What are Clouds?

Kam’s cloud question is about their colour. He wants to know why clouds are white.  So, I thought it’s probably wise to find out about what clouds are, before we look at why they are white.

How Clouds Form

Water vapour and salt particles
Water vapour condensing on Ocean salt particles:NASA

Clouds form when water vapour in the air condenses into water droplets or ice crystals.

The atmosphere contains microscopic (tiny, tiny, tiny) dust particles, called aerosols.

Water vapour and aerosols move around and bump into each other. When they collide some of them stick together.  This is condensation.  Bigger water droplets form around the aerosol particles.  The water droplets then stick to each other to form clouds.  There are hundreds of millions of droplets in a cloud.

Water droplets condenses on a window
Water vapour condenses on windows as well as aerosols in the atmosphere

Clouds contain either ice or water droplets.  Which depends up on the cloud’s height and the atmosphere’s temperature. The droplets are so small they can stay in liquid form in temperatures as low as -30 °C.  Extremely high clouds at temperatures below -30 °C are composed of ice crystals. When a cloud forms the air is saturated and cannot hold any more water vapour.  This are two ways this can happen:

  1. The amount of water in the air has increased, (usually through evaporation), the air cannot hold any more water.
  2. The air cools to its dew point, (where condensation occurs) and the air is unable to hold any more water.

The warmer the air is, the more water vapour it can hold. Clouds usually form because of condensation.  As the air rises, it cools.  This means it cannot hold water vapour and condenses.  The height at which dew point starts and clouds form is the condensation level.


A Note to You and Me

Clouds are full of dust particles, water droplets or ice crystals.  Clouds are essential to our weather systems.  Look out for our future post about cloud colour.

Thanks for reading, of course, you are welcome to look at some of our other posts.

If like this post, please let us know, Kam is always pleased when he sees people asking questions.


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