华南一次飑线升尺度增长过程的机制分析

利用中国自动站与CMORPH降水产品融合的逐时降水量0.1°×0.1°网格数据集、1°×1°NCEP再分析气象资料、常规观测资料和高分辨率的WRF数值模拟资料对2016年4月13日前后发生在华南的一次飑线升尺度增长过程进行了动力和热力环境条件分析。飑线形成前,对流层高层有急流,华南位于急流入口区右侧,有利于高空辐散。高空有弱槽存在,并且温度槽落后于高度槽,有利于槽发展。近地面上有低压系统控制,并且有风场的辐合,加强了抬升运动。模拟的结果表明:WRF模式成功模拟了此次飑线升尺度过程,飑线的降水量和落区较为接近实况。与以往的飑线过程相比,此次飑线过程中,升尺度阶段有效位能较初始对流阶段要高,但是整个华南地区对流有效位能始终处于中低水平。除了天气尺度系统的影响,多种中尺条件的配合对这次飑线升尺度发展很有利。低层的垂直风切变、低位涡和较高温度递减率是触发条件,提供了一定的不稳定条件和抬升条件。低层风场转向加强,垂直风切变的方向改变,充足的水汽供应和后部入流的加深加剧了不稳定和垂直抬升运动,是促进β中尺度飑线升尺度的重要条件。冷池在升尺度阶段不明显,但冷池对维持成熟阶段的α中尺度飑线结构很重要。

Mechanism Analysis of a Squall Line Upscale Growing Process in South China

In this paper,in order to better investigate the process of squall line,the national automatic weather stations and CMORPH product at 0. 1° ×0. 1° resolution、NCEP(National Centers for Environmental Precipitation)1°×1° reanalysis meteorological data、regular observation data and high-resolution WRF numerical simulation data are used to analyze the dynamic and thermal environmental conditions of the upscaling growth process of a squall line in south China around April 13,2016. Before the formation of the squall line,there is a upperlevel jet stream in the upper troposphere. South China is located on the right side of the entrance of the upper-level jet stream. There is a weak height trough in the upper level,and the temperature trough lags behind the height trough,which is beneficial to the development of the height trough. There is a low-pressure system on the surface and There is convergence of airflow in the low level of south China,which enhances the lifting movement.The simulation results show that The WRF model successfully simulates the upscale process of squall line,and the precipitation and the falling area of the squall line are relatively close. At the same time,compared with the previous squall lines,the convective available potential energy during the upscaling phase is higher than the initial convection phase,but the convective available potential energy in the entire south China region is at a low and middle level. In addition to the influence of synoptic scale system,the cooperation of various mesoscale conditions is beneficial to the upscaling development of squall line. The triggering conditions are vertical wind shear,low potential vorticity(PV)and high temperature declining rate in the lower level,which provide certain unstable conditions and lifting conditions. Low-level wind field turning and wind velocity strengthening,changes in the direction of vertical wind shear,sufficient water vapor supply and deepening of the rear inflow enhance instability and vertical lifting motion,which are important conditions for promoting the upscale growing of meso-β-scale squall line. The cold pool is not obvious during the upscale growing,but the cold pool is important for maintaining the meso-α-scale squall line structure in the mature stage.