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<br />OOJ191 <br /> <br />X. GLOSSARY <br /> <br />Acre-foot. - The volume of water required to cover 1 acre to a depth of <br />1 foot: 43,460 ft3 (352,853 gal). <br /> <br />Aircraft seeding. - The use of aircraft to disperse cloud seeding agents. <br /> <br />Artificial nucleation. - Any process whereby the nucleation of cloud particles <br />is initiated or accelerated by human intervention. <br /> <br />Cellular convection. - An organized, convective, fluid motion characterized <br />by the presence of distinct convection cells or convective units, usually <br />with upward motion (away from the heat source) in the central portions of <br />the cell, and sinking or downward flow in the cell's outer regions. <br /> <br />Cloud. - A visible aggregate of minute water and/or ice particles in the <br />atmosphere above the earth's surface. Cloud differs from fog only in that <br />the latter is, by definition, in contact with the earth's surface. <br /> <br />Cloud model. - In general, any idealized representation of a cloud or cloud <br />processes. Increasingly, this term is used for mathematical representations <br />of cloud processes, particularly those formulated for numerical solution on <br />electronic computers. <br /> <br />Cloud modification. - Any process by which the natural course of development <br />of a cloud is altered by artificial means. <br /> <br />Cloud physics. - The body of knowledge concerned with physical properties of <br />clouds in the atmosphere and the processes occurring therein. <br /> <br />Cloud seeding. - Any process of injecting a substance into a cloud for the <br />purpose of influencing the cloud's subsequent development. Ordinarily, this <br />refers to the injection of a nucleating agent, but sometimes alludes to <br />substances which do not directly affect nucleation (such as carbon black). <br /> <br />Cloud seedina agent. - Any variety of substances dispensed for the purposes <br />of cloud see ing. In addition to the commonly used silver iodide and dry <br />ice, a number of other materials have been experimented with for various <br />purposes; for example: calcium chloride, urea, metaldehyde, chlorosulfonic <br />acid, carbon black, common salt, and water spray. <br /> <br />Coalescence. - In cloud physics, the merging of two water drops into a single <br />larger drop. <br /> <br />Condensation. - The physical process by which a vapor becomes a liquid or <br />SOlld; the opposite of evaporation. In meteorological usage, this term is <br />applied only to the transformation from vapor to liquid; any process in which <br />a solid forms directly from its vapor is termed sublimation, as is the <br />reverse process. <br /> <br />Condensation nucleus. - A particle, either liquid or solid, upon which <br />condensatlon of water vapor begins in the atmosphere (see nucleation). <br /> <br />51 <br />