一次大范围暴雨过程的诊断分析

用ECMWF 0.75°×0.75°, 6 h间隔再分析资料、地面加密观测资料、Micaps资料和云图T_BB资料, 对2012年8月20日一次大范围暴雨过程进行诊断分析。结果表明:本次大暴雨过程是在高层急流入口辐散和中低层的低槽切变线的耦合作用以及台风的间接影响使得低槽系统移动缓慢和提供水汽的有利条件下产生的。暴雨带中水汽主要来源于南海和东海。从等熵位涡、湿位涡和总能量分析说明这次暴雨和大暴雨是在水汽条件充沛条件下, 对流不稳定叠加斜压不稳定和对称不稳定等共同作用下, 产生暴雨-大暴雨。另外, 南北两支气流在暴雨区强烈辐合(南侧为上升运动, 北侧为下沉运动)也起到了重要作用, 且总能量垂直廓线与雨团中心对流强度和强降水时段对应较好。低层东海东南暖湿气流和干冷的东北气流对本次大范围暴雨过程的产生起触发作用。

Diagnostic analysis on a wide range rainstorm process

By using the reanalysis data with 6 h interval and 0.75°×0.75° resolution from ECMWF, ground observation data, Micaps and TBB data, a wide range rainstorm process on 20 August, 2012 was diagnostically analyzed. Results showed that the rainstorm occurred in the favourable conditions of the coupling effects combining divergence at jet extrance at high level with the trough shear line at low level, the slow movement of the trough system and the abundant water vapor for the rainstorm belt by the indirect effects of typhoon. The main source of water vapor in the rainstorm belt was from the East China Sea and the South China Sea. Analysis on isentropic potential vorticity, moist potential vorticity and total energy vertical profile showed that in the condition of abundant water vapor, the joint effects of convective instability superimposed with baroclinic instability as well as symmetric instability caused the rainstorm. Furthermore, the south and north air flow converged strongly in the heavy rain area (upward at south side; downward at north side) also played an important role. Vertical profiles of total energy quite well corresponded with the convection strength and strong precipitation periods. The southeast warm air and the dry-cold northeast airflow at low level triggered this wide range rainstorm process.