New look at the potential of hygroscopic seeding in summertime convective clouds

Hygroscopic seeding was conducted in the sixties and early seventies in the USA, but since then, most cloud seeding efforts have used glaciogenic seeding materials, usually silver iodide and dry ice. Very little research has since been conducted on hygroscopic seeding in the USA and very few operational programs use hygroscopic materials. The reasons for this are the high amounts of seeding material needed and the usual corrosive character of these materials and the usual corrosive nature of these materials. Recently, an ongoing summertime convective cloud seeding research program in South Africa started using hygroscopic flares for seeding convective clouds for rainfall enhancement. After one season of randomized seeding highly significant results were obtained indicating that seeded clouds on average produce 100 ktons more water than unseeded clouds as derived from radar data. These results spurred intensive physical studies to determine the effect of the seeding material on the precipitation processes and to understand and document the cause and effect relationships. Some preliminary results from these studies will be presented and the potential for using these hygroscopic flares in convective clouds will be explored.