Curious Kids: what makes the wind?
Curious Kids is a series by The Conversation, which gives children of all ages the chance to have their questions about the world answered by experts. All questions are welcome: you or an adult can send them – along with your name, age and town or city where you live – to firstname.lastname@example.org. We won’t be able to answer every question, but we’ll do our best.
What makes the wind? – Eric, 94-year-old kid, Ipswich, UK.
The wind has always been very important to us humans: from thousands of years ago, when sailors used the wind to cross the sea in ships, right up to today, as we make electricity from wind turbines. But it’s taken a long time for scientists to understand exactly how the wind is made.
Although we can’t see it, the air is made up of billions and billions of tiny particles. There are lots of different types of particles in the air, but the most common ones are nitrogen and oxygen (which is what humans and other animals need to breathe).
The wind blows when these air particles move around in the Earth’s atmosphere. The atmosphere is an envelope of gases, which surrounds the Earth. It’s around 100 kilometres thick, which is about the length of 4,000 blue whales.
Most of the particles that make up the Earth’s atmosphere are found closer to the surface. As you get further out into space, there are fewer and fewer particles, until finally, in outer space, there are none.
The weight of all of these particles stacked on top of each other pushes down on the Earth’s surface – and this force is called atmospheric pressure.
Atmospheric pressure changes, depending on how warm or cold the Earth’s surface is. When the surface heats up, the air closest to it also gets warmer. And when the air gets warmer, the particles will tend to rise upwards and spread out.
When this happens, it leaves fewer air particles at the Earth’s surface, which lowers the atmospheric pressure.
So, you would expect the air over a very warm and sunny place, like a desert, to have lower atmospheric pressure than the air over a cold and dark place, like the North Pole.
When the warmer air rises, cold air particles – which are generally packed in closer together – will sink into those low pressure areas.
This movement of air particles, driven by areas of heating and cooling, is what makes the wind.
From gusts to gales
How fast the wind blows depends on how much of a difference there is in pressure between a low pressure and a high pressure area of air. If there’s a bigger difference in the pressure, the wind will blow faster.
There are 12 different levels of wind speed, measured on a scale called the Beaufort scale. The scale ranges from winds of less than one kilometre per hour (calm) to more than 118 kilometres per hour (hurricane).
Lighter winds are called “breezes”, stronger ones are called “gales”, and the very strongest winds are “hurricanes”.
You might also have heard the weather forecast talking about “easterly” or “northerly” winds. We describe which way the wind is blowing, by the direction it comes from. So an “easterly” blows from east to west, while a “northerly” blows from north to south.
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Hannah Bloomfield does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
source: The Conversation: Environment