重力波与对流耦合作用在一次山地突发性暴雨触发中的机理分析

利用欧洲中期天气预报中心（ECMWF）开发的新一代ERA5再分析资料、中国自动站与CMORPH降水产品融合的逐小时降水资料以及国家卫星气象中心FY-2G卫星云图资料，对2018年5月21～22日发生在四川盆地西南部的一次山地突发性暴雨过程中的重力波特征进行天气动力学分析。得到以下结果:此次山地突发性暴雨受到了波长约为150 km，周期为5 h的重力波活动的影响，是典型的β中尺度天气系统诱发的暴雨事件。此过程中的重力波主要是在地形和切变不稳定的共同作用下触发的。切变不稳定先于重力波的传播出现在下游降水区域，可表征切变不稳定的理查逊数对重力波传播方向及降水落区有很好指示作用。此次暴雨发生前，重力波中的上升支气流输送低层水汽到高空助力对流发展，而下沉支气流使得低层不稳定能量不断累积。随着东北低空急流的发展，在大气低层（700～800 hPa）东西风切变的过渡带内形成临界层，临界层不断吸收高空波动能量造成重力波能量下传，触发低层不稳定能量释放，促使对流不断加强，最终引发此次山地突发性暴雨。

Mechanism Analysis of a Sudden Rainstorm Triggered by the Coupling of Gravity Wave and Convection in Mountainous Area

Based on the ERA5 reanalysis data from ECMWF (European Centre for Medium-Range Weather Forecasts), the China Merged Precipitation Analysis data from stations and CMORPH (CPC (Climate Prediction Center) MORPHing technique], and the FY-2G satellite cloud image data from NSMC (National Satellite Meteorological Centre), the authors conducted a synoptic dynamic analysis on the characteristics of gravity wave during an abrupt rainstorm in the southwest region of Sichuan Basin on 21–22 May 2018. The results indicate that the sudden rainstorm in the mountain area was affected by the gravitational wave activity with a wavelength of 150 km and a period of 5 h. The gravity wave was triggered by the combination of terrain and vertical shear instability. The shear instability appeared in the downstream earlier than the propagation of the gravity wave. The Richardson number was a good indication of the direction of gravity wave propagation and precipitation area. Before the rainstorm, the updraft in the gravity wave transported the water vapor to facilitate the development of the convection, while the downdraft caused the unstable energy in the lower layer to accumulate continuously. With the development of the Northeast low-level jet, a critical layer was formed in the transition zone of the east–west wind shear between 700–800 hPa. The critical layer continuously absorbed the wave energy from the upper air and resulted in the gravity wave energy to be transmitted downward, triggering the release of the unstable energy in the lower layer and stimulating the convection to be strengthened continuously, which finally caused the sudden rainstorm.