What is a Kelvin-Helmholtz Cloud?:
These clouds are also known as billow clouds, shear-gravity clouds, KHI clouds, or Kelvin-Helmholtz billows. The rolling eddies seen at the top of the cloud layers are usually evenly spaced and easily identifiable. The clouds are named for Lord Kelvin and Hermann von Helmholtz. These clouds are often good indicators of atmospheric instability and the presence of turbulence for aircraft.
Animation of Kelvin Helmholtz Instability:
The Formation of Kelvin-Helmholtz Clouds:
When two different layers of air are moving at different speeds in the atmosphere, a wave structure will often form. The upper layers of air are moving at higher speeds and will often scoop the top of the cloud layer into these wave-like rolling structures. The clouds often form on windy days where there is a difference in densities of the air, such as in a temperature inversion.