The Wild and Windy Tale

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Speaker 1 I'm Dr. Adam Rutherford.

Speaker 4 And I'm Dr.

Speaker 6 Hannah Fry.

Speaker 1 And you are going to send us your everyday mysteries.

Speaker 7 And we are going to investigate them.

Speaker 5 Using the power of science.

Speaker 6 Science. Science.

Speaker 1 I like it.

Speaker 1 Okay, hello, Curios. Now, this was an extremely difficult programme for me specifically to record, partially because it included some quite serious maths, and Hannah was very gleeful about that.

Speaker 9 I mean, I do have a bit of a head start when I've got a PhD in fluid dynamics, don't I?

Speaker 1 Which is effectively what this programme was about. And what our two guests also had a PhD in fluid dynamics.

Speaker 4 I had a great time. Yep, yep, yep, yep.

Speaker 1 But it was also extremely difficult for reasons that will become apparent in your first sentence. So here you go.

Speaker 11 Question, my curious friend.

Speaker 12 What are chinooks, haboobs, and willy-willies?

Speaker 1 Well, I think you know me well enough to recognize that I am not nearly mature enough to even attempt to answer that.

Speaker 14 I think I do know that, but they're all mighty winds, you childish plum.

Speaker 10 Now, today's question comes from Georgina, who is on the Isle of Wight, and they ask, I've often wondered where and how winds, be they gentle breezes or storms, storms, start and why or not do they stop?

Speaker 1 And a second question we had in from Chris Elshaw from Headley Down. Why isn't there a smooth transition of air between high pressure and low pressure areas?

Speaker 1 There don't seem to be any obstructions to the flow of air, so why are there periods of calm followed by explosive periods of airflow and 80 mile gusts in winds? Hannah, you look excited.

Speaker 8 I am.

Speaker 4 It's because it's all maths. Yes.

Speaker 1 Now, I fear that I have little to contribute to this conversation except pop culture references and maybe the occasional windy gag.

Speaker 7 Please don't.

Speaker 14 Leave room for the maths to shine for once.

Speaker 1 Now we have two guests in the studio to help us. Professor Liz Bentley, a meteorologist at the University of Reading and chief executive of the Royal Meteorological Society.
Hello Liz.

Speaker 18 Hi.

Speaker 17 And Dr. Simon Clarke, science YouTuber and author of a book on the hidden science of weather.

Speaker 4 Hello.

Speaker 19 Okay well Simon and Liz, I think you are going to have to help me keep Adam in check on this particular episode.

Speaker 1 Great, because I am radically outnumbered by mathematicians. So you three have to convince me what has the weather got to do with maths.

Speaker 19 I'm going to hand over straight to Simon actually.

Speaker 15 Listen, why is this math, Simon?

Speaker 5 Oh, this is maths because the weather is an application of physics at the end of the day.

Speaker 5 It is an example of a fluid flow, and the way that we describe fluid flow, as much as we describe all the physics, is with mathematics.

Speaker 1 Okay, it is my role in this program to ask stupid questions, but you've just described the atmosphere as being fluid. I think it's a gas.

Speaker 5 So, a gas is an example of a fluid.

Speaker 1 No, it's not, it's a gas.

Speaker 4 Those things are different.

Speaker 7 It's just got a different viscosity, Adam.

Speaker 20 That's all it is.

Speaker 1 Gas and fluid, they're interchangeable?

Speaker 6 Yeah, they behave.

Speaker 21 When you write down how they behave in equations,

Speaker 11 there is ultimately no difference apart from a couple of parameters here and there. Liz back me up on this.

Speaker 18 Yeah, absolutely. So we very much look at fluid dynamics when we model the atmosphere.
And you can see it.

Speaker 18 If you look at images of clouds moving, you know, low-level cloud in a valley, it has that fluid motion. So you can physically see it sometimes, you know, happening in the atmosphere.

Speaker 1 I mean, I'm considering that this is borderline institutional bullying here. I'm just

Speaker 1 ganging up on you. You're just outnumbering.

Speaker 6 Okay but you've seen weather reports right?

Speaker 13 You've seen maps of and charts of pressure and temperature and ultimately it does come down a lot to pressure here doesn't it Simon?

Speaker 5 Yeah the ultimate driver of wind is pressure or specifically actually gradients in pressure which is to say there's just more air in some places than there is in other places and the more there's more molecules of nitrogen and oxygen and that fundamentally is what drives all the complex weather that we see.

Speaker 1 Okay I follow you on on that. So and when we look at maps and when we see the weather on TV they talk about high pressure and low pressure.
Why is nice weather associated with high pressure?

Speaker 9 Well it's because PV equals NRT obviously.

Speaker 1 Simon, why is nice weather associated with high pressure?

Speaker 5 I'm somewhat with Hannah on this.

Speaker 1 Liz has got her hand up.

Speaker 4 She's waiting for me. I think Liz is better equipped to answer this.

Speaker 18 Okay so very simply when you've got low pressure the air is going up and when air goes up it gets cooled by the air above and it condenses into clouds and eventually into rain so you get unsettled weather because the air is going up in high in low pressure and in high pressure the air is going down and the air gets warmed as it descends and it dries and you so you lose rainfall you tend to lose cloud not all the time but typically lose cloud and so you get much more settled weather so air going up in low pressure air coming down in high pressure in a way I can see how that feels quite counterintuitive because when you look up and you see that there's clouds in the sky you might imagine that they're quite heavy and they're sort of weighing everything down, but actually, it's the other way around.

