民勤干旱区冬季浓雾形成的边界层条件分析

利用民勤县气象站过程地面小时观测资料、逐日08时和20时每隔50 m探空资料和NECP再分析资料,对2015年11月9—13日出现在干旱区民勤县的一次罕见浓雾天气过程进行了研究分析。结果表明:前期降水后地面相对湿度增大,为大雾形成提供了必要的水汽条件,稳定的高低层环流配置提供了大雾形成的稳定层结和弱风条件。雾层的厚度和强度与近地面逆温层的强度和厚度、边界层高度、水汽垂直运动以及夜间地气温差绝对值密切相关,边界层高度越高,逆温层越厚,雾层越厚;逆温层越强,夜间地气温差绝对值越小,雾层越强。高空环流形势稳定少动,近地层强逆温层、稳定等温层以及饱和湿层长时间维持,导致此次大雾强度和持续时间异常罕见。

Analysis on Boundary Layer Condition of Winter Heavy Fog in Minqin Arid Area

Based on hourly ground observation data, daily sounding data for every 50 m at 08:00 and 20:00 BT in Minqin Weather Station, and the NECP reanalysis data, a rarely seen heavy fog process in Minqin from 9 to 13 November 2015 is analyzed. The results show that the increased ground relative humidity after pre precipitation provided necessary moisture condition, stable high and low level circulation configurations provided a stable stratification and light wind condition for the fog formation. The thickness and intensity of fog layer were closely related to the thickness and intensity of inversion layer near surface, boundary layer height, vertical movement of moisture and absolute value of (Ts-Ta) over night. The higher the boundary layer, the thicker the inversion layer near surface, and the thicker the fog layer. The more intensive the inversion layer, the smaller the absolute value of (Ts-Ta) at night, and the more intensive the fog layer. The stable high level circulation, intensive inversion layer and stable isothermal layer near surface and the long lasting saturated moist layer contributed to the rarely seen intensity and duration of the heavy fog process this time.