Investigation of the vertically-layered structure and surface roughness parameters of the urban boundary layer

Atmospheric flow is the main factor affecting the wind load of urban buildings. The measured data observed continuously from the 325-m-tall Beijing Meteorological Tower (BMT) during 2013-2017 is employed to investigate the vertically-layered structure and surface roughness parameters of the urban boundary layer. Based on the local similarity theory and analysis results of the atmospheric stability and local friction velocity, it can be determined that the height of 80 m is near the bottom of the inertial sub-layer, the range below this height belongs to the roughness sub-layer, 140 m belongs to the inertial sub-layer, and 200 m and 280 m are in the mixing layer. The local friction velocity at 80 m can be considered a relatively reliable value as the friction velocity. Moreover, seasonal effect on local friction velocity is minimal. According to the fitting result of near-neutral strong wind samples by the log-law, it is concluded that to obtain a more accurate wind speed profile, all layers should be included when picking fitting heights. In addition, surface roughness parameters are affected by the wind direction and speed. The variation according to the wind direction corresponds to the topographical distribution surrounding the BMT, and the higher range of wind speed may be more applicable for estimating surface roughness parameters.