Speaker 18 It's the movement of the air coming down. So, high pressure is where you've got more air in the column of air above your head.

Speaker 18 And if you just think, typically, you would have about 10,000 kilograms of air sitting above you in a square meter that you're studying above your head.

Speaker 18 And higher pressure obviously means you've got a bit more air in that column and lower pressure, but it's that movement of air up and down that's actually leading to cloud and rain developing or the rainfall kind of suppressing and evaporating and the cloud dissipating as well.

Speaker 18 So it's the movement up and down really that's leading to the change in the weather.

Speaker 21 Tell me that again, how much air is above your head?

Speaker 18 So it's about 10,000 kilograms.

Speaker 25 That's an incredible number given that it doesn't, you don't, I mean you don't feel it at all.

Speaker 13 Simon, that's that really extraordinary idea. It took quite a long time for people to acknowledge that air has weight.

Speaker 5 Yeah, it was something that dates back to the ancient Greeks. So Empedocles was this philosopher who came up with this idea of four elements.

Speaker 5 So you have fire and water and earth and air, and fire and air were the two elements that had no weight to them.

Speaker 5 And this was something that was picked up by Aristotle when he wrote Meteorologica, which is the book that we get the word meteorology from, stuff to do with stuff in the sky.

Speaker 5 And he assumed that the air had no weight to it. And so that was the textbook, if you like, of meteorology that just carried forwards right up until the Renaissance.

Speaker 5 And it was only with experiments and the construction of the first barometer by Torricelli that we actually found that, you know what, air does have weight and the air pressure on the surface does in fact change.

Speaker 12 You know you can make a barometer yourself, Adam.

Speaker 1 I feel like this is a demonstration about to happen.

Speaker 4 It certainly is. Look,

Speaker 19 as if by magic, I happen to have a glass jar here.

Speaker 1 I mean, the listeners need to know that this is

Speaker 1 quite basic.

Speaker 1 Hannah's got a mason jar, a balloon, and a pair of chopsticks.

Speaker 26 Yeah, they're essential, those two.

Speaker 13 Okay, now, I need someone to hold the jar while I stretch this balloon over.

Speaker 4 Simon, would you mind doing that off here?

Speaker 17 Okay, so I have a balloon, and what I've done is I cut the bottom of the balloon off, so it's now sort of like a mini swimming cap.

Speaker 15 That's essentially what it's made into.

Speaker 24 And what I'm going to do is I'm just going to stretch that over.

Speaker 4 Twice

Speaker 15 satisfying.

Speaker 17 Over the top of this glass jar.

Speaker 4 It's made a small drum. It's made a small drum.

Speaker 17 Okay, so now this is sealed, right now at the moment because I've just put this on it's nice and flat because the pressure inside the jar and outside the jar is the same.

Speaker 17 But if I take a chopstick and I sellotape it just to the middle of this

Speaker 16 so that the center of the balloon in the middle of the jar the end of the chopstick is now sellotape to it at the moment because everything is equal this chopstick is laying perfectly horizontally

Speaker 16 but if the air pressure in the room was lower than the air pressure inside the jar jar, the balloon would start doming, at which point the chopsticks would point downwards.

Speaker 1 Yes, I'm following you like a panther. And Simon, this is something that was only relatively recently described.
I mean, since in the last few centuries.

Speaker 5 Yeah, so the first person to construct a barometer, certainly that we're aware of, was Evangelista Torricelli in the 1640s, who was a student of Galileo.

Speaker 5 And he was the first person to construct something like this with the assumption that he thought that maybe air did have weight.

Speaker 5 And the confirmation of that was actually provided by another great mathematician of the time, which was Blaise Pascal, which is of course where we get the unit of pressure, is Pascal's.

Speaker 5 And this happened because Torricelli communicated to Pascal how to build one of these things.

Speaker 5 And Pascal constructed this barometer, and he hypothesized that, well, if this is correct and air did in fact have mass to it, then if you go to the top of a mountain, there is less air above you than there is at sea level.

Speaker 5 So he wrote to his brother-in-law, who lived near a mountain called Puy de Domme in France because Pascal lived nowhere near any mountains and he described this is how you build a barometer and I want you to build it, take a measurement at the bottom, go up to the top and take another measurement.

Speaker 5 And a little while later, he had a letter back from his brother-in-law saying he had an amazing day out and he took the whole village with him, the vicar went with them and it was this delightful letter that sort of said, Yeah, you were right, it was and it had a great time doing it.

Speaker 1 That's how science should be conducted. We're far too bound to be.

Speaker 4 More jollies. Exactly.

Speaker 21 So if you took this up to the top of a mountain then, you would expect the balloon to start doming.

Speaker 5 And there is actually, to follow up on that, there's an easier way to do this, which is to take a packet of crisps up the top of a mountain.

Speaker 1 And they will expand. And they will expand.

Speaker 5 You'll find that they balloon at the top of a mountain.

Speaker 1 Like they do when they're on an aeroplane. Exactly.

