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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 />A two-dimensional numerical model (GUIDE) will be run to predict <br />the location of fallout of the artificially produced crystals. <br />This model uses a combination of vertical wind and temperature <br />data and parameterized microphysics to account for particle <br />growth and fallout. To help determine the magnitude of <br />subsidence to the lee of the Sierra and evaluate the GUIDE model, <br />tracer experiments will be conducted. <br /> <br />Sulfur hexafluoride (SF6), a nontoxic, nonflammable gas, is a <br />well known tracer used in both weather modification and air <br />pollution studies. The tracer will not exactly match the <br />trajectories of propane generated ice crystals. However, the <br />tracer will indicate the general direction and dispersion <br />patterns of the treated volume of air passing by the dispenser. <br /> <br />The procedure will be to release the tracer at site #7, just <br />above Wades Lake and a new Site 9. Release rates will be <br />approximately 45 lb/hr. The transport and horizontal dispersion <br />of the gas will be monitored with the continuous SF6 analyzers <br />mounted on both the aircraft and in a trailer on Grizzly Ridge. <br />In addition, two sequential samplers, each with nine syringes, <br />will be placed at valley locations to provide both timing and <br />position information of the tracer plume. Each syringe can be <br />set to fill in 15 min allowing 2.25 hr of sampling. <br /> <br />16 <br />