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Monsoons & Monsoonal Circulations

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  • 0:01 What Is a Monsoon
  • 2:03 Monsoonal Circulations
  • 5:04 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.

Monsoons bring a seasonal change in weather to many parts of the world. This lesson will explore two monsoonal circulations and will also discuss how monsoons impact the people who experience them.

What is a Monsoon?

About 65% of the world's population lives in regions affected by monsoons, and the rain that comes from the monsoons impacts the food sources in those areas. In fact, in India and other parts of Asia, the monsoons are so linked to crops, there are two sets of crops: those grown during the wet monsoon season, or the kharif crops, and those grown during the dry season, or rabi crops.

Although the terms 'kharif' and 'rabi' might be foreign to you, I bet you would recognize some of the plants grown during each crop. For example, the kharif crops include rice, peas, corn, and millet; whereas the rabi crops include barley, wheat, and oats. And farming is big business in India, with 70% of Indians either directly or indirectly affected by farming.

So, you might get that monsoons are pretty important, but what are they? Well, for starters, they are winds that change direction depending on the season. This wind change also brings a change in weather. These changes in weather bring rains, which allow kharif crops to flourish, or dry weather, which allows rabi crops to be successful.

Although monsoons can bring welcomed rain, they can also cause dangerous flash floods and landslides, which can kill people, crops, and livestock. And India isn't the only place in the world that has to deal with monsoons. In fact, other parts of Asia, Africa, South America, and (believe it or not) even North America have monsoons. But India experiences the most intense monsoons, so you can say it's the poster child for monsoons.

But what causes a monsoon? Well, it might not seem like the land and oceans would have much to do with the wind in the air, but they're all connected. Let's zoom in on India to investigate how monsoons form. We'll focus on the circulation of air between a landmass and the ocean.

Monsoonal Circulations

Let's take a look at the landscape, since that impacts whether or not a monsoon will form. We'll focus on two monsoonal circulations: summer and winter.

Summer

Let's start with summer. You'll notice there is an ocean along with a large landmass, and you might also notice it's a sunny day. In fact, in this region, it is actually early summer, which you may have already gathered!

The sun warms up the landmass.
sun and ocean with air molecules over land

It looks like that hot sun is warming up that landmass which, in turn, is radiating out and heating up the air. As the air warms, the molecules that make up the air start to move faster and get further and further apart so the warm air becomes less dense. Because the molecules are further apart, they exert less pressure on their surroundings, so they create an area of low pressure.

The air above the ocean is cooler and denser.
air molecules over ocean

Now, let's check out the ocean. During the early summer, the land heats quicker than the ocean so the air above the ocean is cooler and denser than the air above the landmass. This creates an area of high pressure. This is because the air molecules are moving slower and are closer together, therefore exerting more pressure on their surroundings.

So, what does all of this high and low pressure have to do with a monsoon? Well, you may have heard this somewhere already, but air will flow from areas of high pressure to areas of low pressure and this flow of air is actually wind.

If you check out our ocean and landmass, you can see that air is going to flow from the colder, denser ocean air to the warmer low-pressure air on land. That's only part of the monsoon story. The warm air above the land is going to rise because it is less dense and when the cold, moist air from the ocean flows inland, the warm air carries the cold air up with it.

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