中国西北干旱区沙尘暴源地风沙大气边界层特征

应用西北干旱区沙尘暴源地甘肃省民勤县1971-2008年共1 811个大风/沙尘暴个例的逐日08：00和20：00高空资料、降水、日最高气温以及沙尘暴实时资料，详细探讨了不同月份和季节干湿变化、沙尘暴强度、沙尘暴出现时间和持续时间的大气边界层垂直结构变化特征。结果表明：（1）沙尘暴发生时4-5月最大混合层较厚，在2 500 m以上；而强沙尘暴发生时6-7月较厚，7月最厚为2 530 m。3-8月沙尘暴发生时最大混合层厚度低于大风发生时的200～400 m；4-5月下午沙尘暴发生时最大混合层较深厚，在2 700 m左右。沙尘暴持续时间与最大混合层厚度成反比。（2）沙尘暴发生时扰动和锋面逆温频次多而强，扰动逆温明显较强，达2.5 ℃/100m，锋面逆温高度在700～1 000 m，扰动逆温高度在150～400 m之间；而大风发生时辐射和锋面辐射逆温频次多而强，强沙尘暴发生时锋面逆温明显较强，这说明沙尘暴多由风场的剧烈扰动和锋面过境引起。（3）白天800 hPa以上有干气层存在，夜间干暖和逆湿现象显著。近地层越干冷、西北风越强，强沙尘暴持续时间越长。

Vertical Structure of Atmosphere Boundary Layer during Wind-sandstorm Process over Sandstorm Source in Arid Area of Northwest China

Based on the daily observed sounding data at 08:00 and 20:00, precipitations, maximum temperatures and sandstorm real-time data of 1 811 typical wind-sandstorm cases during 1971-2008 in Minqin, a sandstorm source in arid area of Northwest China, vertical structure characteristics of atmosphere boundary layer in different months and seasons is discussed under dry-wet variation, sandstorm strength, sandstorm occurring time and sandstorm duration. The main conclusions are:(1)The maximum atmospheric mixed layer thickness during sandstorm process is larger with more than 2 500 m from April to May, but the maximum atmospheric mixed layer thickness during strong sandstorm process is larger from June to July with 2 530 m in July, the maximum atmospheric mixed layer thickness during sandstorm process is lower by 200-400 m than that during gale process from March to August. The maximum atmospheric mixed layer thickness during sandstorm process is deeper in afternoon with 2 700 m from April to May. The maximum maximum atmospheric mixed layer thickness varies inversely with the sandstorm duration.(2)The disturb and front inversion are more frequent and stronger during sandstorm process, disturb inversion' s strength is strongest up to 2.5 ℃/100m.The front inversion height is 700-1 000 m, disturb inversion height is 150-400 m. The radiation and radiation-front inversion are more frequent and stronger during gale process, and the front inversion is obviously stronger during strong sandstorm process. It shows that sandstorm is mainly resulted from strong wind disturbance in lower atmosphere and cold front above 500 m in upper atmosphere.(3)There is an obvious dry atmospheric layer above 800 hPa in daytime, but it is drier and warmer in nighttime, and a phenomenon of inversion wet is also obvious in nighttime. If the surface layer is drier and colder, northwest wind is stronger, the duration of strong sandstorm will be longer.