Even when the sky is mostly blue, there’s a lot going on at different altitudes. The winds do not move in a consistent direction or at the same speed, something which becomes apparent when watching clouds move relative to one another. When different layers of air move past one another, there is shear between them, not unlike the friction you feel when running your hand along a table. Under the right circumstances, this shear creates Kelvin-Helmholtz waves like the ones in this image over Helena Valley, Montana. Fast-moving winds (blowing right to left in the image) above a layer of clouds created these breaking wave-like curls. The same phenomenon creates many of the ocean’s waves from the shear caused by wind blowing across water. (Image credit: H. Martin, via EPOD)
Waves in the Sky
