Blue Clouds

Ever wondered why some storm clouds appear blue in colour?

blue cloudsThis image was taken on 25th August by PWL chaser Glenn Casey, near Lancelin, Western Australia.

 The moisture in a cloud has no colour. When the sunlight meets those droplets of water, it is scattered in all directions. That is what makes most clouds white, since white is the combination of all the visible colors of the light.

If the cloud is big enough, it ends up by scattering entirely the light of the sun and what appears to be a dark cloud is simply the shade of that cloud. When a cloud appears blueish, it is because the red frequency of the visible light spectrum, which is at the lowest end of the spectrum, is the first to be scattered. This process is called Rayleigh scattering. To put is simply, it appears blue because most of the red light has been filtered out.

It is also important to note that colour may also be affected by the camera’s white balance settings.