Abstract:

Based on the conventional observation data and new monitoring data, the characteristics of satellite cloud images, radar echo and extreme wind speed field from automatic weather stations during the squall line process in North China from 13 to 14 June 2016 were analyzed. The results are as follows: (1) The “0613” squall line process occurred under the vapor environment conditions with dry in upper-layer and wet in lower-layer. Under the influence of Mongolia cold vortex, the convective clouds generating in Hetao area developed and merged into an organized squall line system between the cold shear lines from 700 hPa to 850 hPa. (2) In the strong stage of squall line, there was an obvious weak echo channel, and on the radial velocity map, the cyclonic shear of westerly and easterly winds in western part of the squall line formed, whereas the strong anti-cyclonic shear in eastern part formed. The convergence of wind direction and wind speed was significant at the top of bow echo. The inclining downward inflow jet in the rear of the squall line guided the dry and cold air with high kinetic energy in middle layer to the ground, which strengthened the downdraft of convective storm, and the sinking motion and cold air inflow had come together to strengthen the pressure gradient in the front of the squall line, that was the main reason of surface gale. (3) The convective clouds generating in low pressure warm sector in the front of the squall line developed and merged into a supercell storm near the shear lines in extreme wind speed field of automatic weather stations. The inflow in middle and high levels in the rear of the supercell storm led the dry and cold air with high kinetic energy to the ground, which enhanced the ground outflow and convergence uplift in the front of supercell storm, and then resulted in a longer life of the supercell storm and the large hail lasted nearly 4 hours in Changzhi of Shanxi Province. (4) Under the different environment conditions, the vertical structure, moving velocity and the causing strong convective weather of the same squall line system were obviously different. (5) The generation of shear lines in extreme wind speed field from automatic weather stations was 30 to 40 minutes ahead of the occurrence of strong wind belt, which had indicative significance to the early warning of strong wind during the squall line process.

Key words: hail and gale, supercell storm;, squall line system

摘要：

利用常规气象观测和新型监测资料，分析了2016年6月13—14日华北飑线过程的卫星云图、雷达回波、自动站极大风速风场等特征。结果表明：（1）“0613”飑线过程发生在“上干下湿”的水汽垂直分布环境条件下；在蒙古冷涡影响背景下，河套地区生成的对流云团在前倾结构700 hPa与850 hPa冷式切变线之间发展合并，形成有组织的飑线系统。（2）在强盛阶段，飑线具有明显的弱回波通道，飑线西段为偏西风与偏东风形成的气旋式切变，东段为强的反气旋式切变；弓形回波顶点处风向、风速辐合显著，飑线内部后侧倾斜向下的入流急流将中层高动能的干冷空气向地面引导，加强了对流风暴的下沉运动，并与后侧倾斜向下的冷空气入流共同作用加强了飑线前侧的气压梯度，是地面大风形成的主要原因。（3）飑线前部低压暖区生成的对流云泡在自动站极大风速风场切变线附近发展合并形成超级单体风暴，其后侧中高层入流将高动能的干冷空气向地面引导，促使地面出流及风暴前沿辐合抬升运动增强，使得超级单体风暴生命维持较长，是山西长治大冰雹持续近4 h的主要原因。（4）同一飑线系统在不同环境条件下其垂直结构、移速及带来的强天气有明显差异。（5）自动站极大风速切变线的生成较雷暴大风带的出现提前30～40 min，这对飑线大风预警有指示意义。

关键词: 冰雹大风, 超级单体风暴, 飑线系统