Numerical Simulation of Sea Fog over the Yellow Sea: Comparison between UM + PAFOG and WRF + PAFOG Coupled Systems

Sea fogs over the Yellow Sea in the western coast of the Korean Peninsula were simulated by the coupled systems of 3D regional models (UM and WRF) and a 1D model (PAFOG) with fine vertical resolution. The coupling was conducted by generating meteorological fields with 3D regional model and providing them as the initial fields and boundary conditions (external forcings) of the 1D model. The accuracy of the cold sea fog (T – SST > 0) simulation improved through the proper treatment of turbulent cooling near the surface by the coupling. However, the accuracy of warm sea fog (T – SST < 0) was improved only slightly by the coupling, which is likely due to the inadequate estimation of the external forcing (advection) of heat and moisture below the upper inversion layer. It was found that the resolution of the 3D regional model did not significantly affect the initial fields of the 1D model but the performance of the 1D + 3D coupled systems were still affected by the resolution of the 3D regional model since it affected the external forcings on the 1D model in the coupled system. Surprisingly, the coupled system with coarse resolution 3D model produced generally better fog simulation than that with fine resolution 3D model, due to the high fluctuation of advection (external forcing) for fine resolution. Meanwhile, for the same resolution, the two 3D models (UM and WRF) produced significantly different initial fields and the overall performance seemed better for the UM coupled system than the WRF coupled system. In short, it was demonstrated that fog prediction could be improved by the coupling for cold sea fog cases over the Yellow Sea, but improvement from the coupling was small for warm sea fog cases, which indicates that more research is required to produce promising results for warm sea fogs.