ASK THE METEOROLOGIST
“Aren’t clouds supposed to be blue because they have lots of water in them?”
Anshuman Singh, Bellview Elementary in Ashland
Anshuman is referring to the ocean, and why the ocean, which is made up of water, is blue. Well, clouds are made of water too, but they are white. So what is the difference? It all has to do with water droplets versus water molecules.
Water droplets that make up clouds are large enough to scatter light equally, so no one color dominates. That means that the cloud, instead of appearing blue or red or green, looks white. The one exception to this would be very thick clouds, or clouds that have shadows on them, both of which can instead appear gray.
In the ocean, the amount of water molecules present absorb light on the red end of the spectrum. This means that light on the blue end of the spectrum is scattered, which is the color you see. So why isn’t the water in a glass blue, but instead clear? The amount of water molecules isn’t large enough to absorb light like the ocean does. But in large amounts, it will appear blue. That’s why the deep end of the pool, or the deeper parts of the ocean, are a darker blue than the shallow parts.
Great question, Anshuman!
Chief Meteorologist Kate McKenna