Large Eddy Simulation of a radiation fogGert-Jan Steeneveld
Casimir Ziegler Stipendium
Fog is a severe weather phenomenon with an evident economic impact on society, on transportation, and on agriculture. In addition, the polar climate in summer is chacterised by persistent fog, and it is likely it plays a role in the (currently not well understood) dynamics of sea ice cover. Despite numerous efforts and developments in numerical weather prediction, fog forecasting remains a challenge. A number of physical processes governs the life cycle of a fog layer, i.e. turbulent transport, radiation, interaction with vegetation and land use, and microphysics. This complexity has hampered model development, and therefore current skill scores for fog are relatively low. As an illustration, both the hit rate and the false alarm rate have a similar value. As such it is clear that a better understanding of the fog physics is required in order to improve fog forecasts.
To overcome this problem the Dutch Atmospheric Large Eddy Simulation (DALES) model is used to simulate a full diurnal cycle of a radiation fog. The large eddy simulation technique acts as the atmospheric laboratory because the initial and boundary conditions can be fully controlled in the LES, which is certainly not the case in the atmosphere. From this simulation, the character of the turbulent mixing before and after fog onset will be documented and the aim is to formulate parameterizations for use in operational numerical weather and climate models.