Kelvin Helmholtz clouds, aka billow clouds or shear-gravity cloud

Spotted these Kelvin Helmholtz clouds, aka billow clouds or shear-gravity clouds the other day in the skies of New Hampshire.
The Kelvin-Helmholtz wave cloud looks like crashing ocean waves. These beautiful clouds are named after German physicist Hermann von Helmholtz and British physicist Lord Kelvin, because they form when two different layers of air are moving past each other at different speeds. The above layer is faster. Some parts of the boundary – a shearing layer – move down, and others move up.