Earth Science

Why are clouds white?

By George Garza
Info Guru,

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White clouds
Ever wonder why clouds are white?
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Discover what makes clouds white.

In a previous article, we discussed why the sky is blue. We also have looked at why clouds are gray. But why are clouds white? To understand why clouds are white, we first must talk about color. What is color?

How Colors are Created

There are three primary colors: red, green, and blue. There are also three secondary colors that are created when you combine red and blue: violet. Red and green: yellow. Green and blue: cyan.

By combining all of the colors, you will get white.

In the same way that skies are blue because of scattering, clouds are white because their water droplets or ice crystals are large enough to scatter the light of the six wavelengths (red, yellow, green, cyan, blue, and violet), which combine to produce white light. White means all colors are present.

Color is light energy emitted in a way called the visible spectrum. It's visible but there are other forms that are not visible, like infrared or microwave energy.  

The different levels of visible light energy have different colors because they have different wavelengths. If all colors of the visible spectrum are present, then the shade of light is white. If no light at all is seen, then the shade is black.

Why are Clouds White?

Clouds are made up of tiny water droplets or ice crystals usually a mixture of both. The water and ice scatter all light, making clouds appear white.

Why are clouds white? Clouds are white because the rain and sleet inside of the clouds scatter all sunlight equally, creating white light.

Let's look at a cirrus cloud. It has an altitude of approximately 8km above sea level. At that altitude, all high-level clouds are made up mainly of ice crystals, since the water vapor they were initially formed from has frozen.

The ice crystals reflect sunlight. When flying above clouds during the day, they are always bright white. When we get dark clouds, they are so thick that they soak up most of the sunlight or reflect it upwards, causing things not to look as bright below. Storm clouds are the thickest clouds, and look the darkest from down below, though they still look bright white if we see them from above.

Clouds are white because they reflect the light of the sun. Light is made up of colors of the spectrum; when you add them all together you get white. Clouds reflect all the colors the exact same amount, so they look white.

Mie Scattering

When all wavelengths or parts of light are scattered equally by a particle, it is called Mie scattering. This type of scattering of all colors is different from the type of selective scattering responsible for the blue color of the sky.

And that is the simple answer to why clouds are white: cloud particles happen to scatter and reflect all colors. Since clouds are typically white, then clouds must reflect all colors of the rainbow.

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