State Water Resources Research Institute Program

Project Id: 2009WY46B
Title: Detecting the Signature of Glaciogenic Cloud Seeding in Orographic Snowstorms in Wyoming II: Further Airborne Cloud Radar and Lidar Measurements
Project Type: Research
Start Date: 3/ 1/2009
End Date: 2/29/2012
Congressional District: 1
Focus Categories: Water Quantity, Climatological Processes, Hydrology
Keywords: Weather Modification, Cloud Radar, Aircraft Measurements
Principal Investigator: Geerts, Bart
Federal Funds: $ 12,666
Non-Federal Matching Funds: $ 76,667
Abstract: This proposal is linked to the ongoing Wyoming Weather Modification Pilot Project (WWMPP). In early 2008 and 2009, the University of Wyoming King Air (WKA) research aircraft conducted seven successful flights over the Medicine Bow Range. These flights, funded by the present WWDS/USGS grant (Year 1) and a previous WWDS/USGS grant (expiring 2/28/10; Geerts, PI), took the aircraft repeatedly along fixed tracks over and incrementally downstream of select silver iodide (AgI) generators on the ground, both during on (seeding) and off (no seeding) conditions. Detailed Wyoming Cloud Radar transects, flight-level data, and Wyoming Cloud Lidar transects were collected along each flight leg. Both the radar and the lidar are fixed-antenna, with one antenna looking up and, importantly, one antenna looking down towards the ground in the region where AgI nuclei affected cloud processes. (Nadir lidar data are available only for the last 4 flights.)

The seven cases have been used to construct composites of radar data and flight-level data, in order to tease out the effect of AgI seeding on cloud processes and snowfall. In all cases the static stability was rather low, and the wind speed strong, such that (a) boundary-layer turbulence effectively mixed tracers over a depth of at least 1 km, and sometimes above flight level (2,000 ft above the Med Bow Peak) up to cloud top, and (b) the Froude number exceeded one and thus the flow went over (rather than around) the mountain range.

The main (preliminary) finding is that AgI seeding increases the probability of high equivalent reflectivity (>10 dBZ) near the surface, while lower reflectivity (0-9 dBZ) becomes less likely. Flight level data confirm that this implies that seeding makes heavier snowfall on the ground more likely. Consistent with expectations, seeding reduces the (flight level) concentration of supercooled droplets and the cloud liquid water content. The snowrate enhancement is more prominent away from the AgI plumes (within plumes the heaviest snowrates become slightly less likely), suggesting that excessive AgI seeding can have a negative effect.

Progress/Completion Report, 2009, PDF
Progress/Completion Report, 2010, PDF
Progress/Completion Report, 2011, PDF

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