Evaluation of Two Gustiness Models for Exposure Correction Calculations

Gustiness models from Wieringa and Beljaars are evaluated. The models are used to relate the gustiness from wind speed records to the local roughness length. The roughness length is used to apply exposure corrections to sheltered wind stations. The gustiness models are mutually compared and the influence of measuring chain inertia and the measuring period on the measured gusts is evaluated. Beljaars's model is used to estimate the wind speed at elevated levels from wind speed and gustiness records measured close to the surface. Uncertainties in the computation of roughness lengths from gustiness records are also evaluated.
For measuring periods of one hour the exposure corrections from the two models are equal over smooth terrain. Over rough terrain Beljaars's gustiness model yields smaller corrections, differences up to 10% are possible. For 10-min periods Beljaars's corrections are 3-10% smaller than those of Wieringa.
Other uncertainties, resulting from the assumption of neutral stratification and a value for the blending height, are smaller than 5%.