Speaker 4 Exactly right.

Speaker 1 I'm getting this.

Speaker 1 I understand the idea that air can act as a fluid and it has a weight.

Speaker 8 Okay, but I mean, sure, but how is that helping

Speaker 1 understand the flow, the sort of lateral, I'm trying to imagine what causes the lateral flow of the fluid.

Speaker 11 Okay, so there's an imaginary experiment that

Speaker 12 you can think about with this.

Speaker 22 So I want you to to imagine that you've got a fish tank and it's really long, like a couple of meters long,

Speaker 25 and you get some stones and you put them in the oven, get them really hot, and cover them in red dye, and you plonk them down one end of your fish tank.

Speaker 13 And meanwhile, you get some stones and you cover them in blue dye, and you chick them in your freezer, get them really, really cold, and you put them in down the other end of the fish tank.

Speaker 16 So, hot red stones on one side, cold blue stones on the other.

Speaker 13 The water was before you put the stones in the same temperature throughout.

Speaker 14 But what do you imagine will happen to the dye?

Speaker 24 How will it spread through the tank?

Speaker 1 Okay, I mean

Speaker 1 I'm sort of thinking about what's going to happen to the fish, but that's not what you're asking me that I've got a lot of boiled fish.

Speaker 1 Yeah, sure. Let me think.
So the hot, so the red dye is going to come off the hot stones and it's going to

Speaker 4 rise. Yep.
Right?

Speaker 1 Right. And so it's going to go to the top.
And the opposite happens with the blue dye, which is going to sink to the bottom.

Speaker 1 Okay, so

Speaker 1 you get like a conveyor belt.

Speaker 26 Yeah, well, yeah, so exactly.

Speaker 16 So the top starts moving along towards the coal end and the bottom starts moving along towards the warm end and you end up with these two channels, hot on the top and cold on the bottom.

Speaker 1 I see.

Speaker 26 But this isn't just an imaginary experiment, is it Liz?

Speaker 18 Yeah, so this is how the atmosphere works. But so let's look at it on different scales.
You can have this happening in quite a small scale along a coast where we get sea breezes.

Speaker 18 So imagine those hot stones that we talked about in the fish tank.

Speaker 18 That's the land heating up much quicker on a hot summer's day compared to the sea, which are the cold blue stones in the fish tank that don't warm up as quickly.

Speaker 18 So you get this temperature difference. And over the land that's heating up much quicker, the air starts to rise.
As that air moves up, it has to be replaced by something else.

Speaker 18 So it brings the air in, the cooler air from the ocean. But eventually, you get this circulation going, a whole circulation.

Speaker 18 Air goes up over the land, moves out towards the sea, sinks over the sea, and comes in. And it's at the surface, you get that sea breeze.
And that's on a relatively small scale.

Speaker 18 But this can happen on a global scale, where you have a greater amount of heat at the equator because the sun's concentration is greater, compared to, say, the polar regions, which gets less concentration of sun and therefore less heat.

Speaker 18 And so you get that huge circulation, basically a sea breeze, but happening on a global scale, where the air from the equator will rise upwards, head towards the poles, sink, and then come back towards the equator.

Speaker 18 And if you didn't have a spinning rotation of the Earth, that's effectively what you would have happening in the atmosphere.

Speaker 1 That's a brilliant explanation and I think the fish tank analogy is quite useful for idiots like me.

Speaker 1 But Simon, you know, the Earth is a really complex place and it's not a fish tank, it's not a controlled environment. So how do you actually model

Speaker 1 something which is based on something that's very simple to understand, but is in fact a hugely dynamic system?

Speaker 5 Well, I actually would challenge whether it's simple to understand or not.

Speaker 5 I think that one of the problems with atmospheric science is that actually you do have all of these components, that you can't take any one of these components out in order to understand it.

Speaker 5 You have to have the planet be rotating, you have to have the insulation being greater at the equator, having more energy coming in at the equator. You have to have the fluid mechanics.

Speaker 5 It's one of these things that one of the reasons we didn't understand it for so long is because it is a really hard concept to wrap your head around.

Speaker 5 So, you know, the first attempts to really describe this global flow of air came as late as the 19th century, really.

Speaker 5 People like Will Farrell in America, not the actor, very similar name, but it's where I go.

Speaker 4 I did go there immediately.

Speaker 1 Yeah, thank you for clarifying.

Speaker 5 He, just as a very brief aside, he was an amazing character.

Speaker 5 He grew up on a farm and basically educated himself entirely and got to the point where he could start to teach younger children and then used money from that to buy books from neighbor towns to eventually pay for going to college and then eventually found basically founded sort of the field of geophysical fluid dynamics.

Speaker 27 And then did Ancherman.

Speaker 7 And then did Ancherman.

Speaker 5 It was an extraordinary career pivot late in the day.

Speaker 26 Okay, where we are so far then, Adam.

Speaker 16 We've got the sun, which is heating up different bits of the earth, bits of land, bits of water, columns of air.

Speaker 15 And that means that you end up with some areas of high pressure, some areas of low pressure, and air flows from high pressure to low pressure, hence wind.

Speaker 1 Okay,

Speaker 1 I'm totally on board with this.

