利用变分多普勒雷达分析系统,结合多普勒雷达观测、地面自动站、风廓线仪、加密探空等非常规观测资料,对北京地区2011年8月9日局地雷暴的新生和增强机制进行了较精细的分析。结果表明：该过程是一次发生在弱垂直风切变环境下的局地强对流雷暴大风过程,环境场有较强的不稳定能量（CAPE达2 798 J.㎏-1）,地面高比湿带（〉20 g.kg-1）在山前聚集,城区西部山前存在一较强γ中尺度热辐合中心,前期大气环境条件十分有利于对流发生发展;上游移进北京的强雷暴受地形强迫作用影响,其产生的冷池出流被抬高,冷空气叠加在地面γ中尺度热辐合中心之上,使山前局地大气层结更不稳定,另一方面,强冷池出流产生的边界层高层偏北风与近地面弱的偏南风构成有利于对流新生的垂直风切变,地面热辐合中心、边界层热力和动力不稳定的增强共同作用是局地雷暴新生的主要机制;上游冷池出流边界（阵风锋）伴有的强温度梯度和边界层辐合上升运动是原有局地新生雷暴显著增强的主要原因;多单体雷暴相互碰撞合并产生的辐合上升运动是局地雷暴得以持续的关键因素。%Using data obtained from the four-dimensional Variational Doppler Radar Analysis System (VDRAS), Doppler radar, surface in- tensive automatic weather stations, wind profile and 4 times daily sounding, the initiating and intensifying mechanism of a strong local thun- derstorm on 9 August 2011 in Beijing area was analyzed. The results show that before the thunderstorm initiated, weak vertical wind shear, a large amount of unstable energy (CAPE to 2798 J· kg^-1) on atmosphere environmental field, high specific humidity ( 〉 20 g· kg^-1) air accumu- lating at the foot of mountains and a warm meso- γ scale convergence centre over the western city proper of Beijing were favorable to the for- mation and development of the convection. Cold pool outflow was uplifted because of topographic forcing effect of thunderstorms moved east- wards from the upper reaches of Beijing, thus cold advection superposed on the warm meso-γ scale convergence centre in ground layer made the local atmospheric stratification more unstable; both northerly wind in boundary layer generated by strong cold pool outflow and weak southerly wind in ground layer formed vertical wind shear favorable for convection geneses; the interaction of the surface warm convergence zone and the increasing hermodynamic and dynamic instability in boundary layer was main mechanisms. Upstream cold pool outflow bound- ary (gust front) with strong temperature gradient and upward motion of convergence in boundary layer were the main reasons which led to the significant strength of the original genesis local thunderstorm, while upward motion of convergence generated by collision and merging of multi-cell thunderstorms was a key factor of the local thunderstorm continuation.
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