一次切变线暴雨过程的数值模拟及诊断分析

Numerical Simulation and Diagnostic Analysis of A Shear Line Heavy Rainstorm

采用WRF中尺度模式对2008年6月长江中下游地区一次大暴雨过程进行数值模拟,并利用模式高分辨率资料进行初步诊断分析。结果表明:此次暴雨过程是在高、低空急流和低涡切变线的共同作用下发生的;西南低空急流不但是产生暴雨所需的水汽输送带,也是造成暴雨强对流所必需的位势不稳定能量的输送者。水汽分析表明,水汽通量散度辐合中心与强降水中心有较好的对应关系。能量分析表明,高能舌前部、能量锋区南缘靠近能量锋区处和低空急流左前方三者叠加的区域是暴雨的易发区;高、低空急流及低涡切变线是此次暴雨的动力触发机制,一方面,高层负涡度的辐散和中低层辐合相叠置,使气旋和中尺度低涡切变线进一步加强;另一方面,低层不稳定能量的释放使降水得以维持和加强。

A process of shear line storm rainfall occurred in the valley of middle and lower Yangtze River on June 2008 was simulated by the meso-scale numerical model （WRF） and diagnostic analysis using WRF model outputs. The result showed that this heavy rainstorm was affected by high-low jet and the vortex shear line. The low level jet not only provided water vapor which is needed by the rainstorm,but also is the unstable energy＇s carrier. Moreover,the center of the convergence of water vapor is corresponding to the location of the center of rainstorm; heavy rainfall occurred in the overlapped area of the foreside of high energy tongue,the south of energy front and the left foreside of low-level jet. High-low jet and vortex shear line is the motive mechanism which triggered the rainstorm. On one hand,the high negative vorticity and middle-low convergent coincided,which further strengthen the mesoscale vortex and the shear line; On the other hand,the release of instability energy that maintain and strengthen rainstorm.