Determination of energetic characteristics of urban-rural surfaces in the greater St. Louis area

Abstract

The role of surface geographical characteristics (e.g., albedo, thermal admittance, Bowen ratio, roughness) in the partitioning of energy at the complex and heterogeneous surface of several urban and rural land-use types has been evaluated through an application of Lettau's climatonomy theory. In contrast to the more conventional approach that first specifies all appropriate surface descriptors and then uses them to define climatic features, this application of climatonomy permits the determination of select surface descriptors on the basis of the observed diurnal response of surface temperature to the observed forcing function of available solar energy. Analyses were conducted for a variety of land-use types: urban residential, urban commercial, suburban, and rural farmlands and woods.

The solar forcing function and primary response function (i.e., effective surface temperature) were measured from repetitive diurnal aircraft flights over the greater St. Louis area during clear skies in August 1972. An estimate of surface roughness and subsequent parameterization of the atmospheric sensible heat flux were required for the analyses over nine selected sites. Photosynthetic and anthropogenic fluxes were not considered explicitly. The derived effective thermal admittance (square root of product of heat capacity and thermal conductivity) ranged from a minimum near 20 mly s^−1/2 K⁻¹ for urban and suburban sites to about 85 for wooded sections. The derived inverse Bowen ratio (ratio of latent to sensible heat fluxes) ranged from about 0.22 in the urban area to 2.9 for farmland.