The AgI Seeding Cloud Impact Investigation (ASCII) campaign 2012: overview and preliminary results

Abstract

The ASCII campaign was conducted in early 2012 over the Sierra Madre, a Continental Divide 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-wave radar and polarization backscatter lidar, two Ka-band profiling radars, one upstream of the AgI generators, and one downstream, 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 supported both simultaneous (upstream/ downstream) and non-simultaneous (before/ during) comparisons, in order to tease out the impact of glaciogenic seeding on cloud and precipitation. Unfortunately, suitably cold cloud base temperatures rarely occurred during the campaign. Nevertheless, profiling radar data collected on flights with a no-seeding period followed by a seeding period, as well as simultaneous ground-based profiling radar data, indicate that under suitable conditions AgI seeding can significantly increase radar reflectivity in the boundary layer, and thus snowfall rate near the ground.