Characteristics of the Boundary Layer Structure of Sea Fog on the Coast of Southern China

Using boundary layer data with regard to sea fog observed at the Science Experiment Base for Marine Meteorology at Bohe, Guangdong Province, the structure of the atmospheric boundary layer and the characteristics of the tops of the fog and the clouds were analyzed. In addition, the effects of advection, radiation, and turbulence during sea fog were also investigated. According to the stability definition of saturated, wet air, the gradient of the potential pseudo-equivalent temperature equal to zero was defined as the thermal turbulence interface. There is evidence to suggest that two layers of turbulence exist in sea fog. Thermal turbulence produced by long-wave radiation is prevalent above the thermal turbulence interface, whereas mechanical turbulence aroused by wind shear is predominant below the interface. The height of the thermal turbulence interface was observed between 180 m and 380 m. Three important factors are closely related to the development of the top of the sea fog: (1) the horizontal advection of the water vapor, (2) the long-wave radiation of the fog top, and (3) the movement of the vertical turbulence. Formation, development, and dissipation are the three possible phases of the evolution of the boundary-layer structure during the sea fog season. In addition, the thermal turbulence interface is the most significant turbulence interface during the formation and development periods; it is maintained after sea fog rises into the stratus layer.