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<br />3.2 Numerical Modeling Gp~dance <br /> <br />The model used for guidance in designing the seeding <br />program was developed at NAWC by Robert Elliott for the Bureau <br />of Reclamation-sponsored Sierra Cooperative Pilot Project <br />(SCPP). The model has been described in detail in Elliott <br />et al., (1981). Model development and calibration was done <br />with the SCPP data set. Hence, results of model applications <br />in other regions (Arizona, for example) should be viewed in <br />general terms. However, comparison of results for various <br />seeding strategies should be valid. <br /> <br />In simple terms, the model (called GUIDE) simulates airflow <br />over a barrier and contains modules to compute artificial <br />and natural nucleation of cloud liquid water and the subsequent <br />ice crystal fallout. Both ground-based and aerial seeding <br />can be simulated, and effects of different seeding agents <br />can be modeled. Convection is handled by the use of a mean <br />convective updraft within a specified layer. <br /> <br />Data required by the model include a terrain profile <br />(generally values averaged over a width of 20 km normal to <br />the wind and spaced in 10 km downwind steps), a profile repre- <br />senting a streamline in the middle levels of the atmosphere, <br />an upwind rawinsonde sounding, and cloud liquid water profiles <br />vertically above each terrain step. <br /> <br />The model provides a variety of displays of computed <br />results. In this study, the principal display is a downwind <br />distance VS height above ground plot that shows how far downwind <br />and how high above ground a seeding plume drifts and where <br /> <br />- - <br />the artificially-nucleated ice crystals fall to the ground <br />as snow. This display also shows the seeding-related precipitation <br /> <br />3-9 <br /> <br />