加密观测资料在北京2008年9月7日雷暴过程分析中的综合应用

Synthetic Applications of Intensive Observations to Analysis of the 7 September 2008 Severe Convective Systems in Beijing

利用多种加密观测资料,对2008年9月7日凌晨北京一次雷暴过程进行详细中尺度分析,研究其发生发展的物理机制。研究结果表明,强对流发生前,北京地区处于200 hPa急流轴右后部和850 hPa暖式切变南侧的西南气流里,加上地面暖湿空气输送使得大气不稳定能量积聚,这时只要有恰当的触发机制或系统,强对流就会发展起来;另外城市热岛效应形成的地面辐合线,以及地形辐合抬升后卷形成的边界层扰动,使得移入北京的对流系统再度发展成为强对流,造成北京城区强降水;此后,强对流系统地面高压前部的流出气流与山风相遇形成新的地面辐合线,从而诱发新的对流系统而造成北部强降水。

Using multiple intensified observation data,detailed mesoscale and microscale analyses are undertaken on the severe convective systems in the early hours of September 7,2008 over Beijing.Results show that,before the thunderstorms develop,Beijing lay in the right rear quadrant of 200 hPa jet streams and also in the southwesterly on the south side of the 850 hPa warm shear.Combined with the accumulation of unstable energy due to the low level warm-moist air advection,appropriate low level lifting mechanism or triggering would raise severe convective systems therein.Those MCSs,which moved eastward into Beijing,developed into severe convective systems again,after encountering the surface convergence line caused by urban heat island effect and the boundary layer disturbance caused by uplift and back roll of the topographic convergence,leading to a torrential rain event in the urban area of Beijing.Moreover,in northern Beijing,new thunderstorms were triggered by the surface convergence line,which was formed by the colliding between the outflow in front of surface high and the mountain breeze.