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<br />I. INTRODUCTION <br /> <br />The purpose of the Park Range Atmospheric <br />Water Resources Program is to determine whether <br />natural precipitation can be increased in an area <br />where the ice nuclei process of precipitation forma- <br />tion ,predominates and a strong orographic effect <br />is present. To attempt an increase, artificial ice <br />nuclei (silver iodide crystals) are usually supplied <br />to the atmosphere where its temperature is less <br />than 00 C; the Park Range ridge not only accentu- <br />ates precipitation under natural conditions, but <br />also encourages convective mixing of the artificial <br />nuclei within the passing air mass. <br />This is an engineering research program, desi!?;ned <br />to provide a cause and determine the magnitude of <br />the resulting effect. The program is divided into <br />two phases. This report contains the results of the <br />Phase I work which has been devoted to the collec- <br />tion and processing of nuclei, diffusion and pre- <br />cipitation data under natural conditions, Appen- <br />dix A. In the Phase II effort, many of the storms <br />passing through the area will be nucleated artifici- <br />ally and the results compared with natural data to <br />determine what effect has been caused. <br />The Park Range Program is centered at Steam- <br />boat Springs in northcentral Colorado, figures 1 <br />and 2. It is a cooperative program, administered by <br />the Bureau of Reclamation, operated by E. Bollay <br />Associates, Inc., with field assistance from the U.S. <br />Department of Agriculture-Forest Service and Soil <br />Conservation Service, and further cooperation from <br />Colorado State University and the National Center <br />for Atmospheric Research. The program began <br />1 November 1964, and Phase I operations were <br />completed on 1 July 1965. <br /> <br />In the ensuing 8 months, the program has ad. <br />hered very closely to its original plans and is finish- <br />ing ahead of schedule. Twenty-six storm sequences <br />were tracked through the measurement network, <br />and the data processed and analyzed by the power <br />spectrum method. Diffusion tests have shown the <br />conditions under which artificial nucleation tests <br />should be conducted in Phase II to be confident <br />that the target area is affected. Techniques for <br />detecting tracer materials and artificial nuclei in the <br />air and from snowmelt and replica samples have <br />been developed and proven. <br />In the Phase II work, then, there will be several <br />independent cross-checks available for gaging artifi- <br />cial nucleation effects: <br /> <br />power spectrum and coherence of precipitation-rate his- <br />tories. <br /> <br />storm precipitation ratios for target and nearby stations, <br /> <br />presence of artificial nuclei in snowcrystal replicas and <br />concentration in snowmelt samples, and <br /> <br />artificial nuclei plume characteristics as determined from <br />tracer concentrations in the target area. <br /> <br />Section II of this report discusses the experi- <br />mental design of the program; Section III, the <br />facilities and equipment used to translate the design <br />into a working field program. Sections IV and V <br />describe the data collected in Phase I and results <br />obtained after processing the data. Finally, Section <br />VI presents the operational plan for Phase II. <br />The Park Range Program-Phase I-is indebted <br />to many individuals and institutions for its rapid <br />start-up and successful operation; these contribu- <br />tions are acknowledged in Appendix B. <br /> <br />1 <br />