Speaker 1 But going back to the tank analogy, the water circulates as a result of having hot and cold in one direction, but there's also another big factor which is really striking for the planet, which is that it's spinning.

Speaker 29 Yeah, you got to put

Speaker 14 the tank of water on a merry-go-round.

Speaker 1 Right, which is going to complicate things. So, Liz, how does the spinning Earth make a difference?

Speaker 18 So, this is where it gets now quite complicated because we have something called an apparent force that acts upon parcels of air that move around, and that's called the Coriolis force.

Speaker 18 The Coriolis force, I think, is very hard to explain, and I've seen a lot of scientists have a good old go at this over the years, some of them doing better than others.

Speaker 1 I've got three of you.

Speaker 4 Well, I have three goes. So, we've got three chances.

Speaker 4 Three strokes.

Speaker 18 You go first, please. The first thing to understand is that at different points on the Earth, you will be moving faster because of the rotation of the Earth.
So, imagine you're stood at the equator.

Speaker 18 The Earth spins on its axis a whole revolution in 24 hours. So, that's about 40,000 kilometers.
That if you were stood on the equator, you would move.

Speaker 18 So, you are moving at about 1,600 kilometers per hour. And you are moving that fast, the land is moving that fast, and the air around you is moving that fast.

Speaker 18 If you're at the pole, you don't have any speed at all. Basically, all that happens is you spin on the spot at the axis,

Speaker 18 at the pole, north or south pole. So you turn 360 degrees in 24 hours, but you don't have any speed.
You don't move anywhere. And then in between, it varies.
So imagine now if you're on the equator.

Speaker 18 So I want everybody to use their hands. Their left hand is going to be the surface of the earth and the right hand is going to be the air above.

Speaker 18 So now your hands are at the equator and they're going to move, rotate with the earth. So as the earth moves, the land moves at 1600 kilometers per hour and so does the air

Speaker 4 and they stay together.

Speaker 1 We are all doing this now.

Speaker 5 It's like we're waving our hands at a concert. Yeah.

Speaker 4 It does. It's a bit more common-wise, but keep going.

Speaker 18 So if the air just stayed at the equator, it doesn't have any Coriolis force. It doesn't turn, it just moves in that direction at that speed.

Speaker 18 So now what I want you to do is take your left hand and pretend it's moved about 30 degrees north towards the pole.

Speaker 18 And the air that was at the equator moving at about 1600 kilometers per hour is now going to move north. Okay, so it's moving fast as it was before from left to right,

Speaker 18 but your left hand is moving slower because it's the ground a bit closer to the pole. Are we all following this?

Speaker 18 So I'm now going to move them both, but my right hand is going to be moving faster than my left hand. So my right hand is moving towards the pole, but it's faster than my left hand.

Speaker 18 So it's going to, and you get this relative that it's turning to the right. So the air feels like it's turning to the right compared to the ground.

Speaker 1 It looks like you're doing Tai Chi, but I appreciate it. And I think Hannah wants to go next.

Speaker 8 She's cracking the fingers. She's flexing.

Speaker 7 She's ready for it. Well, so

Speaker 15 this is the reason why hurricanes end up spiraling, right?

Speaker 19 And spiral in different directions in the northern and southern hemispheres.

Speaker 14 I mean, of course, mine's a demo.

Speaker 4 Of course it is. She's got kits.
I've got kits.

Speaker 14 Okay, I'm coming around to you.

Speaker 16 I've got a lazy Susan.

Speaker 20 Right.

Speaker 4 I've got a clipboard and some paper.

Speaker 4 It's like Blue Peter here.

Speaker 11 Except this is not one that I made earlier.

Speaker 25 I'm making it live.

Speaker 10 Okay, hold on.

Speaker 12 Now, I want you to imagine that you are, you're in space, you're floating above the earth, and you're looking down on the planet, okay?

Speaker 16 And you're going to be the wind.

Speaker 24 So hold the pen, you're going to be the wind.

Speaker 16 Now, at the moment, you can just see a clipboard with a piece of paper on top.

Speaker 16 But you and I know that this is a clipboard that can spin quite easily.

Speaker 6 Okay, but what I want you to do is I want you to imagine you can start at the bottom of the clipboard.

Speaker 14 I just want you to draw a straight line.

Speaker 16 Okay, so just draw a straight line towards you and don't be distracted by the fact that I'm going to turn it, okay?

Speaker 19 So just a completely straight line and remove this so I can actually turn it.

Speaker 4 There you go.

Speaker 21 And what happened?

Speaker 12 It's a curvy line.

Speaker 14 Yeah, okay, now let's do it again, but this time I'm going to curve it in the other way around.

Speaker 4 Okay. Ready? Yeah.

Speaker 7 Yes.

Speaker 10 So if you turn it one way, then it curves one way.

Speaker 26 And if you turn it the other way, it curves the other way.

Speaker 12 So that is essentially like you are sitting above the earth, looking at the earth spinning, or you're sitting beneath the earth and the earth spinning.

Speaker 23 And so even though you are the wind blowing effectively in a straight line,

Speaker 26 Because the earth is spinning, it ends up appearing as though it's bending.

Speaker 15 To summarise, though, you've got it that in the northern hemisphere, storms always spiral counterclockwise, and in the southern hemisphere, they always spiral clockwise.

