太行山地形影响其东麓强对流系统触发、发展、移动路径的个例分析

Influence of the Taihang Mountains on the Initiation,Development,and Track of a Convective Precipitation System

2017年5月22日,受500 hPa高空槽、850 hPa切变线、地面冷锋,以及中尺度辐合线的共同作用,一次较强的对流性降水过程发生在太行山东坡200~800 m海拔高度区域。利用高分辨率的WRF数值模式,重点分析了太行山地形对对流系统触发、发展、移动路径的影响。研究发现山脉—平原的陆面分布在日辐射的作用下,能够在特定的地形结构处形成气候场上的地形辐合区。此地形辐合区在冷锋系统的动力抬升作用下形成了更强的地形辐合带,从而促进了对流单体群在此地形辐合带中的触发。研究还发现,对流单体群均是沿着地形走向移动,其移动路径均在山脉坡度较大的位置。对流系统的强度变化与太行山东部的山脉—平原环流系统密切相关。一方面,山脉—平原环流系统的近地层东风异常与太行山脉东麓地形相耦,增强了太行山山脚附近对流发展的动力抬升作用;另一方面,东风气流增强了来自东部平原地区的水汽输送。暖湿气流在地形抬升和山脉—平原环流系统上升支的共同作用下,增强了对流单体的降水强度。研究认为太行山东坡上对流系统的触发、发展、移动均与局地地形的坡度、坡向存在密切关系。能够增进对太行山东坡强对流天气的理解,为其短时强降水预报提供理论参考。

On May 22,2017,strong convective precipitation occurred at an elevation of 200-800 m on the foot of the Taihang Mountains,which was controlled by a 500-hPa cold trough,850-hPa shear line,cold front,and mesoscale convergence line.The effects of topography on the initiation,development,and tracking of convective systems were analyzed based on the results of high-resolution numerical simulations using the WRF model.The results show that a topographic convergence zone was formed under the influence of solar radiation on the mountain-plain land surface.The cold front strengthened the topographic convergence zone and triggered convective clusters from the convergence zone.The results also showed that the convective clusters moved along the orientation of the local topography,where the local slope was steeper.The intensity of the convective clusters was closely related to the Mountain-Plains Solenoid(MPS)on the east side of the Taihang Mountains.First,the low-level easterly anomaly of the MPS coupled with the local terrain enhanced uplift near the foot of the Taihang Mountains.Second,the easterly flow intensified the water vapor transportation from the eastern plain.The large amount of water vapor carried by the MPS-induced easterly wind was forced to ascend due to topographic obstruction;therefore,convective cells developed.The results suggest that the slope gradient and slope aspect of the local terrain played a key role in the initiation,maintenance,as well as the track of the convective clusters along the eastern foothills of the Taihang Mountains.This analysis contributes to the understanding of the development of convective precipitation systems on the eastern slope of the Taihang Mountains and forecasting short-term heavy rainfall events.