Effects of Seeding Isolated Cumulus Clouds with Silver Iodide

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.