2016年陕西地区首场伴随“高架雷暴”区域性暴雪过程机理分析

Analyses of the mechanisms of the first regional snowstorm associated with an "Elevated Thunderstorm" over Shaanxi province in 2016

利用陕西地面气象站观测资料、FY-2G逐小时卫星相当黑体温度(Temperature of Black Body,TBB)资料、闪电定位检测资料、西安CINRAD/CB型多普勒雷达探测资料、美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)的1°×1°逐6 h再分析资料及常规气象观测资料,探讨了2016年11月22—23日陕西地区一次罕见的伴随"高架雷暴"暴雪天气过程成因机制。结果表明:500 h Pa高空槽、700 h Pa低空切变线和低空急流为陕西地区此次暴雪天气过程的影响系统,700 h Pa西南急流提供了充足的水汽条件,850 h Pa低空急流和地面倒槽的偏东气流为暴雪与高架雷暴提供深厚的冷垫。此次伴随暴雪出现的高架雷暴,是典型的"冷区雷暴",700 h Pa以下维持较强的逆温层,700 h Pa以上为湿中性层结,上升气流较强,易引发深厚湿对流;锋面次级环流圈有利于倾斜上升运动的发展;强垂直风切变,对流回波强度为30—50 d Bz,回波顶高为10—12 km,对流层顶高度超过-20～0℃的过冷水层高度,易导致雷电发生。雷电和冰雹出现在低空急流入口区左侧、TBB、水汽通量、θse密集区附近。

Using the surface meteorological station observations,FY-2G hourly satellite TBB(Temperature of Black Body)lightning positioning data,Xi'an CINRAD/CB-type Doppler radar,NCEP/NCAR(National Centers for Environmental Prediction/National Center for Atmospheric Research)1°×1°reanalysis data in every 6 h,and conventional meteorological data,the formation mechanisms of a rare heavy snow process accompanying with an"elevated thunderstorm"occurred on November 22-23,2016 was discussed.The results show that the 500 hPa upper trough,700 hPa low-level shear line and lower troposphere jet are major systems influencing this heavy snow process.The southwest jet at 700 hPa provides sufficient water vapor,and the 850 hPa low-level jet and the inverse trough eastward airflow at the ground provide a deep cold pad.The"elevated thunderstorm"with the heavy snow is a typical"cold sector thunderstorm"which is maintained by the strong inversion layer below 700 hPa and by the wet neutral boundary layer above 700 hPa.The upflow is stronger,so the moist and deep convection is easy to form.The frontal secondary circulation circle is helpful to the development of the slantwise updraft.The vertical wind direction shear is strong.The convective echo intensity ranges from 30-50 dBz,and the echo top height is 10-12 km.The tropopause height exceeds subcooled water layer height with a temperature range of-20~0℃,making the thunder to form easily.The thunder and hail normally appear on the left-hand side of the low-level jet entrance region,which is close to the high concentration zone of TBB,water-vapor flux,andθse.