Is a more physical representation of aerosol activation needed for simulations of fog?

Abstract. Aerosols play a crucial role in the fog life cycle, as they determine droplet number concentration and hence size, which turn controls both fog's optical thickness lifespan. Detailed aerosol-microphysics schemes accurately represent formation growth are unsuitable for weather forecasting climate models, computational power required to calculate would dominate treatment of rest physics model. A simple method account is use an aerosol activation scheme, parameterises based on change supersaturation at given time. Traditionally, parameterisation were designed convective clouds assume that reached through adiabatic lifting, with many imposing minimum vertical velocity (e.g. 0.1 m s?1) unresolved subgrid ascent. In radiation fog, measured updraughts during initial often insignificant, radiative cooling being dominant process leading saturation. As result, there risk will overpredict concentration, may result transitioning optically thick layer too rapidly. This paper presents more physically scheme can saturation due non-adiabatic processes. Using offline model, our results show equivalent rate associated updraught threshold assumption by up 70 % comparison typical found formation. The new has been implemented Met Office Natural Environment Research Council (NERC) Cloud (MONC) large eddy simulation (LES) model tested using observations case study Cardington, UK. this work leads calculation appropriate cloud number. slower transition (well-mixed) line observations. shown demonstrate importance representation modelling impact processes linked development fog. Unlike previous activation, revised suitable simulate regimes.