四川盆地一次西南涡作用下大暴雨过程的短时强降水分析

利用常规地面、高空观测资料、自动站资料、NCEP1°×1°再分析资料和新一代多普勒天气雷达观测资料,分析2015年8月16—18日四川盆地持续性大暴雨过程,给出了此次大暴雨过程不同阈值短时强降水的时空分布特征,研究此次大暴雨过程中造成短时强降水的成因。结果表明:螺旋度的变化对短时强降水有指示作用,螺旋度等值线密集(稀疏),短时强降水增强(减弱)。水汽收支方程中,水汽通量散度项为短时强降水的发生提供了主要的水汽来源。永川雷达反演的风场上具有明显的低空急流、低层辐合,以及局地气旋性涡旋的中小尺度环流特征。通过对比分析发生在2013年6月30日的相似大暴雨过程,发现两次过程的关键影响系统均是西南涡。"8·17"大暴雨过程低涡前部偏南暖湿急流及低涡后部东北冷流均显著,是斜压锋生类短时强降水";6·30"大暴雨过程低涡前侧偏南暖湿急流显著,暖平流建立的不稳定起了主导作用,是暖平流强迫类短时强降水。雷达特征显示"8·17"过程强反射率因子面积小,回波质心发展较高,有明显的辐合特征";6·30"过程强反射率因子面积大,回波质心发展低,并伴有中气旋活动。

Analysis of Short - term Heavy Rainfall in a Rainstorm Process under the Action of Southwest Vortex

Based on conventional surface data, upper-air observation, automatic weather station observation, NCEP 1×1° reanalysis data, and Doppler radar data, one continuous heavy rain in Sichuan Basin from 16th to 18th Aug is analyzed. Time evolution characteristics of the developing rain area and intensity and spatial distribution of multi-level rain frequency are shown. The mechanism of short-time rainstorm in the heavy rain is researched. The results show that, water vapor, dynamic force and energy conditions contribute to the occurrence of short-time rainstorm under the favorable situation of large-scale circulation. Based on the retrieved wind from Yongchuan radar, the position and evolution of low-level jet, convergence lines and local cyclonic vortices can be accurately derived, which unveiled the causes of extreme short-time rainstorm in the west of Chongqing. The deeper the local cyclonic vortex is, the stronger short-time rainstorm becomes.