Speaker 11 Simon, anything to add?

Speaker 5 The thing about storms as we think of them in the mid-latitude regions is they are just an area of low pressure, and rather than the air falling into it, which is sort of what you'd naively expect, if there's an area of low pressure surrounded by high pressure, the air should just fall down into it, and if you like, plug that hole.

Speaker 5 And because of the Coriolis effect, the air spins around the area of low pressure as it falls in, which is why it's a different direction in the northern and southern hemisphere because the Coriolis effect acts in a different direction.

Speaker 1 This is brilliant. I mean, I feel like I've got personal tutorials for sort of GCSE-level explanations for this.

Speaker 4 No, this, I mean, Coriolis, this is pretty hard. This is pretty hard.

Speaker 5 This wasn't discovered until 1835. Like, this is a relatively recent thing.

Speaker 1 And it wasn't discovered by me until 2022.

Speaker 1 I've got a related but different question, just thinking about this. What you just described makes perfect sense with your three analogies.

Speaker 1 Tai Chi, you were Muscle Ninja and you were drawing on a piece of paper.

Speaker 4 I'll take it.

Speaker 1 But

Speaker 1 when we look at weather maps and when we see localised weather and we see high pressure and low pressure areas,

Speaker 1 they're much more localised than this. You know, it can be hot in South London and rainy

Speaker 1 in Huddersfield.

Speaker 1 They're much more localised differences in high and low pressure. So

Speaker 1 what causes those localised pressure effects?

Speaker 18 The sea breeze, again, we can come back to that example. So, you know, it's very localised.

Speaker 18 You can get heating of the land near the coast compared to just off, say, in the across the south coast, just into the English Channel.

Speaker 18 It might just be a few miles between the heat of the land and the cooler sea. And you get that difference in pressure.

Speaker 5 If I could just add on to that as well, I think the atmosphere isn't heated by the sun. You need to get rid of that idea.
The atmosphere is heated by the ground.

Speaker 5 Apart from a few exceptions, there's not very much in the atmosphere that actually cares about what the sun is doing.

Speaker 5 So differences in what is happening underneath the atmosphere, whether whether that's land or ocean or desert or forest or whatever it is, that's what fundamentally drives an awful lot of that small scale stuff.

Speaker 5 So you've got the large scale planetary wide fluid system, but then it's being forced on a much smaller scale by these local effects that really do stack up into this, into the beautifully complex system that we see.

Speaker 17 This calls to mind one part of Chris's question about why isn't there this smooth transition of air between high pressure and low pressure areas?

Speaker 21 Why, I mean, there don't seem to be these obstructions to the flow of air.

Speaker 18 So there are obstructions.

Speaker 18 So again if the surface was completely smooth and similar, so if you put a mountain in the way you'll you'll squeeze the air over the top of the mountain and that speeds it up.

Speaker 18 If you put a building in the way it has to go round it and again you'll get these kind of funnel corridors of wind.

Speaker 18 So any sort of obstruction, any sort of change of kind of land surface will change the wind speed.

Speaker 19 So those are all the major forces then that drive the wind.

Speaker 19 You've got the sun causing these pressure differences, which makes the airflow over the surface of a spinning globe, which makes pressure systems swirl and spin.

Speaker 19 But there are winds which occur in particular areas as a result of much more local conditions.

Speaker 23 And these are winds that have particular names.

Speaker 1 Okay, so these are the chinooks and the haboobs and the willy-willies.

Speaker 16 Yes, but you don't need to be quite so gleeful about it.

Speaker 28 I mean, if you say so.

Speaker 1 Setting aside my extreme juvenile tendencies, Liz,

Speaker 1 what are those examples of specific

Speaker 1 wind systems?

Speaker 18 Yeah, so often winds are given names locally. So they're often given for the place they happen in, or they're given a certain name because of the country they're in and the language of that country.

Speaker 18 So let's start with a willy-willy. This was named in Australia.
And this is just what we would call generally as a dust devil.

Speaker 18 So you get the air heats at the ground, it rises, but you get that circulation happening on a really small scale. So it's

Speaker 18 a bit like a kind of mini-spinning vortex, and they pick up dust from the ground, hence dust devil. And in certain parts of the world, they're given different names.

Speaker 1 Well, what about the others, the Chinooks and the Haboobs?

Speaker 18 Haboob is a big dust storm. So, this is a surface wind that moves, again, would be moving from high pressure to low pressure, but it picks up a huge amount of dust.

Speaker 18 So, you'll have seen pictures of this. There's a wall of dust coming towards you.

Speaker 18 It might be, you know, four or five kilometers deep, and it's, you know, I don't know, four or five kilometres wide, and it's penetrating. And if you're in it, visibility just drops to zero.

Speaker 18 They're the same systems, they just get given different names depending on where you are in the world.

Speaker 23 Talk to me about the trade winds, then, Simon.

Speaker 5 So, the trade winds are a much bigger scale phenomenon, and they're more or less a permanent feature of the tropical atmosphere.

Speaker 5 So, we actually already discussed how they form earlier, because they're effectively a result of the Coriolis force, the deflection.

Speaker 5 So, what we have over the tropics is lots and lots of sunlight, which heats up the air and it it shoots up full of beans and it reaches the top of the troposphere, so the top of the bottom part of the atmosphere.

