AN URBAN CANYON ENERGY BUDGET MODEL AND ITS APPLICATION TO URBAN STORAGE HEAT-FLUX MODELING

To obtain a local-scale urban energy balance by either measurement or modeling it is necessary to determine storage heat flux (Delta Q(s)). This flux cannot be measured directly due to the complexity of the urb an surface. The Grimmond et al. Objective Hysteresis Model (OHM) [C.S. B. Grimmond, H.A. Cleugh, T.R. Oke, An objective urban heat storage mo del and its comparison with other schemes. Atmos. Environ., 25B (1991) 311-326] of local-scale Delta Q(s) combines empirical equations for i ndividual surface types in the proportion that they are present within the urban area. One surface type for which there is very limited fiel d data is the urban canyon, which consists of the walls of adjacent bu ildings, the horizontal street-level area separating them (roadways, g ardens, parking lots, etc.) and the enclosed air volume. Here the stor age heat flux of an urban canyon and the resulting OHM parameters are investigated with a numerical model of a dry urban canyon energy budge t. Substrate heat fluxes are derived from simulated surface and substr ate temperatures; the latter evolve through time according to the fini te difference form of the Fourier heat conduction equation. When compa red against measured fluxes, the model performed satisfactorily. Numer ical experiments show significant effects on the OHM parameters due to changes in the ratio of building height to separation distance and bu ilding wall thermal properties. Effects of intermediate significance w ere attributable to canyon orientation, wind speed and the timing of t he between-building air temperature regime. Air temperature and the ti ming of the wind speed curve showed only minor significance. (C) 1998 Published by Elsevier Science S.A.