An Evaluation of Silver Iodide Cloud Seeding by Aircraft in Western Quebec, Canada, 1960–1963

Abstract

A precipitation physics project aimed at discovering basic relationships in the chain of cause and effect in precipitation mechanisms was operated in western Quebec province, Canada, from 1959 to 1963 inclusive. In addition to many physical measurements taken from an aircraft and on the ground, randomized cloud seeding was employed as one method of study. Clouds over one of two test areas were seeded with silver iodide released from an aircraft during the passage of synoptic-scale weather systems, with the choice of area by a random selection. Comparison of storm rainfall in the two test areas measured by a dense network of raingages was used to evaluate the effect of the cloud seeding. Statistical tests of the relationship of precipitable water and instability with the seeding effect were also conducted. A small negative seeding index was computed and a slight correlation was found between both precipitable water and instability and the seeding index ratio. However, none of these relationships was found to be statistically significant.