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<br />0025J8 <br /> <br />The study questions include a distinct trajectory and placement <br />problem in each basin because of the highly localized windfields <br />near the surface associated with orographic features. <br /> <br />A second issue is the apparent presence of subsidence inversions <br />preceding fronts on some occasions. These inversions have a major <br />influence on the trajectories of the seeding agent if it is released <br />below the inversion layer. <br /> <br />The third problem is the surface wind shift associated with band <br />passage in the Sierra Nevada. This shift of wind direction and <br />its importance must be clarified. <br /> <br />The fourth area of concern is the presence of imbedded convection <br />within a storm system, particularly where the convection is the <br />desired seeding area. <br /> <br />The study will use both aircraft and ground dispersion of tracing <br />material under storm conditions to obtain data for evaluation. <br />Data will be collected on the ratio of the tracing agent, sulfur <br />hexaflouride (SF6), to the seeding agent, silver iodide (AgI), <br />and on cloud microphysical modifications produced by the AgI when <br />possible in airborne detection cases. <br /> <br />Airborne investigations will include examination of Z-R relation- <br />ships (the relationship between actual rainfall or precipitation <br />and the radar reflectivity of moisture in the atmosphere (dBZ)). <br />The size, behavior, and concentration of ice crystals and the <br />size and concentrations of water drops are the primary parameters <br />that determine the effective Z-R for an area. One additional <br />important parameter is whether the ice crystals are water-coated <br />(mel ting) or not. Measurements of these parameters over the pre- <br />cipitation gage network will be of value to the radar studies in <br />developing the most meaningful Z-R relationships. <br /> <br />Analysis of the transport and diffusions studies will include a <br />description of the probable distribution of seeding material within <br />and near the American River Basin, for releases from both air and <br />ground genera tors. The Uni vers ity of Washi ngton also wi 11 recommend <br />the meteorological conditions for which airborne seeding is, required, <br />determine approximate ground-based generator and/or airborne seeding <br />tracts, and evaluate the advantages and disadvantages of ground <br />versus airborne seeding. <br /> <br />Radar Investigations <br /> <br />North American Weather Consultants (NAWC) of Goleta, California, <br />has been engaged to develop a radar climatology of Sierra Nevada <br /> <br />35 <br />