The ASCII campaign was conducted in early 2012 over the Sierra Madre range in Wyoming, to examine cloud microphysical changes resulting from the ground-based injection of silver iodide (AgI) into shallow orographic clouds. The campaign included a dual-polarization Doppler-On-Wheels radar on the mountain pass, the University of Wyoming King Air aircraft with profiling mm-wavelength radar (the Wyoming Cloud Radar or WCR) and polarization backscatter lidar, two Ka-band profiling radars, and a number of instruments on the ground to characterize the cloud liquid water content and the in situ snow particle characteristics. The experimental design supports both simultaneous (upstream/ downstream) and non simultaneous (before/ during) comparisons of snow and cloud characteristics, intended to tease out the impact of glaciogenic seeding on cloud and precipitation. This study examines the seeding impact using profiling mm-wavelength radar data only, both from the Ka-band radars on the ground (one upstream of the AgI generators and one downstream, allowing simultaneous comparison) and from the WCR (non-simultaneous comparison, i.e. untreated period followed by a treated period). Only a few good cases were encountered, as the period was drier and warmer than normal, and storms evolved rapidly. The preliminary analysis indicates that under suitable conditions AgI seeding of shallow orographic clouds can significantly increase radar reflectivity in the boundary layer.
Geerts, Bart; Pokharel, Binod; Friedrich, Katja; Breed, Dan; Rasmussen, Roy; Yang, Yang; Miao, Qun; Haimov, Samuel; Boe, Bruce; and Kalina, Evan (2013). "The AgI Seeding Cloud Impact Investigation (ASCII) Campaign 2012: Overview and Preliminary Results." The Journal of Weather Modification 45.1, 24-43.
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