Yes, we’re still talking about the weather
Good day to you my Alien friends! Are we ready to talk about the weather? Yes, I know it’s taking me forever to get to it, but you’d be surprised how much we’ve already talked about it. Yes, especially when we were talking about Dr. Ryan Stone, Aristotle and Galileo.
Right, what are prevailing winds and why do they blow the way they do?
It’s difficult to understand things we can’t see, hear, feel, touch and taste
I’d like you to imagine something. Imagine a giant circular tube, like one of those rubber rings that you can play with in the water. Now imagine this giant circular tube sitting around the earth’s belly, on the earth’s equator. Now imagine two of them, one sitting just above the equator on the northern hemisphere, and another just below on the southern hemisphere. Now imagine these tubes are full of air swirling around inside them.
You’re getting a headache? I’m not surprised. We humans and aliens find it difficult to understand things in the physical world that we can’t touch, see, hear, feel and taste. It took us thousands of years to accept that the earth goes around the sun, because we can’t see it happening. It’s easier to believe that the sun goes around the earth because we can see it moving above us from east to west and disappearing at night-time. So, trying to understand why the winds blow in the way they do is hard.
Who cares about the weather? Sailors, ship-owners and people who are afraid of the weather
But if you live in a part of the world with weather that can kill you, with hurricanes, typhoons, blizzards and droughts, then you might ask yourself why the weather behaves like this, and if you can predict it, so you can plan to be out of its way when it happens.
And if you’re a sailor who sails across oceans, and you were sailing 500 years ago, you wanted answers to questions like “Where am I, and where is this wind going to take me?”, “Why does the wind here always blow in the same direction, but not all year round?”, “What do those big funny-shaped clouds mean?” and “Why is there no wind here?”. And, “How can I get my ship safely across the ocean and back home in one piece, with all my treasure?”
Because sailing across oceans was so incredibly dangerous, and expensive, we only became seriously interested in answering these questions when we started discovering new “worlds” – the continents outside of Europe – and realised that we, ordinary people, could become rich beyond our wildest dreams if we risked going to these new worlds. Or risked our money to pay for ships to go to new worlds. Any ideas that helped make sailing a little bit less dangerous, like understanding where the trade winds blew, and for how long, or having accurate maps of the stars to navigate with, were very valuable.
Shakespeare wrote a lot about the dangers of sailing because he lived during the Age of Sail
Just over 500 years ago William Shakespeare wrote a play called “The Merchant of Venice”. It’s a story, set in Shakespeare’s time, during the Age of Sail, about Antonio, a rich merchant, in Venice. Antonio had spent all his money on ships going to the new worlds, which would, when they came back full of valuable things from faraway lands, make him even richer. Because all his money was invested in ships, he needed to borrow money from a Jewish man called Shylock.
Why it’s important to Shakespeare’s story that Shylock is Jewish
At that time, Jews, (followers of the religion Judaism), had been persecuted all over Europe for hundreds of years, and had been exiled from most countries, including England, where Shakespeare was from, back in 1290. Jews in Venice, (one of the only places in Europe where Jews still lived), weren’t considered citizens and didn’t have the legal rights of citizens of Venice, for example, the right to own land; they had to live in a ghetto, which they were locked into every evening, and were forced to wear yellow hats to show that they were Jews.
Why were they being persecuted? At that time, lending money, and demanding payment for the loan, (a percentage of the money you lent, called interest) was considered a crime, called usury, forbidden by the Christian bible, so only Jews could lend money. This was very convenient for the citizens of a state. When they needed money, they could borrow it. But then, if too many important citizens owed too much money to the Jews, they could decide that the Jews were criminals because they lent money. Then the citizens would make up stories about the Jews – for example, that they were blood-sucking vampires, yes, really – and then confiscate all the Jew’s wealth, burn down their houses, and finally, force them to leave their state.
