Organic ice nuclei field tests: South Dakota and Leadville cooperative projects, Summer 1975

Organic ice nucleants offer the prospect of effective and ecologically safe cloud seeding materials at much lower cost than silver iodide. We have been developing practical ice nuclei generators for three selected organic nucleants: 1,5-dihydroxynaphthalene (DN), phloroglucinol (PG), and metaldyhyde (MA). In the summer of 1975, we participated in two separate field experiments to investigate the effectiveness of DN for cumulus seeding. Both experiments used the airborne jet-mixing organic smoke generator described by Fukuta et ai. The first experiment, denoted “Special Organic Field Tests” (SOFT) was carried out in June and July in Butte and Meade counties in South Dakota, just north and east of the Black Hills. It was a randomized experiment using radar, visual and photographic observations to detect seeding effects. The second experiment, extending from mid-July to early August, was headquartered in Leadville, Colorado. Seeding and tracer materials were released at cloud base and the NCAR sailplane “Explorer” gathered quantitative data on ice nuclei, ice crystal, and tracer concentrations in a small number of seeded clouds. We describe the SOFT experiment in some detail here, and then give preliminary results from the Leadville experiment…..