Estimating atmospheric turbidity from climate data

Aerosols have several important influences on the climate system. Among the more important of these are their roles in absorbing and scattering radiation, and as condensation nuclei in cloud-forming processes. Despite their importance, knowledge of their spatial and temporal variability and, in turn, their influence on climate, is incomplete. Constraints associated with conventional approaches to measuring atmospheric turbidity – including the requirements for clear skies and costly equipment – have contributed to a paucity of turbidity data. This paper presents a methodology for estimating atmospheric turbidity from readily available surface-weather data, regardless of cloud cover. Using a high-resolution spectral radiation model, clear-sky beam irradiance is parameterized as a function of atmospheric attenuation processes, including scattering and absorption by aerosols. The model is integrated over the day to obtain an expression for estimating potential daily clear-sky beam irradiation. Turbidity can then be estimated by forcing the model with monthly averaged climate data. The methodology can be applied at any location where the requisite climate data are available and therefore holds promise for a more complete, and possibly global, climatology of aerosols.