中国北方2021年3月中旬持续性沙尘天气的特征及其成因

沙尘天气是多发于中国北方春季的灾害性天气，严重危害农业生产、交通运输、空气质量和人民的生命财产安全，长期受到社会各界的广泛关注。利用多源多尺度数据，采用天气学分析、物理量诊断、轨迹分析等方法对2021年3月中旬西北地区东部一次持续性沙尘重污染天气的成因进行了深入分析。结果表明：（1）受强烈发展的蒙古气旋影响，蒙古国南部及中国内蒙古中西部地区于3月14日首先出现强沙尘暴天气，并将沙尘传输至中国西北、华北、东北一带，西北东部的沙尘天气维持达到5 d。（2）沙尘天气维持期，西北东部中低层以弱上升运动为主，大气层结稳定，且西北东部不断有弱锋生发展，不利于沙尘的沉降；自北向南分布的银川、中卫、兰州3站的垂直螺旋度的波动与污染浓度的变化基本一致；混合层高度较其气候平均值明显偏低，不利于大气湍流发展。（3）此次影响西北东部的沙尘主要由蒙古国输入，近20年中蒙边境、蒙古国南部的植被减少可能是此次沙尘天气的沙源主要来自蒙古国南部的原因。

Characteristics and causes of persistent sand-dust weather in mid-March 2021 over Northern China

Sand-dust weather is a kind of disastrous weather frequently occurring in the spring in Northern China， which severely endangers agricultural production， transportation， air quality and the safety of people's lives and properties. It has been widely concerned by all walks of life for a long time.This paper uses multi-source and multi-scale data， synoptic analysis， physical quantity diagnosis， trajectory analysis and other methods to conduct an in-depth analysis of the cause of a continuous heavy dust pollution weather in the eastern part of Northwest China in mid-March 2021. The results show that： （1） Affected by the strong development of Mongolian cyclone， the strong sandstorms weather first appeared in the southern Mongolia and the central and western regions of Inner Mongolia on March 14， and the sand and dust were transported to the northwest， north and northeast of China， and it lasted for up to 5 days in the eastern part of Northwest China. （2）During the maintenance of the sand-dust weather in the eastern part of Northwest China， the middle and low layers are dominated by weak ascending movement， the atmosphere stratification is stable， and the weak frontogenesis process developed continuously， which was not conducive to the sedimentation of sand and dust. The fluctuations in the vertical helicity of the Yinchuan， Zhongwei， and Lanzhou stations distributed from north to south are basically consistent with the variation of dust concentration in these stations in the continuous stage of dust weather. In addition， the height of the mixed layer during the duration of the dust weather is significantly lower than its climatic average， which is not conducive to the development of atmospheric turbulence. （3） The trajectory analysis shows that the sand and dust affecting the eastern part of northwestern China is mainly caused by the import of Mongolia. Nearly 20 years， the vegetation in the border areas between China and Mongolia and southern Mongolia shows a decreasing trend， which may be the main reason that the sand source of this sandstorm is mainly from the south of Mongolia.