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Blog Geography Secondary Teaching Weather

Air Masses

In this article we explore air masses – the idea that, by looking at where our wind is blowing from, and what has happened to the air in the wind on its way to use, we can begin to understand why we’re getting some particular weather.

We live on an island, and the weather can come at us from any direction, although in practice, it comes from some directions more than others  – this wind rose shows the direction the wind was recorded coming from at Heathrow airport, near London. The longer the bar, the more often the wind came from that direction, so you can see that our wind comes from between southwest and west most often.  

Lets take a step back and remember that warm air rises – whether that’s the air being heated in a hot air balloon or the air above a radiator (watch a simple demonstration).

What happens to the rising air? As it rises it cools. Cloud and rain are caused by warm air rising, warm air rising is called convection (watch a simple demonstration).

You can often see convection going on in the atmosphere – you get puffy cumulus clouds, with flattish bases and puffy tops where the cloud is bubbling up.

clouds

More generally, Clouds form when there is more condensation going on than evaporation in the atmosphere.

The colder it is, the less evaporation happens – so cloud forms when the air cools.

This isn’t just when warm air rises.

Now we can think about air masses, they are classified according to where they have come from, and what they have passed over:

One air mass generally covers the whole country.

However, it can bring different weather conditions to different places. For example, Tropical continental air can carry Saharan dust, but it mostly falls on the south of the UK – there isn’t much left in the air by the time it reaches Scotland.

Lets consider Polar maritime (Pm) air first (click on the map to start the animation):

Polar maritime air comes towards us from further North in the Atlantic. It starts cold, but is slowly warmed by the ocean below as it travels over progressively warmer water. It also picks up moisture from the ocean. 

As it is warmed, it becomes more unstable and inclined to rise, leading to convection and puffy Cumulus clouds, mainly over the ocean. As the air hits land (the western coast of Ireland, Wales, Scotland and England) the air, which was already inclined to rise, is forced up a bit more – forming more cloud, and giving rise to rainfall. 

Polar maritime air, our dominant air mass, brings cloud and rain to the west of the UK and relatively dry air to the east. 

This satellite image is typical of Pm air – you can see the puffy cumulus clouds over the ocean, and the belt of cloud over the western side of the country.  

Returning Polar maritime air (rPm) is air which is Polar in origin but which swings round to hit the UK from the west or even slightly south of west – but if you were to follow its path back, you would see that it was Polar. 

Arctic maritime (Am) air is extreme Polar maritime air, coming down to the UK straight from the north, over the Arctic ocean. It tends to bring wintry weather to Scotland and isolated snowy showers further south, triggered by air rising over the local orography. 

Polar Continental (Pc) air will also be cold to start with and get progressively warmer as it moves south, so you would also expect convection. However, the air will be very dry as it passes over continental Europe, so little cloud will form. The UK is a set of islands though and to reach us, the air must pass over the North Sea, picking up water vapour as it does so. The cloud and precipitation (typically snow in winter) it brings therefore primarily affect the east coast. The longer the path it takes over the North Sea, the more precipitation there will be. 

This satellite image is typical for Pc air – you can see the cloud free areas immediately to the west of the land masses, with cloud forming further east (ignore the front to the west of the UK and Ireland).

Of course, the characteristics of the air masses can be very different in the summer and the winter. Siberia, for example, is extremely cold in winter but relatively warm in summer – so a polar continental air mass can bring us bitterly cold weather and heavy snowfall (for eastern counties) in the winter, but much warmer weather in the summer.

The processes at work in Tropical Maritime (Tm) air are a bit different. This is warm air, which is being cooled from below as it moves north. You therefore wouldn’t expect any convection with air rising, cooling and forming cloud. However, the air is being cooled just by moving north and so eventually may reach the temperature at which cloud forms – flat, featureless sheets of stratus cloud because, on the whole, the air is staying at the same level.

As it is maritime air, there is plenty of water vapour available to form cloud droplets. The processes which give us big, fat raindrops are mainly associated with the vertical air motion and circulations in cumulus clouds. So Tm air at best gives a persistent drizzle.

The satellite image below shows the extensive sheet of stratus cloud over the Atlantic associated with Tm air.

We rarely experience Tropical Continental (Tc) air – air that flows up from the Sahara over continental Europe.  This is the warmest and driest air we can get – any moisture picked up over the Mediterranean will be rained out before it reaches us.

