浙北两次地面辐合线触发的极端暴雨对比分析
Comparative analysis of two extreme rainfall triggered by surface convergence lines in Northern Zhejiang
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摘要: 利用常规观测资料、双偏振雷达资料、ERA5(0.25o×0.25o)再分析资料等,对比分析了2023年7月16日、22日浙江两次极端暴雨过程的天气背景、环境条件、中尺度对流系统触发机制、雷达参量特征等,结果表明:(1)两次过程发生在500hPa相似的大尺度环流背景下,副高外围均有西风槽东移、南海存在台风或热带低压,且均由地面中尺度辐合线触发。(2)中低层环流背景及落区不同,过程1发生在850hPa冷切中,暴雨中心位于副高边缘,过程2发生在850hPa一致的西南气流中,暴雨中心位于副高环流内。(3)热动力条件不同,过程1暴雨出现在850和925hPa东南气流增强过程中,边界层气流作用更显著,大气层结不稳定性强,低层以水平锋生为主,中高层也有垂直锋生发展,过程2暴雨出现在925hPa西南气流增强过程中,中低层层结不稳定性弱,以垂直锋生为主。(4)中尺度对流系统及微物理特征不同,过程1前期由多个对流单体新生后北上合并成中β尺度的强降水云团造成,后期由中尺度降水云团“后向传播”和“列车效应”共同造成,降水粒子以浓度较高的小雨滴为主。,过程2前期由多个新生对流单体的“列车效应”造成,降水以直径大、浓度小的粒子为主,后期由系统性的线性对流与前期局地生成发展的对流云团合并加强造成,降水以直径小、浓度高的粒子为主。Abstract: By using conventional observation data、dual polarization radar data、 ERA5(0.25o×0.25o) reanalysis data,the weather background、environmental conditions、triggering mechanism of mesoscale convective system、radar parameter characteristics of the two extreme rainfall processes in Zhejiang on July 16 and 22, 2023 are compared and analyzed,the result show that:(1)The two processes occurrs in a similar circulation background of 500hPa with westerly trough moving eastward around the Subtropical High, and the typhoon or tropical depression in the South China Sea. Both processes are triggered by the surface mesoscale convergence line.(2)The background of middle-low and precipition area are different,process 1 occurs in cold shear at 850hPa and the rainfall center is located at the edge of the Subtropical High,while process 2 occurs in consistent southwest airflow at 850hPa and the rainsfall center is located in Subtropical High circulation.(3)The thermal and dynamic conditions are different,the extreme rainfall of process 1 occurs in the process of 850 and 925hPa southeast airflow enhancement, the boundary layer airflow is more significant, the atmospheric stratification is unstable,