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<br />MS-230 (2-72) <br />Bureau of Reclamation <br /> <br />TECHNICAL REPORT STANDARD TITLE PAGE <br /> <br />l. REPORT NO. I ~ L30'..t:~t<.M!::N- ~~CE:.!:SI:)"i NO. 3. RECIPIENT'S CATALOG NO. <br /> SR-359-47 <br />4. TITLE AND SUBTITLE S. REPORT DATE <br />Final Report on an, Investigation of June 1976 <br />Precipitating Ice ~rystals from Natural 6. PERFORMING ORGANIZATION CODE <br />and Seeded Winter Orographic Clouds <br />7. AUTHOR(S) 8. PERFORMING ORGANIZATION <br /> , REPORT NO. <br />Larry Vardiman and Curtis L. Hartzell <br />9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. WORK UNIT NO. <br />Western Scientific Services, Inc. CONTRACT OR GRANT NO. <br /> Il. <br />328 Airpark Drive l4-06-D-6644 <br />Fort Collins, Colorado 80521 <br /> 13. TYPE OF REPORT AND PERIOD <br /> COVERED <br />12. SPONSORING AGENCY NAME AND ADDRESS <br />U.S. Bureau of Reclamation <br />P.O. Box 25007 <br />Denver Federal Center 14. SPONSORING AGENCY CODE <br />Denver, Colorado '80225 1200 <br />15. SUPPLEMENTARY NOTES <br />16. ABSTRACT This r~port presents the findings of an investigation into the <br />changes expected in ice crystal characteristics caused by silver iodide <br />seeding of winter, orographic clouds in the San Juan Mountains of Colorado. <br />Ice crystal data were collected from 22 storms near Wolf Creek Pass for the <br />period of February, 1973 through March 1975. Additional data on ice nuclei <br />and cloud-top temperatures were also obtained for the period. <br /> Analyses were' performed on the crystal type, size, concentration, and <br />the amount of rime' under seeded and natural conditions. The storms were <br />subdivided into three-hour blocks based on sounding times. Each block was <br />classified into a seed or nonseed category depending on generator operations <br />and ice nucleus concentrations. A total of 66 three-hour blocks was studied <br /> Changes in ice crystal characteristics were observed near Wolf Creek <br />Pass when artificial nuclei were detected in and slightly upwind of the <br />target a rea. Precipitation and ice crystal concentrations were increased <br />and riming was decreased as expected. Relative concentrations of plates and <br />columns were increased. Crystal diameter was increased against expectation. <br />Ice crystal concen:tration measured at KP3 does not appear to be a function <br />of cloud-top temperature for either seeded or nonseeded cases. However, <br />seeding does increase the crystal concentration at all temperatures. <br />17. KEY WORDS AND DOCUMENT ANALYSIS <br />a. DESCR/PTORSu Weather Modification Orographic Clouds <br /> Cloud Physics Cloud Seeding <br /> Ice Crystals Silver Iodide <br />b. IDENTIF IERS-- <br />c. COSATI Field/Group <br />18. DISTRIBUTION STATEMENT 19.5ECURITYCLASS 21. NO. OF PAGE: <br />Available from the National Technical Information Service, Operations (TH IS RE PORT) 129 <br /> UNCLASSIFIED <br />Division, Springfield, Virginia 22151. 20. SECURITY CLASS 22. PRICE <br /> (THIS PAGE) <br /> UNCLASSIFIED <br /> <br />i ~" <br /> <br />-~ <br />