Tc air gives clear skies, as you can see in the satellite image below – again ignore the front to the west of the UK. In the summer, this can mean that some areas get particularly warm – maybe because of their colour (dark) or aspect (facing the Sun) – giving rise to late afternoon localised thunderstorms

A front is where two air masses meet. In the UK, the weather fronts associated with depressions usually separate polar and tropical maritime air.

If there is a front, then different parts of the UK can be experiencing different air masses. The weather on the fronts themselves is more extreme. 

Look out of the window now – what cloud types can you see? Does that tell you anything about where the air is coming from? You can have a look at earth.nullschool to see if you are right.

 

 

Categories
Careers Weather

Weather Forecasting Game

Try your hand at weather forecasting – can you beat the experts from University of Reading and beyond?

Calling all weather enthusiasts and wannabe forecasters! Following its successful launch to the public last summer, The Weather Game, run by the University of Reading is returning for another friendly competition round.

The game offers entrants the chance to try and predict the weather around the world and close to home. Points are awarded for correct weekly forecasts over six weeks, allowing people to take on their friends and try to beat the experts to top the league.

This activity gives school pupils and weather fanatics a glimpse at the science used on television forecasts or to monitor impacts of climate change. A number of high-profile TV weather forecasters like Laura Tobin and Tomasz Schafernaker made some of their first forecasts while they were students at Reading.

Forecasts from leading sources like the Met Office and BBC Weather can be used as a basis for predictions, but players are encouraged to follow their own intuition on where weather might differ from what is expected. For example, if changeable weather is certain or there is only a small chance of showers, going against the expert forecasts for sunshine and rain might earn you the points.

Entrants will make predictions on the temperature, precipitation and sunshine hours for three fixed locations: Reading, UK; Toronto, Canada; Hong Kong, China and also for another city that changes weekly. While travel is off the cards for most of us this year, experiencing the weather is something that connects us all.

Registration opens from Monday 7 June with entries due each Friday for six weeks at 19:00 London time.

Categories
Books Climate Climate Change CPD Geography Microclimates Schools Secondary Teaching Weather

Weather and Climate: a Teachers’ Guide

weather and climate teachers guideIn this teachers’ guide and the accompanying online teaching resources, we aim to give UK geography teachers all that they need to deliver relevant, engaging and thorough weather and climate lessons to 11–14+ year old students. They are not linked to any specific curriculum but should be easily adaptable to all.

The book is accompanied by high quality online background information/professional development resources for teachers.

 

 

 

The Royal Meteorological Society believes that:

  • all students should leave school with basic weather literacy that allows them to understand the weather that affects them, their leisure activities and the careers they choose to follow
  • every student should leave school with basic climate literacy that would enable them to engage with the messages put forward by the media or politicians and to make informed decisions about their own opportunities and responsibilities.

To this end, we have embedded a climate change thread throughout the online resources, showing its relevance to both weather and climate. An understanding of weather and climate is fundamental to an understanding of climate change.

There is a progression of knowledge through the topics, supported by review and assessment activities. The resources also progressively develop key geographical skills such as data, mapwork, GIS, fieldwork and critical thinking.

In this guide, we include common misconceptions which should be challenged in the classroom.

There are 20 topics or chapters. Across these, there are three threads or paths which can be taken through the online resources, depending on the teaching time available:

Basic weather: Weather in our lives, weather measurements, weather and climate, global atmospheric circulation, global climate zones, air masses, pressure and wind and water in the atmosphere

Climate: Weather and climate, global atmospheric circulation, global climate zones, past climate change, polar climate, hot deserts, changing global climate, UK climate, changing UK climate, the climate crisis

Extending weather: Anticyclones, depressions, microclimates, urban weather, tropical cyclones.

Many of the online teaching resources are available with standard or easier versions, as well as extension or alternative activities.

Find the scheme of work, teaching resources, background information for teachers, as well as the Teachers’ Guide (copies of which may be printed on request), here

All the online resources will be updated and revised regularly.

Categories
Blog Climate Climate Change Extreme weather Weather

Weather, Climate, Extreme Weather and Chaos Theory

How does climate relate to the weather?

