一例底层涡旋扰动触发强对流的中尺度分析

A mesoscale analysis of low level vortex disturbance initiating severe convective weather

通过对2009年6月5日一例皖北强灾害天气过程的中尺度分析,发现底层大气中存在西南气流的中尺度汇合线,在汇合线附近、基本西南气流的流场环境下,隐含着中尺度涡旋扰动.利用Shuman-Shapiro平滑滤波方案对日本中尺度再分析资料进行处理,揭示了滤波后出现的中尺度涡旋扰动,该涡旋扰动对应边界层中尺度辐合区和辐合中心,以及气流的最强上升支.这些中尺度扰动特征与之后初始对流回波单体的发生有较好的对应关系,说明中尺度扰动涡旋中心附近及东侧易发生对流,或者扰动涡旋率先触发了对流.

Mesoscale analysis on a disastrous convective weather event is presented.This event occurred in north Anhui on June 5 th 2009,causing large economic loss and casualties.Satellite data,radar data,automatic weather station data,and Japan reanalysis data are used to analyze this case.The results showed that there was a stationary mesoscale convergence line formed by the southwest flow and the northwest flow in north Anhui in that day afternoon.The respective low-level wind field and convergence field showed that a disturbance was embedded in the southwest background flow near the convergence line.By applying the Shuman-Shapiro smoothing filtering method to the Japan reanalysis data,the disturbance characterized by a horizontal vortex circulation is revealed.The vortex disturbance corresponded with a low-level mesoscale convergence zone and convergence center,as well as a strongest upward flow near the convergence center.Radar and satellite pictures showed that new convection occurred near the vortex disturbance by 1500 LST.The mesoscale disturbance features had a good corresponding relationship with the genesis of the first echo of the convection,indicating that convection was more likely to initiate in the center and east of the mesoscale disturbance vortex or the convection was triggered by the upward flow of the vortex.