Lesson video

Hello, geographers.

I'm Mrs. Homagio, and I'm gonna be teaching you today.

I hope you're gonna really enjoy the lesson.

Today's lesson is called "Global Atmospheric Circulation Model, Pressure Belts, and Surface Winds," and it's part of the unit Weather Hazards.

We are going to be learning about what the global circulation model is and how it affects climate across the world.

By the end of the lesson, I hope that you will understand that the atmosphere operates as a global system that determines pressure, winds, and rainfall patterns.

Now, there are four keywords for today's lesson: latitude, atmospheric pressure, surface winds, and the Coriolis effect.

Latitude.

This describes how far north or south of the Equator a place.

Atmospheric pressure.

This is the pressure of a column of air at a point on the Earth's surface, creating relatively high or low pressure.

Surface winds are the movement of air from place to place, generally from an area of high pressure to an area of low pressure.

And the Coriolis effect.

This is the deflection of winds and ocean currents that's caused by the Earth's rotation.

There are three parts to today's lesson, so let's get started on the first.

What is the global atmospheric circulation system? The Earth is surrounded by a thin layer of air called the atmosphere, and the atmosphere operates as a global system.

The large-scale movement of air is driven by the uneven heating of the Earth's surface, and this is what is known as the global atmospheric circulation system.

The curvature of the Earth is the cause of this uneven heating.

And latitude, as we saw on those keywords, describes how far north or south of the Equator a place is.

At the poles, which are at a high latitude, the sun's rays are less concentrated, and you can see on that diagram how they are spread out over a greater surface area.

Whereas at the Equator, which is at a low latitude, the sun's rays are more concentrated.

And again, you can see on that diagram, they heat a smaller surface area.

And this is why we have higher temperatures at the Equator than at the poles.

Quick check for you here.

Which of these areas of the world are at a high latitude? Antarctica, the Arctic, or the Equator? Have a chat to your partner and see what you think.

Pause the video and come back when you're ready.

Did you say Antarctica and the Arctic? If so, well done.

The Equator is at a low latitude.

The further north or south of the Equator, the higher the latitude.

The global atmospheric circulation system redistributes this heat that we receive from the sun.

And in doing so, the warmer air from the Equator moves towards the poles.

This stops the Equator from getting too hot and the poles from getting too cold.

The world's oceans also play an important role in redistributing the heat energy around the globe.

Warm currents transport the warmer water from areas near the Equator, so at lower latitudes, towards the poles, at higher latitudes.

And you can see that by looking at the diagram.

The red arrows represent the warmer currents and they're moving away from areas near the Equator towards higher latitudes.

Cold currents take colder water in the opposite direction, so moving the water from higher latitudes to the lower latitudes.

And again, that's shown by the blue arrows on the diagram.

Let's have another quick check.

True or false? High latitudes are colder than lower latitudes.

Pause the video and see what you think.

Did you say true? If so, well done.

But why? Talk to your partner and see if you can tell us why.

Hopefully you've said something like this.

This is because the curvature of the Earth affects the solar radiation received from the sun.

Solar radiation is less intense at higher latitudes.

Well done.

Now let's move on to our first task.

Two questions for you to have a go at.

Number one, why is it colder at the poles than the Equator? Number two, what does the global atmospheric circulation system do? Think back over what we've learned and see what you think the answer to these questions are.

Pause the video and come back when you're ready.

Let's have a look at what your answers were.

You might have included for number one, the poles receive less intense solar radiation than the Equator as the suns rays are spread over a larger surface area at the poles.

And your answer for number two might have included the global circulation system redistributes heat across the world as the Equator is heated more intensely than the poles due to the curvature of the Earth.

Well done if your answers were similar to those.

Let's move on to learning cycle number two.

How does the global circulation system operate? This image shows the global circulation system and it shows that it redistributes the heat via three circulation cells: the Hadley cell, the Ferrel cell, and the Polar cell.

Quick check here now.

Can you complete these two sentences by filling in the blanks? Number one, the global circulation system and ocean currents transfer around the Earth.

The atmospheric circulation system consists of circulation cells, the Hadley cell, Ferrel cell, and cell.

Have a go.

Pause a video and come back when you're ready.

