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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />I. INTRODUCTION <br /> <br />1.1 Backaround <br />Aerosol particles containing silver iodide have been known to <br />effectively catalyze the phase change of water vapor and/or supercooled <br />water to ice for about 35 years. These particles have been used in <br />weather modification field programs to produce ice crystals in clouds in <br />higher concentrations and at warmer temperatures than would occur <br />naturally. Many weather modification research programs have used silver <br />iodide ice nuclei. generated burning acetone solutions containing silver <br />iodide for cloud seeding. Because of the insolubility of silver iodide <br />in acetone. alkali iodides are used to solubilize the silver iodide. <br />One such solubilizing compound that has been used is sodium iodide. The <br />solution then contains a chemical complex containing silver iodide and <br />sodium iodide. The aerosol particles generated from combustion or such <br />solutions have been used in weather modification projects such as Climax <br />(Grant, et 81.. 1979). the Israeli Rainfall Enhancement program <br />(A. Gagin. personal cODIIDunicationL the Australian program (Smith. et <br />al.. 1966). and others. <br />In attempting to understand how ice nuclei which contain silver <br />iodide behave in clouds. it is necessary to understand how the nuclei <br />function, i.e., the mechanism of ice nucleation. This requires an <br />understanding of the chemical and physical characteristics of the <br />aerosol particles and how they influence the process of phase change of <br />water to ice. The phase change process is controlled by cloud <br />