WMOD00571

• Title: Static Mode Seeding of Convective Clouds - A Review
• Date: 5/23/1984
• Weather Modification - Doc Type: Report

tion time (Fletcher, 1958b; Isaac and Douglas, 1972; DeMott et al., 1983;
Blumenstein et al., 1983), and deactivation by photolysis (Reynolds et al.,
1951; Vonnegut and Neubauer, 195,1; Fl etcher, 1959b) and wa rm temperature
dissolution (St. Amand, 1971; Mathews et al., 1972). These studies have

shown that the ice nucleation characteristics of silver iodide are quite

complex with the production of ice crystals depending in a complicated

manner on the physicochemical properties of the silver iodide aerosols and

the environmental conditions in which it operates. Considerable progress

has been made in understanding the influence of these complex processes,

with conflicting trends and major shifts in thought along the way, but pre-

cisely how many ice crystals any given silver iodide aerosol will produce
.

in natural cloud situations is not yet predictable with confidence.

The best estimates of the potential effectiveness of silver iodide for-

mulations and generating systems have been derived from cloud chamber

tests. The results of these tests (Bl ai r et al., 1973; Garvey, 1975) have

shown that, depending on mode of generation and chemical complexing, the
ice nucleating activity of silver iodide aerosols begins at about -5 to -8
oC, increases by 3 to 4 orders of magnitude with decreasing temperature to

about -16 oC and increases by less than one order of magnitude more with

further decreases in temperature. Aerosols of silver iodide complexes pro-

duced by acetone generators tend to nucleate more ice particles than those

produced by pyrotechni cs and i nc'"easi ng the burn rate of acetone generators

tends to increase their activity at warm temperatures. Silver iodide-

ammonium iodide complexes are considerably more active at warm temper"atures

than silver iodide-sodium iodide and silver iodide-potassium iodide

19