Large-eddy simulation of radiation fog with comprehensive two-moment bulk microphysics: Impact of different aerosol activation and condensation parameterizations

Abstract

In this paper we study the influence of the cloud microphysical parameterization on large-eddy simulations of radiation fog. A deep fog case as observed at Cabauw (Netherlands) is investigated using high-resolution large-eddy simulations with different microphysics treatments for activation and diffusional growth. A comparison of the results indicates that the commonly applied assumption of saturation adjustment produces at maximum 6.9 % higher liquid water paths compared to the explicit diffusional growth method but has no significant influence on the general life cycle of the fog layer. Differences are found to be the most pronounced at the top of the fog layer where the highest supersaturations occurs. Furthermore, the effect of different cloud droplet number concentrations is investigated by using a selection of common activation schemes. We find, in line with previous studies, a positive feedback between the cloud droplet number concentration and both the optical thickness and the strength of the fog layer. Furthermore, we perform an explicit analysis of the budgets of microphysical quantities in order to assess which processes have the largest spatial and temporal influence on the development of the fog layer.