低压倒槽影响下积层混合云形成过程模拟研究

利用多普勒雷达资料和中尺度天气预报模式wRF（Weather Research and Forecasting）模拟结果，对2009年5月9—10日发生在太原及其周边地区的一次积层混合云降水形成过程进行分析。结果表明，在积层混合云的形成初期，局地对流云得到发展，随着其强度不断增强，与周围云发生并合过程（包括局地单体对流的并合、积云团的并合和积层混合云内强中心的并合），形成范围较大的积层混合云云系。局地单体对流和积云团的并合可带来云体的爆发性增长，霰含量、雨水含量大幅增加。积层混合云内强中心的并合对降水强度影响不大，但有利于降水面积扩大。低压倒槽和弱冷锋是此次积层混合云形成和维持的主要影响因素。低压倒槽有利于低层大范围不稳定能量的积累，风向切变有利于近距离云团的发展和并合，山地动力和热力作用有利于局地对流单体、积层混合云内强中心的形成和加强。

Simulation of formation process of convective and stratiform mixed clouds in depression inverted trough

Using the Doppler radar data and simulated results of the mesoscale model WRF （Weather Research and Forecasting）, this paper studies a precipitation process induced by convective and strati- form mixed clouds in Taiyuan and its surrounding areas during 9--10 May 2009. Results show that the local convection clouds are developed in the formation stage of convective and stratiform mixed clouds. With development and strengthening of the convection, the convective and stratiform mixed clouds are formed in a wider range, by means of merging process between the enhanced convection clouds and the ambient clouds. The merging process includes the local single cells merging, the cloud clusters merging and the high cores merging in convective and stratiform mixed clouds. The single cells merging and cloud clusters merging can bring about the explosive growth of clouds with a sharp increase in graupel content and rain water content. The high cores merging in convective and stratiform mixed clouds can enlarge the rainfall area rather than the rainfall strength. The depression inverted trough and the weak cold font are main influencing factors of formation and maintenance of the convective and stratiform mixed clouds. The depression inverted trough is beneficial to the accumulation of large-range convective energy in the lower layer and the wind shear is favorable to the development and merging of cloud clus- ters at a short distance. The dynamic and thermal effects of mountainous region promote the formation and strengthening of local single cells and strong centers in the mixed clouds.