一次副高影响下的局地强风暴触发及维持机制探析

Analysis and Explanation on Triggering and Maintaining Mechanism of a Localized Severe Storm Under the Influence of Subtropical High

利用自动站观测资料、FY-2G卫星资料和多普勒雷达等资料,对发生在副热带高压影响下的重庆局地强风暴过程进行了观测和数值模拟分析,探讨了其中尺度对流系统(MCS)演变,抬升触发和维持机制。结果表明:(1)在副热带高压影响下,重庆处于高温、高湿气团中,大气层结极不稳定;(2)此次局地风暴抬升触发的关键因子是地面附近浅薄边界层中尺度辐合线,辐合线由川渝盆地中西部MCS的雷暴高压与重庆地面热低压共同作用形成;(3)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,并再次触发新的对流单体。承载层平均风为偏南风,使得对流单体向北缓慢移动,冷池出流和边界层辐合线共同作用使得风暴单体向西向北传播和长时间维持。

Based on conventional automatic meteorological data, FY-2 G satellite data, Doppler radar data and other related data, a localized severe storm under the influence of subtropical high in Chongqing is analyzed and simulated. This paper discusses evolution process of mesoscale convective system(MCS), triggering and maintaining mechanism. The results show that mesoscale environment of high temperature,high humidity air mass and extreme unstable atmospheric stratification conditions were provided under the influence of subtropical high. The triggering key factor of the local convective storm was mesoscale convergence line in shallow boundary near the ground. The convergence line was generated by combined contribution from thunderstorm high pressure of MCS in the central and western Sichuan and Chongqing Basin and the surface thermal low in Chongqing. Small range of cold pool outflow was generated by convective storm triggered by convergence line. A new convergence line was formed by small range of pool generated by convective storm triggered by mesoscale convergence line and ground ambient wind, strengthening development of convection storm and triggering new convection cells. The convective cells moved slowly northward under the average south wind in the bearing layer. Thus the cold pool outflow and the boundary convergence lines caused convective cells to propagate northwestward and maintain a long time.