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  • Author or Editor: P.B. Russell x
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G. W. Grams
,
I. H. Blifford Jr.
,
D. A. Gillette
, and
P. B. Russell

Abstract

The angular variation of the intensity of light scattered from a collimated beam by airborne soil particles and the size distribution of the particles were measured simultaneously 1.5 m above the ground. These measurements gave an estimate of the complex index of refraction m=n REn IM i of airborne soil particles, where n RE is the real part and n IM the imaginary part of the refractive index.

Standard microscopic analysis procedures were employed to determine n RE. Although a wide range of values was observed, the value 1.525 was taken as representative. By applying Mie scattering theory to each of the observed distributions of particle size, the expected angular variation of the intensity of the scattered light was calculated for a fixed value of n RE and a wide range of values of n IM. For each set of simultaneous measurements, the value of n IM was taken to be that value which provided the best fit to the experimental data. The upper limit of the value of n IM for the airborne particles studied in the experiment was determined to be 0.005 with an uncertainty factor of about 2. The estimate of n IM was found to be fairly insensitive to the assumed value of n RE.

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Petr Chýlek
,
G. W. Grams
,
G. A. Smith
, and
P. B. Russell

Abstract

Hemispherical backscattering cross sections σb of spherical particles are calculated using a recently derived analytic expression. Results are compared with σb values obtained by numerical integration. It is found that the analytic formula gives exact values of the hemispherical backscattering cross sections and also saves computer time. The behavior of σb in the limits of very small and very large spheres is discussed. As an aid in utilizing simple models of climate change due to aerosols, the percentage of incident solar radiation scattered into the backward hemisphere is calculated for a range of particle sizes and complex refractive indices. Similar results are also presented for the ratio of absorption to hemispheric backscattering, a critical parameter in many aerosol climate models.

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