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|cloud seeding |
A method of making a cloud give up its moisture as rain, especially by releasing particles of dry ice or silver iodide into cold clouds. Dry ice freezes water droplets in the cloud, turning them into nuclei for the formation of raindrops. Silver iodide particles are used because they have a crystal structure similar to ice and can also serve as nuclei for raindrop formation.
A technique for producing rain by dropping chemicals or small objects into clouds.
deliberate introduction into clouds of various substances that act as condensation nuclei or ice nuclei in an attempt to induce precipitation. The first experiments with cloud seeding were conducted in 1946; since then seeding has been performed from aircraft, rockets, cannons, and ground generators. Many substances have been used, but solid carbon dioxide and silver iodide have been the most effective; when used in supercooled clouds (composed of water droplets at temperatures below freezing), they form nuclei around which the water droplets evaporate. The resulting water vapour deposits into ice crystals, which build quickly as water droplets attach themselves. Attempts have been made to use these substances to minimize damage to crops and buildings from hailstones.