Abstract
Abstract. The prediction of fogs is one of the processes not well reproduced by the Numerical Weather Prediction (NWP) models. In particular, the role of turbulence in the formation or dissipation of fogs is one of the physical processed not well understood, and therefore, not well parameterized by the NWP models. Observational analysis of three different periods with fogs at the Spanish Northern Plateau has been carried out. These periods have also been simulated with the Weather Research and Forecasting (WRF) numerical model and their results have been compared to observations. The study includes a comparison of the skill of different planetary boundary layer (PBL) parameterizations, surface layer schemes and a test of the gravitational settling of clouds/fogs droplets option. A statistical analysis of this comparison has been evaluated in order to study differences between the periods and between the various parameterizations used. The model results for each PBL parameterization were different, depending on the studied period, due to differences in the features of each fog. This fact made it difficult to obtain generalized conclusions, but allowed us to determine which parameterization performed better for each case. In general, judging from the models results of liquid water content (LWC), none of the PBL schemes were able to correctly simulate the fogs, being Mellor-Yamada Nakanishi and Niino (MYNN) 2.5 level PBL scheme the best one in most of the cases. This conclusion is also supported by the root mean square error (RMSE) calculated for different meteorological variables.
Highlights
The adverse effects of fog on human activities, especially on transport, are widely known
Several studies comparing different planetary boundary layer (PBL) schemes for the Weather Research and Forecasting (WRF) model have been done in the last years, as Shin and Hong (2011) who did an intercomparison of various PBL parameterizations for a single day, and found differences between unstable and stable conditions
The features of the fogs were different for each period, and the results of the simulations depended on the period more than on the option used to simulate, making it difficult to obtain generalized conclusions from this study
Summary
The adverse effects of fog on human activities, especially on transport, are widely known. While Welch and Welicki (1986) support the theory that turbulence acts favouring the formation of fog, other authors, such as Roach et al (1976), established that turbulence favours its dissipation It seems that there exists a threshold on the relation between turbulence and fog development (Zhou and Ferrier, 2008). Three different periods with fogs (mainly radiation fogs) have been studied and simulated with the WRFARW (Advanced Research WRF solver) in order to evaluate the ability of the model to simulate these events. For this purpose, three planetary boundary layer (PBL) parameterizations have been compared, as well as three different surface layer (SL) parameterizations. Differences between simulated and observed values (bias) and RMSE (root mean square error) for different meteorological parameters have been calculated for each period and for each model option
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