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 ScienceExperiment Base for Marine Meteorology at Bohe, Guangdong Province, thestructure of the atmospheric boundary layer and the characteristics of thetops of the fog and the clouds were analyzed. In addition, the effects ofadvection, radiation, and turbulence during sea fog were also investigated.According to the stability definition of saturated, wet air, the gradient ofthe potential pseudo-equivalent temperature equal to zero was defined as thethermal turbulence interface. There is evidence to suggest that two layersof turbulence exist in sea fog. Thermal turbulence produced by long-waveradiation is prevalent above the thermal turbulence interface, whereasmechanical turbulence aroused by wind shear is predominant below theinterface. The height of the thermal turbulence interface was observedbetween 180 m and 380 m. Three important factors are closely related to thedevelopment of the top of the sea fog: (1) the horizontal advection of thewater vapor, (2) the long-wave radiation of the fog top, and (3) themovement of the vertical turbulence. Formation, development, and dissipationare the three possible phases of the evolution of the boundary-layerstructure during the sea fog season. In addition, the thermal turbulenceinterface is the most significant turbulence interface during the formationand development periods; it is maintained after sea fog rises into thestratus layer.