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E. J. Smith, E. E. Adderley, and F. D. Bethwaite

Abstract

A cloud-seeding experiment was conducted in South Australia from 1957 to 1959 inclusive in which clouds over one of two areas were seeded with silver-iodide smoke released from an aircraft, with random choice of area. No precipitation increases due to seeding were detected.

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E. J. Smith, E. E. Adderley, and F. D. Bethwaite

Abstract

From 1958 to 1963 an experiment was conducted in the New England region of Australia, in which clouds were seeded with silver iodide smoke released from an aircraft. Clouds over two areas were seeded, with random choice of area. Rainfall measurements in the two areas suggest that seeding increased the rainfall during the first year, but no net changes in rainfall could be detected in subsequent years. The seeding appears to have increased the variability of rainfall.

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F. D. Bethwaite, E. J. Smith, J. A. Warburton, and K. J. Heffernan

Abstract

Isolated cumulus clouds with supercooled tops were seeded from an aircraft. Either a large (20 gm), small (0.2 gm) or zero quantity of silver iodide was used, with random choice of treatment. The amount of rain which fell from the cloud was measured at cloud base by means of an impactor on the seeding aircraft.

Clouds with tops −10C or colder which were treated with the larger quantity of silver iodide yielded significantly more rain than similar, untreated clouds. The mean rainfall from clouds seeded with the reduced treatment was also higher than that from the unseeded clouds, but the margin in this case was insufficient to demonstrate the statistical significance of the result.

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