"Every cloud engenders not a storm," Shakespeare tells us and cloudspotters everywhere would surely be quick to agree, pointing out that it's usually the cumulonimbus that brings the storm.
That’s because cloudspotters know that there are ten main types of cloud in the sky. And that is the first lesson of Gavin Pretor-Pinney's new book, Cloudspotting for Beginners.
These ten clouds are all ones we might have heard of, Gavin told Claire Byrne:
"Clouds like the cumulus cloud, that’s the Simpsons cloud, you know, the cartoon cloud forms on a sunny day, the fair-weather cloud. It’s like a generic one, really. If you close your eyes you’re probably thinking of a cumulus."
Another of the ten main clouds is the cirrus, the "high, wispy ice crystals that are cascading from the upper reaches of the troposphere." Gavin describes them as looking like "brushstrokes across the blue," which is quite a poetic way of putting it.
These are, of course, the clouds that hang low in the sky, the ones that we see when we look up. And although the cumulonimbus is the cloud that brings thunderstorms, Gavin points out that there’s another cloud we all want to boo when we see it:
"The nimbostratus is the one that gives all the other clouds a bad name. It’s the sort of low, thick, wet blanket of the sky and it produces rain – rain or snow – but it’s continuous. So the cloud hangs around for a long time like all the layer clouds do – 'cause this is one of the layer clouds – and it hangs around a long time, and this is one that produces quite a lot of precipitation, which can persist."
It sounds like it should be the national cloud of Ireland, doesn't it? But let's not dwell on the dark clouds that engender storms, let’s talk about the pretty skies that clouds make possible:
"When the sky looks dramatically pink, of course it’s when the sun’s low on the horizon [...] It’s when the sun is shining up onto the underside of clouds usually and that is a moment of magic when it comes to the sky because we instinctively know it’s a fleeting moment, a sunrise or a sunset. And the reason is because if the sky’s clear off to where the sun is on the horizon, it can shine across the sky to the clouds above you. But it can only shine up and illuminate their bases with the golden and the ruby hues of sunrise or sunset for a moment because the angle's right for only a brief period of time."
That’s why sunrises and sunsets are times to pause, take in the beautiful sky and be in the moment, Gavin says. The Cloud Appreciation Society – which Gavin founded in 2005 – has as one of its core philosophies the notion of being present and enjoying the moment.
"The sky is something that brings people together. You know, nobody has a big argument about whether a sunrise is a beautiful thing, it’s something we all agree on. And in a time of division, I think those things are worth celebrating."
Gavin’s book is illustrated and one of the things in it that piqued the interest of Claire’s 10-year-old is the role clouds play in the formation of tornadoes. Gavin explained that it involves the cumulonimbus:
"That is part of the ingredients required for a tornado to form. These actually can combine together into a kind of mob behaviour, these cumulonimbus clouds, when they act as individual cells within a larger storm system. And if those cells get really quite organised in terms of the flow of air into and out of them, you end up with what’s known as a supercell storm and this can have a large, rotating central region to it – it's called a mesocyclone – this is really, the base of this is where you’re going to be looking for a tornado."
Take that information with you when you go to see Twisters and judge for yourself whether the filmmakers have got it right or not.
You can hear Claire’s full conversation with Gavin by clicking above. Cloudspotting for Beginners by Gavin Pretor-Pinney and William Grill is published by Particular Books.
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