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Snow and Ice
Earth Sciences

Why do some water droplets in clouds remain liquid at temperature less than zero degrees?


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September 07, 2007 10:48AM

Ice crystals require something to start growing on (a nucleus), such a sdirt/dust etc. If the droplet is pure, there is no nucleus to start off the crystallisation process. Hence a drop of water becomes supercooled. Water will spontaneously freeze at -42C (approx) if it lacks the nucleus.