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<br />6) Deposition and depletion mechanisms - The mechanisms causing <br />deposition and depletion are numerous and often not well understood. <br />These include gravitational settling (fallout), precipitation scavenging <br />(washout, snowout, and rainout), surface impaction (storage), electro- <br />static attraction, adsorption (coagulation) and chemical interaction. <br />A further complication is the possibility of ultraviolet decomposition <br />of the silver-iodide crystals. A third process is the possibility <br />of resuspension and redeposition of the material. <br />No attempt was made to model any of the depletion variables on <br />the model scale. Some of the variables such as the fallout velocity <br />of silver-iodide particles (dia-.02~) is very small and can be neglected. <br />Grant et al., (Ref. 16) suggests that precipitation scavenging, coagu- <br />lation~ultraviolet decomposition and electrostatic attraction have <br />a small effect in depleting the seeding material in the Eagle River <br />Valley and Climax area. However, information does not exist for the <br />other areas. <br />The problem of resuspension and redeposition exists for the field <br />as discussed by Grant (Ref. 15), but it appears that the time scale <br />for this mechanism is somewhat longer than the one of interest in this <br />study. Surface impaction may be an important deposition variable in <br />the case of ground-based sources because of the possible interception <br />by dense stands of trees. <br /> <br />General Similitude Requirements <br />Complete similarity between two flow systems of different length <br />scales require geometrical, kinematical, dynamical and thermal similarity. <br />In addition, certain boundary conditions should also be duplicated. <br />The following outline shows, in general, what requirements are <br />necessary to consider for complete flow similarity: <br />1) Boundary conditions <br />a. Upstream conditions- initial velocity, turbulence, <br />temperature profiles, etc. <br />b. Upper-level conditions <br />c. Lower boundary conditions - surface topography <br />d. Side boundary conditions - topography and wind-tunnel <br />wall effects <br />2) Geometric similarity <br />a. Modeling of terrain features, roughness, trees, etc. <br />b. Boundary-layer thickness <br />3) Kinematic similarity <br />a. Rossby number (Coriolis effects) <br />b. Streamlines <br />c. Velocity profiles <br />4) Dynamic and thermal similarity <br />a. Reynolds number <br />b. Richardson number <br />c. Froude number <br />d. Prandtl number <br />e. Euler number <br />I <br />5) Dispersion similarity - Peclet number <br />The similitude parameters (Reynolds numbers, etc) governing the <br />airflow and dispersion patterns may be derived by dimensional analysis, <br />similarity theory or inspectional analysis. Complete derivations may <br /> <br />~ <br /> <br />2 <br /> <br />~ <br /> <br />~ <br /> <br />20 <br />