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<br />-1- <br /> <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 />ABSTRACT <br />The aark Mesoscale model was applied to two cases from the early winter 1991 Utah/NOAA Cooperative <br />Atmospheric Modification Research Program. The model and its configuration for the field experiment conducted <br />over the Wasatch Plateau of Central Utah are briefly described. The two cases, 2 March and 6 March 1991, <br />represent one period with imbedded convection and abundant liquid water, and another with cold temperatures and <br />a weak subsidence inversion. <br />Airborne and surface observations of sulfur hexaflouride and ice nuclei were used to test the model. The <br />results were in reasonable agreement with field measurements of plume positions; however, plume concentrations <br />were underpredicted. The model was used to test the targeting characteristics from several valley and high elevation <br />releases of silver iodide. Although the elevation of a release point is important for targeting, the model demonstrated <br />that a key factor in choosing a surface release point was its position relative to vertical motion fields. The windward <br />slopes of a barrier appeared to be optimal, whereas crest and positions to the lee were poor sites. The model was <br />run with a Kessler warm rain parameterization to examine the characteristics of liquid condensate. Patterns of liquid <br />water predicted by the model suggested that depletion of liquid water to the lee of the crest could be due at least in <br />part to subsidence warming. This complicates the estimation of liquid water depletion through precipitation <br />processes. <br />