阿拉善盟一次区域性大风沙尘暴天气过程成因分析

Process and causes of a regional gale and sand storm in Alxa League

沙尘暴是发生在干旱、半干旱荒漠化地区的主要灾害性天气之一,对其形成过程及成因探讨能为沙尘暴监测和预警提供参考。以2019年5月11日阿拉善盟一次区域性大风沙尘暴天气为例,在气象实时监测数据基础上,从地面气象要素变化、环流特征、动力条件和热力条件等方面对此次沙尘暴天气过程成因进行了探讨和分析。结果表明:1)阿拉善盟大风沙尘暴最强时段为午后至傍晚,沙尘暴发生时,气压和极大风速急剧增加,气温和能见度明显下降。2)大风沙尘暴的发生与500 hPa冷平流触发作用、700 hPa大气斜压性作用、高空动量下传作用、变压梯度风、锋生作用以及必要的大气层结条件之间存在着密切联系,表明控制大风沙尘暴形成的因素复杂。3)不同地区以及不同时间内发生大风、沙尘暴天气所需的风速条件不一致,强冷空气的侵入是沙尘暴发生的前提条件。此外,混合层,即不稳定层结是产生大范围沙尘暴天气的必要条件,在大风条件具备,但无混合层出现时,沙尘暴天气较难形成。

Sand storm is one of the main disastrous weather in arid and semi-arid desertification areas.Analysis of the formation process and causes of sandstorm can provide a reference for monitoring and early warning of sandstorm.Taking a regional gale and sandstorm in Alxa League on May 11,2019 as an example,based on the real-time meteorological monitoring data,the weather process and causes of the sandstorm were discussed and analyzed from the changes of surface meteorological elements,circulation characteristics,dynamic conditions and thermal conditions.The results show that:1)The strongest period of gale sandstorm in Alxa League was from afternoon to evening.When sandstorm occurred,air pressure and maximum wind speed sharply increased,and temperature and visibility decreased obviously.2)The occurrence of gale and sandstorm was closely related to 500 hPa cold advection trigger,700 hPa baroclinic effect,upper atmosphere momentum downward transfer,variable pressure gradient wind,frontogenesis and necessary atmospheric stratification conditions,indicating that the factors controlling the formation of gale sandstorm were complex.3)The wind speed conditions for strong wind and sandstorm are different in different regions and different times,and the invasion of strong cold air was the prerequisite for the occurrence of sandstorm.In addition,the mixed layer was the necessary condition for the occurrence of large-scale sandstorm weather.When the strong wind conditions were available,but there is no mixed layer,the sandstorm weather is difficult to form.