Did you manage to get the global atmospheric circulation system and ocean currents transfer heat around the Earth? And for number two, the atmospheric circulation system consists of three circulation cells; the Hadley cell, the Ferrel cell, and the Polar cell.

Well done.

Now let's look at the cells in a little bit more detail.

Firstly, the Hadley cell.

At the Hadley cells, warm air is rising at the Equator and moving towards the poles.

As it cools, it sinks and it flows back towards the Equator.

This happens at 30 degrees north and south of the Equator.

As it gets back towards the Equator, it's warmed again, and so it rises, and this forms that circular motion in this cell.

The area where the two cells meet, the two Hadley cells meet, is known as the intertropical convergence zone.

That's marked on the map there.

The second set of cells are Polar cells.

The Polar cells are found near the north and south poles.

Here, cold air is sinking and it's flowing towards the Equator.

But as it flows towards lower latitudes, it warms and it rises and flows back towards the poles.

This happens at 60 degrees north and south of the Equator.

And finally, the Ferrel cell.

These Ferrel cells are sandwiched between the Polar cell and the Hadley cell, and the air movement is affected by both of these other cells.

Their movement creates an airflow in the Ferrel cells that rises at 60 degrees and sinks at 30 degrees north and south of the Equator.

So the air in these cells moves in the opposite direction to the air in the Polar and Hadley cells.

Let's have a quick check.

Can you match the circulation cell names to their correct definition? The three cells, the Hadley cell, the Ferrel cell, and the Polar cell.

Read through the definitions and have a go.

Pause the video and come back when you're ready.

Did you manage to match the Hadley cell to in this cell, heat at the Equator causes air to warm and rise.

The air flows towards the higher latitudes where it cools and sinks at 30 degrees north and south.

The Ferrel cell, air in this cell circulates in the opposite direction to the cells either side of it.

It is found at mid-latitudes, 30 to 60 degrees north and south.

And finally, the Polar cell.

This cell is located in the higher latitudes.

Cold air sinks here and flows to lower latitudes where it warms and rises at 60 degrees.

Well done if you managed to match those correctly.

Now our second task, can you complete the labels on this diagram of the global atmospheric circulation system? Use the diagram to help you and think about what we've just been learning.

Pause the video and come back when you're ready.

Did your labels look similar to this? Between the Hadley and Ferrel cell, air is sinking.

Between the two Polar cells, air is sinking.

Between the Polar and Ferrel cell, air is rising.

And between the two Hadley cells, air is rising.

Well done if you correctly labelled this diagram.

Let's move on to our last learning cycle for this lesson.

How does atmospheric circulation impact climate? The movement of air within these circulation cells creates areas of different atmospheric pressure where each cell meets.

These areas are called global pressure belts.

Low atmospheric pressure occurs where the warm air is rising.

And as the air rises, it cools and condenses to form clouds and this leads to rainfall.

High atmospheric pressure occurs where colder, denser air sinks.

As the air is sinking, no clouds form, and so there is no rainfall.

The pressure belts formed by the movement of air in these three circulation cells lead to distinct climate zones.

Low pressure zones have cloudy, wet climates.

And this happens where the Hadley cells meet and where the Ferrel and Polar cells meet, so where air is rising.

And you can see that on the diagram where those arrows are going up.

High pressure zones have a dry climate, and this happens where the Hadley and the Ferrel cells meet and when the Polar cells meet.

And you can see that on the diagram where the arrows are pointing down where the cells meet.

This map shows how the different pressure belts lead to distinct climate zones.

So these climate zones may be familiar to you, but we can now attribute them to what the air is doing, what the atmospheric pressure is in these zones.

Tropical rainforests are found at the low pressure belt at the Equator.

Hot deserts are found in the high pressure belts at 30 degrees north and south.

Equatorial regions have hot and wet climates.

Rising air where the Hadley cells meet creates low atmospheric pressure, which leads to rainfall.

And we can see that on the map and how that is linked to where the two Hadley cells are meeting and air is rising.

Temperatures are also high here because of the concentration of solar radiation at the Equator.

Quick true or false for you here.

Low atmospheric pressure creates a wet climate.

Talk to your neighbour and see what you think.

I hope you all managed to say true, but why? Can you explain why low atmospheric pressure creates a wet climate? Pause the video and come back when you're ready.

You may have said something like this.

This is because warm air is rising in a low pressure zone.

