台风外围偏北气流下两次强对流天气的对比分析

Comparison and Analysis of Two Processes of Severe Convective Weather with the Effect of a Northerly Airflow at the Periphery of Typhoons

利用常规资料、NCEP 1°×1°再分析资料、卫星、雷达及自动站等资料,分析了广东省2014年7月8日和8月1日2次大范围强对流天气过程,结果表明:2次强对流天气均发生在台风外围第3象限偏西北气流控制下,但触发机制不尽相同。7月8日强对流过程与中低层中尺度辐合线北抬有关,是在中低层转西南风时触发;8月1日强对流过程与下沉气流加强有关,偏北气流在近地面与西南气流交汇形成中尺度辐合线,该辐合线自北向南影响广东省中部触发大范围强对流天气;热力和不稳定指数对强对流天气的发生具有指示意义。

Using data of conventional observation,NCEP 1° × 1° reanalysis,satellites and radars as well as automatic weather stations,we studied two extensive,severe convective weather processes that occurred on July 8 and August 1,2014 in Guangdong province. The result is shown as follows. Triggered by different mechanism,they all took place with a northwesterly airflow in dominance at the third quadrant of the periphery of typhoons. For the July 8 case,the convection was related to the northward progression of a mesoscale convergence line at the middle and lower level and triggered to set off when the southwesterly became the dominant wind at these levels. For the August 1 case,however,the convection was linked with the enhancement of descending airflow,which met with a southwesterly near the surface to form a mesoscale convergence line. Sweeping across the province from north to south,the convergence line triggered extensive,severe convection in its central part. Thermodynamics and instability indexes are indicative for severe convective weather.