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Last modified
7/28/2009 2:39:51 PM
Creation date
4/23/2008 11:59:16 AM
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Template:
Weather Modification
Title
Weather Modification Assessment - Kingdom of Thailand
Date
9/1/1986
Country
Thailand
Weather Modification - Doc Type
Report
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<br />States. A randomized rainfall enhanCE!ment experiment using hygroscopic <br />agents in a static-mode warm cloud seeding strategy (seeding for <br />microphysical effects to improve the precipitation efficiency of clouds) <br />on monsoon clouds was conducted in three climatologically similar <br />regions in northwest India. Analysis of data from 18 experiment-seasons <br />(Biswas et al., 1967) has suggested a positive, statistically signifi- <br />cant result with increases of 41.6 percent, 58.5 percent and 18.6 per- <br />cent in the three areas, respectively. Several other randomized <br />experiments using the same seeding strategy have been conducted in India <br />with a suggestion of a positive effect, but these results were not sta- <br />tistically significant. A randomized rainfall enhancement experiment in <br />South Dakota also used hygroscopic agE!nts in a static-mode strategy to <br />seed warm clouds and found that the sE!eded clouds had radar echoes <br />closer to cloud base and had larger radar estimated rainfalls than their <br />non-seeded counterparts (Dennis et al., 1975). On one day one end of a <br />line of warm stratocumulus clouds was seeded which sUbsequently rained <br />while no rain fell from the unseeded portion of the cloud line or from <br />any other clouds in the area (Biswas and Dennis, 1971). <br /> <br />The closest analogs to the seeding of cloud types involving the mixed <br />phase precipitation process are several projects conducted in the United <br />States. A randomized seeding experiment using silver iodide in a <br />dynamic-mode seeding strategy (seedin~l for dynamical effects to increase <br />the size of the clouds and their resullting precipitation output) was <br />carried out on 23 cold-top tropical clouds over the Caribbean Ocean. <br />Analysis of the data from this classical experiment (Simpson et al., <br />1967) revealed that seeded clouds grew vertically an average of 1.6 km <br />more following the seeding than did the control clouds, the difference <br />being statistically significant. Two randomized precipitation enhancement <br />experiments were conducted over south Florida to determine whether <br />seeding convective clouds for dynamic effects could be used to augment <br />rainfall over a substantial target area. Several analyses of the <br />results of these experiments have been performed with the most recent <br />(Flueck et al., 1986) suggesting a positive treatment effect of 30-45 <br />percent in the first experiment and 10-15 percent in the second experi- <br />ment, but only the result of the first experiment was statistically <br />significant. An examination of the results of seeding on rain-cell pro- <br />perties in the second experiment (Gagin et al., 1986) suggests that <br />seeded cells, particularly those that were seeded early in their life <br />cycle with a substantial amount of silver iodide, had statistically <br />significant increases in cell height and cell rain volume of 22 percent <br />and 100 percent, respectively. Experiments that are conceptually simi- <br />lar to those carried out in south Florida are now underway in Texas and <br />Illinois. <br /> <br />'1 <br /> <br />A randomized precipitation enhancement: experiment on cold-top convective <br />clouds using silver iodide in a static-mode seeding strategy was con- <br />ducted in central ~issouri. The analysis of data from this experiment <br />(Flueck, 1971) suggests a positive treatment effect for clouds with radar <br />echo tops between -100 and -40 oC and negative treatment effects for <br />clouds with colder echo top temperatures. <br /> <br />It is emphasized that the results of similar experiments that may be <br />conducted in Thailand could be better or worse than those given above <br /> <br />~ <br /> <br />;; <br /> <br />15 <br />
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