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Tsunami or Kelvin-Helmholtz clouds

kelvin-helmholtz-wave-cloud by David Bradley

UPDATE: Apparently, residents of Alabama saw giant “tsunami” clouds earlier this week. Well I photographed the waves seen above from my home office window 2 or three years ago…don’t think they were heading across The Atlantic though!

Dramatic clouds sunset by David BradleyCloud appreciation…it doesn’t quite have the same image as other hobbies, rock climbing, sky diving, fell walking, fly fishing.

Cloud spotting is almost on a par with training spotting or stamp collecting, you might think, but just a single hour spent on your back almost anywhere in the world staring up at a cloudy sky can be so good for the soul. At least, that’s the ethos of the Cloud Appreciation Society.

The CAS website is temporarily unavailable (503 server overload error) because of a surge of interest in clouds thanks to surprise bestselling author Gavin Pretor-Pinney who has made clouds his life’s speciality. And The Cloudspotter’s Guide topped the non-fiction charts for months.

undulating clouds by David BradleySo fascinated by clouds is Pretor-Pinney that’s he’s hoping to have a new cloud type classified. The launch of his campaign to get this choppy cloud, he has dubbed Asperatus into the annals of meteorology, neatly coincides with the publication of his second book, The Cloud Collectors’ Handbook, but we’ll forgive him that as a fortunate coincidence, eh?

I have to admit that, sitting behind a laptop from in my first floor office with a wide picture window over looking trees and a few single-story dwellings gives me a wonderful opportunity to watch the clouds unroll. I often see some unusual formations, and if I can grab my camera to capture them before they dissipate.

The photos on this post are all clouds seen from my office, but until I saw Pretor-Pinney interviewed on BBC TV, I hadn’t realised that this one had a special name. Apparently, it’s a Kelvin-Helmholtz wave cloud, named for two of the godfathers of nineteenth century science.

kelvin-helmholtz-wave-cloud by David Bradley

According to scientists on the UIUC Weather World 2010 project, this cloud type appears between two layers of air of different densities, travelling at different speeds. If a warm, less dense layer lies above a layer of colder, denser air, and the wind shear across the two layers is strong enough, eddies will develop along the boundary. This gives the cloud an obvious rolling waves appearance, hence their other name “shear-gravity waves”.

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