Ladies and gentlemen, pagans and non-pagans, nature lovers, dirt worshippers, tree huggers and hippies, I’d like to take you on a journey skywards. Possibly not as high as Amalasuntha’s last journey: we’re not going as far as the Moon. No, for this journey you might only wish to look up – perhaps peer out of the window, or maybe, if you’re enjoying some free time on this magnificent sunny day*, just find a nice shady bit of grass to lie on and look up at the dome of the heavens.
Because as sunny as it is today (happy Solstice, by the way), I notice it’s not an entirely blue sky. There are, in fact, clouds. Nice, friendly, puffy white clouds for the most part, and they have inspired me – as someone with not the slightest qualification in meteorology – to write a few lines on the subject of clouds.
Please: stop me if you’ve heard it.
Let’s begin with those very same friendly, fluffy clouds I mentioned just there. These are one of the three main cloud types, and they’re called cumulus. This is a Latin word meaning “sort of piled up, like” – entirely appropriate for these clouds which appear as fluffy lumps and blobs, and can merge together to form hills and mountain ranges in the sky.
Cumulus are generally amiable in nature. They’re not normally ‘rain clouds’ – at least while they’re on their own or gathered in small groups. When they look as they do in the picture, they’re pretty safe to be around. Just leave them to their own devices and they’ll mill about, grazing and basking in the Sun, minding their own business. They can look a bit fearsome sometimes: you’ll occasionally see them looking a bit dark and lowery; but most of the time this is all talk. They’ve probably just got the Sun behind them and they’re blocking the light out. In such cases you’ll often notice their ‘silver lining’ – the gleaming sunny outline that tells you they’re just teasing you with a bit of shadow play. That said, if they start to cluster together in serious groups, and move lower, it’s worth keeping an eye on them. That can lead to the appearance of stratocumulus who, if I’m honest, are a bit more dense, and they they can get a bit sulky and rainy. And it’s possible, as cumulus clouds stack up higher and higher, that ultimately they’ll reveal themselves as cumulonimbus clouds, and they can be quite troublesome, especially for pilots, as we’ll see shortly.
Speaking of ‘stratocumulus’ leads us neatly to the basic stratus cloud type. You’ll have met this one countless times although, frankly, it’s a little shapeless; so you’d be forgiven for not paying it much attention:
Stratus isn’t really just a grumpy nobody trying to spoil your day. Despite appearances it rarely actually drops any significant precipitation on people; but it’s not very outgoing, and it has an identity problem. It’s often mistaken for its unruly twin, nimbostratus, who’s earned itself a bad reputation as a serious deluge-causer. At first glance you can’t tell the difference, and although most of the time all stratus really wants to do when it turns up in a new place is hang around a bit before drifting away, sure enough it doesn’t take much for someone to assume it’s going to let rip with the precipitating.
Cirrus doesn’t have this problem. Cirrus keeps itself above all this sort of thing. You don’t hear people making unfounded accusations of rain or snow against cirrus, oh no. Everyone looks up to cirrus:
Look at those. See the wispy, delicate looking clouds, high up in the sky there? Try to ignore the pesky cumulus bubbles bouncing around in front of the camera saying ‘hello, mum’. Those ethereal filaments above are the ones we’re interested in just now. Cirrus are some of the highest clouds there are, which probably explains why they tend to be a little cold – but it’s got to be said, you can rely on them not to make things miserable for us down here. Honestly they’re just not that interested in us. Sometimes they get tired of people thinking they aren’t capable of raining, but they like to do a little magic trick. Occasionally, they’ll let a load of rain go, but then they wave their hands and make it vanish before it gets down here. Even their rain doesn’t want to lower itself to our level, and we end up with odd rain sheets called virga, which can be seen falling from the cloud high above and fading from view.
But don’t be put off by cirrus. They may seem a little aloof, but actually they’re very friendly – and on occasion, when they feel in the mood, they’ll take the light from a low Sun and bounce it down to us in some beautiful halo effects.
When it comes to showing off, cirrus are good at what they do – but if you want real artistry, you need to look to their even higher cousins, the nacreous clouds:
Nacreous clouds sit at the very top of the sky, taking the light from a recently-set Sun and scattering it on the Earth below in a rainbow of colours. They use tiny ice crystals to diffuse and reflect the light, creating wonderful spectrum effects. Nacreous clouds don’t show up very often, and they never book in advance – so count yourself very lucky if you get to see them perform.
Sadly, we’re getting short of space, so though the clouds we’ve met have many relatives and friends, we’re going to have to leave it there, at least for now. These are some of the more regular visitors; most of whom really don’t aim to cause you any particular problems. They’re just doing their thing, you know?
There is one word of caution I ought to offer you, though. There’s one which… Well, it’s a bit big, and it has a lot of energy, and it pays not to get on the wrong side of it. It’s not what you’d call a ‘people’ cloud. I mentioned it earlier on, and it’s called cumulonimbus. You’ll recognise it when you see it: it’s quite rare to get the full view of its magnificent form, but if you ever see a very very tall cloud, maybe far off in the distance, with a big, swept-forward flat ‘platform’ on the top, that’s cumulonimbus:
And it’s probably best if you do keep it at a distance, too. If it gets up close to you, it’ll throw water down on you in sheets and buckets; and it’ll stab at you with lightning; and it’ll shout and roar. Occasionally it can do really serious damage; and if you’re flying a plane, then you don’t want to mess with cumulonimbus. Sedate as the cloud may look from a distance, the howling, shrieking winds inside that column and base are so vicious they could quite easily pull an aeroplane to pieces. But give it its space, and you can’t help but be impressed.
I hope you’ve enjoyed meeting some of our vapourous visitors; before too long I’ll introduce some of their more spectacular, and harder to find, relatives.
* Which, as you can see, I’m spending sitting in front of a computer. But if you know me, well, you expected no different, am I right?