Comparison of Radar-Derived Properties of Texas Clouds Receiving One of Three Treatments: AgI Ejectable Flares or Hygroscopic Flares or No Seeding

William L Woodley, Daniel Rosenfeld

Abstract


Four clouds on 15 August 1996 provided an opportunity to observe and measure with radar their behaviors under various treatments: hygroscopic flares at cloud base, AgI flares near cloud top, indirect treatment with AgI ("secondary seeding") and no treatment. It was not possible to determine the expected behavior of the seeded clouds had they been left untreated, nor was it possible to reach any conclusions based on statistical analyses. Instead, the behaviors of the clouds were compared and interpreted based on physical reasoning. The cloud, which was seeded with 19 1-kgm hygroscopic flares over 43 min, was the tallest  (14.9 km) and most rain productive (1,693 kilotons) of all of the clouds within scan of the radar. Based on this and other evidence, it is concluded that hygroscopic seeding may have been the most appropriate treatment for suitable clouds on this day. Because the cloud treatments were not randomized in view of the known and high natural variability of convective clouds in any region, this and other assessments presented herein must be viewed as speculative.

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