重庆西部平行岭谷地形作用下的一次局地暴雨天气过程的分析

Analysis of a Local Rainstorm Process in Western Chongqing Under the Effect of Parallel Ridge-Valley Topography

利用加密自动站降水资料、ERA5再分析资料和雷达资料,分析了2020年6月16—17日重庆西部地区平行岭谷地形影响下的一次局地暴雨过程。结果表明:受副热带高压外围西南暖湿低空气流和高空槽引导入侵四川盆地的偏北气流在重庆西部形成稳定的低涡切变,以及平行岭谷地形作用下维持的中尺度辐合线的共同影响形成了此次暴雨过程。17日00—03时(世界时)在岭谷地区850 hPa以下边界层存在明显的水汽聚集、辐合上升以及不稳定性的强中心区,导致局地强降水产生。在岭谷地形作用下,冷锋配合沿辐合线北抬的辐合中心在迎风坡抬升,加强了垂直上升运动,使得锋前垂直环流风速加大,这是导致华蓥山南端以及东侧宽谷丘陵过渡区暴雨增幅的重要原因。中尺度对流系统的发展演变与地面辐合线的位置变化关系密切,平行岭谷地形辐合抬升作用使对流系统在华蓥山附近停滞,并在其南端两次发展加强。

Using the precipitation data of dense automatic weather stations,ERA5 reanalysis data and radar data,we analyze a local rainstorm process influenced by the parallel ridge-valley topography in western Chongqing from 16 to 17 June 2020.The results show that the rainstorm process happened under the combined influence of the stable low vortex shear formed by the southwest warm and humid low-level airflow around the subtropical high and the northward air flow intruding into the Sichuan Basin under the guidance of the high trough in western Chongqing,and the maintaining mesoscale convergence line under the influence of the parallel ridge-valley topography.From 00 UTC to 03 UTC 17 June 2020,there existed obvious moisture convergence,ascending motion and strong instability center in the boundary layer below 850 hPa in the ridge-valley region,which triggered the localized severe heavy rainfall.Due to the ridge-valley topography,the cold front and the convergence center moving northward along the convergence line lifted on the windward slope,strengthening the vertical ascending motion that enhanced the vertical circulation wind speed ahead of the front.This is an important cause for the rainstorm amplification in the southern end of Huaying Mountain and the eastern transition area of wide valleys and hills.The development and evolution of the mesoscale convective systems were closely related to the postion change of the surface convergence line.The convergence uplift of the parallel ridge-valley made the mesoscale convective systems stagnate near the Huaying Mountain and strengthen twice at its southern end.on the windward slope,strengthening the vertical ascending motion that enhanced the vertical circulation wind speed ahead of the front.This is an important cause for the rainstorm amplification in the southern end of Huaying Mountain and the eastern transition area of wide valleys and hills.The development and evolution of the mesoscale convective systems were closely related to the postion change of the surface convergence line.The convergence uplift of the parallel ridge-valley made the mesoscale convective systems stagnate near the Huaying Mountain and strengthen twice at its southern end.