Validation of surface layer similarity theory to describe far offshore marine conditions in the Dutch North Sea in scope of wind energy research

With the ongoing development of offshore wind farms it becomes increasingly important to have an accurate description of offshore atmospheric conditions. A new meteorological mast constructed in 2011 sited 85 km offshore in the Dutch North-sea area has been used to validate the relations expected from Monin-Obukhov similarity theory. It is shown that wind shear and turbulence (second order moments and turbulence spectra) are a function of the non-dimensional stability parameter zeta, which is in agreement with literature. Wind shear is well described by the stability corrected logarithmic wind shear profile, though scatter is significant for stable conditions. This is explained by considering the relative height within the boundary layer where observations are taken. The non-dimensional second order moments of the three wind components are found to be either constant (neutral), proportional to (-zeta)(-1/3) (unstable) or proportional to zeta(-1/2) (stable). The Kaimal spectrum has been validated for specified stability classes. The non-dimensional scaling frequency f(0) for the three wind components increases for stable conditions, and decreases for unstable conditions. Besides, we find that f(0) is smallest for the longitudinal wind component, and largest for the vertical wind component. These results support the validity and applicability of Monin-Obukhov similarity theory to describe atmospheric conditions far offshore. (C) 2014 Elsevier Ltd. All rights reserved.