Arctic Fog Droplet Size Distribution and Its Effect on Light Attenuation

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  • 1 U. S. Army Cold Regions Research and Engineering Laboratory, Ilanover, N. H. 03755
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Abstract

Arctic fog droplets were sampled on narrow glass plates precoated with chloride-sensitive gelatin film at Point Barrow, Alaska, in the summer of 1971. The relation between the radius of the log droplet and the radius of the imprint on the film was determined experimentally. The collection efficiency of the fog droplet was determined. About 20,000 fog droplet radii were measured.

The results of the analysis of the concentration and the size distribution of fog droplets are presented in the form of tables and figures. It is shown that the concentration and the size distribution changed rapidly with time and space; the droplet radii ranged widely between 3.3 and 65 µm; the maximum concentration was 24 droplets cm−3 and the liquid water content was 0.09 gm m−3 at a visibility of 250 m. Calculations were made of the attenuation by fog at wavelengths of 0.55 and 1.06 µm for the observed size distributions and concentrations of fog droplets. The values of the visual range calculated at a threshold constant of 5% were closer to the observed values than those at a threshold constant of 2%.

Abstract

Arctic fog droplets were sampled on narrow glass plates precoated with chloride-sensitive gelatin film at Point Barrow, Alaska, in the summer of 1971. The relation between the radius of the log droplet and the radius of the imprint on the film was determined experimentally. The collection efficiency of the fog droplet was determined. About 20,000 fog droplet radii were measured.

The results of the analysis of the concentration and the size distribution of fog droplets are presented in the form of tables and figures. It is shown that the concentration and the size distribution changed rapidly with time and space; the droplet radii ranged widely between 3.3 and 65 µm; the maximum concentration was 24 droplets cm−3 and the liquid water content was 0.09 gm m−3 at a visibility of 250 m. Calculations were made of the attenuation by fog at wavelengths of 0.55 and 1.06 µm for the observed size distributions and concentrations of fog droplets. The values of the visual range calculated at a threshold constant of 5% were closer to the observed values than those at a threshold constant of 2%.

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