Numerical simulation and physical understanding of a locally initiated sea fog event over the eastern Yellow Sea with a transition of air–sea temperature difference

Formation and evolution of a sea fog event with a transition of air–sea temperature difference (ASTD) were investigated by using the Weather Research and Forecasting (WRF) model. Based on in‐situ observations and satellite images, sea fog that formed locally and then spread to the coast of the Korean Peninsula was detected over the eastern Yellow Sea on 24 and 25 February 2019. During this period, the Yellow Sea was influenced by a local high‐pressure system and a shallow boundary layer with a low‐level inversion, which favored fog formation. WRF simulations were conducted using a single‐domain, 2‐km horizontal grid, and 10‐m vertical spacing below 300 m altitude. Three planetary boundary layer (PBL) parameterization schemes (Yonsei University [YSU] scheme and Mellor–Yamada [MY]‐type schemes) and two surface layer schemes were tested. The simulation with the YSU scheme successfully reproduced temperature and relative humidity as well as the horizontal distribution of fog. Cross‐sectional analysis across the initial fog formation point (IFFP) and onshore showed that the fog penetrated inland and later dissipated through turbulent mixing and daytime drying. Potential temperature and mixing ratio tendencies at the IFFP revealed that surface turbulent cooling partially contributed to fog formation but long‐wave radiative cooling was the dominant mechanism for fog formation, leading to change in ASTD and vertical evolution of fog. The vertical growth of the fog layer was driven by buoyancy‐produced turbulence near the surface. The MY‐type schemes, regardless of the surface layer schemes used, underestimated the horizontal extent of fog, possibly due to underestimating water vapor mixing ratio near the IFFP. These findings illustrate the physical mechanisms for fog formation and evolution and underscore accurate representation of subgrid‐scale turbulence for simulating locally initiated sea fog.