Where Does the Wind Come From?

Note: this post was originally written as an Instagram post for Level 2 air cadets at the 540 Golden Hawks Squadron.

Earth’s wind patterns during April, 2018. Source: https://www.youtube.com/watch?v=wVRbeGc_6zM

Where does wind come from?

And what does it have to do with throwing horses into the ocean?! 😱🐴

While little gusts of wind around you may happen pretty much randomly, there are major wind systems that affect the whole world. 🌎

To understand global weather, you first have to remember one simple rule: hot air rises, cold air sinks. Also, think of air as a sort of thick soup: it’s made up of stuff, and it tries to stay sort of level.

Hot air rises because the air molecules are excited and float up. As the hot air in one area moves up, the cooler air next door rushes in to fill up that space (just like when you take a spoonful of soup, and the rest of the soup fills in the space).

Here is a diagram that might help. The arrows show which way the wind is moving. The centre green line is the equator, and the other green lines are 30 degrees apart. Notice how the air warms up on the surface of the earth, goes up to the sky, cools off, and falls back down to earth… just to get warmed up again!

A side view of the earth’s wind patterns. The red lines indicate warm air, and the blue lines indicate cool air. Source: https://en.wikipedia.org/wiki/Horse_latitudes

This movement of warmer air over colder air is what creates wind and weather! ⛈

In the picture below you’ll see the earth in a flattened map. The arrows show where the air is blowing to — the trade winds (in red) blow east to west; and the westerlies (in blue) blow west to east.

Wind patterns. Source: https://history.amazingspace.org/news/archive/2016/01/ill-01.php

Notice how there are some latitudes where the arrow tails are moving away in the opposite direction? ⬇ ️⬆ ️

Those are areas with very little wind! (Look back at the first gif and notice how few clouds there are!) They’re known as the Horse Latitudes, and they’re at both 30°N and 30°S. 🐴

Why are they called that? Imagine you’re the captain of a sail boat in the 1700s, bringing lots of cargo (including horses) from Europe to the Caribbean. ⛵️

You expect your trip to take about two weeks… But oh no! You got caught in an area at 30°N with virtually no wind for A WEEK!

You’re running out of food and water, and your crew and horses are both getting hungry. You can’t feed them all, so you have to make some tough decisions…. 🐴🌊

Earth from a geostationary orbit. Source: https://www.youtube.com/watch?v=0aWlkreybTI

What about local winds? The basic principles are the same: some parts of the air around you somehow get a little warmer; the air there rises, causing the slightly cooler air around it to rush in to replace it.

You also don’t have to worry so much about your horses!