Abstract
A two-stream solar radiation model was combined with a mixed-layer model to study the effects of absorbing aerosols on the thermal structure of the daytime convective boundary layer. A number of simulations were conducted with the model. The results showed that the criterion used in climatic models to determine the cooling or warming effect of aerosols was not readily applicable to micrometeorological scales. It was also found that soil-interface properties were at least as important as aerosol properties in determining aerosol-induced effects. Any conclusions about aerosol effects on the PBL have to be qualified by statements about surface parameters to be meaningful.
An average of the PBL and surface temperatures (θa) is suggested as a physically meaningful indicator of aerosol effects. The results show that aerosols increase θa over surfaces which are relatively wet or have high reflectances; dry, low-albedo surfaces, however, are associated with a decrease in θa in the presence of aerosols.
Another important conclusion of the study is that the soil-PBL system has a built-in mechanism to regulate aerosol-induced heating of the PBL and cooling of the surface. The degree of regulation is dependent on soil-PBL interface properties.
