The Global Wind Patterns of the Three Wind Belts

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  • 0:01 What Is a Wind Belt?
  • 1:11 Polar Easterlies
  • 3:14 Tropical Easterlies
  • 4:37 Prevailing Westerlies
  • 5:54 Lesson Summary
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Lesson Transcript
Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

You are familiar with wind, but did you know there are different wind belts depending on where you are on the earth? This lesson will examine the three main wind belts: polar easterlies, tropical easterlies and prevailing westerlies.

What is a Wind Belt?

You've surely heard of the Three Little Pigs fairy tale, right? But you probably didn't hear about the Three Little Pigs and the Wind Belts. Don't worry, though; I'll tell you the story. But before I start, I should fill you in on wind belts, or wind generated by the earth's rotation and unequal heating from the sun. We'll get into the details of that definition when we examine the three main wind belts: the polar easterlies, the tropical easterlies, and the prevailing westerlies. Oh yeah, all of our piggies inhabit the Northern Hemisphere, so even though we'll mention the Southern Hemisphere, the focus will be on the Northern Hemisphere.

Before we get into the details, there are some things you should know about wind that will help you on this fairy tale. Wind blows from high-pressure areas to low-pressure areas. Cold, dense air causes high pressure, and warm, less-dense air causes low pressure. This is because cold air has more molecules packed into a certain volume, and the more molecules that are present, the greater the pressure exerted. Okay, onto our story!

Polar Easterlies

Once upon a time there were three little pigs: each one lived in a different part of the world. Let's start with pig number one who lived in an igloo at the North Pole. Technically he lived in the 60-90 degree north latitude part of the world.

Now this little piggy had to deal with the polar easterlies, because of where he lived. The polar easterlies are winds that are found between 60 and 90 degrees north and south latitude that blow from the poles and are deflected towards the west.

Although our little piggy lives near the North Pole, you may have gathered from that definition that the polar easterlies can be found near both poles. Before the polar easterlies try to blow our little piggy's igloo down, let's look at how they form.

The air at the poles is cold and dense, creating high pressure. This high-pressure air heads to the equator, towards lower-pressure air, but since the earth is rotating, these winds are deflected in what is called the Coriolis Effect, or the deflection of wind due to the rotation of the earth. It can get a little tricky to remember which way the winds are deflected, so let me give you some rules. Remember, wind travels from high to low pressures, so as they do, here is the deflection:

Wind is deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

So, based on our rules, and since the polar easterlies are blowing away from the poles, we can assume that the winds are blowing towards the right, or west, in the Northern Hemisphere. You may be wondering why they are called polar easterlies then, right? Well, winds are named based on where they start, so since they start in poles, and due to the Coriolis effect, blow from the east, they are called polar easterlies.

Uh oh, and here come those polar easterlies! The little piggy is taking shelter but can't help but notice the winds are cold and dry, and, thankfully for our polar piggy, not very strong. So all is well in the north.

Tropical Easterlies

Now to our second little pig who lives near the equator in a house made from palm trees and is worried about the tropical easterlies, or winds that blow from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere and are located between 0 and 30 degrees north and south latitude. Their more familiar name is the trade winds. Before these winds flow over the palm hut, let's see how they are formed.

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