A serious drought in the spring of 1971 occurred in South Florida. In view of NOAA's research experience in dynamic cumulus modification (massive silver iodide seeding to invigorate cumulus updrafts by means of release of latent heat of fusion), the state government sought our aid in combating this drought by means of a seeding effort. NOAA responded by an extension of its experimental program with both practical and research objectives.
Two of the NOAA Research Flight Facility aircraft were used for airborne pyrotechnic seeding from 1 April to 31 May 1971. A one-dimensional numercial cumulus model was run in real time on each day, eliminating 38 days in the period as unsuitable. Flights were conducted on 16 days, with actual seeding on 14. Seven suitable days were lost due to routine aircraft maintenance. Radars and raingages were used to calculate rain amounts from all seeded and many unseeded clouds.
Seeding was conducted in an attempt to promote merger by treating clouds close together in space and also the upshear towers of each previously seeded complex. A total of not less than 180,000 acre-ft of water was calculated to have fallen from the seeded clouds in two target areas totaling about 7200 n mi2. A conservative estimate attributed 100,000 acre-ft as due to seeding, although without randomization this evaluation cannot be made firm. Satellite and synoptic studies accompanied rainfall evaluation on all seeding days. Among the important scientific results is that some frontal conditions appeared suitable for dynamic seeding in Florida, offering hope for extension of the technique into dry periods.
Some aspects of NOAA's future policy in the rain enhancement aspects of weather modification are presented.
1 Dr. Simpson is Director of the Experimental Meteorology Laboratory, Coral Gables, Fla.
2 Dr. Woodley is a Research Meteorologist at the Experimental Meteorology Laboratory.
3 Dr. White, Administrator of NOAA, prepared those parts of this paper concerned with policy and administrative aspects of the South Florida drought mitigation effort. The technical and scientific portions of the work were performed by the first two authors.