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<br />~ <br /> <br />1 <br />I <br /> <br />I <br />J <br />I <br />I <br /> <br />Sizes, concentrations, and chemical properties of all nuclei <br />present in the atmosphere combine to play an important role in <br />determining the efficiency with which a particular cloud system can <br />produce precipitation. At any given time there are massive amounts of <br />water in the atmosphere in the form of water vapor. Precipitation <br />often will not occur because certain required conditions for the <br />formation of precipitation are absent. <br /> <br />There are two natural cloud types which a~e produce all <br />precipitation, the "warm cloud" and the "cold cloud". <br /> <br />A "warm" cloud, is a cloud in which temperatures are never below <br />freezing and does not produce ice crystals. This cloud is generally <br />characterized by the relatively slow growth of cloud water droplets <br />which eventually attain sufficient size and weight to fall from the <br />cloud. While falling, these comparatively larger drops collect, or <br />scavenge, other cloud droplets from the air along its path. Although <br />this type of cloud may occasionally appear in Western Kansas, it is <br />not the kind of cloud that plays a dominant role in the overall <br />production of rainfall here. However, these large warm-rain droplets <br />can be important embryo sources for the production of hail when they <br />are carried aloft by natural cloud updraft action into SUb-freezing <br />clouds (not of the warm-rain variety). <br /> <br />Of primary importance to Western Kansas is the cold cloud. Cold <br />clouds have temperatures below freezing in all or some part of the <br />cloud and produce supercooled water droplets which can initiate the <br />precipitation process. Cold clouds are reponsible for most of the <br />significant precipitation occurring in western Kansas. <br /> <br />The prevailing hypothesis under which the hail suppression <br />portion of the WKWM Program operates is that hailstones grow to large <br />sizes because there are too few ice crystals formed naturally in <br />clouds during vigorous thunderstorm development thereby allowing <br />abundant supercooled water to collect upon relatively fewer numbers of <br />ice particles or otheI hail embryos, Subsequently, those particles are <br />able to grow larger into hailstones frequently too large to melt <br />before reaching ground. Therefore, we theorize the need to increase <br />ice crystal concentrations within the ice crystal-deficient clouds so <br />that hailstones large enough to reach those sizes capable of damaging <br />crops and property cannot develop. There are other theories about hail <br />development and movement within a cloud and it is likely that hail <br />doesn't always form exactly the same way, every time, in every cloud, <br />It is interesting to note, however, that since hail suppression cloud <br />seeding began, long-term cloud seeding programs around the world, <br />using the same hypothesis as the WKWM Program, usually have shown <br />varying degrees of reduction in crop damaging hail at high levels of <br />statistical confidence, <br /> <br />Earlier it was mentioned that silver iodide and dry ice remain <br />the primary materials used in treating clouds. The WKWM Program <br />currently uses both, In the first case an aircraft delivers silver <br />iodide into updrafts at cloud bases. In the second case an aircraft <br />delivers dry ice into growing clouds at atmospheric levels, usually <br />around -20C---approximately 20,000 feet in mid-summer Kansas. Over the <br />years, results from worldwide weather modification and cloud physics <br />research has been applied to the WKWM Program to maintain state of the <br />art capability. <br /> <br />^- <br /> <br />" <br />