OBSERVATIONS AND MODELING OF DOWNWARD RADIATIVE FLUXES (SOLAR AND INFRARED) IN URBAN/RURAL AREAS.

Abstract

Measurements were taken, over several weeks, of downward radiation over the city of Toulouse, France and a rural reference site. The downward IR flux was larger at the urban site by day and night. Attenuation of the incident solar radiation at the urban site was observed. A radiative model showed that the IR flux increase is mainly due to higher air temperature associated with the urban 'heat island'. The emissivity increase due to the addition of absorbing constituents in the urban area was very weak. The attenuation of solar radiation was due to absorption by urban aerosol. Total incoming radiation was similar at the two sites by day and was slightly higher at the urban site during the night.