Variability of energy fluxes in relation to the net-radiation of urban and suburban areas: a case study

Abstract

This paper addresses the relation between the net-radiation (Q ^*) and the ground heat flux (Q _G), the energy stored in the soil ($\Updelta Q_{\rm S}$), and the residual of the energy partition (R = Q ^* − Q _H  − Q _E ) of urban and suburban areas of Oklahoma City, USA. These three forms of energy were observed or estimated from observations taken during Joint Urban 2003 Campaign. The database includes net-radiation, soil temperature, ground heat flux, and turbulent fluxes. In most cases the estimates of the energy stored in the soil were obtained by assuming roughly a certain type of soil and an effective soil depth. From the residuals it seems to be possible to distinguish the urban boundary layer from the suburban boundary layer when plotted as a function of net-radiation. Hysteresis coefficients were computed for fits of net-radiation against R, $\Updelta Q_{\rm S}$ and Q _G. In particular, the hysteresis patterns show that Q ^* vs. R represents clearer urban areas or suburban areas under the influence of an urban “plume”. On the other hand, hysteresis curves obtained from $\Updelta Q_{\rm S}$ or Q _G account for better the ground composition. A possible consequence is that the land use of urban areas could be roughly inferred from curve shapes such as Q ^* vs. R, or Q ^* versus another input variable representing the storage term. The objective is to show the variability of the subsurface-related energy fluxes across an urban area using these three different quantities and also to show that $\Updelta Q_{\rm S}, \,Q_{\rm G}$, or R (and their corresponding hysteresis curves) are likely to be quantitatively different, which have not been clearly stated in the literature.