中文摘要：

利用NCEP1°×1°再分析资料和常规气象观测资料,使用WRF模式对2012年7月21日发生在北京地区的一次特大暴雨天气过程进行数值模拟.在模拟结果的基础上,分析了此次暴雨过程的形势演变和水汽条件,并分别计算了暴雨发生过程中北京全市范围内的水汽输送、水汽收支、大气可降水量和空中各相态水物质的量值大小、空间分布情况及其相互转化关系.结果发现：这次降水主要受高空槽、低涡和地面切变线的影响.有东南、西南两条水汽输送通道,计算区域上空水汽收支变化与地面雨强的演变对应很好.中低层持续而强烈的水汽净输入,为暴雨的发生发展提供了很好的水汽条件.北京各站点大气可降水量普遍超过历史极值,反映了降水的极端性.降水发展不同阶段,云内微物理过程存在差异,降水量初期以暖雨为主,降雨量不大,之后冷雨过程增强,降水量迅速增大.

英文摘要：

Using NCEP 1°×1 ° reanalysis data and conventional observation data,a numerical simulation and analysis on a rainstorm on July 21,2012 in Beijing were studied with the WRF model.Moreover,the large-scale weather situation and water vapor conditions were analyzed,and then the water vapor transportation,budget,atmospheric precipitable water,the concentration,distribution and transformation of water at each phase during the rainfall were calculated.The results indicated that the upper-level trough,low-level vortex and surface wind shear were the main influencing systems to the rainfall.There are two water vapor transportation channels：southeast and southwest.The water vapor budget in mid-low level corresponded well with rainfall intensity.The sustaining and strong net input of southeast and southwest warm wet air was an important water condition for the heavy rainfall.Atmospheric precipitable water at all meteorological stations in Beijing were higher than those in history.In the early period,precipitation was mainly warm rain process with moderate amount,then the cold rain process enhances quickly and the rain amount rapidly increases.