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<br />01 <br /> <br />assist with weather and cloud forecasting and also provide covariates for the evaluation process. <br />Modeling can help assess which atmospheric; conditions are suitable for cloud seeding in the Headwaters <br />Region. <br /> <br />The availability of affordable, powerful computer workstations will allow use of sophisticated models for <br />cloud seeding targeting decisions. Processes of particular interest include the three-dimensional airflow <br />and associated transport and diffusion of ground-released seeding agents, and the growth and fallout of <br />precipitation particles. The model should be tested for determining likely seeding release points for <br />individual storms. Different cloud treatment strategies should be tested through modeling. <br /> <br />3.4. Cloud Seeding Hypotheses <br /> <br />A conceptual operational seeding model specific for the Headwaters Region will emerge from the design <br />phase. Specific component hypotheses that are appropriate for the conceptual seeding model will be <br />generated. The design phase will seek answers for each hypothesis. The following presents loosely <br />stated examples of hypotheses that may apply to the Headwaters Region. Properly constructed <br />hypotheses will be developed upon completion of design studies. The seeding hypotheses given here are <br />based on knowledge gained in the COSE experiments (Rauber et aI., 1986; Rauber and Grant, 1986; <br />Rauber, 1987), the Bridger Range Experiment (Super, 1974; Super and Heimbach, 1983), the more recent <br />Grand Mesa experiments (Super et aI., 1986; Holroyd et aI., 1988; Super and Boe, 1988), and recent <br />Wasatch Plateau, Utah experiments (Super, 1999; Super and Holroyd, 1994; Super, 1995; Super, 1996; <br />Super and Holroyd, 1997; Holroyd and Super, 1998; Holroyd et aI., 1995). <br /> <br />The seeding hypotheses are based on dealing with orographically-enhanced supercooled winter clouds <br />over the Park Range, using ground-based high-elevation propane dispensers and/or AgI generators. <br /> <br />Gl. There exists SLW in excess of that naturally converted to snowfall when the prevailing <br />wind produces a positive component normal to the mountain barrier. <br /> <br />G2. Cloud seeding devices (propane gas or Agl) reliably lead to the creation of ice particles in <br />an environment favorable to the survival of ice, while in transport to cloud volume <br />containing SL W. <br /> <br />G3. Seeding creates ice crystals in numbers, estimated by models and limited measurements, to <br />be adequate in concentration, that turbulence and/or convection lead to transport and <br />diffusion throughout a substantial portion of the targeted SL W zone. <br /> <br />G4. Favorable environments exist and growth time is adequate during transport such that ice <br />particles can grow large enough to reach the intended target area before <br />evaporation/sublimation occurs in the lee-side airflow. <br /> <br />G5. Additional precipitation caused by cloud seeding occurs in amounts that are detectable in <br />the intended targeted areas when compared to control amounts. <br /> <br />The seeding hypotheses resulting from the design phase are expected to be largely based on the static <br />seeding mode. However, the modeling results of Orville et al. (1987) suggested that seeding layer clouds <br />may cause embedded convection under some atmospheric conditions, leading to enhanced liquid water <br />production. Because dynamic effects may sometimes occur by presumed static seeding, observations in <br />the Headwaters Region must be viewed in light of possible dynamic effects under favorable atmospheric <br /> <br />10 <br />