Kelvin-Helmholtz Waves

When two bodies of fluid are moving in different directions interesting things happen at the boundary. The result is usually some sort of wave… Waves on the surface of the ocean or waves in the sky.

Waves on the sea surface are easy to see. Waves in the sky? Not so much. These waves are only betrayed if clouds form in the waves, revealing these structures.

Kelvin-Helmholtz Waves in the Saddle
Kelvin-Helmholtz Waves in the Saddle with Mauna Loa in the background. Photo by Joe Gargiulo, used with permission
This sort of wave is called a Kelvin-Helmholtz wave after Lord Kelvin and Hermann von Helmholtz who first investigated how these waves form. Yes this is the same Kelvin for whom the units of temperature are named. KH waves are visible all around us for those who know to look, from the surface of our ocean to the clouds of Jupiter, these characteristic swirling patterns are seen.

In the Saddle region over Mauna Kea and Mauna Loa, there are usually two air masses moving in different directions. Below the inversion level the tradewinds push westward. While above the inversion level, usually about 6-7,000ft, the upper air moves to the east. Where these two meet there are often KH waves, and occasionally some clouds to outline these fascinating structures.