雷暴大风环境特征及其对风暴结构影响的对比研究

2009年6月3日,受冷涡后部次天气尺度横槽的影响,在相邻的两个区域先后出现雷暴大风天气,造成两地强风的风暴类型、地面大风分布及灾害程度差异显著。风暴结构分析表明:产生晋陕大风的雷暴类型为一般单体风暴和脉冲风暴,而产生商丘致灾大风的则为典型的弓形回波。结合观测和数值模拟资料分析产生上述两类雷暴大风的环境要素,并构建其环境温、湿度廓线,结果表明:(1)晋陕大风区环境探空温、湿度廓线呈倒V形,为典型的干下击暴流探空廓线,类似探空在中国西部高原地区夏季常见;(2)商丘雷暴大风区环境温、湿度廓线类似典型湿下击暴流探空。数值模拟给出了典型的一般单体特征结构,老雷暴单体出流在其前方触发新单体。在中低层相对干的环境下多个对流单体的冷下沉形成冷池,强风由对流单体下沉辐散气流叠加在冷池密度流上造成。两类雷暴大风环境风垂直切变特点为:深层环境风垂直切变较弱、强水平风垂直切变集中在中低层。数值模拟表明:在这种风垂直切变配置下,低层湿度成为风暴结构的决定因素:中-高湿度环境下形成高度组织化的飑线,且其单体具有较强中层旋转;低湿度环境下产生组织程度差的一般单体和脉冲风暴,并基于高分辨率数值模式模拟结果给出了环境影响风暴结构的物理图像。

Comparative study of environmental characteristics of a windstorm and their impacts on storm structures

Thunderstorm high wind occurs on 3 June 2009 in the two adjacent regions under the influence of the subsynoptic scale tough, which is in the rear part of a cold vortex. These two wind areas are significantly different in terms of storm structure, surface high wind distribution and severity degree. The storm structure analysis results show that the Jinshan strong winds are caused by single-cell storms and pulse storms, and Shangqiu high winds are caused by typical bow echoes. Environmental factors of these two wind stroms are investigated based on the observation and numerical simulation, and the composite environmental temperature and humidity profiles are built. The results show that: (1) The Jinshan environment temperature and humidity profile is the "inverted V" profile, which is the typical sounding of dry microbursts. This kind of sounding is common at China's western plateau area in summer time. (2) The Shangqiu temperature and dew point profile is similar to typical wet downburst sounding. The high resolution numerical simulation results show the structure of an single-cell storm, that is, the outflow from old convection triggers new cells on it's leading edge. The cold pool is generated by the cold downdrafts of multiple isolated convection cells in relatively dry environment. High wind occurred at the position where cold pool density airflow is overlapped with downdraft divergence airflow of a relatively strong single-cell. The bulk vertical wind shear is weak in the two windstorm regions, and the strong vertical wind shear concentrate at low levels. The numerical simulation results show that under this vertical wind shear, lower humidity conditions determines the storm structure. Under a medium to high moisture environment, it is highly organized as squall lines. Under a low humidity environment, poorly organized single-cell storms or pulse storms are generated. The formation processes with respect to the different storm structures are described in detail at the last part of this article.