Abstract:

This paper investigates a five-day fog process on the west coast of the Taiwan Strait, utilizing observational data from an automatic station, microwave radiometer, and wind profile radar in Xiang'an, Xiamen, from March 30 to April 3, 2021. The boundary layer characteristics of the fog are analyzed. Our findings reveal that: (1) Mild precipitation during the fog's development enhanced its intensity; (2) The presence of an inversion layer was crucial for fog maintenance, with its weakening leading to fog dissipation or reduction. Two distinct scenarios were observed in the inversion layer thickness decrease: (i) the inversion layer top remained relatively stable while its bottom rose, and (ii) both the top and bottom of the inversion layer ascended. These variations are associated with temperature changes near the inversion layer top. The first scenario weakened inversion intensity, whereas the second caused complete inversion layer dissipation and subsequent fog dispersal. Additionally, southwest winds transported warm and moist air, supplying the necessary water vapor for fog formation. When surface water vapor was abundant, strong updrafts lifted the fog to form stratiform clouds, with accumulated water vapor eventually leading to precipitation. On one hand, precipitation during the fog process caused ground evaporation, intensifying the fog or paving the way for subsequent precipitation. On the other hand, it consumes atmospheric water vapor, accelerating fog dissipation. Notably, three significant jumps in liquid water content were observed above the inversion layer top during the fog process, each followed by precipitation.

Key words: sea fog, the west coast of Taiwan Strait, microwave radiometer, wind profile radar, inversion layer, water vapor conditions