用SA雷达产品对京西三次局地暴雨落区形成的精细分析

Comparative Analysis of CINRAD-SA Doppler Radar Product in Three Local Torrential Rains in the West of Beijing

利用新一代Doppler雷达各种探测产品,对2006年6月底至7月上旬北京西郊香山、石景山、门头沟一带落区相同的三次局地暴雨和大暴雨过程,进行精细分析和研究。重点分析雷达探测产品对落区在同一地点形成的短时临近影响系统和指示意义。研究表明,发生在北京西郊山前、落区相同的三次局地暴雨和大暴雨,其雷达回波发展和演变形式各不相同。但三次过程强降雨前,近地面平原东南风和边界层偏西风的垂直风廓线结构在地形作用下对暴雨落区形成的影响是一致的:近乎与山脉垂直的平原近地面东南风长时间(6小时左右)维持,增加山前局地近地面温湿条件,并在北京西郊山脉阻挡下,形成山前近地面局地辐合和强迫抬升。山顶附近边界层的偏西风为近地面空气强迫抬升后在边界层的后卷辐散提供了有利条件。研究还显示,落区附近单体风暴、逆风区辐合带、中气旋等中小尺度回波系统的活动和发展,是暴雨落区形成的重要因素。

Three local heavy rain events have similar location of rainfall, which occurred in Xiang- shan, Shijingshan and Mentougou area in the west of Beijing from the end of June to early August of 2006. Product of Doppler radar exploration is used to do fine analysis and research. The result shows that development and evolvement of radar echoes in these three events are different though similar kvation of rainfall. The influence of vertical wind profile of westerly in boundary layer on location of torrential rain is consistent under the action of topography. The south - east wind from the plain in surface layer is almost vertical to the mountain lasting about 6 hours and strengthens temperature and hu- midity rendition in surface layer in the front of mountain. Convergence and lifting in surface layer in the front of mountain form under obstruction of mountain in the west of Beijing. Westerly winds in boundary layer around top of the mountain provide benefidal factor for divergence in boundary layer by lifting in at- mospheric surface layer. Studies also indicate that development and evolution of meso-scale and micro-scale systems such as thunderstorm cell around location of rainfall and mesocyclone are key factors that decide the location of torrential rain.