2015年11月22日内蒙古中部地区回流暴雪天气过程分析

Analysis of Reflow Snowstorm Process on November 22, 2015 in central Inner Mongolian

利用气象常规观测资料、NCEP 1°×1°再分析资料、卫星云图及呼和浩特多普勒天气雷达资料,对2015年11月22日内蒙古中部地区暴雪天气过程进行诊断分析,结果表明:在中高纬"两槽一脊"的环流形势下,500和700 h Pa短波槽、700h Pa西西南急流和地面倒槽是这次暴雪的主要影响系统,属于回流暴雪天气过程。700 h Pa西西南急流对暖湿空气的输送和水汽的强烈辐合为暴雪提供了充足的水汽条件,低层水汽辐合出现时刻降雪开始且辐合最强时出现最强降雪;高低空急流耦合加强了系统性上升运动,700 h Pa西西南暖湿空气在850 h Pa偏东气流上爬升,冷暖空气交汇及其垂直切变导致强烈的上升运动;"冷垫"与"暖盖"相配合是产生暴雪的热力条件,强降雪出现在锋区最强至减弱期间且低空急流建立后。中尺度系统云团是造成暴雪天气的直接系统,最强降雪中心与TBB≤220 K移动区域一致。片状回波中30~35 d Bz的强带状回波造成此次暴雪过程中局部强降雪,零速度线呈现"S"结构,当冷锋过境,低层转为偏北风后降雪趋于结束。

Using the conventional observations, NCEP reanalysis data （1°×1°）, satellite cloud image and Doppler weather radar data of Hohhot, this paper analyzed the snowstorm occurred on Nov.22, 2015 in Inner Mongolian. The results showed that in the current situation of ＂two trough one ridge＂ in the middle and high latitude, the short-wave trough at 500 and 700 hPa, western and southwest jet and surface inverted trough were the mainly infuencing systems of the snowstorm, which belonged to refow snowstorm process. The transportation of warm-wet air by western and south-western jet and the strong moisture convergence supplied necessary conditions in moisture for snowstorm, and not only the snowfall happened when the water vapor convergence appeared in low level but also the strongest convergence time was corresponding to the strongest snowfall time. The coupling of high and low level jet strengthened the systematic ascending motion. Because the western and southwest warm-wet air at 700 hPa climbs on eastern airfow at 850 hPa, the intersection and vertical shear of cold and warm air caused the strong ascending motion. The “cold cushion” and “warm cover” provided thermal conditions for the snowfall. The severe snowfall happened when the frontal zone was strongest and began to weaken, and after the low-level jet was established. The snowstorm was directly caused by mesoscale convective clouds and the severe snowfall center was consistent with TBB less than 220 K. The strong band echo with 30-35 dBz caused the local heavy snowfall in the snowstorm process. The zero velocity line appeared “S” in radial velocity feld and the snowfall ended when the cold front passed and winds veered to northerly winds in low level.