Amazing cloud formation: Kelvin Helmholtz
Will Lewis from Glasbury, Powys sent in this amazing picture, taken on 14 January 2012 over looking Llangors in Powys. This is a photo of billows:
The fog or stratus is colder and denser than the overlying air, so the two don't normally mix.
However, if the wind is strong enough, shear between the cloudy and non cloudy layer forces mixing, which manifests itself as unstable waves on the interface between the cold, dense air and the warm, less dense air.
These roll up into billows, or breaking waves. It is not often that you see the process so clearly illustrated but this is a great photo which could easily grace the cover of a weather or fluid dynamics book!
has more information about this fascinating cloud
says "Kelvin-Helmholtz clouds are a result of wind shear in a stable atmosphere"
And check out this over Birmingham, Alabama.
Thanks to Will for sharing his photo with us.
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