As the warm air rises, it cools, condenses, and forms clouds, and this leads to rainfall and a wet climate.

Well done if you managed to get that answer.

Hot deserts are found at 30 degrees latitude.

For example, the Sahara Desert in Africa.

This region is dry because it is in a high pressure zone where the Ferrel and Hadley cells meet.

And that's shown in the diagram and in the map.

The sun's heat is still concentrated here.

And because there is no cloud cover, temperatures get very high.

Temperate climate zones, found at 60 degrees latitude, are cool and wet.

And this is because they occur where the Ferrel and Polar cells meet.

And so there is low atmospheric pressure.

This is typical of the UK.

And you can see that band on the map and linking it to the Polar and Ferrel cells meeting.

Temperatures are lower because of the curvature of the Earth.

That means that the sun's radiation is less concentrated here.

Polar climate zones are found at 90 degrees latitude.

The climate is cold and dry.

These regions are dry as cold air is sinking as the two Polar cells meet, creating high atmospheric pressure.

Polar climate zones have very cold climates because of the curvature of the Earth, meaning solar radiation here is spread over a much larger area.

Let's have a little check.

What type of climate do we find where the Hadley and Ferrel cells meet? Hot and dry? Cold and dry? Hot and wet? Use the diagram to help you and come back when you think you know the answer.

Did you say hot and dry? Well done.

It is dry because it is a high pressure zone where colder air is sinking.

It is hot as solar radiation is still concentrated at 30 degrees north and south of the Equator.

Well done if you managed to get that answer.

The movement of air in a global atmospheric circulation system creates surface winds.

The Hadley, Ferrel, and Polar cells each have surface winds associated with them.

We can see those winds are represented by the arrows on the diagram across the globe.

They blow from areas of high atmospheric pressure to low pressure.

And they are deflected due to the Coriolis effect, so the rotation of the Earth.

And that is why they are curved in their path.

These surface winds are important because they transport heat and water vapour from one place to another.

The UK is located close to 60 degrees north.

This is a low pressure zone as it is where the Ferrel and the Polar cells meet, which means that we have a wet climate.

Surface winds blow from the southwest, bringing moisture from the Atlantic Ocean.

True or false.

Global pressure belts affect surface winds and patterns of rainfall.

Chat to your neighbour and see what you think.

Did you say true? Well done.

But can you tell me why? Pause the video and come back when you think you know.

Did your answer look something like this? Global pressure belts are belts of high atmospheric pressure where air is sinking and it is dry, and belts have low atmospheric pressure where air is rising, which leads to rainfall as the air cools.

Surface winds flow from areas of high pressure to low pressure.

Well done if you had something similar to that.

Let's move on now to our final task.

Using this model of the global atmospheric circulation system and your own understanding, explain why: A, areas close to the Equator have high temperatures and high rainfall.

And B, the UK has a cool, cloudy, wet climate.

Think carefully about what we've learned over all of this lesson.

Pause the video and come back when you've got an idea.

So for the first question, did your answer look something like this? The Equator receives high solar radiation as the sun's rays are concentrated on a small area, so temperatures are high.

The warm air rises as the two Hadley cells meet.

This causes low pressure.

The warm, moist air cools as it rises to form clouds, and so rainfall is high.

If so, well done.

And for B, the UK is found at 60 degrees north of the Equator.

This is where the Polar and Ferrel cells meet and where air is rising.

Rising air creates a low pressure zone.

The air cools as it rises, leading to clouds and rainfall.

Surface winds coming from the southwest bring wet conditions as well.

Well done if you managed to answer something similar to that.

Some really tricky ideas in this lesson, so you've done a great job understanding.

Let's have a look now at a summary of the lesson.

Firstly, the global atmospheric circulation system redistributes heat from the Equator towards the poles.

Two, there are three circulation cells involved: the Hadley cell, the Ferrel cell, and the Polar cell.

Different pressure belts are created where the cells meet as warm air rises, which is low pressure, or cold air sinks, high pressure.

Together with differences in temperature caused by the curvature of the Earth, these areas of high and low atmospheric pressure create the global climate zones.

High pressure belts are associated with dry climate zones and low pressure belts are associated with wet climate zones.

Well done.

You've worked really hard today.

I hope you've enjoyed it, and I hope you've understood it.

I'll see you all again soon.