Evidence of Effectiveness of Hygroscopic Collector Embryos

Albert H Schnell, Wallace E Howell

Abstract


Faced with insufficient rainfall, the Cabildo (Municipality) of Grand Canary has experimented with cloud seeding as well as expanding its use of desalinated sea water. Its natural rainfall comes almost entirely from maritime clouds blown against the windward side of the island during disturbed weather too warm for glaciogenic seeding. The lifetime of these clouds is usually too short for full growth of natural collector drops to produce rain. The cloud seeding program, carried out for eight winter seasons 1983-84 to 1990-91 by AIRAO Enterprises, a Colorado company, dispersed 20 micrometer diameter hygroscopic droplets in collector embryos in updrafts at cloud base which were capable of shortening the time reqired for appearance of collectors and production of rain. The material used was a highly-concentrated eutectic solution of urea and ammonium nitrate in distilled water. Evaluation of the rainfall results is being reported elsewhere. Here we present cloud droplet collector impact samples and raindrop impact samples, indicating substantial effects of the seeding in increasing the population of collector drops that fell as rain within the time available. These results are consistent with the theory that underlay the operational design.

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