Vertical wind profiles over an urban area
Long-term measurements of wind and turbulence profiles over urban areas from acoustic remote sensing have not been available so far. 17 months of Doppler-SODAR measurements in the town of Hannover, Germany, are evaluated here with respect to mean wind speed, variance of the vertical velocity component, and turbulence intensity for heights up to 210 m agl. The resulting monthly means show that all vertical profiles are influenced by the high roughness and by the thermal properties of the urban surface. Main features are a missing diurnal course of the wind speed a few tens of meters above mean roof-top level and variances that increase considerably with height not only during daytime but also in many nights. While the first feature is typical for boundary-layers over rough surfaces, the second feature is only explainable by the larger heat input into the urban boundary-layer from the surface below. It is proposed to rely more on vertical remote sensing than on the vertical extrapolation of Prandtl-layer similarity theories when assessing the vertical structure of an urban boundary-layer.