Application of Soil Dust Optical Properties in Analytical Models of Climate Change

Philip B. Russell Stanford Research Institute, Menlo Park, Calif. 94025

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Gerald W. Grams National Center for Atmospheric Research, Boulder, Colo. 80303

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Abstract

Several analytical models of the radiative effects of aerosol layers on global climate provide the common result that the critical value (ρc) of the ratio (ρ) of aerosol layer absorption to hemispheric backscattering is given by
ρcA2A
where A is taken to be the albedo of the earth's surface, or of the present earth–atmosphere system. The models predict that introduction of a new aerosol layer with ρ > ρ c will cause a decrease in system albedo, and a layer with ρ < ρc will cause an increase. In this paper we demonstrate this common result for &rho c and then employ recently published data on the complex refractive index and size distribution of atmospheric surface layer soil particles to compute values of ρ. The resulting values (5 < ρ < 28) are quite large compared to previous estimates. Together with the above model result they indicate that increased generation of such airborne soil particles will tend to increase the input of solar energy to the earth–atmosphere system. This “heating” effect results, in part, from the relatively large mean particle sizes used in the computations. The effects of particle asphericity on the computed ρ values are discussed.

Abstract

Several analytical models of the radiative effects of aerosol layers on global climate provide the common result that the critical value (ρc) of the ratio (ρ) of aerosol layer absorption to hemispheric backscattering is given by
ρcA2A
where A is taken to be the albedo of the earth's surface, or of the present earth–atmosphere system. The models predict that introduction of a new aerosol layer with ρ > ρ c will cause a decrease in system albedo, and a layer with ρ < ρc will cause an increase. In this paper we demonstrate this common result for &rho c and then employ recently published data on the complex refractive index and size distribution of atmospheric surface layer soil particles to compute values of ρ. The resulting values (5 < ρ < 28) are quite large compared to previous estimates. Together with the above model result they indicate that increased generation of such airborne soil particles will tend to increase the input of solar energy to the earth–atmosphere system. This “heating” effect results, in part, from the relatively large mean particle sizes used in the computations. The effects of particle asphericity on the computed ρ values are discussed.
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