一次东北冷涡下槽后强风与飑线后向入流演变及成因分析

本文利用NCEP分析资料、多普勒雷达观测资料、常规气象观测资料以及数值模拟结果,对2016年7月30日发生在华北、辽宁附近的一次强飑线过程中后向入流的演变及成因进行研究。结果表明,此次飑线发生在中纬度新生冷涡槽前,低层有水汽辐合区和地面辐合线对应,且过程中伴有较强的对流有效位能释放。飑线后部中层(冷涡槽后)一直存在α中尺度西风大值带,此大风速带造成了上下层相反的水平涡度,并形成喇叭形环流结构,该结构不同于经典飑线结构。飑线后部水平方向上水平涡度分布不均匀,并形成水平涡度旋度上正下负的分布,即导致中层强风区上部上升运动、下部下沉运动,该下沉运动引发飑线中的后向入流和低层强风速带形成。在中层,飑线的后部边缘始终有较强的风速大值带伴随飑线的发展,该大值带的形成与对流强弱和非热成风涡度有关,对流过程中低层非热成风涡度为负,中上层非热成风涡度为正,导致飑线后部中层西风加速和低层西风减速,有利于后向入流的发展和飑线的维持,当对流减弱时,非热成风涡度与后向入流均减弱。文中给出了后向入流形成演变的概念模式。

Cause and evolution analysis of rear inflow in a squall line with the influence of strong wind after trough of Northeast cold vortex

By using the NCEP analysis data, Doppler radar observation data, conventional meteorological observation data and the numerical simulation results, the evolution and causes of rear inflow during a squall line, occurred in North China and Liaoning area on July 30, 2016, have been investigated. The investigation shows that squall line occurred in front of the trough line of mid-latitude new Northeast cold vortex, where lower layer has water vapor convergence and wind convergence line on surface, which is accompanied by strong convection effective potential energy release. There is meso-a-scale westerly wind belt in the middle of the back of the squall line (and behind of trough of Northeast cold vortex), which results in the opposite horizontal vorticity and trumpet circulation structure in the vertical direction. The negative vorticity of horizontal vorticity in the middle-lower layers, which is favorable for the formation of the sinking motion, leading to the real inflow and strong wind zone in the lower layer, which formats and develops the squall line; meanwhile, the positive vorticity of horizontal vorticity of middle-upper layers is favorable to the ascending movement. The structure is different from the classical squall line structure. In the middle of squall line rear edge, there is a strong wind speed area with the development of the squall line. The formation of the strong wind speed area is connection with the convection strength and non-thermal wind vorticity. When convection develops strongly, there are negative non-thermal wind vorticity in the lower layer and positive in higher layer, which results in the rear westerly acceleration in middle layer and deceleration in lower layer and is favorable for the strengthening of rear inflow and convergence of airflow in front of convection system. On the contrary, when the convection is weakened, so do the non-thermal vorticity and rear inflow. The conceptual module of formation and evolution of rear inflow has been analyzed in paper.