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<br />in the cloud? <br />b. What path does seeding material <br />take from generator to seedable <br />locations? <br />c. What concentrations of ice <br />crystals actually occur in the <br />cloud from the introduction of <br />given amounts of seeding agent <br />and by certain application <br />techniques? <br />d. How rapidly do the seeding <br />agents and ice crystals re- <br />sulting from ground or airborne <br />seeding diffuse through the <br />cloud systems and cause nuclea- <br />tion? <br />e. Does sufficient time exist for <br />seeding material to reach <br />seedable locations in a cloud <br />from ground or airborne seeders <br />and in sufficiently dilute but <br />widespread concentrations to <br />create additi ona 1 useful preci pi- <br />tation on the mountain barrier? <br />f. What are the horizontal and <br />vertical wind fields and <br />turbulence relative to the <br />mountain barrier and storm <br />systems? <br />g. How do storm elements such as <br />convective bands or cells <br />modify flow fields? <br />h. Is conditional or absolute <br />instability necessary for <br />sufficient vertical transport <br />of seeding material? <br /> <br />1.4 Does the natural climatology of the <br />American River Basin in the Sierra <br />Nevada and seeding methods required <br />suggest a significant benefit from <br />cloud seeding and will they allow a <br />reasonable design for an experiment <br />on precipitation augmentation? <br /> <br />a. What is the climatology of <br />clouds by type and size? <br />b. Where do the clouds form, <br />grow, and dissipate? <br />c. How do they move in relation <br />to steering winds and meso- <br />scale organization? <br />d. What is the cloud top structure <br />and is it an important nucleation <br />source for natural clouds? <br />e. How are precipitation amount, <br />frequency, and mechanism <br />related to cloud type? <br />f. Does the space time distribution <br />of natural precipitation and <br />potentially seeded precipitation <br />allow for economic benefit in <br />runoff? <br />g. Does the space time distribution <br />of natural precipitation and <br />potentially seeded precipitation <br />allow experimental units to be <br />selected for a randomized <br />experiment? <br /> <br />r - ". <br /> <br />1.5 What is the best method of measuring <br />seeding effects in Sierra storms? <br /> <br />a. What is the .most accurate and <br />reliable method of measuring <br />snow and rainfall from stable, <br />orographic clouds; convective <br />cells, and convective bands <br />over a mountainous area of <br />several thousand square kilometers? <br />b. What precipitation gage density <br />is sufficient for evaluation <br />of the seeding experiments? <br />c. What type of gage or combination <br />of gage types is best in rain, <br />snow, or mixed rain and snow <br />conditions? <br />d. Is a combination of radar and <br />gage evaluation the best <br />approach, and, if so, what is <br />the optimum configuration? <br />e. Does seeding lead to significant <br />changes in drop-size and <br />crystal-size distributions <br />and, hence, the Z-R relation- <br />ship? <br />f. How important is evaporation, <br />sublimation, and/or growth at <br />low levels? <br /> <br />3. STUDY AREA AND FACILITIES <br /> <br />In an attempt to answer these questions, <br />preliminary meteorological measurements were <br />undertaken in the winter of 1976-77 and 1977- <br />78. Radars, rawinsondes, aircraft, and <br />ground instrumentation were deployed in and <br />upwind of the American River Basin. <br /> <br />The study area for the 1977-78 winter season <br />is shown in figure 1, outlined by the dashed <br />line. Locations of major facilities and <br />measurement sites are also shown. The area <br />boundaries are the American River watershed <br />to the north and south, and the crest of the <br />Sierra to the east. The 10- and 100-km- <br />radius circles around the SWR-75 (Skywater <br />radar) and the 50-km circles around the three <br />doppler radars indicate the approximate <br />observation areas of each. <br /> <br />The major facilities and equipment were: <br /> <br />3.1 A SWR-75 (5-cm Skywater radar) <br />operated by North American Weather <br />Consultants (NAWC). <br /> <br />3.2 Two 3-cm doppler radars from the <br />National Oceanic and Atmospheric <br />Administration (NOAA) and one 5-cm <br />doppler radar from the National <br />Center for Atmospheric Research <br />(NCAR). <br /> <br />3.3 A cloud physics and cloud dynamics <br />aircraft (King Air 200) operated by <br />the University of Wyoming. <br /> <br />3.4 A seeder aircraft and mobile ground <br />release vehicle operated by Aerosystems, <br />Inc. <br /> <br />161 <br />