中文摘要：

针对2009年4月23-24日出现在我国内蒙古中西部的一次强沙尘暴天气过程,利用专门组织观测实验得到的加密探空资料、地面自动观测站资料和其他常规观测资料,深入分析研究了此次沙尘暴发生前后及发生期间,近地层气象要素变化及其内部热力、动力结构特征变化.结果表明,1）沙尘暴发生前,大气的温度垂直递减率大,湿度较大,近地层风速小,风向偏东;在沙尘暴发生期间,大气中出现逆温现象,大气湿度很小,各层风速明显增强,风向偏西且稳定;之后,低层温度显著下降,大气湿度迅速增大,各层风速减小,沙尘暴天气结束.2）沙尘暴发生前,大气层结是条件不稳定的,在沙尘暴过境时,低层大气层结是稳定的,在800600 hPa之间大气层结是中性的,此时低层大气干燥,而在沙尘暴移出测站后,湿度明显增大,因此,“3θ”曲线可以为沙尘暴的监测和预报提供一个有价值的参考数据.3）沙尘暴爆发时的螺旋度是所有观测时次中的最大值,螺旋度与沙尘暴的强度在时间上具有良好的对应关系,即螺旋度越大,对应沙尘暴越强.4）此次强沙尘暴的形成与发展不仅受到环境风速的影响,沙尘暴内部的切向旋转速度和垂直运动速度也对其起到重要的作用.

英文摘要：

Based on the encryption sounding data, the automatic meteorological observing data and other conventional observing data, we analyzed a severe sandstorm occurring in the Midwest Inner Mongolia autonomous region on 23-24 April 2009. The ground meteorological elements and its internal dynamical and thermal changes in the process were studied.The result showed that： 1 ）Before the sand- storm ,the temperature lapse rate was big, the relative humidity was large, the wind speed near the ground was small and the wind direction was easterly; when the dust storm occurred, there was an inversion in the atmosphere temperature, the relative humidity was small, the wind speed increased obviously and the wind direction was westerly and stable：when the sandstorm ended, the temnerature decreasedthe relative humidity increased fast and the wind velocity reduced rapidly in all layers;2）The atmos- pheric stratification had been conditionally unstable before the sandstorm took place and turned to be stable in the low layer and neutral between 800 hPa and 600 hPa when the dust storm occurred, and the low layer atmosphere was extremely dry at the time. Then the humidity became large when the sand- storm ended.So ＂3θ＂ curve could provide a valuable reference for the monitoring and forecast of dust storms ;3） The relative storm helicity （RSH）, which was available when the dust storm occurred, was of the maximum value compared with all the other observation times, and it had a good correlation with the sandstorms in intensity.That was to say, the bigger the RSH was, the severer the sandstorm would be;4） The intensity of the sandstorm was not only closely related to the surrounding velocity, but also to the values of the tangential and vertical velocities in the sandstorm.