关键词: 特大暴雨, 环流背景, 对流条件, 对比分析

Abstract:

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.

Key words: torrential rain, atmospheric circulation situation, convective condition, comparative analysis