A typical severe convective storm on August 23rd, 2001 in Miyun District, Beijing was firstly simulated via the Weather Research and Forecasting (WRF)model and then the focus was taken on the extraction of a β meso-cale downburst near Miyun reservoir as well as the analysis on its evolution. The results showed as follows. (1)The horizontal and vertical stream structure of the downburst whose life was about 1 hour and horizontal scale was about 20km, was generally consistent with the theoretical structure of downburst while the divergent flow velocity near surface was slower than 18m/s, which did not meet the definition of downburst. (2)The perturbation potential temperature and water mixing ratio were highly interrelated with the instability of stratification profiles and updraft, and their relationship also confirmed that the downburst was primarily produced by rain loading and enhanced by the updraft motion caused by high perturbation potential temperature and the warm and damp mass.%应用中尺度气象数值模式WRF模拟再现了2001年8月23日北京时间14时至24日00时发生在北京密云县附近的一次典型强对流风暴天气，重点发掘并分析了密云水库附近一次茁中尺度下击暴流的形成与演变过程。研究表明：（1）WRF模拟结果显示该茁中尺度下击暴流的生命期为1 h左右，水平尺度约为20 km，其水平和垂直流场与下击暴流流场的理论结构基本一致，但辐散气流流速在近地面层未能达到下击暴流定义的18 m/s；（2）模拟的下击暴流环境场中扰动位温、各水成物的比含水量与层结不稳定性以及上升气流的联系紧密，并可推断强下沉气流主要由雨水粒子拖曳作用产生，较大的位温扰动则加强了气流上升运动，迫使暖湿气块更大程度抬升，进一步维持和发展下击暴流系统。
展开▼
