Local similarity relationships in the urban boundary layer

To investigate turbulent structures in an urban boundary layer (UBL) with m any tall buildings, a number of non-dimensional variable groups based on tu rbulent observations from a 325-m meteorological tower in the urban area of Beijing, China, are analyzed in the framework of local similarity. The ext ension of surface-layer similarity to local similarity in the stable and un stable boundary layer is also discussed. According to local similarity, dim ensionless quantities of variables: e.g., velocity and temperature standard deviations sigma (i)/u(*l) (i=u,v,w) and sigma (T)/T-*l, correlation coeff icients of uw and wT covariance, gradients of wind and temperature Phi (m) and Phi (h), and dissipation rates of turbulent kinetic energy (TKE) and te mperature variance Phi (epsilon) and Phi (N) can be represented as a functi on only of a local stability parameter z/Lambda, where Lambda is the local Obukhov length and z is the height above ground. The average dissipation ra tes of TKE and temperature variance are computed by using the u spectrum, a nd the uw and wT cospectra in the inertial subrange. The functions above we re found to be in a good agreement with observational behaviour of turbulen ce under unstable conditions, but there were obvious differences in the sta ble air.