Kelvin-Helmholtz

 The Kelvin-Helmholtz instability or wave can occur when there is a velocity shear between adjacent layers of the atmosphere. When a cloud finds itself interacting with both layers as is the case with this stratocumulus off the coast of Nice, the wave is revealed. I've been after a shot of one of these for a long time and eventhough much better examples can be found on the internet, this one is mine and I like it.