Lesson video

Hi, geographers.

My name's Ms. Hoggett and I'm really excited you're here to learn some geography with me today.

I'm sure you are going to be absolutely fantastic if you try your best.

Don't worry too much if you haven't studied this topic before.

I'm here to help you every step of the way.

So, the title for today's lesson is Anticyclones and this sits within the unit, Weather and Climate: How do they vary? Our learning outcome for today's lesson is that I can explain the weather associated with an anticyclone and its impact on people and the environment.

To help us through today's lesson, we have three key words that are going to be really useful, impact, pressure, and heatwave.

Impact is to have an effect on someone or something.

Pressure is a force pushing or pressing on a given area.

And heatwave is a prolonged period of abnormally hot weather.

So, our key keywords, impact, pressure, and heatwave are going to help us through today's lesson.

Today's lesson is split into three learning cycles.

What is an anticyclone? What conditions do anticyclones bring? And what are the impacts of anticyclones? We are going to start now with learning cycle one, what is an anticyclone? So, to start thinking about anticyclones, we need to think about pressure.

Air pressure is the force exerted by the weight or mass of the column of air above us.

At ground level, we experience areas of high and low pressure.

We can see from the diagrams that high pressure is where air is sinking towards the earth and low pressure is where air is rising away from the earth.

I remember this because if I was to press hard on a surface, I'm applying high pressure.

If I was to lift away, the pressure is lower.

So, high pressure, air is sinking.

Low pressure, air is rising.

Pressure differences cause winds to blow.

Air moves from areas of higher pressure to areas of lower pressure.

The greater the pressure difference, the stronger the winds.

So, as we know, the sun heats the earth's surface and the warm air above it rises, leaving low pressure behind.

As that air continues to rise, it cause and condenses to form clouds.

Where we have our higher pressure, we've got our cooler air sinking.

As it sinks towards the surface, the air flows into the partial vacuum created and that causes winds to blow.

Now, high pressure is caused by air sinking towards the earth.

And anticyclones are large-scale weather features in which winds circle around an area of high pressure.

Let's check your understanding so far.

Which two statements are correct? A, high pressure is a feature of anticyclonic conditions.

B, high pressure occurs when air is sinking.

C, high pressure occurs when air is rising.

And, D, low pressure is a feature of anticyclonic conditions.

Pause the video and have a go at answering this question.

Well done for giving that a good go.

The correct answers are statement A and statement B.

High pressure is a feature of anticyclonic conditions and high pressure occurs when air is sinking.

Good work, geographers.

Synoptic, or surface pressure charts, show how air pressure varies across geographical space.

On the screen, we can see a synoptic chart that's been taken from the Met Office.

Synoptic charts use isobars, which join areas of equal pressure.

Izzy said, they look a little bit like contours on OS maps, those orange lines that join up the areas of the same height.

It's the same thing, but this time, we're talking about equal pressure.

The numbers on this chart show air pressure in millibars.

Every point along this isobar has a pressure measurement of 1,007 millibars, whereas every point along this isobar has a pressure measurement of 1,020 millibars.

The pattern of isobars shows how steep or shallow the pressure gradient is and what the wind speed is like.

When the isobars are further apart, it shows a shallow gradient, with pressure changing more gradually and gentle wind speeds.

But when the isobars are closer together, it shows a steep pressure gradient.

That means that the pressure changes really quickly.

This is associated with higher wind speeds.

Surface pressure charts also indicate areas of higher and low pressure, and provide the central pressure value.

High pressure is represented with a H and we can see that circled on the synoptics chart on the screen.

If we take a look at the one on the right-hand side, we can see that the central pressure value here is 1,012 millibars.

Anticyclones can be identified by high pressure at their centre and widely spaced isobars that surround the high.

Jacob says, I can see areas of high pressure over land and sea on this map.

Let's check what you've understood so far.

Which of these help you to identify an anticyclone on a surface pressure chart? A, isobars are closer together.

B, isobars are far apart.

C, higher numbers.

Or, D, lower numbers.

Pause the video and have a go answering this question.

Well done for giving that a go.

The answer is B, isobars far apart, and, C, higher numbers.

Good work, geographers.

Another quick check for understanding then.

Which of the following shows an anticyclone, A, B, or C? Pause the video and have a go at answering that question.

Well done if you said B.

We can see that B is showing an anticyclone where we have our high pressure in the centre.

We are now gonna have a go at practising what we've learned so far.

So, I'd like you to firstly complete the following sentences.

Air pressure refers to the force exerted by the blank of air above us.

Blank pressure is caused by sinking air.

Blank pressure is caused by rising air.

