Abstract: Based on the NCEP reanalysis data, conventional observation data and microwave radiometer data, the background field, characteristics of the boundary layer and formation cause and maintenance mechanism of a sustained heavy fog process during 11-15 January 2019 in central and southern Hebei Province were analyzed. The results show that the fog generated under the background of stable zonal circulation, during which weak short-wave troughs moved eastward quickly, and two dry short-wave troughs promoted the formation of heavy fog and the strengthening of the fog, respectively. The fog was mainly radiation fog and only a few tens of meters in  height. The two-layer structure of temperature inversion layer, weak water vapor convergence and southwest water vapor transport  on the ground inversion layer provided water vapor source for heavy fog, the cooling of weak cold air caused by northerly wind and cooling of radiation at night were thermodynamic conditions for the development of the fog. The positive vorticity in the lower layer and the divergence and sinking in the middle troposphere were dynamic factors promoting maintainess  and development of the fog, the combination of long-wave radiation in the clear night sky and turbulent mixing promoted cooling and humidification in the boundary layer. During the later period of the heavy fog, the temperature inversion layer changed from two-layer structure to a single-layer structure. The dissipation of the fog was caused by the intrusion of strong cold air and destruction of stationary structure.

Key words:  sustained heavy fog, radiation fog, dry short wave trough, inversion layer

摘要： 利用NCEP再分析资料、地面观测资料和微波辐射计资料，分析2019年1月11—15日河北中南部持续大雾过程的大尺度背景场、边界层特征、形成原因及维持机制等。结果表明：此次大雾产生于稳定的纬向环流背景下，其间有弱短波槽快速东移，两次干性短波槽分别促成了大雾的形成、雾区范围扩大及强度增强；大雾高度仅有几十米，以辐射雾为主，双层逆温结构为大雾的形成酝酿了先期条件，贴地逆温层内的弱水汽辐合和西南水汽输送为大雾形成和维持提供了水汽，偏北风带来的弱冷空气降温与夜间辐射降温的叠加效应是促进大雾发展的热力学条件；低层正涡度、对流层中层的辐散下沉运动是大雾维持和发展的动力因子，晴夜长波辐射和湍流混合作用促进了边界层内的降温增湿；大雾发展后期，双层逆温结构转为以单层逆温为主，最终大雾的消散主要是强冷空气入侵，大气静稳结构被破坏所致。

关键词: 持续性大雾, 辐射雾, 干性短波槽, 逆温层