WMOD00298

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

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occurence of collisions at cloud temperatures warmer than OOC did not

significantly reduce the activity of the AgI, at least at tempertures

below -lOoC. Their experiments did not have the proper sensitivity at

warmer temperatures.

A complete quantitative characterization of an ice nucleus should

include descriptions of its action to form ice crystals by all of the

potential nucleation modes. Only a few studies have been performed with

this intent, most notably those of Langer et al. (1978) and Schaller

and Fukuta (1979). Unfortunately, these most comprehensive of studies

performed previously suffer from their lack of relevance for the actual

aerosols used in weather modification. Both studies noted generated

pure AgI thermally. This is not a method used operationally. Most

relevant to the research reported in this dissertation are studies of

nucleation by AgI aerosols produced by the solution combustion method

operationally employed for both ground-based and airborne aerosol

generation. In this method, solutions of AgI, acetone, water and some

type of solubilizing agent for the AgI are burned. Although these

aerosols can act to form ice by all of the defined nucleation modes,

the predominant mode is influenced by the particular solution

chemistry. When the solubilizing agent is ammonium iodide (NH4I) , the

NH41 is destroyed by combustion and the resultant nucleant is simply

AgI, with little hygroscopic character (St. Amand et al., 1971). Other

chemicals can be added to this solution to cause the formation of mixed

or composite nucleus aerosols and to synergystically influence the

efficiency of ice nucleation without changing the essentially

hydrophobic character of the nuclei. An example is the AgI-AgCl ice

nucleant studied by DeMott et al. (1983), which is generated by