[intro plays]

Sabrina: You know what I've been thinking about lately? Hanging out on a beach with sand between my toes and a cool breeze blowing through my hair. I mean, strictly in the interests of science. Because the breeze in my hair and the wind and even the big cycles going on out there in the ocean are all great ways of understanding currents.

A few episodes ago we learned that the uneven heating of land and water creates wind by forming different pressure zones. The air above the land is warmer and less dense, so it rises, and the air over the water is cooler and heavier. The cool air rushes in toward the low pressure zone over the land forming a lovely sea breeze. But you may have noticed you don't need a beach to feel a breeze. Nope, wind is everywhere.

Air is constantly moving all around the world in cycles, of currents. Sometimes they're small like a light breeze blowing off the sea, and sometimes they're massive, mighty rivers of wind.

Let's see how currents move around the world.

[text: Big Question]

You know the Earth is a sphere, so the sun's rays hit the middle of the Earth straight on. This part of the Earth receives direct sunlight. Meanwhile, Earth's poles receive indirect sunlight, or sunlight coming in at an angle. Here, the light is spread out over a larger area and it's less intense. This means the Earth's equator is much warmer than the poles. I mean, you wouldn't pack a swim suit for a trip to the arctic.

And you know that when we have differing temperatures, we're going to have different pressure zones. The area around the equator is a low pressure zone. Here the warm air rises and starts to slowly move towards the poles. Now, it the Earth weren't spinning on an axis, and if it didn't tilt, and if it wasn't covered in water, then the warm air  from the equator would just rise towards the poles and the cool air would move in at the equator, where the warm air just left. This would create two giant air currents called cells.

But of course things on Earth are much more interesting. The sun hits the equator causing warm air to rise and the air moves away from the equator, but it doesn't have time to get all the way to the poles. About a third of the way the air cools, falls, and moves toward the equator again, creating a smaller cell. Another cell is created at the mid latitudes and another at the poles. In each cell, cold air sinks and warm air rises. There are six of these cells circling in the Earth's atmosphere.

And at the boundaries of these cells, something really weird starts to happen: we get jet streams. Whaaa? Air in these cells is trying extra hard to get from one cell to another, since there's a big temperature difference between the air over the poles and the air over the mid-latitudes.

But, the Earth is spinning faster at the equator than at the poles. If you were to stand at the Earth's axis on the North Pole, you would spin around more slowly than if you were standing on the equator. So, as air rises towards the equator and makes its way toward the poles, it keeps moving eastward at the same rate, even though the higher it goes, the slower the Earth is spinning. This creates ribbons of very fast moving air called jet streams.

Jet streams move in wiggly patterns across Earth caused by the interactions with other high and low pressure systems, and also with seasonal changes, too. These streams are usually between six to fourteen kilometers off the ground and can reach speeds of 442 kilometers per hour. Simple enough, but of course, there's more.

We know from our little trip to the beach that there are other actors here. Remember our nice sea breeze? Those small differences between high and low pressure caused by the heating of the land and water taking place on all the coast lines around the world. This makes air patterns even more complicated.

And jet streams and wind patterns aren't the only currents flowing around the world. Water actually moves a lot like air. Warm, light water rises, and cold, salty heavy water sinks. And just like with air, the sun heats the water that's at the equator and that warm water then spreads out toward the poles, cold water slowly moving back down toward the equator where it'll warm again in an endless cycle.

This massive movement of water, called ocean currents helps regulate global temperatures just as much as air circulation. All of this interaction between the land, air, and water created some pretty complicated wind, weather, and climate patterns. These currents make large parts of Earth livable. Without them the poles would be far too cold and the equator scorching hot.

[text: Conclusion]

So, currents are a little complicated, and messy, and they're always on the move. They're caused by uneven heating of the Earth's surface, whether that's between land and water or between the poles and the equator, and they're all driven by energy from the sun. Without that energy, our air and water would be still. And all of these complex currents blowing and flowing around all over the places makes it really hard to predict where the wind will blow, and therefore, what kind of whether you're gonna have next week. But that's a problem for another episode, and until then, Imma keep planning my beach vacation.

[endscreen]