There was an amazing sight to behold in Alabama yesterday. Giant, tsunami-shaped clouds rolled along the morning skyline. Fascinated residents sent photos into their local news stations to get the scoop on the strange looking clouds.
Experts say the clouds were prime examples of “Kelvin-Helmholtz waves.” This strange type of turbulence can be seen either in the skies or the sea, and always forms when a fast-moving layer of fluid slides on top of a slower layer, thereby dragging its surface.
Water waves, as an example, form when the layer of fluid above them is moving faster than the layer of fluid below. When the difference between the wind and water speed increases to a critical point, the waves “break,” and they take on the classic shape of Kelvin-Helmholtz waves.
According to Chris Walcek , a meteorologist at the Atmospheric Sciences Research Center at the State University of New York, Albany, fast-moving air found at very high altitudes can drag the top of slow-moving clouds underneath it in much the same way.
“In the pictures [of the Birmingham sky] there is probably a cold layer of air near the ground where the wind speed is probably low. That is why there is a cloud or fog in that layer,” Walcek said. “Over this cloudy, cold, slow-moving layer is probably a warmer and faster-moving layer of air.”
It was quite a sight to behold, indeed.