引发广西一次区域性暴雨的低涡发展机制

Development mechanisms of the vortex causing a regional rainstorm in Guangxi

低涡是造成广西区域性暴雨的关键系统,了解其发展维持机制对于暴雨预报具有重要意义。利用多源观测数据及欧洲中期天气预报中心ERA5再分析数据,对引发2022年6月10—11日广西区域性暴雨的低涡发展维持机制进行诊断分析。结果表明:低涡生成于桂西北后稳定少动,为区域性暴雨的发生发展提供热、动力条件,对流云团及降水落区主要分布在低涡东侧及南侧。涡度方程诊断表明,低涡的发展维持主要受涡度平流项和水平散度项影响,其中地转风分量使局地涡度不断减小,而非地转风分量则使局地涡度不断增加,水平散度项是造成低涡发展维持的主要原因。在惯性振荡机制影响下,低涡中心偏北一侧非地转风场随时间变化具有明显的顺时针旋转特征。非地转风旋转为偏北风时与低涡中心附近的偏南非地转风辐合,造成非地转风分量水平散度项对局地涡度的显著贡献,使得低涡发展维持。对流层中层附近的潜热加热正反馈也有利于低层低涡的发展维持。

Vortex is the key system that causes regional rainstorms in Guangxi,it is important to clarify its development and maintenance mechanism for rainstorm forecast.Based on the diagnosis analysis method,the development and maintenance mechanism of the vortex causing a regional rainstorm in Guangxi on June 10-11,2022 is studied by using multi-source observation data and ERA5 reanalysis data of the European Centre for Medium-Range Weather Forecasts.The results show that the vortex generated in northwest Guangxi and stayed stably and moved little,which provided thermal and dynamic conditions for the occurrence and development of the regional rainstorm.Convective cloud clusters and precipitation areas were mainly distributed in the east and south sides of the vortex.The diagnosis of vorticity equation shows that the development and maintenance of the vortex are mainly affected by the vorticity advection and horizontal divergence terms.The geostrophic component consumes the local vorticity continuously in the whole process,while the ageostrophic wind component contributes to the local vorticity.The horizontal divergence term of the ageostrophic wind component is the main reason for the development and maintenance of the vortex.Under the influence of the inertial oscillation mechanism,the ageostrophic wind on the north side of the vortex center shows obvious clockwise rotation with time.The ageostrophic wind rotates to the northerly wind and converges with the southerly ageostrophic wind near the vortex center,which leads to the development and maintenance of the vortex.The positive feedback of latent heating near the mid troposphere is also conducive to the development and maintenance of the vortex.