We like to talk about the weather, to complain about its variability and to blame the weather forecasters for getting it wrong. But what is ‘climate’, and how does the weather we experience on a day-to-day basis relate to climate change, a subject which is increasingly dominating our newspapers and television screens? Why is it that we can’t make a perfect weather forecast? How can we hope to predict the climate of the 21st century, when we can’t say what the weather will be doing in a week’s time? If the climate changes, how does the weather change?

Firstly, how does the climate relate to the weather we experience on a day-to-day basis? We know from experience that the weather can be very different from one day to the next, let alone from one year to the next, without any change in the climate.

Surprisingly, dice are a good way to think about the difference between weather and climate…

The animation below allows you to choose how many times to roll a dice and then see how often you get each of the six sides. Try a low number of rolls, then try some larger number of rolls and see what happens:

 

Throw the dice a few hundred times. What is the average (mean) of the scores? The more throws, the closer the average gets to 3.5. If you were to throw the dice one more time, you would not be able to predict the number that the dice would land on, as the probability of throwing each number is the same. However, you could be very confident that the mean would still be 3.5.

But what has this got to do with weather and climate?

What if we associate weather types (for example, cloud cover) with each number on the dice?

Try rolling the dice in the animation, again explore what happens as the number of rolls increases.

As when there were numbers on the sides of the die, you can’t predict what the weather will be on the next throw. Climate is defined as being the average of the weather over a long (typically 30 years) period of time. The ‘climate’ of this die is 50% cloud cover. A single throw of 0% or 100% cloud cover won’t affect the climate very much if you are taking the average of 100s of throws. In the same way we can have a very hot summer one year, and a very wet one the next, without the climate, the weather we expect to happen, necessarily changing.

Climate is what we expect, weather is what we get

So why do the weather forecasters never get it totally right? Mostly because the weather is a ‘chaotic’ system.

Very small changes to the starting conditions can lead to completely different weather patterns developing. This observation led Ed Lorenz to suggest that the flap of a butterfly’s wings in the Amazon rainforest could lead to a tornado in Texas. It is very unlikely, but it could.

This means that, to make a perfect weather forecast, we need to know what the atmosphere is doing currently, down to the scale of individual butterflies flapping their wings, which is obviously impossible!

So, since tiny changes in the starting conditions of a weather system can make significant differences to the outcome, when making a forecast we have to try to take into account what might be happening now, as well as what might happen in the future to affect the atmosphere. The best we can do is to produce a range of forecasts, with some indication of what is most likely, or least likely, to happen.

To help illustrate this, consider throwing two dice instead of one:

 

With two dice, the probability of throwing a combined score of a number between 2 and 12 is not the same. There is only one combination of number that would give you a 2 or a 12 (two 1s or two 6s respectively) but, for example, for a combined score of 4 you could throw a 3 and a 1, two 2s or a 1 and a 3 – so you are 3 times as likely to throw 4 as 2 or 12. There are most possible ways of throwing a combined score of 7, and no way at all of throwing a 1 or 13 or more.

Move the slider to pick a number and throw the dice a large number of times. Notice the shape of the graph that is produced – the middle numbers are rolled more often than the smallest or largest numbers.

This sort of shape of ‘bell shaped’ graph is very common. For example, temperature measurements will often show a similar distribution, although temperature can of course take any value, not just the numbers one to twelve.

In this way, the results of many weather and climate forecasts can be combined to show what is most likely to happen, what is unlikely to happen and what almost definitely won’t happen.

But what about extreme events? How will the likelihood of an extreme event change as the climate warms? It is never possible to attribute one particular event to a particular cause. To go back to the dice example, you could load a die so that sixes occur twice as often as normal. But if you were to throw a six using this die, you could not blame it specifically on the fact that the dice had been loaded. Half of the sixes would have occurred anyway, even with a normal die. Loading the die just doubles the odds of throwing a 6.

In general, if the climate warms, the whole bell-shaped curve of temperature for a particular place shifts to warmer temperatures:

Graph 1

Taken from the Synthesis report on Climate Change, 2001, ipcc.ch

Record hot events are more likely in a warmer world, and record cold events are less likely.

So, for example, we can say that the hot summer of 2003, which killed 22,000 – 35,000 people in central Europe, is twice as likely because of the global warming that has resulted from the man-made emissions of greenhouse gases. By 2050, we can expect summers as hot as that every other year.

