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WRF Sensitivity Analysis of Boundary Layer Clouds During the Cold Season

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WRF Sensitivity Analysis of Boundary Layer CloudsDuring the Cold SeasonNeil Davis, Andrea Hahmann, Niels­Erik Clausen, Mark Zagar1: DTU Wind Energy; 2: Vestas Technology R&D Aarhus, DK Motivation • Icing can be modeled based on output from NWPmodels such as WRF, but first models must be studiedwith regards to the properties important for turbine icing. • Previous studies of microphysical schemes havefocused on clouds outside of the boundary layer or fog,for turbine icing the intermediate levels are of greatestimportance. Methodology • WRF was run on 2 domains 30 km and 10 km withresults coming from the 10 km domain (fig 1.) • A total of 9 studies: 3 Planetary Boundary Layer (PBL)schemes coupled to 3 microphysical (mp) schemes • Mp Schemes: SUNY­Lin, Thompson, WSM5• PBL Schemes: MYNN2, MYJ, YSU• Simulation ran 2010­12­31 ­ 2011­01­30 in 10 daychunks with 12 hours of spinup time • Input and boundary conditions were from 1 degree FNLdataset, and 30 km domain was nudged using this dataevery 6 hours. • 63 vertical levels were used with 10 levels in the rotorplane defined as between 35 and 125 m. Figure 2: Percentage of period which has had icing. Max indicates at least one level in the rotor plan had icingconditions. The mean graph shows locations where the average values across the rotor plane met the criteria.Groups show different mp schemes, while colors indicate different PBL schemes. Percentage of active icing hours • At most sites differences in icing are dominated by microphysics. • SUNY­Lin consistently lowest, with Thompson consistently highest • Amount of icing decreases up to 10% or 72 hours with mean vs max Figure 1: 10 km Modeling domain and sites of interest. Sites are approximatelocations of wind parts found on Google Earth satellite photos & labeledalphabetically from south to north. Figure 3: Violin plot of mean temperatureacross rotor plane for icing (1) and no icing(0) conditions across all four sites. Temperature vs icing • WSM5 and SUNY­Lin both show wa

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