广西南宁一次“龙舟水”暴雨空报事件对流生消成因分析

Causes for Convection Generation and Dissipation in an Unsuccessful“Dragon Boat Water”Rainstorm Prediction Event in Nanning of Guangxi

2022年6月13日,广西出现大范围暴雨过程,而南宁市区一带暴雨空报;雷达回波在南宁市区北侧衰减、东侧强度维持、南侧新生发展,过程演变复杂。文章采用常规观测资料及ERA5再分析资料,对此次过程中对流生消演变成因进行分析。结果表明:此次过程为典型广西前汛期强降雨环流形势及环境背景;然而受天气尺度冷平流及风暴冷池共同影响,冷空气快速移过南宁市区,北侧风暴出流边界远离母体,风暴前侧低层水汽输送偏东,热力、动力条件均较差,导致回波衰减消散;南宁市区东侧风暴在推进过程中出流边界紧贴母体,风暴前侧低层维持西南急流,沿出流边界不断有对流触发,风暴得以加强或维持;南侧低层高温高湿环境形成,有利于对流有效位能重建或增强。最后建立了此次过程对流生消演变机理概念模型,并通过分析冷池、出流边界、环境条件等要素演变,可对短时临近预报进行补充订正。

On June 13,2022,a large-scale regional rainstorm event occurred in Guangxi.During this period,a rainstorm false alarm was issued for the downtown area of Nanning.The echo attenuated in the north side of Nanning City,maintained in the east side and developed in the south side,which made the process complicated.This article investigates the causes for the generation and dissipation of the convection during this event by utilizing various observational data and ERA5 reanalysis data.The results are as follows.The circulation background of this process was the typical heavy rainfall circulation and ambient condition in the first rainy season in Guangxi.However,under the combined influence of synoptic-scale cold advection and storm cold pool,the cold air quickly moved over Nanning City,and the outflow boundary formed by the storm in the north side of Nanning moved away from the storm parent body.Meanwhile,the low-level water vapor transport in the front of the storm moved eastward,resulting in poor thermodynamic and dynamic conditions,leading to the attenuation and dissipation of echoes in the north side of Nanning City.In the east side of Nanning City,the outflow boundary of the storm was next to the storm parent body during its advancing,and the lower layer ahead of the storm kept the southwest jet stream so that the storm was strengthened or sustained by continuous convective cells triggered along the outflow boundary.There was a low-level high temperature and high humidity environment in the south side of Nanning,which was conducive to the reconstruction or enhancement of convective available potential energy.Based on the above,a conceptual model of the evolution mechanism of convection generation and dissipation in this process has been built,and with it,the short-time and nowcasting forecasts can be supplemented and corrected by analyzing the evolution of cold pool,outflow boundary and ambient conditions.