Similarly, in the U.K., we can expect the number of extremely rainy days, with associated flooding, to increase. Already, the kind of rainfall that you could have expected once every 30 years in the 19th century is happening once every 12 years now. By the end of the century, it could be expected every 4 years.

So, we can adapt the earlier phrase about weather and climate to 

Climate is what you affect, weather is what gets you

So, to summarise:

  • Even with perfect forecasting techniques, we could never say exactly what the climate will do over the next century. This is because:
    • weather is chaotic
    • we don’t know how the world will develop and how much greenhouse gas will be emitted
    • We don’t know what other, natural, factors may affect the climate in the future – volcanic eruptions, changes in solar activity etc.
  • We can, at best, say what the climate is most likely to do, and what it probably won’t do.
  • The longer into the future a forecast is made, the less certain you can be about what will happen.
  • We can expect extreme events – such as abnormally hot seasons and storms, to become more frequent in a warmer world.

The animations were originally developed by climateprediction.net  and The University of Oxford Department for Continuing Education (Technology Assisted Life-long Learning Unit).

Categories
Geography Secondary Weather

The Weather of 2020

Last week, Sylvia Knight from the Royal Meteorological Society gave a talk for Geography education online on the Weather of 2020.
This year it felt like we had summer weather in Spring and Autumn weather in Summer. In this session, we examine the global processes that determine the weather in the UK, as well as the impact of COVID-19 on weather and climate around the world.
The talk is aimed at A Level students, but would also be useful CPD for geography teachers or for younger students who have already covered a weather topic.

Categories
Climate Climate Change Weather

Weather, Climate and Covid-19

Sylvia Knight, Head of Education at the Royal Meteorological Society, recently recorded a podcast for the Royal Geographical Society with IGB, looking at the impact of COVID-19 on the weather and climate across the world. You can access the podcast here.

Further reading:

Categories
Geography Weather

Arctic Maritime Air

Over the weekend, we saw Arctic Maritime air descend over the UK, with temperatures dropping by around 10C.

The following snapshot from http://earth.nullschool.net from the morning of Monday 11th May, shows winds blowing clockwise around a High pressure area to the northwest of the UK. This means a northerly air flow over much of the UK, swinging round to easterlies over southern counties.

We can see in these charts from the preceding weekend how the polar front (shown as a cold front) swept down across the UK. This first chart shows 6am on Sunday 10th May, with the cold air over Scotland, Northern Ireland and some of northern England.

The second chart shows midnight on Monday 11th May – cold air now covers the whole of the UK.

Observations show the temperatures plummeting as the cold front passed, moving us into Arctic maritime air – these observations are from Reading University’s weather station, showing both a week and a 2 day view:

Temperatures clearly drop from around 19C on Sunday morning to 12C by lunchtime, and below 5C overnight. This temperature drop was later further south in the country, and earlier further north. The following graph corresponds to the same time period as the Reading data, but shows data from the Whitworth observatory in Manchester (with thanks to Michael Flynn):

The northerly winds, funnelling surface waters down the North Sea, came at the same time as a Spring tide – the following image is taken from tidetimes and shows the tide height at Whitby. Spring tides are marked by a greater tidal range – higher high tides, and lower low tides.

This led to extremely high tides – and the Thames Barrier was closed overnight to protect London from flooding. A flood alert was issued by the Environment Agency for the South Devon coast.

To make this case study memorable for students, it could be linked to Boris Johnson’s speech at 7pm (18UTC) on the evening of Sunday 10th.

Categories
Weather

Passage of a Depression

We are delighted to have worked together with Fuzzy Duck to produce this animation (which will be interactive shortly) showing the cloud, wind, rainfall, temperature and pressure associated with the passage of a depression.

Find the animation and an associated worksheet here.

Categories
Science Weather

Coriolis Effect Film

We are delighted to announce a new and exciting short animation explaining the physics behind the Coriolis Effect.

The film can be found on our In Depth – the Coriolis Effect page.

Categories
Weather

Will El Nino affect our winter weather?

One of our associated teachers has put together an excellent summary of the El Nino Southern Oscillation and how it affects the rest of the world at http://rgsweather.com/2015/11/01/el-nino-how-does-it-impact-uk-winter-weather/.

We’ve also got a list of other useful links and there have been some lovely images recently of the Atacama desert in bloom as a result of increased El Nino related rainfall in South America.