Speaker 5 And then they have to spread out and they can't go any higher up and so they move towards the poles.

Speaker 5 Eventually they'll descend and return back to fill in the gap that was left, that layer of low pressure caused by air rising from all that sunlight hitting the tropics.

Speaker 5 And in so doing they are deflected and they'll be deflected moving from east to west.

Speaker 5 And so what you end up with is this really quite narrow band of fast moving wind that we call the trade winds because it's had a very significant effect on human history.

Speaker 5 These are the winds that took Europeans in the 16th century across to the Americas and basically changed all of world geopolitics.

Speaker 5 And ever since, and this is also not just Europe to America, it's also in the Indian Ocean basin as well.

Speaker 5 A key part of how trade has been done historically.

Speaker 26 What I think is quite intriguing about what you said there, Simon, is this idea that wind could be a permanent fixture of a particular place.

Speaker 4 And of course, we know that there are certain parts of the earth that are naturally windier than others.

Speaker 14 And in fact, the windiest place on earth is a coastline where Antarctica meets the southern ocean.

Speaker 16 And for this, we spoke to Professor John Turner, he's a researcher with the British Antarctic Survey, about what it is around the structure and the conditions of this area that make it so incredibly windy, and also what it's like to be stuck in a tent for days during an Antarctic blizzard.

Speaker 30 Antarctica is over four kilometers high in the middle and during the winter there is no energy coming in from the sun.

Speaker 30 South Pole has six months of darkness so it gets intensely cold up on the plateau and their temperatures can fall to minus 50 or minus 60 and so the air becomes very dense.

Speaker 30 Gravity starts to pull it down to the edge of the continent.

Speaker 30 So it moves very very slowly on a gentle slope initially but then then at the edges of the Antarctic the glacial valleys are very very steep and so the air drifts into these valleys and then really accelerates intensely as a dense current of air out onto the ocean around Antarctica.

Speaker 30 In the deep field you live in tents, very strong tents obviously, because the winds can get up very rapidly to quite high levels. And so people often get stuck in field camps for days on end.

Speaker 30 And I've been stuck in the middle of nowhere. And in the most severe conditions, you can't get out of your tent.
Everything you cook, you have to live inside a tent because it is just so dangerous.

Speaker 30 You have to wait for the plane when planes can get in. We have two people per tent usually with boxes of fuel and food in between them.

Speaker 30 And you have to survive for days.

Speaker 30 Well, I mean, that sounds just awful.

Speaker 1 Liz, help us unpack

Speaker 1 the windiness of that situation. So it's a similar phenomenon as to the localised ones that we've been talking, but just a sort of extreme version of that.

Speaker 18 Yeah, that's right. It's because of the really low temperatures in the Antarctic, and that makes the air extremely dense.

Speaker 18 And therefore, when it reaches the edge of the kind of land into ocean mass or ice into ocean, it descends very quickly. It moves very quickly because it's extremely dense air.

Speaker 12 In conclusion, quite a lot more complicated than a fish tank.

Speaker 12 It's fair to say.

Speaker 15 Well, I should thank our guests in the studio today, Professor Liz Bentley and Dr.

Speaker 19 Simon Clarke.

Speaker 1 So, Dr. Fry, when it comes to the question of what makes it a breeze, a gust or a gale, was the answer blowing in the wind?

Speaker 8 Only if you haven't been listening, Dr.

Speaker 14 Rutherford.

Speaker 1 Well, it's maths, isn't it? The sun heats up the ground, which heats up the atmosphere, in turn lowering air pressure, and the need for pressure to equalize causes wind.

Speaker 4 Not bad, go on.

Speaker 1 And because the Earth is spinning, the winds bend in different directions in the northern and southern hemispheres thanks to the Coriolis effect. Good.

Speaker 1 And trade winds have fundamentally shaped how civilization has unfolded.

Speaker 15 I'm so impressed. Anything else?

Speaker 1 Yes, haboobs and willy-willies are very funny.

Speaker 11 And now you understand all of meteorology.

Speaker 8 Thank you.

Speaker 1 How many haboobs and willy-willies are we allowed in one half-hour BBC BBC Radio 4 programme?

Speaker 19 I'm not sure I need to call the editor and just to make sure that we don't use too many haboobs and willy-willies.

Speaker 1 I mean, there is actually a quota system, isn't there, for vaguely rude words.

Speaker 19 I seem to remember once, actually, we got some feedback on a script and it was like, you can have three boobs and one nipple.

Speaker 4 Do you remember that?

Speaker 4 It was a few years ago.

Speaker 4 I have no idea.

Speaker 22 I have no recollection of what the episode was about.

Speaker 1 No, but it was about an episode and not about our physical presence in the studio, because that would be super weird. I mean, we're not judging.

Speaker 4 You know,

Speaker 4 yeah.

Speaker 7 You know, one thing about Willy Willy,

Speaker 12 they're smaller in winter.

Speaker 1 See, you know, in that recording, I was all sort of juvenile, and you were like, oh, this is very mature science, but actually, you're sitting there giggling.

Speaker 15 We all know that the 58008 in a previous episode was me, not Adam.

