The Wind Profile in the Coastal Boundary Layer: Wind Lidar Measurements and Numerical Modelling
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The Wind Profile in the Coastal Boundary Layer: Wind Lidar Measurements and Numerical Modelling R. Floors · C. L. Vincent · S.-E. Gryning · A. Peña · E. Batchvarova
Received: 30 May 2012 / Accepted: 4 December 2012 / Published online: 13 January 2013 © Springer Science+Business Media Dordrecht 2013
Abstract Traditionally it has been difficult to verify mesoscale model wind predictions against observations in the planetary boundary layer (PBL). Here we used measurements from a wind lidar to study the PBL up to 800 m above the surface at a flat coastal site in Denmark during a one month period in autumn. We ran the Weather Research and Forecasting numerical model with two different roughness descriptions over land, two different synoptic forcings and two different PBL schemes at two vertical resolutions and evaluated the wind profile against observations from the wind lidar. The simulated wind profile did not have enough vertical shear in the lower part of the PBL and also had a negative bias higher up in the boundary layer. Near the surface the internal boundary layer and the surface roughness influenced the wind speed, while higher up it was only influenced by the choice of PBL scheme and the synoptic forcing. By replacing the roughness value for the land-use category in the model with a more representative mesoscale roughness, the observed bias in friction velocity was reduced. A higher-order PBL scheme simulated the wind profile from the west with a lower wind-speed bias at the top of the PBL. For easterly winds low-level jets contributed to a negative wind-speed bias around 300 m and were better simulated by the first-order scheme. In all simulations, the wind-profile shape, wind speed and turbulent fluxes were not improved when a higher vertical resolution or different synoptic forcing were used. Keywords Internal boundary layer · Low-level jet · Weather Research and Forecasting model · Wind lidar · Wind profile
R. Floors (B) · C. L. Vincent · S.-E. Gryning · A. Peña DTU Wind Energy, Risø Campus, Technical University of Denmark, Frederiksborgvej 399, 4000 Roskilde, Denmark e-mail: [email protected] E. Batchvarova National Institute of Meteorology and Hydrology, Sofia 1784, Bulgaria
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1 Introduction The change of wind speed with height in the lower planetary boundary layer (PBL) and its development in time are key issues for the wind energy industry. As wind turbines become taller, our knowledge of the wind-speed profile above the surface layer has to be improved. The Monin–Obukhov similarity theory (MOST) provides a solid framework for predicting wind profiles in the surface layer (Businger et al. 1971). However, many questions remain unsolved about the wind profile throughout the PBL, due to the interaction of synoptic, mesoscale and microscale processes. A variety of tools is used to study these interactions, for example the resistance law (Zilitinkevich and Esau 2005), mixing length theory (Gryning et al. 2007) or numerical models such as the Weather Research and Forecasting model (WRF
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