地形、冷池出流和暖湿空气相互作用造成北京一次局地强降水的观测分析

摘要

利用地面和探空常规探测资料、多普勒天气雷达以及风廓线雷达资料,对2015年8月7日发生于北京的一次伴随有闪电和冰雹的突发性局地强降水过程的成因进行了分析.结果表明:这次过程发生在强层结不稳定环境中,对流层中层低槽配合低层切变线,促进河北西北部对流发展,并向东南方向移动,形成北京西北部短时强降水;北京中部地区强降水的直接制造者则是新生的局地性雷暴单体,由雷暴冷池出流和暖湿空气在边界层交绥和辐合所触发.北京西北部地形促使冷池出流下山速度加快、冷池出流高度抬高,以及偏东暖湿气流的辐合抬升作用,则是局地雷暴新生的重要影响因子.%The causes of a sudden local heavy rainfall with lightning and hail occurred in Beijing on 7 August,2015 are investigated by composite analyses of surface and conventional sounding data,Doppler weather radar data and wind profile radar data.The following results are given:The heavy rain occurred in a strong unstable stratification.The middle level trough,lower-troposphere shear line and surface wind convergence facilitated the development of convection in northwest of Hebei,which then moved southeast and caused heavy rain in the northwest of Beijing.The direct producer of heavy rainfall over central Beijing was thunderstorms locally triggered by convergence between the cold pool outflow of pre-existing thunderstorms and the warm,moist southeast airflow in the boundary layer.The terrain in the northwest of Beijing accelerated downhill cold pool outflow and lifted the thunderstorm cold pool outflow.Then,the cold westerly outflow overlapped above the warm and moist easterly flow near surface that increased the convective instability of atmosphere and contributed to the initiation of thunderstorms at the east side of the mountain.