Wind Shear Fluctuations Downwind of Large Surface Roughness Elements

Abstract

Wind measurements in the lowest 50 m of the atmosphere approximately 1 mi downwind of an urban area are examined to provide estimates of the short-term fluctuations of the vertical and lateral shear of the longitudinal component of the wind during six periods of slightly to moderately unstable atmospheric conditions. The fluctuations are described by a Pearson Type IV probability distribution. Models are presented for the standard deviation, skewness and kurtosis of the distributions. The distributions are slightly skewed and more peaked than Gaussian but tend toward Gaussian as separation increases. Time scales for the shear fluctuations are described.