The Wave

15 December 2018 – I have not yet joined the Cloud Appreciation Society, but, more and more, I appreciate the clouds that form the final dimension in my city/mountains/sky view to the north.

Especially this morning.

I really did have to blink, wonder if my eyes were correctly processing what lay before them.

I have never seen clouds like this, I muttered to myself. What’s going on?

Asperitas (aka Undulatus Asperitas) is what’s going on, I learned on the evening news, and — according to the UK Met Office — it is indeed “a distinctive and relatively rare cloud formation.”

Everybody agrees the name makes sense: the clouds look like great undulating waves. There is less agreement on why or how they form. As the Met Office puts it, it is a subject of “much debate and confusion,” with one theory suggesting they form when “mammatus clouds descend into areas of sky where the wind direction changes with height, causing the wave-like movement.”

They are also the newest (2017) addition to The International Cloud Atlas, which is the bible of cloud classification, published by the World Meteorological Organization in Geneva.

Thank you, WMO, but the credit really goes to the CAS (Cloud Appreciation Society — but you know that by now, don’t you). It launched a campaign for recognition back in the mid-first decade of this century, and just never let up.


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  1. My father was a meteorologist and received the Patterson Award in 1970, I think it was for something he built during the war to do with compiling weather information. I came along later in his life and he never knew what to do with me so he taught me the names of various types of clouds. That and watching Star Trek were our only common activities both of which are still favourite pastimes of mine though I admit I don’t remember many cloud names anymore; Nimbus, cumulous, strata cumulous, hmmm, Mackerel? And now I prefer STNG to the original. :p

  2. Those are cool!

  3. I’m excited for you! What a fabulous sight. I think I saw this once, and I remember reading that descriptive word for them, mammatus. My memory is a sieve….

  4. On second thought, my memory isn’t a sieve, it’s a funnel – everything goes to the bottom and slowly dribbles out. A few odds and ends, like the word mammatus, remain, but ask me when or where I learned it and whether for sure I saw this phenomenon in person, and sorry, those bits are long gone. 😉

  5. Fascinating stuff. Read Gavin Pretor-Pinney’s book, “The Cloud Watchers Guide” Cheers!


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