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Last modified
7/28/2009 2:38:46 PM
Creation date
4/16/2008 11:10:48 AM
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Weather Modification
Title
Validation of Precipitation Management by Seeding Winter Orographic Clouds in the Colorado River Basin
Date
9/1/1993
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 />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />3.2 Seeding Hypothesis <br /> <br />A detailed hypothesis concerning the effects of seeding winter orographic clouds will be stated <br />prior to the onset of the statistical experiment (sec. 5). The hypothesis will be based on the <br />results of the direct detection experiments (sec. 4) and on numerical modeling. The hypothesis <br />likely will be based on what is generally referred to as the static seeding mode as. opposed to <br />dynamic seeding, which is' intended to release abundant latent heat. However, the modeling <br />results of Orville et al. (1987) suggested that seeding layer clouds may cause: embedded <br />convection under some atmospheric conditions, leading to enhanced liquid water production. <br />Hence, dynamic effects sometimes may be produced by presumed static seeding, and this <br />possibility will be investigated with the direct detection experiments. If significant dynamic <br />effects do occur, they are expected to increase the seedability of the cloud systems bel~use of the <br />additional SLW availability. <br /> <br />The seeding hypothesis for ground-based AgI and propane cloud seeding is exp1ected to be <br />similar to, but more specific than, the following statements: <br /> <br />. When the prevailing wind is approximately normal to a mountain barrier, forced uplift of <br />moist air sometimes produces SL W in excess of that naturally converted to snowfall. The <br />SLW zone is concentrated in the lowest kilometer over the windward slopes lmd barrier <br />top. <br />. Routine and reliable cloud seeding requires production of AgI ice nuclei, or release of <br />propane gas seeding agent, well up the windward slope of the target barrier (or from an <br />upwind barrier). <br />. Mechanical turbulence, sometimes aided by convection, results in the T&D of the AgI ice <br />nuclei or propane-created crystals throughout a substantial fraction of the SLW zone. <br />When the AgI-seeded portion of the SLW zone is cold enough, significant ice crystal <br />formation results. Propane expansion within liquid cloud below 0 oC will cause similar ice <br />crystal formation. <br />. When the atmospheric temperature, moisture, and wind environment are suitable, a <br />fraction of the seeded ice crystals grow to snowflake or snow pellet (graupel) :sizes while <br />being transported toward the target area. <br />. Some seeded snowflakes and pellets fall to the target surface before being carried into the <br />lee subsidence (and evaporation/sublimation) zone. When suitable conditions exist for <br />prolonged periods (hours), the accumulation of seeded snowfall can be significant. <br /> <br />3.3 Overview of Experimental Approaches <br /> <br />The approach at each experimental area will involve conducting a series of direct detection <br />seeding experiments. Past experience has shown that three winters will be required to obtain a <br />reasonably large population of these experiments over the range of atmospheric conditions <br />which typically affect a mountain region. Analysis of the direct detection experiments will <br />indicate the range of cloud conditions and specific seeding techniques most likely to lead to <br />enhanced snowfall. This knowledge will significantly sharpen the design of the statistical <br />experiment to follow. <br /> <br />A four-winter randomized statistical experiment will incorporate considerable physical <br />monitoring. Four winters are considered necessary to build up a sufficiently large population of <br />experimental units for adequate statistical power. The combination of statistical and physical <br /> <br />13 <br />
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