福建沿岸一次飑线过程发生发展机理分析

Analysis on the Genesis and Development Mechanism of a Squall Line over Fujian Coast

利用常规观测资料、NCEP/NCAR(1°×1°)的逐6h再分析资料结合ARW-WRF中尺度数值模式模拟结果对2018年6月20日发生在福建沿岸的一次飑线过程的发生发展机理进行了分析,结果表明:①本次飑线过程属于槽前型,对流层低层存在发展的低涡切变,切变南侧有冷空气南下,低空西南急流不明显,但有持续的暖湿气流输送至福建中北部地区,飑线生成于低涡南侧的沿岸附近。②飑线发展期间系统南侧低层风速不断增大且维持高的水汽输送和不稳定能量;前期对流的触发因子包括锋面对流系统的冷出流、地形的抬升以及海风锋造成的冷堆强迫抬升;后期冷出流边界与海风锋边界碰撞合并,加强了低层辐合促进了对流的发展,是飑线形成的主要原因。③飑线成熟时期地面存在中高压和尾流低压,高压后部为强烈的辐散区,风速较大;成熟时期内部存在两支气流,前向入流为低层暖湿气流在飑线前方流入并在对流云区被抬升,后向入流为中层干冷空气在飑线后方流入,在低层形成下沉运动,是地面大风形成的重要原因之一。

Based on the routine observation,NCEP/NCAR reanalysis data and simulation data,a squall line occurred over the coast of Fujian on 20 June 2014 is analyzed.Results show:(1)This squall line was belonged to the pre-trough type,and there was a developing low vortex shear in the low-level of the troposphere,with a weak cold air going southward.The low-altitude southwest jet was not obvious,but there was continuous warm and humid air flow delivered to the northern central area of Fujian.The squall line was formed on the south side of the low vortex.(2)The simulation results show that during the development of the squall line,the low-level wind speed on the south side of the system increased continuously and maintained high water vapor transport and unstable energy.At the early stage,the triggering factors of the convection include the cold outflow of the front-system,the elevation of the terrain,and the forced uplift of the cold pile caused by sea breeze.At the later stage,the collision between the cold outflow boundary and the sea breeze front boundary strengthened the low-level convergence and promoted the development of convection,which was the main reason for the formation of the squall line.(3)The pressure field of the squall line appeared to be a meso high and a wake low in its mature stage.A surface divergence zone slightly lagged the meso high where there was strong surface winds.There were two airflows in the squall line at its mature stage.The forward inflow which was lifted in the convective cloud area was a low-level warm and humid airflow in front of the squall line.The rear inflow was a middle-layer dry and cold airflow behind the squall line,forming a sinking motion in the lower layer,which was one of the important reasons for the formation of strong winds on the ground.