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Asked by blueniamhdoyle to Enda, Jean, Kate, Kev, Tim on 17 Nov 2012.
Question: kevin why do clouds turn grey
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Tim Downing answered on 17 Nov 2012:
Hi Blueniamhdoyle,
Cloud colour reflects what makes up the cloud – a big ball of microscopic water droplets suspended in the air. We see their colour as a reflection of the sunlight as it bounces off the droplets. So it will depend on whether it is dark and gloomy or bright and sunny as well. As the concentration of droplets increases, the colour of the cloud changes from light grey to a very dark grey. At some threshold point, the droplets will aggregate into bigger droplets and fall as rain. However, we can’t quite predict this from the cloud colour because this depends on the temperature, the wind and the humidity (the concentration of water in the non-cloud air).
If you go cloud-spotting, you should be able to find dark grey ones far away that are raining, where you can spot the dark grey trails of rain falling down fom the cloud.
Tim
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Jean Bourke answered on 23 Nov 2012:
The effect is known as light scattering. Particles scatter light that hits off them. As the size of the water and ice particles in the cloud increase they scatter more light making the clouds look darker. Eventually the particles get so big they cannot stay in the sky and we get precipitation (water falling from the sky: rain, snow, hailstones).
There are many interesting and unusual types of clouds. New Scientist have a good gallery of them http://www.newscientist.com/gallery/dn17178-extraordinary-clouds
Fall streak holes are gaps in clouds that have a streak of ice crystals (look like a different type of cloud going through them). Roll clouds look like a giant tube going through the sky. Pink UFOs look, unsurprisingly, just like pink UFOs. Cloud caps form over mountains and look like the mountain is wearing a hat. Virga clouds look like jelly fish in the sky. There are many more.
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