Beautiful wave-like Kelvin-Helmholtz clouds captured by Gene Hart on December 25, 2012, on Jonesport, Maine. Image © Gene Hart
“The number varied as I watched. The pattern was backlit by the dawn sun and appeared over Moosabec Reach.”
The Kelvin–Helmholtz instability (after Lord Kelvin and Hermann von Helmholtz) can occur when there is velocity shear in a single continuous fluid, or where there is a velocity difference across the interface between two fluids. An example is wind blowing over water: The instability manifests in waves on the water surface. More generally, clouds, the ocean, Saturn’s bands, Jupiter’s Red Spot, and the sun’s corona show this instability.