2012年7月中旬克拉玛依罕见强对流天气的数值模拟分析

Numerical Simulation on a Rare Severe Convective Event in Karamay City in July 2012

本文利用NCEP—FNL分析资料、自动站观测资料、卫星云图、天气雷达探测资料以及WRF模式的模拟结果,对2012年7月14日新疆克拉玛依罕见的短时强降雨和冰雹强对流天气的机理进行了诊断分析,结果表明:在大尺度湿性不稳定层结的环境场中,冷空气的入侵在山区地形配合下,在背风坡侧造成强烈的水平温度梯度和地面辐合线,利于强对流的发生。WRF模拟结果显示,高低空风速大值区的配置,环境风场的垂直切变,垂直方向上假相当位温的鞍形配置给垂直上升运动的加强提供基础,使最大上升速度达到6.5 m·s^(-1),上升高度达9 krn,同时也看到,由于中层湿中性层结较薄,难以长时间维持上升运动的发展,上升运动区较为窄小,强降雨发生区域仅为二十几千米。山区地形对强对流发展的作用较为复杂但也很明显,地形阻挡加强了地面风场的切变辐合,同时气流过山引发正负位势涡度带的生成和传播,激发垂直环流的形成,为强对流发展提供动力条件。

One severe convective weather event which is so rarely seen in arid areas,occurred in Karamay City of Xinjiang on 14 July 2012.The convective event lasted for more than an hour,accompanied by short-time severe downpour and hail.The process of convection is studied with composite dataset including NCEP-FNL analyses,automatic weather station observations,satellite cloud image,Doppler weather ra-dar and simulations of mesoscale numerical model WRF.The results show that,in the background of large-scale instable moist stratification and complex mountain terrain,horizontal temperature gradient and topographic convergence shear get enhanced on the lee side of mountain where convective weather develops easily.The numerical simulation results of WRF model indicate that the configuration of high-and low-level wind,vertical shear of horizontal wind and saddle type of vertical pseudo-equivalent potential temper-ature provides power for the ascending motion,driving the W-wind speed rapidly to the maximum 6.5 m· s-1 and top level of ascending up to 9 km.The thin layer of moist neutral stratification limits the growing of vertical ascending motion so that the area of ascending motion is narrow and small,causing the severe precipitation to happen only in a local area.Mountainous terrain plays an obvious and complicated role in developing strong convection.The convergence of ground wind is enhanced by orographic effect,and the nonlinear disturbance of airflow over mountain prompts the rapid development of severe convection.