基于多源资料的一次弓状强飑线成熟结构研究

Analysis on the mature-stage structures of a arc-shaped strong squall line based on multi-source data

利用局地分析和预报系统(Local Analysis and Prediction System,LAPS),结合多源资料,分析了2018年3月4日暖区强飑线成熟阶段的热动力结构和大风形成机制。结果表明:暖区内层结不稳定范围向东扩展和强的垂直风切变,驱动飑线组织化加强并向前移动和发展。成熟阶段飑线热动力结构呈现出两支强入流和冷池的典型特征,即前侧入流在低层(0~3.0 km)辐合上升,部分气流在高层翻转流向系统前侧,无后向流出;后侧中层(4.0~5.5 km)入流进入云体后部,在水凝物强烈相变降温作用下,密度增大转而下沉;下沉气流区降雨蒸发冷却增强了雷暴冷池。相比于飑线南段单一的对流线,北段弓形特点突出,后侧入流下降,加之存在尾随层状云,有更大的潜在冷却作用,促进气流加速下沉增强地面雷暴高压,最终导致更强的极端大风。

Local Analysis and Prediction System(LAPS),combining multiple data sources,were used to investigate the severe surface wind formation mechanism and the mature-stage structures of a warm-sector severe squall line occurring on 4 March 2018.An organized squall line was formed and moved forward due to the strong vertical wind shear and instability stratification spreading eastward in the warm zone.At the squall-line mature stage,the thermal dynamic structure was characterized by two strong inflows and a cold pool.The front-to-rear inflow converged in the low layers and then rose,and part flowed forward aloft without obvious rearward storm outflow.The mid-tropospheric rear inflow at a height of 4.0-5.5 km intruded into the back edge of the storm,and then sunk due to strong sublimation cooling.Over this downdraft region,cold pools strengthened due to rain evaporative cooling.The north and south structures of the squall-line bow echo displayed only a convective line and convective line followed by a narrow stratiform precipitation region,respectively.In the northern section,the presence of a stratiform precipitation region can lead to a more significant cooling potential.That can cause the rear inflow to descend closer to the surface,resulting in a stronger thunderstorm high and potentially reinforcing severe surface winds.