Why do clouds move?

05 December 2017

Question

My name’s Anya and I’m in Year 5. Why do I see the clouds moving? Are they moving because of the spinning of Earth or due of wind?

Answer

One of the youngest listeners of The Naked Scientists put this question to Chris Smith and the panel. Chemist Phillip Broadwith and Physicist Matt Middleton floated upon an answer... 

Phillip - I’d say Anya, there’s a little bit of both of those things happening. The spin of the Earth does have an effect, but the biggest effect is probably the wind. But the interesting thing is that the wind at high altitudes where the clouds are can be totally different to the wind at the surface where you’re standing, which is why you might sometimes see the clouds going one way and feel the wind blowing the other way.

Chris - Everything’s spinning in the universe, isn’t it Matt? Pretty much everything is spinning

Matt - Yeah. Angular momentum is everywhere. Look at the formation of the solar system from a big ball of gas and dust and it was rotating, and that’s why the planets now rotate.

Chris - That’s where I was going with that point that the Earth is turning, but why is the Earth turning as are the other planets in our solar system, it’s because they had spin to start with?

Matt - Absolutely. They’ve from a protoplanetary disc, so it was rotating and it was collapsing down and condensing and angular momentum is a conserved quantity. So the final product was also spinning because it couldn’t get rid of that energy, it couldn’t get rid of that rotation. Absolutely, this is why they’re spinning.

Chris - I was watching a stunning documentary on the channel BBC4 the other day about the Voyagers because it’s 40, it’s 40 years since the Voyager probes were launched. And one of the commentators on that programme pointed out that they’re making a 250 million year orbit of the galaxy, and when you think of it like that they're actually circuiting all the way round the galaxy, round the central black hole in our galaxy every 250 million years. I think it’s 250 million?

Matt - Something incredible number.

Chris - An incredible distance, isn’t it.

Matt - Yeah.

Chris - Thank you for that. Coming back to Anya’s question: the air is spinning therefore the air is moving, and the air is also moving in random directions because there’s additional air movements and input from the Sun.

Phillip - Yeah. The wind comes from - the Sun heats up the land, and over the water you get convection which is air heats up, it gets lighter, it moves up, but then you have to have more cold air coming in underneath to replace it. So that starts the whole thing moving and that’s where the wind comes from. But wind’s really important because it picks up moisture which is where the clouds come from. The whole atmospheric chemistry and physics of that system is important but also intriguing.

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