Source of Seasonal Variations in Solar Radiation at Mauna Loa

Abstract

Solar radiation transmission data taken at Mauna Loa exhibit a seasonal variation with the minimum in summer. On the basis of Barrett's model for the depletion of solar radiation by aerosols, it is suggested that these variations are due to the seasonal generation of organic aerosols by the biosphere. It is suggested that the naturally produced atmospheric background aerosol of organic origin causes the typical seasonal turbidity variations. Furthermore, changes in the amplitude or phase of transmission data could be used to indicate whether aerosols from anthropogenic sources would influence the earth's albedo. Precipitable water calculations suggest that humidity data above Mauna Loa are not accurate enough to make a quantitative estimate of the effect of atmospheric water vapor on Mauna Loa radiation data. However, water vapor apparently cannot account for these variations on the basis of phase angle considerations.