Flow Characteristics Above a Very Low and Gently Sloping Hill

摘要

Tower measurements of wind and turbulence in near neutral conditions at the top of a very low and gently sloping hill (height ca 20 m, with a length scale ca 1000 m) are analysed in terms of current flow over hill theory. Measurements of wind maximum height and the change of the variances of the three wind components from the inner to the outer region are found to be in agreement with predictions from the theory. Spectra of the longitudinal and vertical wind components in the inner region, come close to the corresponding Kansas curves in the high frequency range. They have higher energy in the low frequency region, probably a spectral lag effect caused by rougher upwind terrain. In the outer region the spectra coincide with the corresponding Kansas curves if normalized by their respective variances and plotted against frequency ratio. (ERA citation 10:030636)