Improving High-Resolution Fog Simulations using LANFEX Observations

The Local and Non-local Fog Experiment (LANFEX) is an 18 month field campaign designed to provide intensive observations of fog at two contrasting sites in the UK - one with reletively simple, flat terrain, and the other with more complex terrain and valley systems. This paper will discuss kilometer and sub-kilometer scale modelling of some LANFEX intensive observation periods, identifying the key processes affecting fog evolution. Reasons why accurate numerical weather prediction of fog is such a challenging problem, and potential improvements to model parametrizations will be discussed. It will be shown that aerosol-fog interactions and the correct prediction of the cloud droplet number is crucially important in the simulation of fog evolution. An unrealistic choice of how to represent cloud droplet number can lead to the model forming well-mixed, optically thick fog very quickly, while optically thin fog exists in a stable boundary layer in reality.