2006年4月28日山东强飑线过程中尺度结构和动力机制分析

Analysis of mesoscale structure and dynamic mechanism for a severe squall line process in Shandong Province on 28 April 2006

利用探空、地面自动气象站、多普勒天气雷达和NCEP/NCAR再分析等资料,对2006年4月28日影响山东大部的强飑线过程的中尺度结构进行了诊断分析。此次强飑线是由东北冷涡横槽沿西北气流下滑激发对流发展形成的,冷涡横槽底部为后倾的干冷下沉气流区,干空气侵入有利于位势不稳定能量的储存。冷涡横槽在300hPa最为强盛,并连接横槽前后南北两支急流,对流层顶折叠特征明显;高空横槽区的地转调整运动引发中尺度重力波,促进了高空急流动量向对流层中下部的传输,加剧了地面大风灾害。风暴发生区具有明显的等熵面倾斜、对流不稳定和垂直风切变,具有倾斜涡度剧烈发展的条件。风暴发生区中低层散度场、垂直速度场和地面风压扰动场均具有典型中尺度重力波的结构特征,风暴和中尺度重力波相互耦合促进,是强飑线发展维持的重要动力机制。

Using data of sounding, surface automatic weather stations, and doppler radar, as well as NCEP/NCAR reanalysis data, a severe squall line process that affected the greater part of Shandong Province on 28 April 2006 is diagnosed and analyzed.The severe squall line was generated by convections triggered by a moving transversal trough of a northeast vortex.The backward-tilting dry and cold downdraft dominated the bottom layer of the transversal trough, and the dry intrusion was favorable for accumulation of unstable energy.The transversal trough was the strongest at 300 hPa, connecting southern and northern upper jet streams with obvious tropopause folding;the geostrophic adjustment of the upper transversal trough induced mesoscale gravity waves (MGWs), which promoted the downward transmission of upper momentum, acting as an important dynamic source for severe surface wind.The storm area had characteristic of slantwise isentropic surface, convective instability, and vertical wind shear, which satisfied the key condition of slantwise vorticity development.In the mature period of the squall line, the divergence, vertical velocity, and the perturbations of surface wind and pressure showed the characteristics of typical MGWs in the lower and middle layer of troposphere.The storm and MGWs forms a self-developed system, and it is a key dynamic mechanism to enhance the squall line.