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Last modified
7/28/2009 2:28:44 PM
Creation date
10/1/2006 2:16:53 PM
Metadata
Fields
Template:
Weather Modification
Contract/Permit #
#97-3
Applicant
Western Kansas Groundwater
Project Name
Kansas Weather Modification
Date
1/1/1997
Weather Modification - Doc Type
Report
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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 /> <br />clouds naturally deficient in them and to promote supercooled water <br />droplet freezing within clouds. A cloud growing to maturity must <br />be treated with enough time allowed so that the generated ice nuclei <br />can be lifted by natural cloud action into the appropriate <br />temperature and moisture regime and kept there for a sufficient time <br />to interact with the supercooled cloud water. If this window is <br />missed when attempting rainfall stimulation, clouds may collapse <br />prematurely resulting in wasted effort and resources. "Residence <br />time" in the supercooled cloud volume is critical to the success of <br />both rain stimulation and hail reduction. <br /> <br />The behavior of weakly and moderately growing cumuliform clouds <br />can be altered through what is called the "dynamic effect". Under <br />certain atmospheric conditions, cumulus clouds may be stimulated to <br />grow larger and rain longer than would be the case if otherwise left <br />unseeded. This is done by getting sufficiently large amounts of <br />seeding agent into the supercooled portion of a cloud to promote the <br />rapid conversion of water droplets into ice crystals. When this <br />water-to-ice conversion process occurs rapidly, the latent heat of <br />fusion is released on a massive scale which makes the cloud slightly <br />warmer and more buoyant. The updraft then becomes invigorated and <br />draws in greater amounts of water vapor to supply more moisture for <br />cloud growth and "processing" into rainfall. This enables the seeded <br />cloud to produce more rain for a longer time than if left unseeded. <br /> <br />Although silver iodide produces greater numbers of ice nuclei <br />than does dry ice, gram for gram, large numbers of ice nuclei can <br />be. produced more quickly by dropping dry ice directly into the <br />moisture-laden cloud updrafts creating new-growth clouds. Relatively <br />large amounts of dry ice are needed to produce an equivalent number <br />of ice crystals fro~ a given mass of silver iodide---roughly 1000 <br />to 2000 grams of dry ice to one gram of silver iodide. Supercooled <br />cloud dr0plets contacting dry ice falling through clouds, or <br />droplets brought into the wake of falling dry ice, immediately <br />change into ice crystals. Whereas, silver iodide-based seeding <br />agents, while rising in the cloud, begin to activate to become ice <br />crystals at temperatures near -4C to -5C---roughly 2,000 to 2,500 <br />feet above the freezing level. <br /> <br />Dry ice is dispensed from a hopper auguring dry ice into an <br />opening in the aircraft floor which lets the dry ice fall directly <br />into the clouds. The hopper carries about 200 Ibs of pelletized dry <br />ice which is released at a rate of 5 lbs per minute. <br /> <br />Dispensing ejectable silver iodide flares at cloud top is not <br />done on the WKWMP primarily because it is a much more expensive form <br />of seeding agent than dry ice, despite its sublimation while stored <br />between operational periods. <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 />7 <br />
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