Evaluation of spatially-averaged fluxes of heat, mass and momentum in the urban boundary layer
This paper investigates the applicability of standard boundary layer theory and observational methods to the urban system. It considers the spatial and temporal sampling problems posed by the large size of the roughness elements and the considerable horizontal spatial variability of the sources and sinks. The discussion is illustrated by reference to a series of studies conducted over suburban terrain in Vancouver, B.C., Canada. Special attention is paid to the validity of micrometeorological theory and method utilizing eddy correlation or profile methods to evaluate turbulent exchanges. It is concluded that despite the physical problems presented by the nature of the 'surface' it is possible to obtain valid areally-averaged fluxes from fixed-point observations provided that careful site selection, height of measurement and temporal sampling procedures are followed.