2018年7月四川盆地西部一次区域性暴雨成因诊断分析

Diagnostic Analysis of the Cause of a Regional Rainstorm in Western Sichuan Basin in July 2018

摘要: 利用来自中国气象局业务系统Micaps的常规观测资料、降水资料以及风云卫星资料等，从天气形势、物理量和卫星云图等角度进行分析总结，揭示了2018年7月9日至7月12日四川盆地西部一次区域性暴雨过程的成因。结果表明：1) 本次暴雨的环流形势属于典型的“东高西低”型，高原槽向东移动，槽前正涡度平流诱导低空西南涡的生成，引发暴雨；台风“玛莉亚”推动西太平洋副热带高压西伸北抬，向四川盆地西部持续不断地输送水汽，并且阻挡低值系统东移出川，使其长时间稳定在四川盆地上空，导致暴雨的维持和增强。除此之外，南亚高压、高空急流、低空切变线、低空急流等影响系统相互配合，以及地形的抬升作用，都促进暴雨不断发展增强。2) 在本次暴雨过程中，四川盆地西部水汽充沛并且有强烈的辐合；大气低层辐合、高层辐散，具有强烈的上升运动；但能量条件并不理想，动力作用在本次暴雨过程中占据主导地位，充沛的水汽供应和强烈的上升运动才是本次暴雨发生的关键。3) 在暴雨发生期间，四川盆地上空对流云团发展旺盛，尤其是“7•11”特大暴雨发生期间，伴随着有中尺度对流复合体(MCC)生成。

Abstract: Based on the conventional observation data, precipitation data and satellite data from MICAPS, the causes of a regional rainstorm in the Western Sichuan Basin from July 9 to July 12, 2018 are revealed. The results show that: 1) the circulation pattern of the rainstorm is a typical “high in the east and low in the west”. The plateau trough moves eastward, and the positive vorticity advection in front of the trough induces the formation of the low-level southwest vortex, which leads to rainstorm; typhoon “Maria” pushes the subtropical high of the Western Pacific to extend westward and northward, and continuously transports water vapor to the Western Sichuan Basin, and blocks the low value system from moving eastward out of Sichuan, making it long time stable over Sichuan Basin, leading to the maintenance and enhancement of rainstorm. In addition, the interaction of South Asia high, high-altitude jet, low-altitude shear line, low-altitude jet and other influence systems, as well as the uplift of terrain, all promote the continuous development and enhancement of rainstorm. 2) In this rainstorm process, there is abundant water vapour and strong convergence in the west of Sichuan Basin; the convergence in the lower layer and the divergence in the upper layer of the atmosphere have strong upward movement; however, the energy condition is not ideal, and the dynamic effect plays a leading role in this rainstorm process, and the abundant water vapour supply and strong upward movement are the key to this rainstorm. 3) During the rainstorm, convective cloud clusters developed vigorously over Sichuan Basin, especially during the “7.11” rainstorm, accompanied by mesoscale convective complex (MCC).