Abstract:

Based on the NCEP reanalysis grid ( 1° × 1°) data，conventional observations，numerical forecast products as well as wind profiler data，a large scale fog weather event occurred in the central Urumqi on 25 December 2011 was investigated from circulation background，temperature and humidity feature，stratification condition，the surface layer wind field features． The results show that the warm ridge after the upper trough，no obvious cold air activities over middle latitude，and stable atmospheric circulation background were advantageous to temperature inversion formation，and the formation and maintenance of the temperature inversion in the boundary layer played an important role on the development and sustentation of the fog weather． When the heavy fog occurred，the southeast wind was more than 20 m·s － 1 ，meanwhile southeast gale from south suburbs and northern wind from urban area formed strong convergence around surface layer over southern urban area，which was not conducive to horizontal and vertical diffusion of urban pollutants． The heavy fog also tended to occur towards the cold air side near the convergence of the surface． Southeast gale was an important index of wind field for the heavy fog event in the central Urumqi． Wind profiler data and EC numerical forecast production can exactly provide forecasting in advance for the southeast gale in south suburbs of Urumqi，and were helpful to predict the generation，development and dissipation of fog，which could reduce the damage caused by the heavy fog event．

Key words:

heavy fog, southeast wind, temperature inversion, humidity

摘要：

利用ＮＣＥＰ 逐日４ 次１° ×１°再分析资料、常规观测资料、边界层风廓线雷达资料及数值预报产品，从天气背景、温湿特征、层结条件、近地面风场特征等方面分析了２０１１ 年１２ 月２５ 日白天乌鲁木齐城区一次大范围大雾天气的成因。结果表明：高空槽后暖脊型，中纬度无明显冷空气活动，天气形势比较稳定的大气环流背景易形成逆温，而边界层逆温层的形成与维持对大雾的发展持续具有重要作用；浓雾时，南郊一带东南风维持在２０ ｍ／ ｓ 以上，与城区偏北风在城南近地层形成强辐合面，不利于城区污染物的水平和垂直扩散，且大雾也多发生在地面辐合面偏向冷空气的一侧，分析认为南郊东南大风是城区大雾维持加强的一个重要风场指标；边界层风廓线雷达资料和欧洲数值模式产品能准确提供南郊一带东南大风的提前预报量，对城区及北部出雾有较好指示作用，有助于及时准确预报大雾的形成、发展、消散过程，减轻此类灾害性天气的危害。

关键词: 大雾, 东南大风, 逆温, 湿度, 诊断