2018年7月9日~11日四川暴雨天气过程分析

An Analysis of the Heavy Rain in Sichuan Basin from July 9 to July 11 in 2018

摘要: 本文利用ERA5再分析资料，网格距为0.25 × 0.25，对2018年7月9日~11日四川暴雨天气过程的高低空环流形势、涡度场、散度场、水汽通量和水汽通量散度等进行了详细的诊断分析，得到以下结论：(1) 此次暴雨天气过程是在中高纬倒“Ω”流型和台风“玛莉亚”的共同影响下，高原短波槽东移，引导来自西北部的冷空气南下至四川，同时副高西伸稳定于重庆，是造成本次暴雨的直接环流背景。(2) 强盛的偏南气流结合台风外围环流合并丰沛的水汽，在稳定西伸的副高边缘南部形成合流并向北流动，由此打通了自南向北的水汽通道，源源不断地为川东暴雨提供充足水汽，既增加了降水强度又对低层的低涡暖湿结构起到了维持作用。(3) 高原东移短波槽和台风“玛莉亚”相互作用，对暴雨的持续性有重要影响，同时副高稳定于重庆地区，致使暴雨落区集中分布于四川东部区域，从而造成了川东地区持续暴雨。

Abstract: Using the ERA5 reanalysis data with grid distance of 0.25 × 0.25, the circulation pattern, vorticity field, divergence field, water vapor flux and water vapor flux divergence over the upper and lower levels of the heavy rain process in Sichuan from July 9 to 11, 2018 were analyzed in detail. The results are as follows: (1) Under the combined influence of the mid-high latitude inverted flow pattern and typhoon Malia, the plateau shortwave trough moved eastward, leading the cold air from the northwest down to Sichuan, at the same time, the westward extension of the subtropical high is stable in Chongqing, which is the direct circulation background of the rainstorm. (2) The strong, southerly air current combined with the outer circulation of typhoon combined with abundant water vapor, formed a confluence at the southern part of the edge of the subtropical high extending westward and flowed northward, thus opening the water vapor passage from south to north, to continuously provide sufficient moisture for the torrential rain in eastern Sichuan. It not only increases the intensity of precipitation, but also maintains the low-level vortex warm and wet structure. (3) The interaction between the short-wave trough moving eastward over the plateau and typhoon Malia has an important effect on the persistence of the rainstorm, and the subtropical high is stable in Chongqing area, which causes the rainstorm areas to be concentrated in the east of Sichuan. That’s causing continued heavy rain in the Eastern River.