Syllabus: Important Geophysical phenomena
Context: Delhi government and IIT Kanpur conducted two cloud-seeding trials to induce artificial rain for pollution control, but remained unsuccessful.
Cloud Seeding
- Definition and Purpose
- Cloud seeding is deliberate introduction of substances into clouds acting as condensation/ice nuclei.
- Aims to induce precipitation artificially by modifying cloud formation processes for rainfall generation.
- Historical Development
- First experiments conducted in 1946 by American chemist and meteorologist Vincent J. Schaefer.
- Since then, seeding performed from aircraft, rockets, cannons, and ground generators for precipitation.
- Substances Used
- Many substances tested; solid carbon dioxide (dry ice) and silver iodide proven most effective.
- Calcium chloride particles used in clouds at temperatures above freezing providing condensation nuclei.
- Process in Supercooled Clouds
- In supercooled clouds (water droplets at temperatures below freezing), substances form nuclei around droplets.
- Water droplets evaporate around nuclei; resulting water vapour deposits into ice crystals rapidly.
- Ice crystals build quickly as water droplets attach themselves forming precipitation-ready particles.
- Process in Warmer Clouds
- In clouds above freezing temperature, calcium chloride particles provide condensation nuclei effectively.
- Raindrops form around these nuclei through condensation process leading to induced rainfall.