And high pressure is associated with blank.

At the bottom of the screen there are some words you can use, anticyclones, high, low, and weight.

That's part one.

Part two of our first practise task is I'd like you to circle the areas of high pressure on the surface pressure chart.

Have a go at completing this now by pausing the video.

Well done for giving that a good go, geographers.

I'm sure you've done fantastically.

Let's check your answers.

So, complete the following sentences.

Air pressure refers to the force exerted by the weight of air above us.

High pressure is caused by sinking air.

Low pressure is caused by rising air.

And high pressure is associated with anticyclones.

And for our second part of that practise task, you should have circled around where we can see the Hs on the surface pressure chart.

Good work, everybody.

Fantastic start.

We are now ready to move onto learning cycle two.

What conditions do anticyclones bring? So, in an anticyclone, air is sinking and warming, so clouds do not form.

Anticyclones bring clear skies and no rain.

Anticyclones bring very gentle winds.

This can be seen on our surface pressure charts by the widely spaced isobars.

Alex has said that, I remember that widely spaced isobars mean that there is shallow pressure gradient.

It's a bit like a shallow slope on the ground, but it's a shallow slope in air pressure.

Thank you, Alex.

That's really helpful.

But yes, you're absolutely spot on.

In the summer, the lack of cloud cover can lead to hot temperatures that last for days.

We call this a heatwave.

The UK has experienced lots of different heatwaves and one example of this was at Greenwich Park in London in August, 2022.

We can see that people are sat out enjoying the heatwave, but also, we can see the grass is really, really dry.

So, the weather associated with an anticyclone is usually dry.

Occasionally, intense heating of the ground can lead to the warming of the air above it.

This warm air rises and leads to heavy convectional rain, and sometimes thunderstorms. Now, convectional rain is just one type of rain that we know occurs across the world.

The other types are relief rain and frontal rain.

But convectional rain occurs when the sun heats the earth's surface and causes the air above it to rise up into the atmosphere.

As the air rises, it cools down and condenses, forming clouds.

And then, the water droplets, once they become too heavy, then fall precipitation.

That cycle continues because as the water falls, it then ends up back in the sea or the ocean, and then the process repeats itself.

So, an anticyclone can occasionally cause there to be some heavy rainfall.

In winter, anticyclones bring cold, frosty weather.

The lack of clouds leads to rapid heat loss at night, whereas in the daytime, the sun's rays may be too weak for it to warm the ground.

Notice though how we still have really clear skies.

Fog can also form overnight during a winter anticyclone.

Fog is thick, and low level clouds can be made up of water droplets.

When the ground cools down at night, so too does the air just above it.

Water vapour condenses because the air is so cold.

Lucas says, if fog is slow to clear, it can make for a really chilly morning.

And there's fog that can be some quite severe impacts as well.

It makes visibility quite tricky.

So, when there is fog, some people might struggle to travel around, get to work on time, or there could be some accidents.

So, as we can start to see the conditions that anticyclones can bring, might be a little bit risky.

So, true or false, anticyclones always bring hot weather.

Pause the video now and have a go at answering this question.

Well done if you said false, because we now know that in winter, anticyclones can bring bright but cold, frosty weather.

So, the skies are generally clear, but the temperature can change.

We are now going to have a go at practising what we've learned so far, and comparing what we know about anticyclones into summer and winter.

So, for this practise task, I would like you to sort the following features of anticyclones into summer, winter, or both.

So, the first statement is sinking air.

Number two is dry conditions.

Number three is few clouds.

Number four is heatwave.

Number five is widely spaced isobars.

Number six is fog.

Number seven is cold temperatures.

And number eight is gentle winds.

So, on the Venn diagram, I'd like you to write where you think those different conditions of anticyclones would apply to.

Pause the video and have a go at completing this practise task.

Well done for giving that a really good go.

Let's check you've got those correct.

So, as we can see, in our summer circle, we have that there is a heatwave.

In our winter circle, we can see that there's fog and cold temperatures.

But sitting across both summer and winter, we know that the air is always going to be sinking and there's going to be dry conditions.

There's going to be few clouds.

And on a surface pressure chart, there's going to be widely spaced isobars.

And we know that this means there's going to be gentle winds.

Good work, team.

You are doing a fantastic job today.

We are now at the end of learning cycle two and we are ready to move on to learning cycle three.

What are the impacts of anticyclones? So, in 2022, the UK experienced a series of heatwaves.

You might remember those.

In July, the temperature reached a record-breaking 40.

3 degrees Celsius.

The previous record high set in 2019 was 38.

7 degrees Celsius.

40.

