一次苏皖特大暴雨过程中边界层急流结构演变特征和作用分析

Analysis on Variable Characteristics of Boundary Layer Jet Structure and Its Function in the Process of Super Heavy Rainstorm Occurred in Jiangsu and Anhui Provinces

利用加密自动气象站、多普勒雷达和NCEP再分析资料,结合中尺度数值模式的模拟结果,详细分析了2008年8月1日苏皖地区特大暴雨过程的演变特征及形成机理。研究表明,与特大暴雨过程始终伴随的边界层急流促进了降水的发展与加强,在特大暴雨产生的动力和水汽输送条件上扮演着重要角色。边界层急流的波动与降水的发展密切相关,中层弱冷空气的入侵使边界层急流明显减弱,导致了降水区中大气对流不稳定结构与垂直风切变的增强,使对流性降水发展,在经历短暂的减弱之后,边界层急流后部南风再次增强并推动其北侧切变线的发展,在两者的共同作用下,暴雨区内局地的辐合与气旋性涡度大大增强,并强迫出一支狭窄而深厚的上升气流,促进了暴雨区及附近的中小尺度对流系统发展,使降水发展至最强。另外,与边界层急流相伴随的一支水汽通量辐合带是这次暴雨主要的水汽输送通道。

Using the intensive automatic weather station data,Doppler radar data,NCEP reanalysis data and the simulated results with mesoscale numerical model,the rainstorm occurred in Jiangsu and Anhui Provinces is studied.The precipitation evolution characteristics and formation mechanism of the rainstorm are also analyzed in detail.The results show that the boundary layer jet accompanying with rainstorm all the time accelerats development and enhancement of precipitation,especially it plays the important role in dynamical and vapor transport condition of the formation of heavy rainstorm.The boundary layer jet disturbances is closely connected with the evolution of precipitation,the invasion of cold air from mid-level apparently weaken the boundary layer jet,but intensified the atmospheric convection instability structure and vertical wind shear in rainstorm region,thus convective precipitation enhanced.After brief weakened,southerly in the rear of the boundary jet strengthen,which promote development of the shear line on its north side.During to the joint effects of them,local convergence and cyclonic vorticity greatly intensify in rainstorm region,meanwhile a narrow and deep updraft is forced,which promote the development of mesoscale and microscale convective system in rainstorm region and vicinity and lead to a climax of precipitation.Besides,the boundary layer jet always goes with a water vapor flux convergence band and it is main water vapor transport channel.When the boundary layer jet develops,the water vapor flux convergence in rainstorm region enhances and precipitation developes as a result.