A device intended to suppress hailstorms by blasting out sound waves is being tested in the US by the car manufacturer Nissan. The company hopes to protect the large fleet of new vehicles made at its plant in Canton, Mississippi, from the damage that can be caused by falling hailstones.
Nissan spokesman Frank Limpus told New Scientist that the device works by firing sound waves into a cloud in order to disrupt the formation of hailstones.
The system is said to have a range of 15,000 metres and to generate 120 decibels of noise at ground level when in use. It is also said to switch on automatically when weather conditions conducive to hailstorms are detected.
“The economic consequences of hail damage are quite severe,” says Phil Brown, a cloud physics expert at the UK’s Metrological Office. Preventing hailstorms could protect crops and even airplanes from serious damage.
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Shock waves
But Brown also told New Scientist that he is unsure that the system being tested by Nissan would be effective: “I can’t imagine any physical mechanism by which it would work.”
Limpus says the system is supplied by a Canadian company called HailStop. Its website says it fires “ionized shock waves” into a cloud every six seconds, each generated by igniting acetylene gas.
The site also claims that more than 420 Hail Suppression Systems have been installed in 16 countries. However, several attempts by New Scientist to contact the company were unsuccessful.
Layer upon layer
Hailstones begin to form when super-cooled water freezes onto fine particles of dust or sand within a cloud. The ice-encrusted seeds then drift downwards but if there is sufficient updraft within the cloud, the particles can cycle through it several times. Each cycle adds another layer of ice, until the particles becomes so heavy it drops out of the cloud completely as a hailstone.
Brown says there is a more established method for trying to prevent hail from forming, known as “glaciogenic seeding”. This involves firing rockets into clouds that then explodes and release extra ice-forming particles.
The idea is to cause a bigger number of small hailstones to form, instead of fewer, larger ones. However, even this approach remains experimental and, as yet, unproven.
Brown adds that disrupting hailstorms in one area could even have a negative impact on the wider weather system. “It easily conceivable that, if you change something at the bottom [of a cloud], you must be changing what happens elsewhere as well,” he says.
