Results of Experiments on Convective Precipitation Enhancement in the Camaguey Experimental Area, Cuba

Abstract

Experiments on randomized seeding of individual convective clouds and cloud clusters were conducted in the Camaguey experimental area, Cuba, from 1985 through 1990 in order to elucidate whether cold-cloud dynamic seeding can be used to augment convective rainfall. An information measuring system was set up, and primary tools included three instrumented aircraft (AN-26, AN-12 CYCLONE, IL-14), MRL-5 and ARS-3 radars, a system for radiosounding, two special rain gauge networks, and surface weather stations. A total of 232 randomized experiments were carried out during this experimentation period, and 117 individual clouds and 115 cloud clusters were studied during 136 ?go? days. Pyrotechnic flares containing silver iodide were ejected in a selected cloud when the seeder aircraft was flying through its top. The seeding effects were monitored by the MRL-5 radar, which was equipped with an automated system for digital processing of data. A total of 46 convective clouds, 29 seeded and 17 nonseeded, were studied during an exploratory experiment in 1985. Analyses of the radar properties of seeded and nonseeded clouds have indicated that the response of convective clouds to AgI seeding is dependent on their type, and the treatment within the range of cloud tops from 6 to 8 km?that is, at top temperatures between ?10° and ?20°C, is found to increase their maximum height by 13% and the lifetime by 30%, and to enhance rainfall. A confirmatory phase of the experiment in the Camaguey experimental area was conducted during 1986?90. A total of 46 individual convective clouds, 24 seeded and 22 nonseeded, were identified, and their properties were determined using three-dimensional radar data. The results have shown that the AgI seeding of growing clouds with top temperatures over the range from ?10° to ?20°C increases their lifetime by 24%, maximum height by 9%, area by 64%, and rain volume by 120%, as compared to unseeded clouds. The lifetime, area, and rainfall results are significant at better than the 10% level using the Mann?Whitney test. A total of 82 cluster cells, 42 seeded and 40 nonseeded, were studied. An analysis of stratified data has shown that as in the case of individual clouds, the greatest positive effect was achieved when treating the cells with top temperatures between ?10° and ?20°C. The seeding increased the lifetime by 21%, maximum cell height by 17%, maximum cell area by 28%, and rain volume by 65% at better than the 5% level. The results of cold-cloud dynamic seeding in Cuba are very consistent with those obtained in Florida, West Texas, and Thailand.