WMOD00298

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

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With the development of the CSU dynamic (controlled expansion)

cloud chamber (DCC) some of the severe limitations of the laboratory

study of ice nuclei have been removed or ameliorated. No substrate is

needed to capture or support the ice nucleating particles (as for

membrane filters). Gradients in temperature and supersaturation are

controlled so that conditions in the chamber are nearly uniform, unlike

condi tions in static or laminar flow chambers. Furthermore, cloud

formation rates are comparable with those in many natural clouds, and

cloud condensation temperatures and pressures can be controlled over

most of the atmospheric range. The different environmental paths by

which nuclei arrive at a certain point in a cloud can also be simulated

in the cloud chamber. As will be discussed, cooling rates and

particulars of the ice crystal detection system introduce some

complexities, but these are surmountable. All of the factors affecting

nucleation can be measured and independently controlled in cloud

chamber experiments and in theoretically based computer model

simulations. Experiments of this type have not been done before.

1.2 Objectives of Research

The general objectives of this research program were to design a

series of experiments to study the ice forming processes of artificial

ice nuclei under a variety of well-defined cloud environmental

conditions (equivalent to conditions in atmospheric clouds) in the

laboratory; to compare results of these laboratory experiments with the

best descriptions currently available for use in numerical cloud

models; to provide experimentally determined descriptions of ice

formation which can be incorporated in conceptual and quantitative