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Analysis of profiles of meteorological measurements from a 160 m high mast at the National Test Site for wind turbines at Høvsøre (Denmark) and at a 250 m high TV tower at Hamburg (Germany) shows that the wind profile based on surface-layer theory and Monin-Obukhov scaling is valid up to a height of 50-80 m. At higher levels deviations from the measurements progressively occur. For applied use an extension to the wind profile in the surface layer is formulated for the entire boundary layer, with emphasis on the lowest 200-300 m and considering only wind speeds above 3 m s −1 at 10 m height. The friction velocity is taken to decrease linearly through the boundary layer. The wind profile length scale is composed of three component length scales. In the surface layer the first length scale is taken to increase linearly with height with a stability correction following Monin-Obukhov similarity. Above the surface layer the second length scale (L MBL ) becomes independent of height but not of stability, and at the top of the boundary layer the third length scale is assumed to be negligible. A simple model for the combined length scale that controls the wind profile and its stability dependence is formulated by inverse summation. Based on these assumptions the wind profile for the entire boundary layer is derived. A parameterization of L MBL is formulated using the geostrophic drag law, which relates friction velocity and geostrophic wind. The empirical parameterization of the resistance law functions A and B in the geostrophic drag law is uncertain, making it impractical. Therefore an expression for the length scale, L MBL , for applied use is suggested, based on measurements from the two sites.

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The advantages and limitations of the ZephIR®, a continuous-wave, focused light detection and ranging (LiDAR) wind profiler, to observe offshore winds and turbulence characteristics were tested during a 6 month campaign at the transformer/platform of Horns Rev, the world's largest wind farm. The LiDAR system is a ground-based sensing technique which avoids the use of high and costly meteorological masts. Three different inflow conditions were selected to perform LiDAR wind profiling. Comparisons of LiDAR mean wind speeds against cup anemometers from different masts showed high correlations for the open sea sectors and good agreement with their longitudinal turbulence characteristics. Cup anemometer mean wind speed profiles were extended with LiDAR profiles up to 161 m on each inflow sector. The extension resulted in a good profile match for the three surrounding masts. These extended profiles, averaged over all observed stabilities and surface roughness lengths, were compared to the logarithmic profile. The observed deviations were relatively small. Offshore wind farm wakes were also observed from LiDAR measurements where the wind speed deficits were detected at all LiDAR heights. Profile-derived friction velocities and roughness lengths were compared to Charnock's sea roughness model. These average values were found to be close to the model, although the scatter of the individual estimations of sea roughness length was large.where ū is the mean wind speed at height z; u * is the friction velocity; k is the von Karman constant (∼0.4); z o is the aerodynamic roughness length, and y M is the universal stability function. This last term depends on both the height and the Obukhov length L.For wind resource assessments, equation (1) has been used to extrapolate wind speed measurements normally performed at low heights, e.g. 10 m. The vertical wind profi le is determined from equation (1) by estimating u * and L, e.g. from measurements of turbulence fl uxes. The surface roughness length z o can be estimated in relation to the land cover or by using roughness models for the sea state. 2 Equation (1) has been validated from experiments at heights up to 32 m (e.g. the Kansas experiment 3 ) and 50-80 m in Gryning et al. 4 Beyond these levels, deviations have been reported in different boundary layer studies. The height of the boundary layer is introduced in Gryning et al. 4 as a length scale to correct vertical wind profi les measured up to 250 m. The inversion height is estimated in Lange et al. 5 from air density differences to correct offshore wind profi les at Rødsand (Denmark). These attempts to extend vertical profi les are important for the development of the wind energy because the knowledge of the wind resource at high levels in the atmosphere is still immature.Conventional techniques (e.g. cup and sonic anemometers) have been extensively used to observe winds and turbulence. They have reached a limit in the vertical range which is similar to the current turbine's hub height. This is due mainly to the costs of er...

Operational since 2004, the National Centre for Wind Turbines at Høvsøre, Denmark has become a reference research site for wind-power meteorology. In this study, we review the site, its instrumentation, observations, and main research programs. The programs comprise activities on, inter alia, remote sensing, where measurements from lidars have been compared extensively with those from traditional instrumentation on masts. In addition, with regard to wind-power meteorology, wind-resource methodologies for wind climate extrapolation have been evaluated and improved. Further, special attention has been given to research on boundary-layer flow, where parametrizations of the length scale and wind profile have been developed and evaluated. Atmospheric turbulence studies are continuously conducted at Høvsøre, where spectral tensor models have been evaluated and extended to account for atmospheric stability, and experiments using microscale and mesoscale numerical modelling.