Hail cannon

From Wikipedia, the free encyclopedia

There are very few or no other articles that link to this one.
Please help introduce links in articles on related topics. After links have been created, remove this message.
This article has been tagged since September 2006.

A Hail cannon is a shock wave generator used to disrupt the formation of hailstones in the atmosphere in their growing phase. An explosive charge of acetylene gas and air is fired in the lower chamber of the machine. As the resulting energy passes through the neck and into the cone it develops into a force that becomes a shockwave. This shockwave, clearly audible as a large whistling sound, then travels at the speed of sound through the cloud formations above, disrupting the growth phase of the hailstones.

The device is repeatedly fired every 4 seconds over the period when the storm is approaching and until it has passed through the area. What would otherwise have fallen as hail stones then falls as slush or rain. It is critical that the machine is running during the approach of the storm in order to affect the developing hail stone. These machines can not alter the form of an already developed solidified hailstones.

While the history of Hail cannons date back into the 18th century, the modern Hail Cannon has been developed extensively over the last 30 years with most development in the last 10 years.

The protected area for an individual machine is approximately a 500 meter radius with a lower level of effectiveness as distance from the device increases.

Radar controlled systems are available to replace human operation of the unit which is particularly important in areas subject to hails storms at night.

There is little scientific evidence of the effectiveness of these devices. 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 says, "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."