Microphysical Properties and Turbulence Evolution Characteristics of a Typical Coastal Fog Event in the Beibu Gulf, China

A fog field observation experiment was carried out in the Beibu Gulf, Guangxi, China from February to April of 2023, with observational instruments including fog monitor, visibility meters, and the three-dimensional ultrasonic anemometer. This study is the first to use the field observation data conducting a fog microphysics in this area. A dense coastal fog case during 10–11 February 2023 is chosen to understand the evolution of the microphysical characteristic parameters, dominant microphysical processes, as well as the turbulence characteristics. The main results are as follow: (a) The average values of fog droplets number concentration(N), liquid water content (LWC), average diameter ($\bar{D}$), are 6.5 cm⁻³,0.0005 gm⁻³ and 3.1 μm, respectively. The N and LWC over the Beibu Gulf are much lower than those in other coastal areas of China. (b) The droplet size distribution of the Beibu Gulf fog is monotonically decreasing, with peak diameter of 2.8 μm. The average droplet number distribution roughly conforms to the Junge distribution. (c) For the whole coastal fog event, condensation nucleation and droplet condensation growth are the dominant processes, and well-developed turbulence is observed. (d) During the development stage of this fog, condensation nucleation and condensation growth is the dominant processes; in the mature stage, turbulence is relatively stable, and the collision process plays a dominant role; during the dissipation stage, there is evaporation of fog droplets.