Daily News Analysis

Anti-hail guns

11th June, 2021 Science and Technology

GS PAPER III: Science and Technology- developments and their applications and effects in everyday life.

Context: To help out horticulturists who face crop damage due to hailstorms, the Himachal Pradesh government will be testing the use of indigenously developed ‘anti-hail guns’.

What are anti-hail guns and how do they ‘prevent’ a hailstorm?

  • An anti-hail gun is a machine, which generates shock waves to disrupt the growth of hailstones in clouds, according to its makers.
  • It comprises a tall, fixed structure somewhat resembling an inverted tower, several metres high, with a long and narrow cone opening towards the sky.
  • The gun is “fired” by feeding an explosive mixture of acetylene gas and air into its lower chamber, which releases a shock wave (waves which 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.
  • Hail is produced 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 is repeated several times, till the hailstones become too heavy and fall down.
  • It is this hail formation process that the shock waves from anti-hail guns try to disrupt in a radius of 500 metres, so that the water droplets fall down before they can be lifted by the updrafts.
  • The machine is repeatedly fired every few seconds during an approaching thunderstorm.
  • However, the effectiveness of anti-hail guns has remained a contentious issue.

Have anti-hail guns been used before?

  • In 2010, the Himachal state government had imported three anti-hail guns from the United States and installed them in three separate villages in the apple-growing belt of Shimla, where hailstorms in summer cause severe damage to the fruit every year.
  • A few years ago, residents of around five villages in Shimla imported similar guns from New Zealand on a collective basis, but these machines have reportedly not worked so well.
  • Perhaps the state government said it is crucial to fire the guns at the correct time to get positive results.
  • The operator has to remain updated with the weather forecasts as well as nowcasts from weather observatories and radars.
  • One also has to be able to correctly identify the hail-forming cumulonimbus clouds and fire the guns before hail can be formed in that area.
  • Once hail is already formed in the clouds, the guns can do little to stop it