Analytical Shear Statistics Based on Nocturnal Wind Profiles

Abstract

For a number of periods since 1978, wind and temperature profile measurements have been taken at two radio masts of 300 m height located in northern Germany. From wind profiles obtained during nocturnal conditions, wind shear data were calculated throughout the boundary layer for six layers of 25 m thickness. The data were analyzed taking into account dependencies on temperature gradients, geostrophic winds, local variations of kinetic energy and cooling rates. Minimum shear values were found for geostrophic winds about 5 m s?1 and strong shear values when the wind field was highly accelerated or decelerated and cooling rates were strong. In addition, increasing shear was found to be associated with increasing temperature gradients up to approximately 4 K per 100 m.