海风辐合线对雷暴系统触发、合并的动热力过程

Analysis on Dynamical and Thermodynamic Process of Thunderstorms Triggered and Merged by Sea-Breeze Convergence Lines

利用加密自动气象站和雷达监测资料,结合VDRAS资料(其时间分辨率12 min、水平垂直分辨率分别是3和1 km左右),分别针对单纯海风辐合线触发和海风辐合线与已有雷暴系统合并的两个实例,揭示海风辐合线对雷暴系统影响的动力和热力过程。结果表明:(1)在环境系统风很弱时,天津沿海海风伸入内陆的移速约为15~18 km·h^(-1),且海风过后,气温降低、湿度加大。(2)海风辐合线配合地面高不稳定区,从而触发和加强了雷暴系统,对雷暴系统的预警时间可达2 h。(3)雷暴单体在海风辐合线附近产生,这与倾斜海风锋锋面(向海洋一侧倾斜)上的中尺度垂直环流相对应。(4)海风辐合线与雷暴系统合并后,雷暴系统强烈发展是由于海风辐合线附近积聚着水汽,同时也是辐合上升运动大值区的缘故。

Using radar and intensive AWS (automatic meteorological station)data as well as VDRAS data whose temporal resolution is 12 min,horizontal and vertical resolutions are respectively 3 km and 1 km or so,the dynamical and thermodynamic processes of thunderstorm systems that are impacted by sea-breeze convergence lines are investigated by analyzing the two cases triggered by pure sea-breeze convergence line and by the merged sea-breeze convergence and existing thunderstorm system.The results showed that:(1)When the environmental wind system is very weak,the moving sea breeze speed of Tianjin coastal sea breeze into the inland is about 15-18 km·h-1 ,and,after the leaving of sea breeze,temperature there de-creases and humidity increases.(2)The sea-breeze convergence line cooperates with the surface highly un-stable region,triggering and strengthening the thunderstorm system,so that the thunderstorm warning can be 2 h in advance.(3 )Thunderstorm cell forms near the sea-breeze convergence line,which corre-sponds to the mesoscale vertical circulation in the frontal surface (to the sea side)of the tilting sea breeze front.(4)After sea-breeze convergence line merges with the thunderstorm,the severely development of the thunderstorm is attributed to the accumulated water vapor near the sea breeze and the large zone of convergent updraft.