Transcription: On a sunny day the sun may heat up one place on the ground more than another. Bubbles of warm air form over this hot spot and rise through the cooler air above. As the air rises it cools and spreads out. The air contains water vapour. When the air has cooled sufficiently for this to condense a cumulus cloud forms. Cumulus clouds can form in this way above a hillside which is warming up because of the passage of a plane through the air or where warm air escapes from the cooling towers of power stations or from industrial chimneys.
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