副高异常偏西背景下一次阵风锋主导的雷暴大风天气分析

Analysis of Thunderstorm and Gale Weather Dominated by the Gust Front in the West Background of Subtropical High Anomaly

利用西安多普勒天气雷达、L波段风廓线雷达和加密自动站探测资料,结合天气实况,对2018年7月26日发生在陕西一次副热带高压影响下的强风暴过程进行中尺度分析。结果表明:(1)本次强风暴伴随的阵风锋共维持了4 h,其中有3 h出现7级以上的大风,且最大风力达10级。阵风锋发展阶段和旺盛阶段,主体回波的最强反射率因子维持在55 dBZ以上,强中心位于6 km左右,对流单体顶高约在8 km,C-VIL基本在40 kg·m^(-2)以上。14:41西安雷达站速度剖面显示,风暴后侧有倾斜下沉气流存在,从风暴尾部自上而下直至风暴底部,最终在地面产生下击暴流。(2)副高西伸到陕西西界,使得西侧西风槽不能东移,有组织的风暴出现概率减小,提前预警的难度增加。(3)此次强风暴在高的对流有效位能(CAPE)环境下,抬升触发的关键因子是关中地区中尺度辐合线,当初生的对流云团下山后,中尺度辐合线触发的对流风暴形成小范围冷池出流与环境风场形成新的辐合线,加强对流风暴发展。(4)当阵风锋移动过程中遇到前方的对流云团时,将低层暖湿空气抬升,并随着上升气流输送到主体对流风暴中,迅速补充了主体风暴的能量,使得主体风暴再次强烈发展,延长了阵风锋的生命史。

Based on the observation data of Xi’an doppler weather radar,l-band wind profiler radar and encrypted automatic station,combined with the weather situation,a mesoscale analysis was conducted on the process of a severe storm under the influence of a subtropical high in Shaanxi province on July 26,2018. The results showed that:(1) The gust fronts accompanied by this severe storm maintained for 4 hours,among which 3 hours saw gale with force more than 7,and the maximum wind force was 10. In the development and vigorous stages of gust front,the strongest reflectivity factor of the main echo is above 55 dBZ,the strong center is about 6 km,the top height of convective cell is about 8 km,and the C-VIL is more than 40 kg/m^(2). The velocity profile of Xi’an radar station shows that there is inclined downdraft behind the storm,from the tail of the storm from top to bottom to the bottom of the storm,and finally produce downburst on the ground at 14:41.(2)The subtropical high extends westward to the western boundary of Shaanxi,making the west wind trough on the western side unable to move eastward,reducing the probability of occurrence of organized storms and increasing the difficulty of early warning.(3) The strong storm under the environment of high convection and effective potential energy(CAPE),the key factor of the trigger is the Guanzhong area mesoscale convergence line,after the initial convective cloud cluster descends the mountain,the convective storm triggered by mesoscale convergence line forms a small scale cold pool outflow,the outflow of the cold pool meets the environmental wind field and forms a new convergence line,it strengthen the development of convective storm.(4)When the gust front meets the convective cloud ahead in the moving process,it lifts the lower warm and humid air and delivers it to the main convective storm along with the updraft,rapidly replenishing the energy of the main storm,making the main storm develop strongly again and extending the life history of the gust front.