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J. Rosinski and F. Parungo

Abstract

Silver iodide particles deposited on vegetation may photolyse and combine with natural terpenes from tree oils to form compounds which either themselves become aerosols, or become attached to aerosol particles. In either case the new compounds may become active centers acting as freezing nuclei. Silver iodide particles may persist for several months when deposited on coniferous trees, and may release variable doses of such freezing nuclei during that time. Although the concentrations of ice nuclei so produced are probably too small to influence precipitation, they may nevertheless contaminate large areas and thus may be significant for long-range research programs concerned with measuring natural concentrations of freezing nuclei.

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C. C. Van Valin, R. F. Pueschel, and F. P. Parungo

Abstract

Aitken nuclei and ice nuclei concentrations in the smoke plume from an oil well fire near Glenrock, Wyo., on 14 December 1973, were found to be elevated by at least an order of magnitude as compared with the surrounding atmosphere. The composition of most particles in the plume was suggestive of the clay minerals; these could account for the increased ice nuclei concentrations.

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Farn Parungo, Joe F. Boatman, Stan W. Wilkison, Herman Sievering, and Bruce B. Hicks

Abstract

A statistical analysis using published data on the global distribution of total cloud cover and cloud type amounts over the ocean, reduced from the Comprehensive Ocean–Atmosphere Data Set (COADS), shows a significant positive trend (4.2% increase from the 1930 baseline) in total oceanic cloud amount in the period between 1930 and 1981. The increase of total cloud amount for the Northern Hemisphere (5.8% ) was twice that for the Southern Hemisphere (2.9% ), The more consistent 30-yr ( 1952–1981 ) data show that the change in cloud amount ( 1952 base) was 1.5% for the globe, 2.3% for the Northern Hemisphere, and 1.2% for the Southern Hemisphere. The analysis also shows that the greatest cloud amount increase was for altocumulus and altostratus clouds and that this increase was most pronounced at midlatitudes (30°–50°N). The trend and the pattern of cloud amount variations appear to be in accord with the temporal trend and geographic distribution of S02 emissions. It is hypothesized that sulfate particles converted from S02, may modify cloud droplet spectra, causing affected clouds to be more colloidally stable than unaffected clouds. The longer residence times of affected clouds could cause increases of cloud frequency and cloud amount.

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