Speaker 28 Yeah, but no one on Twitter recognised that.

Speaker 1 They were like, oh, you're such a child. And Hannah's a very clever mathematician professor, and you're such a child.

Speaker 28 She wrote that joke.

Speaker 4 It's true.

Speaker 27 But I think that actually i've sort of reached you know a kind of level of nirvana now where i can do whatever i want and you take the blame for it

Speaker 8 okay should we do curio of the week let's do the week can i tell you just one thing oh yeah that idea about there being

Speaker 24 fixed winds as it were so certain places which are notoriously windy

Speaker 26 there's um a little uh place in south of england where um

Speaker 20 there are hills and cliffs and as the wind goes up over them it creates the perfect conditions for paragliding.

Speaker 29 And in fact, I have been paragliding in those conditions, and it was terrifying.

Speaker 1 I would not naturally put you in the category of extreme sports enthusiast.

Speaker 19 So, it was tandem, to be fair, and it was for a TV programme, obviously, as all of my experiences outside of sitting in a room with some chalk and then writing equations on a wall are all to do with TV.

Speaker 1 There was a point when I was doing TV a lot a few years ago when I came to the conclusion that the only reason to do TV was you get to do stupid things

Speaker 1 that you don't get to do in the real world.

Speaker 20 Obviously, very soon I'm flying to Japan to go and look at a lake of xenon where they're trying to find dark matter on Earth.

Speaker 4 I mean, who doesn't want to do that? I do want to do that.

Speaker 14 Okay, wait, let me tell you about the paragliding though, because I was there on the same day when there were loads of novices who were learning how to paraglide.

Speaker 21 Slightly chuckling, possibly shouldn't.

Speaker 15 But learning how to paraglide for the first time.

Speaker 14 And what they would do is they would like, they'd learn how to pull the ropes and stuff and do little bunny hops and like little tiny jumps.

Speaker 27 And then I was there for when they took their first solo flight, these absolute newbies took their first solo flight and had to run down a hillside and then jump and then take off and then land in the valley below.

Speaker 29 And quite a lot of them did quite well.

Speaker 19 It was very good.

Speaker 13 But there was one

Speaker 7 person there,

Speaker 10 one middle-aged man who took off and then I think got a bit freaked out or something and didn't know which chord to pull.

Speaker 15 And everyone was just just on the ground shouting at them as they just floated off into the air.

Speaker 1 And he has never returned.

Speaker 10 I think he was fine. But anyway, very brave.

Speaker 15 Solo paragliding flight for your first time.

Speaker 4 Incredible. What programme was that?

Speaker 4 They all blend into one after a while.

Speaker 23 I do like the

Speaker 1 stupid stuff that we get asked to do on TV. Like, I mean,

Speaker 1 I deliberately burnt my arm and have a permanent scar as a result of that. I can't remember if I told this story or not, but I think it's worth recounting because enough distance has passed.

Speaker 1 We were doing a wound healing section where I burnt myself, which is a remarkably hard thing to do. So I burnt myself on the inside of my forearm and then

Speaker 1 with a spoon. So I heated up a spoon on a Bunsen burner and then and just sort of burnt myself.
And, you know, we'd done all the health and safety checks and all,

Speaker 1 and I said about 18 times, please do not try this at home. This is an extremely foolish thing to do.

Speaker 1 Anyway, the point was we were doing a time-lapse on wound healing and showing how cells regenerate and how they regenerate the same tissue over, which is quite an almost magical thing that you don't grow back lumpy and disformed.

Speaker 1 Our cells replace themselves. Anyway, one of the

Speaker 1 junior researcher on this trip, on this filming trip, which lasted about three weeks in America, had the job of taking a still photo, a couple of still photos, one in the morning, one in the evening.

Speaker 1 But the scab fell off after about three days. And I'm sorry to say, we slightly faked it.

Speaker 1 And we faked it because this junior junior researcher had to carry around my scab in a matchbox for three weeks.

Speaker 1 And

Speaker 1 every day we'd stick it back on again and take a photo.

Speaker 15 It's absolutely disgusting, but it's not the most disgusting story you've told me about you and filming.

Speaker 7 So, um, but anyway, let's let's save our listeners from that.

Speaker 15 Should we do a cure of the week?

Speaker 4 I think we probably should.

Speaker 4 Rutherford and Fries, Curio of the Week.

Speaker 1 This comes from Lucy Gleave, a 15-year-old from Bath. Now, having been an avid curio since the year 1PP, brackets, pre-pandemic.

Speaker 4 I like that. It's a new

Speaker 4 CCE.

Speaker 1 Let's do PP. I mean, isn't it just before times? So, what is one? One PP is like 2019, is it?

Speaker 4 Yeah. Right.
Yeah. Yeah.

Speaker 1 So she's not been there.

Speaker 8 She's not there since the beginning.

Speaker 19 You can't go post-pandemic because that's also PP.

Speaker 22 It should be BP.

Speaker 1 Okay, well, Lucy, we'll work on this.

Speaker 1 We approve of the introduction of a new chronology, but it needs some work. That isn't the letter.

Speaker 1 I've become quite accustomed to your moustache-clad complexions that feature on the thumbnails of your podcasts.

Speaker 6 Or used to before we got rid of them for this series.

