摘要:四川盆地位于青藏高原的东侧，受其地理位置的影响，该地区的天气和气候复杂多变。尤其暴雨预报，是气象工作者一直面临的难题。本文利用欧洲中期天气预报中心ERA-Interim再分析资料、格点化的降水资料（CN05.1）以及常规气象观测站探空资料，从环流背景、水汽条件、动力和热力条件对比分析了2015年夏季四川盆地7月13~15日（"7.13"过程）和8月16~18日（"8.16"过程）两次暴雨过程的环境场，以期加深对四川盆地暴雨机制的认识。结果表明：1）相对稳定的大尺度环流形势为两次大暴雨发生发展提供了有利的背景场。2）两次过程均存在明显的高空急流和低空急流，并且"8.16"过程高空急流明显强于"7.13"过程，这也是两次过程降水强度存在明显差异的原因之一。"7.13"过程主要以低空北向急流输送孟加拉湾水汽到四川南部；"8.16"过程低空急流输送孟加拉湾水汽受四川东北部、重庆上空西南涡影响，主要以气旋性环流输送水汽到暴雨上空。3）从暴雨预报的指示意义上分析，两次暴雨过程大气均处于不稳定状态，假相当位温对于暴雨的强度和落区有较好指示。位涡扰动向低层传输，位涡的增大预示着强降水的发生。
关键词:暴雨/
环流背景/
水汽条件/
大气不稳定
Abstract:Sichuan Basin is located to the east of the Tibet Plateau. Due to its geographical location, weather and climate in this area are complicated and capricious. In particular, the rainstorm forecasting is one of the toughest problems that meteorologists need to solve. In order to understand the rainstorm mechanism in Sichuan Basin, the authors used the ERA-Interim reanalysis data, a gridded precipitation dataset and several conventional upper-air sounding data to analyze the environmental fields of two rainstorms that occurred in the summer of 2015 (the '7.13' process during 13-15 July and the '8.16' process during 16-18 August) from the following perspectives:The circulation background, the moisture condition, and the dynamic and thermal conditions in Sichuan Basin. Results show that:1) The relatively stable large-scale circulation provides a favorable background for the occurrence of the two heavy rainstorms. 2) There existed upper-level jet stream and low-level jet stream in both processes, and the upper-level jet stream in the '8.16' process was much stronger than that in the '7.13' process. This is one of the reasons why there was significant difference in the precipitation intensity between the two processes. For the '7.13' process, the low-level jet stream flowing northward transported water vapor from the Bay of Bengal to southern Sichuan. During the '8.16' process, the water vapor transported from the Bay of Bengal by the low-level jet stream was affected by the southwestern vortex over Sichuan and Chongqing, and then was transported to the rainy area by cyclonic circulation. 3) The atmosphere was unstable during the two rainstorm processes. And θse was a good indicator of the rain intensity and falling area for the two rainstorms. The potential vorticity disturbance propagated downward to lower levels, and its increase indicated the occurrence of heavy rain.
Key words:Heavy rainstorm/
Circulation background/
Water vapor condition/
Unstable atmosphere
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