Wind‐gust parametrizations at heights relevant for wind energy: a study based on mast observations

Wind gusts are traditionally observed and reported at the reference height of 10 m and most gust parametrization methods have been developed only for this height. In many practical applications, e.g. in wind energy, the relevant heights are, however, up to a few hundred metres. In this study, mean gustiness conditions were studied using observations from two coastal/archipelago weather masts in the Gulf of Finland (northern Europe) with observation heights between 30 and 143 m. Only moderate and strong wind cases were addressed. Both masts were located over relatively flat terrain but the local environment, and hence the surface roughness length, differed between the mast locations. The observations showed that above all the gust factor depended on the surface roughness. Stability had a more pronounced effect over the rough forested surface than over the smooth sea surface. At both locations the stability had a larger effect on gusts than the observation height. Two existing parametrization methods, developed for a 10 m reference height, were validated against the observations and a new parametrization was proposed. In the new method, the gust factor depends on the standard deviation of the wind speed, which is parametrized on the basis of the surface friction velocity, the Obukhov length and height and the boundary-layer height. The new gust parametrization method outperformed the two older methods: the effects of surface roughness, stability and the height above the surface were well represented by the new method.

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