The Artificial Stimulation of Precipitation by Means of Dry Ice

Abstract

In experiments carried out near Sydney, supercooled water clouds were " seeded " with ice crystals by dropping pellets of solid carbon dioxide into them. Up to August 25, 1948, 20 experiments were made under conditions sufficiently well defined for the experiments to be significant. In 15 of them precipitation is believed to have been released artificially. Of 11 clouds with tops colder than -7°C., 10 precipitated. The depth of the treated clouds ranged from 1000 to 15,000 ft. In none of these did natural precipitation occur within 20 miles. Further evidence that the effect is genuine is given by the fact that both the likelihood of success in inducing precipitation and the time between treatment of the cloud and the appearance of precipitation at its base, varied consistently with the cloud characteristics. The observations are consistent with the view, as postulated by Bergeron, that the precipitation grew from ice crystals (formed by the dry ice pellets).