Relative Efficiencies of Turbulent Transfer of Heat, Mass, and Momentum over a Patchy Urban Surface

Abstract

This study uses observational data from a suburban site in Vancouver, British Columbia, Canada, to investigate the relative facility with which heat, water vapor, and momentum are transported by turbulence in the unstable surface layer. The ratios of linear correlation coefficients ?rwT/ruw and ?rwq/ruw increase approximately linearly with instability and are generally smaller than typical rural values due to bluff-body effects. The ratio rwT/rwq is greatest near neutral and larger than unity at all stabilities. This inequality may be caused by the complex source/sink patterns of the urban surface, cloud effects on the radiative forcing, and the unusually well-developed interaction between the surface and the upper portions of the urban boundary layer. Inequality of transfer between T and q will make it difficult to measure turbulent fluxes for cities using standard gradient approaches.