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<br />1I00SR'-l <br /> <br />3. Modeling the effectiveness of ground-based seeding, <br />particularly diffusion of material into cumulus <br />clouds <br /> <br />Field Areas <br />Key instruments to successfully providing the model input <br />and assessment of results are standard recording rain <br />gages with resolutions to 0.01 inch and digitized weather <br />radar with recording capability for computerized post- <br />analysis. Other critical instrumentation in an integrated <br />recognition and surveillance system include rawinsondes <br />and probing aircraft with particle and droplet counters, <br />inertial platforms for updraft definition, and tracer <br />sensors. The effective normal range of the quantitative <br />weather radars is some 50 to 70 miles, but clouds can be <br />"seen" out to 90 miles or more. Assuming one weather <br />radar per area, its range defines a central "core" area <br />of about 10,000 to 15,000 square miles for best measurement <br />and analysis and a total observation and operational con- <br />trol area of some 25,000 square miles. <br /> <br />Cloud Case Frequency <br /> <br /> <br />During a typical summer season (April-September), precipi- <br /> <br /> <br />tation of 0.01 inch or more occurs on 40 to 50 days in <br /> <br /> <br />the High Plains region. These days include precipitation <br /> <br />23 <br />