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<br />lated to grow larger and rain longer than it ordinarily would if <br />left unseeded. This is accomplished when relatively large amounts <br />of seeding agent get into the supercooled part of a cloud to <br />promote the rapid conversion of water droplets into ice crystals. <br />When this water-to-ice conversion process occurs rapidly, latent <br />heat of fusion is released from water droplets on a massive scale <br />making the clOUd slightly warmer and more buoyant, thereby causing <br />its updraft to become invigorated, ingest greater amounts of water <br />vapor to supply more moisture for cloud growth and "process" it <br />into rainfall. This, then, is how the seeded cloud is enabled to <br />produce more rain for a longer time than if unseeded. <br /> <br />Gram for gram} silver iodide produces greater numbers of ice <br />nUClei than does dry ice, however, large numbers of ice nuclei can <br />be produced more quickly by dry ice. Relatively large amounts of <br />dry ice are needed to produce an equiValent number of ice crystals <br />from a given mass of silver iodide---roughly 1000 to 2000 grams dry <br />ice to one gram silver iodide. When cloud droplets contact dry ice <br />falling through clouds, or are brought into its wake, immediately <br />they are converted to ice crystals; whereas, silver iodide only <br />starts to activate at temperatures below -5C---about 1,500 to 3,000 <br />feet above freezing and converts more actively at higher altitudes. <br /> <br />Dry ice is dispensed from a hopper auguring dry ice into an <br />opening in the aircraft floor which allows the dry ice to fall into <br />the clouds. The hopper carries 200 lbs of pelletized dry ice and <br />automatically releases dry ice at a rate of 5 Ibs per minute. <br /> <br />Dispensing ejectable silver iodide flares at cloud top is'more <br />expensive than dry ice because flares have to be manufactured. The <br />cost of using silver iodide at cloud top to get equal ice crystal <br />nucleation is presently greater than the cost of dry ice despite <br />the dry ice losses due to its sublimation before being dispensed. <br /> <br />The cloud systems listed below, and variations of them, are <br />most responsible for producing rain and hail in Western Kansas: <br /> <br />(1) air-mass storm complex <br /> <br />(2) multiple-celled storms <br /> <br />( 3) squall line <br /> <br />Air-mass storms begin as a single cloud system having a well- <br />organized clOUd base and an obvious updraft region extending below <br />its base. Frequently, these single cloud systems evolve into <br />complex arrangements of storms developing multiple-celled systems. <br />Fig. 4 on the following page shows a "classic" air-mass storm with <br />new growth on its left side. Drawing a line through the center of <br />precipi tation in its direction of movement and another line at <br />right angles to it, also through the center of the precipitation <br />area, updrafts found upwind in the complex are termed "trailing" or, <br /> <br />9 <br />