Wintertime Snowfall Augmentation Scientific Basis for Operations & Research Needs

1. Wintertime Snowfall AugmentationScientific Basis for Operations & Research Needs Water in the West Evolving Technologies and Emerging Issues 15-17 Nov 2006 Arlen Huggins Desert Research Institute Reno, Nevada

2. A conceptual model for wintertime cloud seeding. What we know from successful programs. Some of the unknowns. New evaluation techniques.

3. A Generalized Conceptual Model for Wintertime Cloud Seeding • Seeding material must be reliably produced • Seeding material must be transported into a region of cloud that has supercooled liquid water (SLW) • Seeding material must be dispersed sufficiently into the SLW so a significant volume is affected by the desired concentration of ice nuclei • The cloud temperature must be low enough for substantial ice crystal formation • Ice crystals formed by seeding must remain in cloud long enough to grow large enough to enable them to fall into the target area

4. Research in Wintertime Cloud Seeding • Has verified all the links in the chain of the conceptual model • Has verified ice crystal and precipitation enhancement through physical observations • Has shown evidence of precipitation enhancement through statistical evaluations • Has revealed situations when cloud seeding is ineffective • Does not have all the answers to every meteorological situation where cloud seeding is applied

5. A cloud seeding case study to help visualize the conceptual model • A ground seeding experiment on Utah’s Wasatch Plateau using silver iodide (AgI) as the seeding agent • AgI released at high altitude on the windward slope • Ground and aircraft instrumentation used to verify the steps in the conceptual model

7. Mapping the AgI Plume

8. Seeding response in aircraft data

9. Seeding response in radar data

10. Seeding response in precipitation data

11. Some Important Wintertime Cloud Seeding Research Programs • Bridger Range Experiment* – Montana (1970-1971; 1985) • CO River Augmentation Demonstration Program* (1986) • Sierra Cooperative Pilot Project* (1985-1987) • Utah-NOAA Atmospheric Modification Program (1991-1995) Utah Weather Damage Modification Program* (2003-2004) • Arizona Snowpack Augmentation Program* (1987-1988) AZ-NOAA Atmospheric Modification Program (1994-1995) • NV-NOAA Atmospheric Modification Programs (1992-1995) * USBR Programs

12. Key Contributions of Each Program • Bridger Range Experiment (Ground Seeding) • Verification of several links in the chain of cloud seeding processes • T & D of seeding material verified • Ice crystal enhancement verified • Statistical evidence of precipitation increases in 2-year experiment (100 case days) • Physical observations matched statistical results • Best results in cold and relatively shallow orographic clouds

13. Key Contributions (Cont.) • CO River Augmentation Demonstration Program (Ground and Aircraft Seeding) • Verification T & D of seeding material • Verification of ice crystal enhancement • Verification of precipitation enhancement • First case studies showing complete links in the chain of cloud seeding processes • Results similar to BRE in finding best results in relatively cold, shallow orographic clouds

14. Key Contributions (Cont.) • Utah AMP and WDMP (Ground Seeding) • Additional (and more numerous) case studies showing complete links in the chain of cloud seeding processes • Modeling simulations of T & D • First experiments to show positive results for propane seeding • Randomized experiment with propane showing 20% precipitation increase in seeded periods

15. Key Contributions (Cont.) • Sierra Cooperative Pilot Project (Aircraft Seeding) • Case studies showing complete links in the chain of cloud seeding processes • Evidence of seeding effects in radar data • Initial use of “warm temperature” AgI • Simple but effective targeting model • Supportive trace chemical evidence in snowfall

16. Key Contributions (Cont.) Arizona AMP and USBR Programs (Aircraft and Ground Seeding) • Model simulations of T & D with verification by aircraft observations • Model simulations suggesting importance of gravity waves in T & D and seeding potential • Departure from standard conceptual model • Unique observation of seeding effects using a new technology (polarized radar)

17. Key Contributions (Cont.) Nevada AMP and USBR Programs (Ground Seeding) • Extensive documentation of SLW using dual-channel radiometer • Detailed seeding chain-of-events case studies • Development of dual-tracer snow chemistry evaluation method • Mesoscale and plume dispersion modeling

18. Frequency of Silver:Indium Ratios that exceed one (Australia)

19. Trace Chemistry Statistics and Seasonal Estimates of Snowfall Enhancement (Australia)

20. DRI Particle Dispersion Model Results Two DRI ground Generator sites Part of Dual-tracer Ice Crystal Enhancement Experiment

21. Continued Research/Evaluation Areas • New snow sampling techniques for snow chemical evaluation and density measurements • Development of remote automated sampling system • Basin evaluation of snowfall enhancement based on chemical and physical measurements of snowfall • Use of “target” and “control” based on chemistry • Mesoscale modeling and plume dispersion simulations – Incorporation of microphysics • Remote sensing to evaluate seeding potential, track seeding plumes, detect seeding effects • Effects of pollution on precipitation (natural or seeding induced) • Effect of a warming climate on cloud seeding potential

22. Sometimes conditions are more than adequate! Thank you. Questions welcome!