3 degrees Celsius was in Coningsby in Lincolnshire, but it was 40.

2 still at Heathrow in London.

So, we can see that the temperatures were really, really hot, not what we're used to.

Let's check your understanding.

So, what was the record temperature recorded in 2022? Was it, A, 38.

7 degrees Celsius, B, 40.

3 degrees Celsius, or, C, 48.

9 degrees Celsius? Pause the video and have a go at answering this question.

Well done, geographers.

Absolutely spot on if you said, B, 40.

3 degrees Celsius.

We know that that was recorded in Lincolnshire.

Now, scientists think that a high pressure system located over the North Atlantic called the Azores High became enlarged and pushed hot, dry weather further north.

Climate change made the 2022 heatwave more likely.

So, this is said to be possibly responsible for that heatwave in 2022.

Now, heatwaves can have huge impacts on people in the environment, and some of those impacts are positive, whereas others are negative.

We are going to take a moment to think about the positive impacts of anticyclones.

So, we are thinking here about the good things.

So, firstly, we have a boost to tourism.

People are more likely to visit beaches, parks, and outdoor attractions, creating jobs.

We saw that when we saw the picture of Greenwich and people were outside enjoying the sun.

There could be higher crop yields.

So, things like grapes and sunflowers grow faster in warmer conditions.

There's lower energy use, so there's less of a need for heating.

So, energy bills cost less.

Bonus sales, so industries such as ice cream companies, drinks companies, and air conditioning companies benefits from more sales.

And also, improved wellbeing.

Hot weather encourages outdoor activities, which can improve mental health.

Now, if we take a look at these, we can see that we have some social, economic, and environmental positive impacts.

Social is to do with people, environmental is to do with the landscape, and economic is to do with money.

So, things like boost to tourism and bonus sales are going to be economic positives.

Improved wellbeing is going to be a social positive.

And higher crop yields, for example, is going to be environmental.

So, we can see that the positive impacts of anticyclones can be social, economic, and environmental.

But there are also negative impacts of anticyclones.

Sometimes bad things happen as a result of heatwaves and we're going to look at what they are now.

So, health risks, dehydration and heat stroke can occur.

Some people died as a result of the 2022 heatwave, which was very sad.

Wildfires.

So, dry conditions.

In 2022, this led to wildfires in London, Kent, and Lincolnshire.

Damage to infrastructure, so roads can melt and rail lines can warp.

Water shortages, increased demand for water can cause reservoirs to run low.

And poor air quality.

So, pollution is trapped over cities and high pollen counts persist for days.

So, again, if we take a look at this in a little bit more detail, we can see that health risks are social, wildfires are environmental, and damage to infrastructure can have huge economic impacts.

So, we know that the impacts of anticyclones can be social, economic, and environmental as well.

So, let's check your understanding.

Which of the following impacts of heatwaves are environmental? A, people can save money on energy bills.

B, tourism is boosted.

C, wildfires can be caused by hot, dry conditions.

Or, D, water reserves can run low.

Pause the video and have a go at answering that question.

Well done for giving that a go, geographers.

The answers are, C, wildfires can be caused by hot, dry conditions, and, D, water reserves can run low.

Good work.

So, I now want you to practise what you've learned so far in learning cycle C by completing the table outlining the impacts of summer anticyclones on people and the environment.

So, you have a table there with two rows, people and environment, and two columns to fill in positive and negative.

Have a go at completing this practise task.

For giving that a really good go.

Now, your table may include some of the following, but you might have also put some extras in there.

So, positive on people is that more jobs are created in tourism.

There's improved wellbeing and businesses sell more goods.

Positive impacts on the environment are that there are higher yields for some crops and more renewable energy means less pollution.

Negative impacts on people are that there are greater health risks for older people.

There are water shortages and people are prevented from travelling.

And lastly, negative impacts on the environment, include things like wildfires, scarring the landscape, damaged roads and rail lines, and poor air quality in cities as pollution is trapped.

That's to the end of learning cycle number three.

You have been absolutely brilliant today, geographers, and you've done a really, really good job.

To summarise today's lesson, we know that anticyclones are large high pressure systems in which air is sinking towards the ground.

Anticyclones are characterised by dry, stable weather.

These weather systems have gentle winds that may be identified on synoptic or surface pressure charts by widely spaced isobars.

Anticyclones can bring heatwaves in summer, but very cold conditions in winter.

And anticyclones have positive and negative impacts on people and the environment.

These can be social, economic, or environmental impacts.

I hope you have a brilliant rest of your day, geographers.

You've been absolutely superb today and I will see you soon for our next lesson.

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