双TC和梅雨锋共同作用下的一次暴雨过程分析

通过NCEP再分析资料计算各种物理量和应用卫星云图、雷达资料,并用WRF中尺模式做数值模拟,从动力过程、水汽输送过程、中小尺度系统等3个方面对TC和梅雨锋共同作用在浙北产生的一次暴雨过程进行分析。结论如下:(1)动力过程特点:300 hPa急流出口区辐散,中层3支气流汇合形成变形场锋生,产生强烈上升运动。低层TC外围的东南气流输入暖平流和湿位涡,使海上台风倒槽向北传播发展,最终形成气旋。TC高层流出气流对梅雨锋南侧垂直环流的维持有利;(2)水汽主要由两个TC外围的环流输送;(3)卫星云图和雷达回波显示有不同的降水云团合并且有加强的过程。用WRF中尺模式做数值模拟显示:700 hPa中小尺度的切变线或辐合区与强降水回波相对应。过程主要特点是中低层两个TC外围的气流与西风带气流在华东地区汇合,形成变形场锋生,产生强烈的辐合上升。在不同的气流汇合后产生了强急流输送水汽,加强垂直环流和中小尺度的辐合,是强降水产生的主要原因。西南季风经过台风绕流后在合适的环境场下仍有可能到达华东地区,这时往往与中纬度西风带汇合,在这种情况下会加强梅雨降水。

Analysis on a rainstorm caused by double tropical cyclones and Meiyu front

A torrential rain caused by double tropical cyclones and Meiyu front in northern Zhejiang was analyzed through calculating the synoptic situation and physical quantity by NCEP reanalysis data. Based on satellite imagery and radar data, numerical simulation by WRF was conducted to analyze the dynamic process,water vapor transmission,mesoscale and small-scale systems of the rainstorm. The results show:(1) Characteristics of the dynamic process:the frontogenesis deformation caused by divergence of 300 hPa jet stream in exit area and convergence of three airflows in middle layer could produce an strong upward movement. Southeast airflow in the periphery of the lower TC "Guchol" provided warm advection and moist potential vorticity,making the typhoon inverted trough on the sea spread northward and form cyclone eventually. Outflow from the upper TC "Guchol" was good at preserving vertical circulation in the south side of Meiyu front. (2) Water vapor was mainly delivered by two circulations in the periphery of tropical cyclones. (3)Satellite imagerys and radar echo data showed a merging and strengthening process of different precipitation clouds. Numerical simulation by WRF shows that mesoscale shear line or convergence zone at 700 hPa is corresponding with heavy precipitation echo. The main feature of the process is the meeting of peripheral airflow of TCs with westerly airflow, which not only caused deformation frontogenesis, strong convergence and upward movement, but transported water vapor by strong jet and enhanced the vertical circulation and mesoscale convergence.Southwest monsoon still might arrive at Jianghuai region after flowing around the typhoon in good condions, which would strengthen the Meiyu precipitation when it is confluent with the mid-latitude westerlies.