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<br />00.1193 <br /> <br />Nucleus. - In physical meteorology, a particle of any nature upon which, or <br />the locus at which, molecules of water or ice accumulate as a result of a <br />phase change to a more condensed state; an agent of nucleation. <br /> <br />Orographic cloud. - A cloud whose form and extent are determined by the <br />disturbing effects of orography (mountains) upon the passing flow of air. <br />Because these clouds are linked with the form of the terrestrial relief, they <br />generally move very slowly, if at all, although the winds at the same level <br />may be very strong. <br /> <br />Parameter. - In general, any quantity of a problem that is not an independent <br />variable. More specifically, the term is often used to distinguish, from <br />dependent variables, quantities which may be more or less arbitrarily assigned <br />values for purposes of the problem at hand. <br /> <br />Plume. - The volume of air space containing any of the substance emitted from <br />a pOInt source. The path of seeding materials during their fall to the <br />ground. <br /> <br />Precipitation. - Any or all of the forms of water particles, whether liquid <br />or solid, that fall from the atmosphere and reach the ground. <br /> <br />Precipitation efficiency. - For a given cloud or storm system, the ratio of <br />the amount of precipitation actually produced to the maximum amount theoret- <br />ically possible by that system. <br /> <br />Precipitation gage. - General term for any device that measures the amount of <br />precIpitatIon; principally, a rain gage or snow gage. <br /> <br />Randomize. - To make random. Specifically, in weather modification contexts, <br />it refers to the design of experiments and projects in such a way as to <br />minimize the sources of bias in the evalution of results by dictating that <br />"seed" or "do not seed" decisions (for example) be made on a purely random <br />basis. If the total number of such decisions is sufficiently large, this <br />procedure ensures that a comparison of "seed" versus "do not seed" results <br />contains minimal bias. <br /> <br />Use of sequences in application of treatments, seeding or nonseeding, to <br />obtain trustworthy statistical data in experiment. <br /> <br />Seeding rate. - The quantity of seeding agent (in grams or kilograms) released <br />either per unit of time (if applied to ground-based generators) or per unit <br />of distance (traveled by an aircraft) used in cloud seeding. <br /> <br />Silver iodide (AgI). - The compound of silver and iodine whose crystalline <br />structure very closely approximates that of ice crystals. <br /> <br />Silver iodide generator. - Any of several devices used to generate a smoke of <br />silver iodide crystals. Most burn an acetone solution of silver iodide; the <br />other important (and newer) category is that of protechnic generators. <br /> <br />Silver iodide seeding. - The method of cloud seeding, where, by any of <br />several techniques, silver iodide crystals are introduced into the super- <br />cooled portions of clouds to induce the nucleation of ice crystals. <br /> <br />53 <br />