Based on the observation data from the automatic weather stations, sounding station, Doppler radar, wind profile radar and NCEP reanalysis data, two torrential rain processes occurring on 20 July 2016 (hereafter referred to as "7·20") and 21 July 2012 (hereafter referred to as "7·21") were comparatively analyzed.The results are as follows: (1) Beijing area of "7·20" process was mainly affected by the low pressure trough in northern vortex, and the vortex moved slowly because the subtropical high stretched toward the northwest, while during "7·21" process Beijing was located in wide trough district at the bottom of cold vortex.(2) The strong water vapor convergence center appeared during two processes, and the specific humidity was high near the surface.(3) There were the dense belts and steep areas of pseudo-equivalent temperature isolines during two processes, but the dynamic force of front area in "7·20" process was stronger, and the upward transport effect of water vapor and energy in low level were more obvious.(4) The thickness in middle and upper level explosively increased in earlier stage of "7·21" process, which restrained the occurrence and development of convection.However, the thickness for the whole layer decreased owe to the invasion of cold air from the upper level to North China before the "7·21" process, the oblique pressure characteristic was obvious, which was benefit to the develepoment of convection.(5) Meso-scale analysis showed that the rainfall of "7·20" process was more stable, and the lightning hardly occurred, while the convective rainfall of "7.21" process was obvious, the convective cloud cluster merged and strengthened constantly on cloud images, and the structure of radar echo was closer, the organization was stronger.%利用自动站资料、探空资料、多普勒雷达和风廓线雷达资料以及NCEP再分析资料,对北京地区2016年7月20日(简称"7·20")和2012年7月21日(简称"7·21")2次特大暴雨过程进行对比分析.结果表明:(1)"7·20"过程主要受低涡北部的低压倒槽影响,副热带高压西伸北抬使得低涡移动缓慢,而"7·21"过程北京地区位于冷涡底部宽广的槽区;(2)2次过程都出现了强的水汽辐合中心,近地面存在高比湿区;(3)2次过程均存在假相当位温等值线密集带和陡立区,但"7·21"过程锋区的动力强迫作用更强,低层水汽和能量向上输送作用更为明显;(4)"7·20"过程前期高空有厚度"爆增效应",抑制了对流发展,而"7·21"过程整层厚度下降,前期冷空气从高层侵入华北地区,表现为明显的斜压性,有利于对流发展;(5)中尺度分析显示,"7·20"过程以稳定性降雨为主,降雨过程中几乎没有闪电发生;"7·21"过程主要以对流性降雨为主,云图上不断有对流云团合并加强,雷达回波结构更紧密,组织性更强.
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