Local Similarity Relationships In The Urban Boundary Layer

Abstract

To investigate turbulent structures in an urban boundary layer (UBL) with many tallbuildings, a number of non-dimensional variable groups based on turbulent observationsfrom a 325-m meteorological tower in the urban area of Beijing, China, are analyzedin the framework of local similarity. The extension of surface-layer similarity to localsimilarity in the stable and unstable boundary layer is also discussed. According to localsimilarity, dimensionless quantities of variables: e.g., velocity and temperature standarddeviations σi/u*l (i=u,v,w) andσT/T*l,correlation coefficients of uw and wT covariance, gradients of wind and temperatureΦm and Φh, and dissipation rates of turbulent kinetic energy (TKE) andtemperature variance Φe and ΦN can be represented as a functiononly of a local stability parameter z/Λ, where Λ is the local Obukhovlength and z is the height above ground. The average dissipation rates of TKE andtemperature variance are computed by using the u spectrum, and the uw and wTcospectra in the inertial subrange. The functions above were found to be in a goodagreement with observational behaviour of turbulence under unstable conditions, butthere were obvious differences in the stable air.