Observations of Silver Iodide Plumes over the Grand Mesa of Colorado

A series of wintertime airborne tracing experiments was examined to determine some characteristics of the plumes of silver iodide smoke released either from the ground or from an aircraft over the Grand Mesa of Colorado. The plumes were identified in nearly every experiment by detecting the airborne AgI particles and often also by observing resulting ice particle plumes in essentially the same airspace. The lateral and vertical plume positions of ground-released AgI from eight sites were determined for several wind, cloudiness and stability conditions. The instantaneous ground-released plume had a median spreading angle of 15° and meandered within a median angle of 38°. The median plume height above the crest exceeded 500 m. The lateral spreading rates of aircraft-released AgI were estimated at over 2 m s−1 for cloudy conditions and less in clear conditions. The implications for future cloud seeding strategies are discussed.