Estimation of aerodynamic roughness length and displacement height of an urban surface from single-level sonic anemometer data

A method for estimating the aerodynamic roughness length and displacement height of an underlying surface from single-level sonic anemometer data is applied to an urban surface in Beijing. Both surface roughness length and displacement height are found to vary considerably with wind direction. The results show that during the selected period average values of the aerodynamic roughness length and the zero-plane displacement height were 1.6 m and 36.0 m respectively. Comparison of the present results with previous studies for this site demonstrates that the roughness length and zero-plane displacement have increased over the last eight years. These increases were associated with an increase in the height of urban buildings.