The use of single seeding events to evaluate the effect of hail suppression
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During the years 1977–82 a randomized hail suppression experiment, Grossversuch IV, was conducted in Central Switzerland, testing a Soviet seeding method, which was called the “competing embryo concept”. Due to logistical and technical difficulties there were several seeded hail cells with insufficient seeding coverage. This fact complicates a statistically proper evaluation of the experiment.
To overcome the problem of insufficient seeding, a method is demonstrated, which takes a single seeding event (in our case one rocket) as the statistical unit instead of the seeded cell. The assumption is made that each rocket, which hit the zone of hail formation, reduces the hail production and can be investigated independently from the others. 19 seed cells with 226 truly fired rockets and 18 control cells with 170 simulated rockets, representing over 90% of the total global kinetic energy of all Grossversuch IV cells, were selected. A randomization test is introduced to test the average differences of the true and simulated seeding events. A highly significant increase of kinetic energy after seeding (p-value around 1%) is observed. This result supports the statistically non-significant trend obtained in the confirmatory analysis.
KeywordsKinetic Energy Randomization Test Seed Cell Statistical Unit Single Seeding
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