WEATHER-MODIFICATION - A THEORETICAL VIEWPOINT

Early progress in weather modification is attributed to a healthy inte raction between theory and experiment. During the 1970s, a divergence of approaches took place. A ''theoretical/experimental'' approach, exe mplified by the Cascade Project, focused on testing scientific hypothe ses; an ''observational/experimental'' approach, exemplified by the Co lorado River Basin Pilot Project, sought to enhance understanding of t he seeding process through more detailed observations. The theoretical /experimental school soon came to focus almost exclusively on natural cloud processes, leaving the field of weather modification nearly devo id of a theoretical component. It is suggested that this theoretical c omponent is necessary to revitalize the field of weather modification. Key questions are addressed. These include 1) identification of cloud s that are amenable to seeding; 2) glaciogenic versus hygroscopic seed ing; 3) optimizing critical seeding variables, such as seed particle c oncentration for glaciogenic seeding and seed particle size for hygros copic seeding; and 4) seeding for hail suppression.