WMOD00298

• Title: Quantifying Ice Nucleation by Silver Iodide Aerosols
• Date: 5/1/1990
• State: CO
• Weather Modification - Doc Type: Report

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I. INTRODUCTION

1.1 Background
The research reported in this dissertation has been conducted to

define and quantify important fundamental aspects of ice nucleation by

artificial ice nuclei in supercooled clouds. Experiments have shown

that temperature and water vapor supersaturation are of primary

importance for the formation of ice (e.g., Grant, 1971; Gagin, 1972;

Vali, 1975;1976). It is also known that the chemical composition, the

mechanisms (modes) of nucleation, and the history of the nucleating

particles can be of primary importance (Edwards and Evans, 1971;

Cooper, 1974; Gerber, 1976; Schaller and Fukuta, 1979; Rogers, 1982;

DeMott et al., 1983; Blumenstein et al., 1987), but descriptions of

these aspects are far from complete. In addition, it is not clear to

planners of weather modification programs whether to or how to

implement the evolving understanding of the complex function of ice

nuclei into decision making; ie., what seeding agent to use for

specific cloud characteristics and how, when, and where to deliver it

for optimum effect (Hindman, 1985; Braham, 1985; AMS, 1986).

Seeding a cloud with a silver iodide (AgI) containing nucleant

aerosol is expected to result in the production of ice crystals in the

supercooled parts of the cloud. The assumption is made that the nuclei

will function to form a specified concentration of ice crystals if

delivered to the appropriate cloud location in a known concentration.