Here Comes the Science
(image via: Muddy Tracks)
According to Chris Walcek, most of the time a fast-moving air layer will “simply slide smoothly over the slower-moving air, like a hockey puck sliding along an ice surface.” Factor in a great enough physical differential between the two layers and so-called “random turbulence” begins to break up the boundary separating the two layers.
Kelvin-Helmholtz Instability is expressed at that special “sweet spot” that occurs before the turbulence gets too random. Indeed, it’s the often eerie order of the cloud waves and their decided lack of randomness that attracts our attention and at the same time, raises our hackles: a fish out of water is one thing, but waves out of water??
(image via: Panda’s Thumb)
If their strange appearance isn’t enough to set Kelvin-Helmholtz Clouds apart from the fluffy flock, add in their impermanence: a perfect line of consecutive waves can form and break up in mere minutes. Perhaps this attribute explains, partially at least, why these clouds are as rarely described as they are actually seen.
The Birmingham appearance of Kelvin-Helmholtz Instability in morning fog didn’t last very long; much like ordinary, non-wavelike fog, the rising sun and the accompanying rise in temperature burned away the fog – not before photographers had captured the towering waves for posterity (and our enjoyment), however.
Castles in the Air
(images via: Siskiyous)
Kelvin-Helmholtz Clouds may be rare but they also can form under a range of weather conditions. For example, the Birmingham event took place in the early morning and involved a thick layer of opaque ground fog. Most other instances of Kelvin-Helmholtz Instability expressed in clouds occurs in much higher portions of the troposphere, often highlighted by a clear blue sky background. Isolated mountain peaks such as California’s Mount Shasta can also induce the formation of these unusual cloud formations.
Photographers fortunate enough to observe Kelvin-Helmholtz Clouds in the pre-dawn or late-day twilight bring us a special treat: dark waves silhouetted against a Rainbow Sherbet background.
Mila Zinkova was serendipitously situated in San Francisco one evening in January of 2006, admiring the ocean waves below a Pacific sunset when “Suddenly I saw a different wave at the sky. I’ve never seen such clouds before and they were just amazing.” No argument here, Mila!
Kelvin-Helmholtz Instability is a physical property and as such, is not exclusive to earthly weather. Astronomers have recorded the phenomenon in the sun’s wispy corona and along cloud bands racing around the gas giant planets Jupiter and Saturn, for example. It’s somewhat humbling to think that some of the larger crests of these interplanetary waves are large enough to curl around our comparatively small blue planet!
(image via: NonPrints.com)
You might wonder why the startlingly familiar shape of Kelvin-Helmholtz Clouds combined with their decidedly out-of-place setting hasn’t inspired folk tales, myths, legends and art among us easily impressed humans. Maybe they have: some say the “swirling clouds in violet haze” that highlight Vincent van Gogh’s exquisite painting “The Starry Night” were inspired by the Dutch artist’s previous observance of Kelvin-Helmholtz Clouds. Was van Gogh trying to express some deeper sentiment through his ethereal artwork? If so… “They would not listen, they did not know how. Perhaps they’ll listen now.”