2011年5月11日内蒙古地区强沙尘暴天气过程分析

Synoptic Analysis of Severe Sand-dust Storm on May 11, 2011 in Inner Mongolian

基于1°×1°NCEP资料、常规气象观测资料及地面加密观测资料,对2011年5月11日发生在锡林郭勒盟地区的强沙尘暴过程进行天气学分析和诊断,得出如下结论:(1)此次强沙尘暴过程特点是落区集中、强度大、强沙尘暴持续时间长、沙尘暴区与大风区(6级以上)非常一致。冷涡及强锋区、蒙古气旋和冷锋是触发这次强沙尘暴天气过程的重要天气系统,此次强沙尘暴天气过程则属于蒙古气旋和冷锋共同作用引起的类型;(2)高空急流左中和左后方的辐合区,及左前侧的高空辐散区均出现了沙尘暴,下沉只在动量下传中起到了重要作用。垂直螺旋度在东移的过程中正值中心与强沙尘暴区域对应较好,且具有典型的上负下正的垂直结构,构成了低空强辐合、高空强辐散的深厚上升运动区,这样螺旋度垂直分布是十分有利于沙尘暴发展的一种形式;(3)在沙尘暴发生前,具有不稳定特征。沙尘天气开始时,等位温线几乎垂直于横坐标,表明此时大气层结非常接近绝热状态(中性层结),由于中性层结能够减小抬升所需的能量,因而有利于干对流的产生。

Using the NCEP reanalyzes data, the conventional observation data and ground encryption observation data, the strong sand-dust storm process was analyzed and diagnosed which occurred on May 11,2011 in Xilin Gol league, The results show that ：（1）There are several features of the severe sand-dust storm process： Concentrating of sand-dust storm area, strong intensity, long duration and the distribution of the severe sand-dust storm area and gale （Level 6 or above） are consistent. The cold vortex and strong frontal zone, Mongolia cyclone and cold front are important weather system to the severe sand-dust storm process. The severe sand-dust storm process belongs to the type of common effects of the Mongolia cyclone and cold front. （2）The severe sand-dust storm occurred in the left middle and the left rear of high jet which is convergence zone, and the left front which is divergence region. Descending branch played an important role in momentum spreading, and severe sand-dust storm occurred at the center of the descending and the rising branch and near by. Over the severe dust storm area the helicity was negative at higher levels and positive at ]ower levels, this vertical distribution of helicity is very conducive to form the development of the severe dust storm;（3）Before the occurrence of the severe sand-dust storm, it was instable. At the beginning of the severe sand-dust storm, the potential temperature line was almost perpendicular to the horizontal axis, so the air is close to adiabatic, which is conducive to the dry convection generated because the neutral layer can reduce the energy of ascending motion.