Back to the Merchant of Venice. The problem was, Shylock and Antonio hated each other. Antonio hated Shylock because it was fashionable to hate Jews at the time, and Shylock hated Antonio because Antonio took every opportunity to publicly mistreat and humiliate Shylock for being Jewish, by spitting at him, calling him names, ruining his business reputation, and worse.
Shylock’s loan, and what he wants in return
So, when Antonio asked Shylock to lend him money, Shylock made him sign a contract which said that he would not charge Antonio interest, but if Antonio didn’t pay back the loan in exactly three months, he would have to give Shylock a pound of his flesh, taken from whatever part of Antonio’s body Shylock wanted. That’s right, a pound – that’s just under half a kilo – of his body. If Antonio didn’t pay back his debt.
And, guess what, Antonio’s boats all sank. I’ll tell you how this story ends another time. It’s a great story, and luckily for us, people of that time would have to wait almost a hundred years for insurance to be invented – or Shakespeare’s story would have been very different.
Insurance – another invention from the Age of Sail
Insurance was invented to protect people like Antonio from losing all their money on ships which at the time had a very high chance of not returning, because they could get lost, sink in a storm, be attacked by pirates, get stuck in the doldrums – which I’ll tell you about in a minute – and any number of other things. Insurance is a contract you buy to protect yourself against losing money, for example in case your house catches fire, or in case the ships that you’ve spent all your money on sink. You pay a little money every month, called a premium, and you promise to be careful, in other words, to avoid setting fire to your house or deliberately sinking your ships. If the worst happens and your house catches fire or your ships don’t come back, the insurance company gives you a sum of money to cover the cost of what you’ve lost.
Explaining trade winds: George Hadley and his “Hadley Cells” – or “Hadley Slightly Squashed Circular Tubes”
Anyway, back to prevailing winds and circular tubes. A man called George Hadley in 1735 was the first to come up with the circular tubes idea to explain why the winds blow the way they do, which also explains why we have rainforests and deserts, why there are parts of the world with no wind, and which proves that the earth rotates on its axis. The name of this explanation – or model – for how winds blow is “Hadley cells”, because “Hadley cells” sounds better than “Hadley slightly squashed circular tubes”.
George Hadley’s model explains why winds don’t blow straight up and down from the cold poles to the hot equator, but zig zag across the northern and southern hemispheres, blowing from west to east near the equator, then east to west closer to the poles, and then west to east from the poles. Now imagine a big coil or spiral of cooling and heating air, going round and round inside your giant circular tubes. Can you picture it?
How to make wind
Have you ever been inside a warm house in winter and opened a window and felt the cold air rush in? That’s wind created by the difference in temperature between the outside and the inside. The warm air flows up and out of the window and the cold air rushes into the space left by the warm air.
We have warm air rising from the equator, pushed towards cooler parts by the earth’s spinning, where the air cools off, falls back towards the earth and then rushes back towards the equator where it warms up and rises again. So, we don’t really have circular tubes sitting around the equator, it’s just this circular movement of the air. And the cold air close to the ground moving towards the hot equator creates prevailing winds called trade winds which blow towards the east because the earth is spinning towards the west.
The connection between cold and hot air, wind, rainforests and deserts
All the heat, evaporation of water, and hot air rising at the equator also creates a lot of hot, wet weather, which gives us rainforests all around the equator. And where the cool air falls, there’s no water evaporation and no rain, and that’s where you get circular strips of desert all around the world, on both sides of the equator. You can see this if you look at a physical map of the world.
And then a very strange thing happens in the space between the circular tubes on the equator. This is the area I mentioned before called the doldrums. If you’re in a sailing ship and you find yourself in the doldrums, in that part of the sea that’s on the equator, there’s no wind, and it’s boiling hot. Well, there’s either no wind or you’re in the middle of a hurricane-force storm. This was a very bad place for your ship to get stuck in during the Age of Sail, as there could be no wind for weeks, and then suddenly, violent storms. And it was impossible to avoid the doldrums if you were sailing from the northern hemisphere to the southern hemisphere.
Ok, that’s enough talking about the weather today.