“7.28”山西中部强对流天气的中尺度分析

Meso-scale Analysis of A Strong Convective Weather Process Occuring on 28 July 2016 in Central Shanxi Province

利用常规观测资料、中尺度加密气象站资料以及卫星和雷达产品等资料,对2016年7月28日出现在山西中部的一次强对流天气进行综合分析。结果表明:此次强对流天气发生在低涡低槽后部西北气流控制的环流背景条件下;低层切变线、地面辐合线和干线是此次强对流天气的主要触发因素;较低层冷空气的渗透,使得大气层结不稳定度加大,促使垂直上升运动加强,为强对流天气的发展提供了有利条件。强对流发生前,850 h Pa存在明显的逆温层,有利于低层能量积累。对流层高低层湿位涡的正负垂直叠置,使大气对称不稳定性增强,强对流天气发生在湿位涡等值线前沿的湿位涡舌附近、冷暖空气交汇的区域。卫星云图上出现的椭圆形雹暴云团,是造成冰雹大风天气的主要中尺度系统。雷达回波强度图上出现的旁瓣回波和三体散射长钉是典型的冰雹特征,且较降雹时间提前约15~20 min,雷暴大风发生在弓形回波头部、强回波中心断裂处,强回波快速减弱对雷暴大风的发生具有指示意义;径向速度图上出现中等强度的中气旋以及中层明显的径向辐合有利于雷暴大风出现;回波顶高和垂直累积液态水含量(VIL)的跃增表明出现大冰雹的可能,VIL的快速降低也意味着出现雷暴大风的潜势较大。

Based on conventional observation data,mesoscale encryption weather stations data,satellite images and radar products,a local strong convective weather process occurring in centre Shanxi Province on 28 July 2016 was analyzed. The results show that the strong convective weather occurred under the circulation background of northwest airflow behind the vortex. The low-level shear line,surface convergence line and dry line were the main triggering factors of the strong convection weather. The instability of atmosphere increased due to invasion of the lower level cold air,which promoted the vertical upward motion and provided favorable conditions for the development of strong convective weather. Before the occurrence of strong convection,there was an obvious inversion layer on 850 h Pa,which was beneficial to the accumulation of energy in low level. The vertical superposition of positive and negative moist potential vorticity in the upper and lower troposphere layer was conducive to the development of symmetrical instability. Strong convective weather happened near moist potential vorticity tongue which was on the edge of moist potential vorticity contour and the junction of warm and cold air. Elliptic hailstorm clouds appearing on the satellite cloud image was the main mesoscale system causing the hail and severe wind weather. Analysis on radar reflectivity factor,there were obvious side lobe echoes and three body scattering spikes,which was a typical characteristic of the hailstones,and it appeared 15-20 minutes before the hail falling. Thunderstorm wind occurred at the head of bow echo and the fracture of strong echo center. Strong echo weakening fast had important indicative significance to the occurrence of thunderstorm gale. According to the radial velocity products of Doppler radar,the medium-strength meso-cyclone and the obvious radial convergence in the middle level were favorable to the occurrence of thunderstorm gale. The leap of the echo top height and the vertically integrated liquid water content indicated that there was a possibility of large hail,at the mean time the rapid decrease of the vertically integrated liquid water content also meant that there was a great potential for thunderstorm gale.