WMOD00298

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

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II._BASIS FOR RESEARCH

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2.1 Status of Experimental Knowledge of Ice Nuclei Function

Standard terminology for the nucleation modes by which ice can

form have been given by Vali (1985). These are,

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"Deposition nucleation. The formation of ice in a (supersaturated)
vapor environment."

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"Conaensation freezing. The sequence of events whereby a cloud
condensation nucleus (CCN) initiates freezing of the condensate"

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"Contact freezing. Nucleation of a supercooled droplet subsequent
to an aerosol particle's comming into contact with it."

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"Immersion freezing. Nucleation of supercooled water by a nucleus
suspended in the body of water."

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Vali pointed out that "broader, narrower, or perhaps altogether

different definitions might be needed at times". This is true for this

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study, as will be made clear in Chapter 4. Regardless - of the exact

terminology used, there is much laboratory evidence (Edwards and Evans,

1960; Langer et al., 1978; Schaller and Fukuta, 1979; Tomlinson, 1980;

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Rogers, 1982; DeMott et al., 1983; DeMott et al., 1984a,b; Blumenstein

et al., 1987, DeMott, 1988; Feng and Finnegan, 1989) that artificial

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ice nucleus aerosols will function by all of these various nucleation

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modes and can nucleate ice at different rates, depending on the

chemical and physical properties of the nuclei and on the environmental

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conditions (temperature, saturation ratio and droplet concentration).

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