Abstract:Using the fog droplet spectrum and visibility data of two dense fog processes in 12-13 January 2019 in Shouxian, Anhui Province, the microphysical characteristics (such as the size distribution, droplet number concentration, liquid water content, average diameter, spectral width, etc.) and the correlations among microphysical properties (number concentration, liquid water content, average diameter) in the different stages of fog are analyzed. The results show that both the fog processes were radiation fog. If the strong inversion structure close to the ground maintains, the water vapor can be restrained in the inversion layer, conducive to the long-term maintenance of dense fog. The formation time of the fog at 20 m was later than that on the surface. In the early stages of formation, development and maturity, the microphysical characteristics of the surface fog were all larger than that at 20 m. At the late stage of maturity, the release of latent heat by condensation and ground heating might increase the intensity of turbulent mixing in the fog, making the fog uniform in the vertical direction. The fog processes at two heights were dominated by nucleation and condensation growth, but the collision-coalescence process also played an important role in the fog on the surface. From the stages of formation, development to maturity, the collision-coalescence processes of the ground fog gradually strengthened. The correlation among the number concentration, water content, and average diameter generally changed from strong positive correlation to weak positive or negative correlation. From the early stage to the late stage of the mature stage, the relationship between average diameter and number concentration of the fog at 20 m height changed from a positive correlation to a negative correlation, which was likely to be related to the factors such as turbulent motion, entrainment mixing, etc.