2011年7月四川盆地两次突发性暴雨过程的对比分析

Comparative Analysis of Two Abrupt Heavy Rain Processes in Sichuan Basin in July 2011

本文利用常规观测资料、多普勒雷达产品和NCEP 1°×1°再分析资料,对2011年7月3日和7月23日四川盆地出现的两次突发性暴雨过程的雷达回波特征、环境条件和动力触发机制进行了对比分析。结果表明:"7.3"暴雨出现在典型东高西低环流背景下,水汽输送条件好,强降雨持续时间更长,而"7.23"暴雨出现在高空冷涡后部,对流不稳定能量大,垂直风切变较强,因此伴有冰雹、大风等强对流天气,其回波强度比"7.3"暴雨要强5 dBz左右,并具有低层弱回波和中高层回波悬垂等强风暴特征;大气非静力平衡强迫激发低层辐合是两次突发性暴雨的动力触发机制,大气非平衡值能提前6 h左右反应暴雨的启动和演变趋势,暴雨中心出现在非平衡负值中心附近。

By using the conventional meteorological data, Doppler radar data and NCEP/NCAR reanalysis data, the characteristics of Doppler radar＇s reflectivity, environmental condition and trigger mechanism of the heavy rain are analyzed and compared between two abrupt heavy rain processes occurring in Sichuan Basin on 3 July （7.3） and 23 July （7.23） 2011. The results show that： the ＂7.3＂ heavy rain happened un- der a typical circulation background, and moisture transporting to the heavy rain area from the South China Sea was smoothly, thus the heavy rainfall maintained so long, but the ＂7.23＂ heavy rain occurred behind the upper cold-vortex, and convective unstable energy was abundant and vertical wind shear was strong, thus this heavy rain process happened with hail and thunderstorm weather accompanied, its radar reflectiv- ity was 5 dBz stronger than ＂7.3＂ case and had the characteristics of severe storms such as the low-level weak-reflectivity and the upper echo-overhang. As a whole, the non-equilibrium force is contributed to the occurrence of heavy rain and it is the excited mechanism of the two heavy rainfalls, and the change of the divergence evolvement is consistent with the strength and the position of the heavy rain which would hap- pen 6 hours later.