Weiter, Axel (2017) Evaluation of the WRF mesoscale model regarding the wind conditions in the planetary boundary layer. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 74 pp.

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Abstract

Wind resource assessment requires accurate knowledge of the wind conditions at a potential site. Mesoscale modeling offers a cost-saving possibility, but the quality of these simulations needs to be examined. In this thesis, a simulation for Germany of the Weather Research and Forecasting (WRF) mesoscale model, which is additionally extended by an optimization method for wind speE)d, is evaluated for heights of 40-200 m using observational data from 48 wind measurements and 12 wind farms. A detailed description of how to use wind turbine data for model evaluation is included. The results show a remarkable positive bias of the WRF model in the lower part of the planetary boundary layer (PBL). This is crucially reduced by the optimization method. In general, model skill decreases towards the ground, which motivated the investigation of the influence of the surface. It is shown that model skill is also declining with increasing surface roughness. Complex terrain reduces the positive bias. However, this is actually due to speed-up effects, which influence measurements in complex terrain, since these were taken on hill tops rather than in the valleys. The diurnal cycle is investigated as well. A higher model performance during daytime is revealed. This is linked to more unstable atmospheric conditions, which the model is more able to simulate due to the increased vertical exchange of important quantities in the PBL. Finally, it is found that the WRF simulation overestimates wind speed over its entire range and that the optimization method results in underestimation of extreme winds.

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