Update: Several really nice hail cannon photos are available at NewtonFabrication.com.
I've written about hail cannons several times before. Some claim they prevent hail from damaging food crops and other property, but others aren't convinced. According to Eggers Hail Cannons, a vendor, "Hail cannons ignite a charge of acetylene gas in a specially designed blast chamber releasing an explosive pressure wave creating a cavitation effect which disrupts the formation process of the hail stone embryo." Among others, USA Today has covered them. (Photo from HailCannon.com.)
Today Boing Boing picked up on a good post by Nacken, who said "This weekend we went to the [Piedmont] Roero wine area and after a loooong lunch we sat with friends outside and looked fearfully at the looming, darker growing clouds. When suddenly we heard a loud boom in the distance. Followed by more booms closer by … and within minutes it sounded like we were in the middle of a WW1 battlefield....Totally baffled about what was going on, the locals explained to us that this is the noise of air cannons, which shoot hot, compressed air against the clouds in order to prevent hail." Nacken includes a video, recommended for those who want to hear the sound of the cannons.
Is this an example of the triumph of hope over evidence? The Wikipedia page on hail cannons reviews the scientific evidence (not favorably, I might add): "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." You can see the research for yourself in If cannons cannot fight hail, what else? [17-page pdf here]. Here's how the authors explain it in their abstract: "Hail suppression is an uncertain meteorological subject in premature agricultural servitude. Commonly known is the method of seeding menacing cumulonimbus clouds with silver iodide by means of rockets or aircraft flares. Less discussed but widely practised alternatives are also reviewed here, in particular the useless but still quite popular practice to attempt destroying hailstones with explosives or with sound blasts from so-called hail cannons."
Those who don't know the history of hail cannons are condemned to repeat it. A 1981 Bulletin American Meteorological Society article, History Repeated: The Forgotten Hail Cannons of Europe, reminded readers that this attempt at weather modification had been tried at the turn of the century... as in 1900, the turn of the *20th* century [8-page pdf here]. But it "went unnoticed by the 'pioneers' of 1950-1970."
Wherever hail cannons go, cranky neighbors can't be far behind. Unwelcome noise has become a key component of the hail cannon experience. Fox News has reported on disagreements in Vermont over hail cannon noise: "Scientists snicker at such devices. But farmers swear by 'em. As for the neighbors, they just swear." In 2004, WLBT reported that a Jackson, Mississippi Nissan automobile dealership was using hail cannons to protect the cars on its sales lot. "The sound at ground zero is about 120 decibels, or about the same as a tornado warning siren. Workers are installing fences around two of the machines in the 140-acre parking lot at Nissan and filling the fences with hay in an effort to reduce the sound level."
Emerging trend? Anti-bird cannons. Absurd Intellectual is wondering if hail cannons work on crows. And other flavors of cannons are also causing controversy: In some areas, people are using propane cannons to keep birds away from berry crops -- which has prompted creation of the anti-anti-bird-cannon site called Ban the Cannons.
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