Speaker 1 Oh, have we? Yeah, we have. Oh, I haven't noticed that.

Speaker 19 Yeah, I'm just getting it on tape so that we have to.

Speaker 4 Oh, yes, a good point. Yes.

Speaker 1 Little did I know, says Lucy, you present a very different appearance to the wider non-curio masses. Oh, a year ago, I spotted Hannah Fry on a BBC documentary and was shocked to discover

Speaker 1 I'm gonna add a lip here that she doesn't have a moustache.

Speaker 1 No, what Lucy said is she decided against sporting facial hair for the for the occasion.

Speaker 9 It was a one-off.

Speaker 15 I um I just decided it was a special occasion, so I decided to take it off or to put it on? Just to not wear it for that day.

Speaker 10 Yeah.

Speaker 1 I mean, she has Lucy has identified correctly that the moustaches are only

Speaker 1 done for that one photo shoot. And what was the reasoning behind it?

Speaker 25 Sherlock, something.

Speaker 1 Sherlockian. I don't think he even had a moustache.
We had a pipe.

Speaker 11 I remember you with a pipe.

Speaker 1 That was because I was just smoking a pipe those days.

Speaker 6 I don't, I still love those photographs.

Speaker 4 I think they're absolutely great.

Speaker 1 I think we did it because we thought it was funny and for no other reason.

Speaker 4 I mean, it was. And

Speaker 1 it was funny. Anyway, she goes on to say that she felt saddened, Hannah, that you chose to represent mathematics and withhold such mustachio pleasure from the wider world.

Speaker 1 So she's attached a repertoire of moustaches for both of us

Speaker 1 that we may don if we ever feel the need to appear on Horizon.

Speaker 15 With a moustache ever again.

Speaker 17 You know what, though? There's not just one type of moustache.

Speaker 21 There's not just two types.

Speaker 19 There's six different types of moustache here.

Speaker 13 We've got the quirly twiddly one where clearly

Speaker 27 you spend quite a lot of time twisting the ends I would describe that as evil Victorian scientist lovely we've got the full bearded one that makes you look like you're called Bernard

Speaker 10 yeah or a Stephen Fry character yes absolutely absolutely we've got the like tiny little Italian waiter one yeah and then top left that's a sort of

Speaker 1 Restoration Charles II

Speaker 29 style nice little pointy jazz beard going on in there absolutely and slightly droopy one and then bottom left, there's the sort of one that you regularly see around Dalston.

Speaker 1 They're all pretty East London at the moment. There's a sort of Poirot one going on there as well.

Speaker 4 Is it excellent?

Speaker 1 If you were going to choose one, Hannah, which would be your tash of choice?

Speaker 25 I think bottom left, you know.

Speaker 1 And is the rule, and this is a question for Lucy, really, is the rule that we both have to be sporting the same facial hair?

Speaker 4 Absolutely. Oh, really? At all times, yeah.

Speaker 25 At all times.

Speaker 13 And as you'll see, you've chosen to wear a full beard today.

Speaker 12 And I'm sticking to the rules.

Speaker 1 Can I tell you a quick story about beards?

Speaker 1 I play in a cricket team, and a few years ago on tour, we decided that the theme for the tour would be facial hair.

Speaker 1 So we spent six weeks growing our beards, and then the night before our first match, we drew out of a hat different moustache and facial hair styles.

Speaker 1 And

Speaker 1 it was ridiculous, obviously, because we turned up for a match where we got thoroughly and soundly beaten by a much, much stronger team and included the ignominy of having ridiculous facial hair.

Speaker 1 I got sort of 70s rock priest.

Speaker 28 Sure.

Speaker 1 Was the theme. One of my team members had just chin beard.

Speaker 4 Sure.

Speaker 1 One of them had a pointy moustache. One of them had big sideburns, no, no beard.

Speaker 4 Can I see photographic evidence?

Speaker 1 I have photographic evidence, and it's not for public consumption, but I'll show you.

Speaker 21 Something to look forward to.

Speaker 1 We had a woman playing for us at the time as well. She didn't grow any facial hair, but she didn't grow, she did grow underarm hair for the six weeks.

Speaker 1 And then in the club night, she had to to dance with her arms up in the back.

Speaker 4 That was one story too far. Thank you very much Adam.

Speaker 7 That is the end of this episode. We'll see you next week.

Speaker 15 Send us in your questions. Send us in your curie of the week.

Speaker 4 Send us in your stories about anything other than armpit hair if you could.

Speaker 7 Curious cases at bbc.co.uk. See you next week.

Speaker 28 I'm Gus Casely Hayford. As a historian I love to unpick the hidden histories behind what we wear.
In my series Torn for BBC Radio 4, we hear about the fashion items that have changed the world.

Speaker 31 From the humble tote bag, the heavy textile dating from late 17th century and it is quite like a modern tote bag with a beautiful pattern of crisscross and flowers and just two elongated handles.

Speaker 1 To the mini skirt.

Speaker 32 There were other possibilities in the air and the mini skirt was the beginning of saying we are somebody different.

Speaker 1 That's Torn from BBC Radio 4.

Speaker 28 Listen to stories that are woven into the fashion items in your wardrobe.

Speaker 1 Subscribe now on BBC Sounds.

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