民勤“2010.4.24”黑风天气过程的稳定度分析

 2010年4月24日民勤出现黑风天气，给当地经济和社会造成严重影响。利用民勤黑风发生前后2010年4月24日08时~25日08时的探空观测资料，对大气不稳定能量、热力参数“V—3θ”和动力参数“相对风暴水平螺旋度”进行了计算分析。结果表明：黑风发生时，民勤近地面存在正不稳定能量，促使黑风在近地面层爆发性发展，使沙尘粒子在正不稳定能量区聚积，形成黑风墙。民勤黑风爆发前和爆发时大气温湿结构呈现出上湿下干的分布特征，低层湿度较小不利于降水产生，为沙尘扬起提供了较好的垂直方向的环境场条件；黑风爆发前大气层结500 hPa以下风场的垂直分布形成顺时针滚流，为对流性不稳定层结，气层有利于黑风生成和发展；黑风过境后，风场的垂直分布顺时针滚流下降至700 hPa以下，说明大气层结的对流不稳定层结变薄、减弱，700～500 hPa存在逆时针滚流，抑制上升运动，预示黑风将减弱。黑风爆发期间在河西走廊中部存在一个相对风暴水平螺旋度负值中心，中心值达到-870 m2 /s2，远小于强沙尘暴发生的临界值-600 m2 /s2，沙尘暴的强度与相对风暴水平螺旋度负值中心存在很好的对应关系。当民勤测站的相对风暴水平螺旋度＜0，其上游存在≤-600 m2 /s2的最小中心时，民勤测站将出现强沙尘暴；当民勤测站的螺旋度＜0，其上游存在正值中心时，下游存在负值中心时，民勤测站的沙尘暴结束，能见度好转。

Stability of black sandstorm in Minqin on April 24, 2010

Black sandstorm has an important effect on the products of industry and agriculture and the people’s livelihood in Minqin County,Gansu Prouince,China,on April 24,2010.More parameters associated to strong storms are studied,such as Instability Atmospheric Energy and thermal parameter V-3θ and dynamic parameter for Storm-Relative Horizontal Helicity(SREH),by using 24-hour sounding observation data in Minqin between April 24 and April 25,2010.The results indicated that the positive instability energy still exist in atmospheric surface layer as black sandstorm starts blowing in Minqin,black sandstorm suddenly sprang up at surface boundary layer,cause sand-dust particulates concentration increased in the areas of positive instability energy,then it formed a terrifying wall of black sandstorm.black sandstorm is a kind of the potential instability energy that caused by the air with upper-layer wet and lower-layer dry.low humidity is not conducive to more precipitation in the low layer atmosphereare,and provides a better environmentin the vertical direction for the occurrence of sandstorm.The atmospheric stratification was convective instability state bellow 500 hPa before the sand-dust storm,the vertical distribution characteristics of wind field is the clockwise rotation from bottom to top,which favours the development of Black Sandstorm.The influence of convective instability has been remarkably weakened after black sandstorm,the vertical distribution characteristics of wind field is the counterclockwise rotation in mid-lower troposphere,which are unfavorable for the development of vertical ascending motion.all this signs the wind toned down.A low value center of SREH exists in the middle part of of Hexi Corridor,the centers rate is-870 m2/s2 during Black Sandstorm,which is far lower than the critical value-600 m2/s2 for strong sandstorm.The good corresponding relationships among sandstorm intensities and the low value center of SREH.When Minqin’s SREH < 0 and SREH≤-600 m2/s2 in the upper hand,there will be a strong sandstorm in Minqin;When Minqin’s helicity < 0 and SREH>0 in the upper hand,dust storm is over and visibility improved.