Investigating the sensitivity of marine fog to physical and microphysical processes using large-eddy simulation

Marine fog is both costly and hazardous to those living and working in coastal and offshore environments. Despite major progress in numerical weather prediction over the last few decades, improvements in forecasting of coastal and marine fog have lagged behind other hazardous weather types. Difficulties in modeling marine fog arise from both the large range of temporal and spatial scales involved and the complex interplay of physical and microphysical processes that lead to fog formation. The inherent challenges in studying marine fog via field observation further enhance these issues, and are the basis for the recent C-FOG campaign off the coast of Newfoundland, Canada.

Over the past few years large-eddy simulation (LES) has demonstrated success in modeling continental radiation fog. Several recent studies have used LES to investigate the sensitivity of radiation fog formation to physical processes such as turbulent mixing and surface heat and moisture exchange. The sensitivity to key microphysical parameters such as the cloud droplet number concentration and background aerosol content has also been tested.

There are several important differences in the formation of marine and continental fog; moisture availability is no longer a decisive factor, and surface temperature changes over a much longer time scale. Here we use LES to examine the sensitivity of marine fog formation to the cloud droplet number concentration, turbulent mixing, and air-sea temperature difference. We find that the strength of the fog is highly sensitive to all three factors. We examine similarities and differences to the findings for continental radiation fog, and we discuss important considerations for future improvements in marine fog forecasting.