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Mahesh

12/11/23 14:49 PM IST

Process of Cloud Seeding

In News
  • Delhi environment minister Gopal Rai wrote to chief secretary Naresh Kumar, asking him to coordinate with IIT Kanpur over a detailed proposal to create artificial rain over Delhi.
Cloud Seeding
  • Water vapour condenses around small particles to form the droplets that make up a cloud. These droplets collide and grow; as they get heavy and the cloud gets saturated, it rains.
  • With cloud seeding, clouds are usually injected with salts like silver iodide, potassium iodide, or sodium chloride, which is the ‘seed’.
  • These salts are expected to provide additional nuclei around which more cloud droplets can form.
  • They are dispersed into the cloud either using aircraft or through generators on the ground.
  • Seeding accelerates cloud microphysical processes. You need sufficiently large droplets that can reach the surface of the earth and not evaporate on the way.
  • The substance that is dispersed into the cloud needs to have cloud condensation nuclei and ice nuclei and these two come from two different salts.
  • The cloud condensation nuclei help form cloud droplets, and ice nuclei help to form ice crystals. Ice crystals grow faster than drops, and they become large and fall.
Conditions for Cloud Seeding
  • Firstly, cloud cover and clouds of a certain type are necessary.
  • Cloud seeding can only happen if there is a sufficient number of clouds and a particular depth to these clouds.
  • Inside, there needs to be an adequate number of cloud droplets. Cloud seeding is done to increase the radius of the cloud droplets so that they will grow bigger and because of gravity, they will come down as rainfall.
  • But with a clear sky, you can’t do it.
  • In winter, clouds form over Delhi when a western disturbance moves over the region.
  • These are storms that originate in the Caspian or Mediterranean Sea and bring non-monsoonal rainfall to northwest India.
  • With a stable atmosphere in winter, clouds are expected to form when a western disturbance disturbs this stability of the atmosphere.
  • In winter, you don’t see the kind of clouds that are needed for seeding, but western disturbances are the way through which clouds form. Even if clouds are there, you need to see what their height is, what their liquid water content is.
  • While the possibility of cloud formation can be determined in advance through radars, other conditions will have to be studied on the day seeding is likely to be done.
Artificial Rain
  • Artificial rain, also called cloud seeding, involves introducing chemicals like silver iodide, potassium iodide and dry ice into the atmosphere via aircraft or helicopters.
  • These particles attract water vapour, leading to cloud formation and subsequent rainfall.
  • The methods include seeding supercooled clouds with silver iodide or dry ice and using hygroscopic materials like salt particles for warm clouds.

Recent attempts in India
  • Seeding has mostly been attempted during the monsoon in India, in places such as Karnataka, Maharashtra and Tamil Nadu.
  • A more recent experiment, the fourth phase of the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX-IV) that took place in the monsoon seasons of 2018 and 2019, was conducted in drought-prone Solapur in Maharashtra. It pointed to a relative enhancement of 18 per cent in rainfall.
  • IIT Kanpur attempted it in April and May of 2018, which are the pre-monsoon months, on their campus. It said five out of six trials resulted in rain.
Cloud Seeding around the world
  • Outside India, experiments with cloud seeding have most notably been conducted in China, where different cities have their own plans.
  • China takes assistance from the military to carry out this exercise.
  • In France too, this is done in coordination with over 20 different departments, largely to prevent hail from falling on agricultural fields in the spring and summer months.
Source- Indian Express

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