Radiation Fog Case Study: Observational Analysis and WRF Modeling

The negative impacts of the fogs in transport are widely known. For this reason, it is important to get good predictions in order to minimize human and economic losses. There exist many physical factors affecting the development of fogs, turbulence among them. The role that turbulence plays in the formation or dissipation of fogs is not well known and therefore, it is not correctly parameterized by the Numerical Weather Prediction (NWP) models. Some authors think that the effect of turbulence is to favor the formation of fogs and others state that turbulence acts favoring the dissipation. A combination of both theories leads to the conclusion that there exists a threshold on the relation between turbulence and the fog development. This study includes a full observational analysis including turbulent parameters of one fog event occurred in the Northern Spanish Plateau. Data from the instrumentation available at the Research Centre for the Lower Atmosphere (CIBA in Spanish) was used. The instrumentation used consisted of standard instrumentation measuring temperature, relative humidity and wind, sonic anemometers, microbarometers and particle concentrations measurements. The CIBA site is located 25km north-west of Valladolid city (Spain), on a region known as Montes Torozos, which forms a high plain of nearly 200 km2 elevated above the main plateau, being an ideal place for the development of radiation fogs in winter. This fog event has also been simulated with WRF-ARW model and several options of the model have been compared, with particular attention in the use of distinct planetary boundary layer (PBL) parameterizations.