Scientific Evidence
There is very little empirical evidence in favor of the effectiveness of these devices. A 2006 review by Jon Wieringa and Iwan Holleman in the journal Meteorologische Zeitschrift summarized a variety of negative and inconclusive scientific measurements, concluding that "the use of cannons or explosive rockets is waste of money and effort."
From a theoretical perspective there is reason to doubt that hail cannons are effective. For example, thunder is a much more powerful sonic wave, and is usually found in the same storm that generates hail, yet doesn't seem to disturb the growth of hailstones. Charles Knight, a cloud physicist at the National Center for Atmospheric Research in Boulder, Colorado was quoted in a newspaper article of July 10, 2008 as saying, "I don't find anyone in the scientific community who would validate hail cannons, but there are believers in all sorts of things. It would be very hard to prove they don't work, weather being as unpredictable as it is."
Read more about this topic: Hail Cannon
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