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

Severe downslope wind triggered by the interaction between the gap jet and the asymmetrical topography in the Tianshan canyon which caused severe disasters of trains rolloverin the Turpan Depression in Xinjiang on February 28, 2007. To understand the mechanism of downslopewindstorm between the interaction of large-scale circulation background，mesoscale system and complex topography in this extreme windstorm.We use a WRF model to simulated it.Base on the mesoscale diagnostic analysis to simulative results，We propose a mechanism for the windstorm : Under the pressure gradient between north-south sides of the Tianshan Mountain, the air parcel climbs windward slope and flowsinto the Tianshan Gorge and then forms gap jet due to effect of narrow，the jet generated gravity waves forced by the asymmetric terrain of the Tianshan Canyon, and produces a lee waves in the leeward, which transmits the energy of the gap jet to the ground，andSevere downslope windstorm formed finally. In this process, the turbulence formed by the wave breaking and the critical layer absorb the upper layer energy downward, which strengthens the energy of the gap jet,and the atmospheric stability stratification exacerbates the sinking movement, which sinks energy to the ground.