Important People Decided It Was Time For Some New Clouds

Important People Decided It Was Time For Some New Clouds

People like giving official names to things — other groups of people, weird new animals, stars, round planets, and even the shapes that blobs of water vapour condense into in the sky. But move over, other names describing water vapour. There’s a new name in town: Asperitas.

The new Asperitas cloud (mage: Gary McArthur/Cloud Appreciation Society)

Today, the World Meteorological Organisation is publishing the newest edition of its International Cloud Atlas, an online portal where you can check out all the different shapes of water vapour blobs, and learn their given names. It also happens to be World Meteorological Day (or at least it was yesterday in Australia), with the theme “Understanding Clouds”, but this is the first new edition of the atlas since 1987. The Atlas includes a few updated names with more pictures, including the brand new Asperitas cloud that some people are very excited about.

I didn't really get why this was a big deal, so I called someone who studies meteorology.

"Clouds are basically a visual representation of other things that might be going on," said David Babb, assistant professor at Penn State. "Having cloud classifications gives us a language to communicate what we're seeing."

Clouds are caused by a combination of a few factors, predominantly air carrying moisture moving upwards in the atmosphere. At a certain temperature, called the dew point, water vapour carried by that upward moving air condenses, forming a cloud. The speed of the wind, dew point, and other atmospheric factors determine what the final cloud looks like.

That means the appearance of a cloud carries important information. White, puffy clouds mean it's a nice day. As clouds grow taller, that could signal coming bad weather.

"One of the things we drill into our students it that by looking at the nature of the cloud, you can say something about the atmosphere," said Babb. "If you're hiking" and see different shapes of clouds, like a featureless blanket versus a cauliflower, "you have different decisions to make".

Us humans, ever the fans of categorising things, then applied a slew of criteria, combined with the altitude of the cloud, to create a list of all the different shapes condensing water vapour could create in the sky. The outcome of that categorisation was first published in the International Cloud Atlas in the late 19th century.

Today, there are 10 different cloud "genera", categories that describe a general combination of cloud shape and height. Within those genera, there are around a dozen species to more precisely describe the cloud shape and what's going on inside of it, and a dozen varieties to describe how the clouds arrange themselves and how much light passes through them. Cloud names come from the combination of genera, species and variety. The World Meteorological Organisation is adding a new species with the Atlas update, called volutus, or roll clouds, which seems important. Asperitas, the one everyone is excited about, is a supplementary feature, a fourth add-on word to describe specific elements of the cloud. Asperitas describes a kind of wavy cloud, like the image at the top of this article. Joining it on the supplementary features list are cavum, cauda, fluctus and murus clouds, according to a press release. 

Roll cloud (Image: Daniela Mirner Eberl /Wikimedia Commons)

Roll cloud (Image: Daniela Mirner Eberl /Wikimedia Commons)

The asperitas excitement likely comes from the fact that citizen scientists at the UK's Cloud Appreciation Society all thought it looked cool enough to be worth a name, and now it has a name.

I'm going to be honest. The 10 genera, I get, that's important. Even species and varieties, that sounds important for meteorology. But there are so many different ways that air, the ground and water vapour can combine to produce clouds, I have to wonder how we know precisely when we've stopped seeing one type and started seeing the other. Wouldn't it be more useful to simply teach people how clouds form, and the explanation behind different cloud features, so they know when not to go outside?

Babb disagreed with me ("I think it's kind of cool that every cloud has a name," he said) as did George Anderson, member of the WMO task team for revision of the International Cloud Atlas. "The new official cloud names introduced to the International Cloud Atlas provide meteorologists worldwide with a common classification for these cloud features," Anderson noted. The rest of the news media likes the new clouds too, apparently. Anyway, if you like clouds, enjoy your new clouds.