwater near the ground.