Development of three-dimensional numerical short range forecast model of fog and visibility Matthieu Masbou and Andreas Bott Cooperation in project COST 722 "Short range forecasting methods of fog, visibility and low clouds" The presence of fog and low clouds in the lower atmosphere can have a critical impact on both airborne and ground transports. High quality predictions of fog formation and dissipation, together with the associated changes in visibility, would therefore be of immense operational value in the field. However, the many physical processes involved in fog formation interact in a complex and highly non linear fashion. These interactions are not adequately resolved by current operational mesoscale models. Numerical simulations require high horizontal and vertical resolutions combined with a sophisticated cloud microphysics. A new microphysical parameterization based on the one dimensional fog forecast model, PAFOG (Bott and Trautmann, 2002), was implemented in the COSMO Modell. The implementation of cloud condensation nuclei as new prognostic variable, into the dynamical core of COSMO, integrates the new microphysics into the three-dimensional frame. LM-PAFOG runs over a small, local area (100x100 Pixels) with a horizontal of 2.8 km. The high vertical resolution is concentrated near the ground : In LM-PAFOG 25 of 35 levels are located in the first 2000 meters. The aim of this project is to develop a fog forecast model for advection fog events and radiative fog events. Reference: Bott, A. and T. Trautmann, 2002, PAFOG - A new effcient forecast model of radiation fog and low level stratiform clouds, Atmospheric Research, 64, 191-203.

Comparison of 3D fog models and satellite fog/ very low stratus products Matthieu Masbou, Meteorological Institute, University of Bonn, Germany. Mathias D. Müller, Institute of Meteorology, Climatology & Remote Sensing, University of Basel, Switzerland. Jan Cermak, Laboratory for Climatology & Remote Sensing, University of Marburg, Germany. Cooperation in project COST 722 "Short range forecasting methods of fog, visibility and low clouds" Fog and low stratus have a critical impact on transport safety, air quality and within the climate system. High quality predictions and near-real time assessments of fog area are therefore of great economical and ecological relevance. The plausibility assessment of 3D fog forecasts requires an adequate spatially coherent comparison data set. A fog and very low stratus product derived from geostationary satellite data delivers this information at a sufficiently high temporal resolution. In return, the model output can provide an estimate of satellite-based ground fog detection accuracy (vertical domain). With these aims, a comparison of 3D model fog forecasts with satellite fog classification was performed for selected cases from the COST 722 Lindenberg comparison campaign (9-12/2005). Both 3D fog forecast models run with the same fog microphysics scheme coming from PAFOG (Bott & Trautmann, 2002), but each one has its own dynamical core: LM-PAFOG is based on the COSMO Modell of the DWD (Steppeler et. al. 2003), while NMM-PAFOG (M&uum;lller et. al. 2005) uses NMM (Janjic et. al. 2001, Janjic 2003). The satellite product makes use of Meteosat 8 data (see Cermak & Bendix, 2008). Parameters available are very low stratus area and ground fog confidence level. For the comparison, the spatial extent of the modeled fog patches was contrasted with the satellite classification on a per-pixel basis. To compensate for the different spatial scales, a bilinear interpolation of satellite cloud confidence levels was performed and compared with the modeled fog presence. Verification is done using ROC computed from different confidence level thresholds. The comparison results show good agreement between modeled and satellite-classified fog area. Further research will focus on ways to operationally incorporate model output into satellite product generation. References: Bott, A., Trautmann, T. , 2002, PAFOG - a new efficient forecast model of radiation fog and low-level stratiform clouds. Atmospheric Research, 64, 191-203. Cermak, J., Bendix, J., 2008, A novel approach to fog/low Stratus detection using Meteosat 8 data. Atmospheric Research, 87, 279-292 Müller, M. D., Bott, A., Masbou, M., Janjic, Z., 2005, Fog prediction in a 3D Model with Parameterized Microphysics, Proceeding of the World Weather Reasearch Programme Symposium on Nowcasting and Very short forecasting, 6.26. Janjic, Z. I., 2003, A nonhydrostatic model based on a new approach, Meteorology and Atmospheric Physics, 82, 271-285. Janjic, Z. I., Gerrity, J. P. & Nickovic, S. (2001), An alternative approach to nonhydrostatic modeling, Monthly Weather Review, 129, 1164-1178. Steppeler, J., Doms, G., Schättler, U., Bitzer, H.W., Gassmann, A., Damrath, U., Gregoric, G., 2003, Meso-gamma scale forecasts using nonhydrostatic model LM, Meteorological Atmospheric Physics, 82, 75-96.

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