Context: ‘Anti-hail guns’, developed indigenously, will be tested by the Himachal Pradesh government to help out horticulturists who face crop damage due to hailstorms.

What are anti-hail guns?

• An anti-hail gun is a machine that generates shock waves to disrupt the growth of hailstones in clouds.

Who has developed these anti-hail guns?

• These anti-hail guns have been developed indigenously by IIT Bombay along with Dr Y S Parmar University of Horticulture and Forestry at Nauni (Solan). They are likely to be much cheaper than the imported ones.

How do anti-hail guns prevent a hail storm?

• Anti-hail gun comprises a tall, fixed structure somewhat resembling an inverted tower, several meters high with a long and narrow cone opening towards the sky.
• The gun is “fired” by feeding an explosive mixture of acetylene gas & air into its lower chamber. This releases a shock wave (waves that travel faster than the speed of sound, such as those produced by supersonic aircraft).
• These shock waves supposedly stop water droplets in clouds from turning into hailstones, so that they fall simply as raindrops.

What are Hailstorms?

• A hailstorm is an unusual weather phenomenon in which balls of ice, called hail, fall from the sky. The ice balls are nothing more than solid precipitation that forms under certain conditions.

How are Hails formed?

• Hails are formed by cumulonimbus clouds which are generally large and dark and may cause thunder and lightning.
• In such clouds, winds can blow up the water droplets to heights where they freeze into ice.
• The frozen droplets begin to fall but are soon pushed back up by the winds and more droplets freeze onto them, resulting in multiple layers of ice on the hailstones.
• This fall and rise are repeated several times, till the hailstones become too heavy and fall down.

Previous such anti-hail guns used in Himachal

• In 2010, the Himachal Pradesh government had imported three anti-hail guns from the United States. They were installed in the apple-growing belt of Shimla where hailstorms in summer cause severe damage to the fruit every year.
• Two of the machines are currently functional, while the third one was rejected by local residents.
• State horticulture department officials maintain that since the installation of the guns, hail has occurred very few times in the villages.