Abstract: A continuous rainstorm process occurred in the west of Sichuan Basin from 8 to 11 July 2018, which lasted for a long time and concentrated in the west of the basin, and resulted in serious flood disasters. Based on NCEP/NCAR reanalysis data, meteorological observation data from conventional weather stations and intensive automatic weather stations of Sichuan, the water vapour condition, dynamic condition and mutil-scale systems of the continuous rainstorm process were diagnosed and analyzed. The results are as follows: (1) The persistent rainstorm took place in favorable atmospheric circulation background. The west Pacific subtropical high moved westward and maintained steadily, which restricted the moving direction and speed of upper trough in the mid-latitude region, and further led to the information of block high over Sichuan Basin. Meanwhile, the pressure gradient between the west Pacific subtropical high and typhoon increased under the gradually moving westward of typhoon ‘Maria’, and the southerly wind in low level strengthened.  (2) The abundant water vapor from the South China Sea was transported to Sichuan Basin, which was the necessary condition for the formation of persistent rainstorms in Sichuan Basin. The southerly wind in the lower troposphere was gradually maintained and enhanced with the moving westward of typhoon. The northeasterly airflow in the west side of typhoon shifted to the southeasterly airflow in the south side of the west Pacific subtropical high, and strengthened in the southeast side of southwest vortex, which formed the obvious airflow convergence, and made water vapor accumulate rapidly. (3) The interaction between multi-scale systems prompted the information and development of southwest vortex, which was a main cause of the maintaining and enhancing at later stage of continuous rainstorm in Sichuan Basin. The westwards extending location and intensity of subtropical high between the southwest vortex and the landing typhoon ‘Maria’ determined the sinking branch of secondary vertical circulation, and further restrained the falling areas of rainstorm.

Key words:  continuous rainstorm, the west Pacific subtropical high, typhoon, southwest vortex, water vapor condition

摘要： 利用常规气象站和地面加密自动站气象观测资料、NCEP/NCAR再分析资料等，针对2018年7月8—11日四川盆地西部的一次持续性暴雨天气过程，从水汽条件、动力条件及多尺度系统等方面进行诊断分析。结果表明：(1)此次持续性暴雨过程是在有利的环流背景下发生的，西太平洋副热带高压西行并稳定维持，制约了中纬度高空槽的移动方向和速度，导致在四川盆地形成阻塞。与此同时，在台风“玛利亚”的逐步西行下，台风与西太副高之间的气压梯度增大，低空南风气流增强。(2)此次暴雨过程的充沛水汽主要来源于南海，强台风西侧的东北气流在西太副高南侧转为东南气流，并在西南低涡东南侧加强，形成明显的气流辐合，使得水汽迅速堆积。(3)多尺度系统之间的相互作用促使西南低涡生成发展，是此次持续性暴雨得以维持并在后期增强的一个主要原因，而西南低涡与台风之间西太副高西伸位置及强度决定了次级垂直环流的下沉支，进而约束暴雨的落区。

关键词: 持续性暴雨, 西太平洋副热带高压, 台风, 西南低涡, 水汽条件