天山峡谷穿谷急流触发强下坡风暴的 中尺度特征分析

Mesoscale Analysis of Severe Downslope Windstorm Caused by Gap Jet in Tianshan Mountain Canyon

天山峡谷穿谷急流与峡谷内非对称地形交互作用触发的下坡风暴,造成2007年2月28日新疆吐鲁番盆地境内旅客列车侧翻的重大天气灾害。为了解这次极端大风过程中大尺度环流背景、中尺度系统和复杂地形相互作用触发下坡风暴的机理,使用WRF模式进行了数值模拟和中尺度诊断分析,结果表明:在天山两侧强气压梯度作用下,气流爬坡进入天山峡谷后因狭管效应形成穿谷急流,与此同时气流爬坡进入天山峡谷过程中受地形强迫形成重力波,并在背风坡的断崖式突降地形区产生背风波,将穿谷急流的能量向地面传输,最终形成背风坡下坡风暴。在此过程中重力波波破碎形成的湍流活跃层和中低空风向切变的临界层吸收上层波能量向下传输加强了穿谷急流的能量,大气稳定层结则加剧了将能量向地面输送的下沉运动。

Severe downslope windstorm triggered by the interaction between the gap jet and the asymmetrical topography in the Tianshan Mountain canyon caused severe disasters of trains rollover in the Turpan Depression in Xinjiang on February 28,2007.To understand the mechanism of downslope windstorm between the interaction of large-scale circulation background,mesoscale system and complex topography in this extreme windstorm,we use a WRF model and conduct numerical simulation and mesoscale diagnostic analysis.The results show that under the pressure gradient between north-south sides of the Tianshan Mountain,the air parcel climbed windward slope and flew into the Tianshan Mountain canyon and then formed gap jet due to effect of funnelling,and at the same time,the jet generated gravity waves forced by the asymmetric terrain of the Tianshan Mountain canyon,and produced lee waves in the leeward,which transmitted the energy of the gap jet to the ground,forming the severe downslope windstorm finally.In this process,the turbulence formed by the wave breaking and the critical layer absorbed the upper layer energy downward,strengthening the energy of the gap jet.Moreover,the atmospheric stability stratification exacerbated the sinking movement which sank energy to the surface.