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What are clouds made of?

Clouds Clouds are made of tiny ice crystals or drops of water that form around dust particles in the atmosphere. The droplets are minute—measuring just a hundredth of a millimetre across. Whether a cloud is made up of ice or water droplets depends on the height of the cloud above the ground and the temperature of the atmosphere around it. Being so tiny, water droplets can remain in liquid form at temperatures of down to –30°C (–20°F), when normally they would have turned to ice. At extremely low temperatures found at high altitude, clouds are made up of ice crystals only.


Water droplets and ice crystals

Clouds form when water vapour in the air (which is invisible) condenses into water droplets or ice crystals (which are visible). Tiny particles, such as salt and dust, which are known as aerosols, float around in the air along with water vapour moleculeswater that has evaporated from the Earth’s surface. The particles and molecules are constantly bumping into one another. When the air cools, some of the water vapour sticks to the aerosols: this is called condensation. The water droplets around the aerosol particles may get bigger and bigger as more and more water condenses. They then may start to stick together with other droplets. This is how clouds form. The water droplets grow until they become so heavy they start to fall as rain or snow.
Grey clouds gather ahead of a storm

Every cubic metre of cloud contains around 100 million droplets of water or ice crystals.

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