本文对上海地区一次双台风环境影响的暴雨过程进行数值模拟及分析,探讨了强降水过程中大气中低层的涡旋特征及发展机理.结果表明:(1)暴雨过程处于双台风、大陆高压的共同影响下,中低层伴随有较明显的中尺度低涡发展.(2)与涡旋相关的局地垂直涡度由低层开始发展,先期涡度发展集中于850 hPa以下,之后向大气中上层发展增强,涡旋尺度强度也随之发展,最终形成在对流层下半部具有闭合式气旋性环流的深厚涡旋.(3)影响局地涡度变化的水平平流项、垂直平流项、散度制造项和倾斜项对不同时间、不同高度的涡度作用各不相同,其中散度制造项是中低层涡度的主要来源,垂直平流项的输送作用对中上层的涡度发展有重要作用,倾斜项对涡旋发展移动也有部分贡献.(4)通过敏感性试验考察了对流潜热反馈的贡献,发现潜热释放过程通过加热改变大气温压场结构,从而维持并改变局地涡度倾向的中低层辐合及对流上升运动,对涡旋的发展和移动起了重要影响.%Numerical simulation is carried out for a heavy rainfall event influenced by two typhoons to study the mesoscale vortex related to the event.The results show that:(1) the rainfall event was jointly influenced by continental high,Typhoon Fitow and Typhoon Danas.Obvious mesoscale vortex activity was found in the mid-to-lower levels during the event.(2) Vertical vorticities related to the vortex started to develop from the lower level of atmosphere.At first,vorticities concentrated below 850 hPa,and then strengthened upward.Meanwhile,the vortex was growing in size and intensity,and finally became a deep meso-β scale vortex accompanied by closed cyclonic circulation.(3) The terms of horizontal advection,vertical advection,convergence making and tilting of local vorticity tendency had different effects in different times and levels.The convergence making term was the main contributor to the mid-to-lower level vorticity source.The vertical advection term was the main contributor to the upper-level vorticity by transporting lower vorticity to the higher levels.The tilting effect had some influence on the development and movement of the vortex.(4) The latent heating effect of precipitation had important influence on the development and movement of the vortex.It changed thermodynamic condition and stability of the atmosphere.Therefore,it was responsible for the maintenance and development of the convergence and convection term of the local vorticity tendency.
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