OCR 2016 Geography B GCSE

Recommended Resources to Support the Teaching of Weather and Climate within this Specification

1.1 How can weather be hazardous?

a) Why do we have weather extremes?

  • Outline of the global circulation system including the effects of high and low pressure belts in creating climatic zones.
  • How the global circulation of the atmosphere causes extremes in weather conditions in different parts of the world.
  • The extremes in weather conditions associated with wind, temperature and precipitation in contrasting countries.
  • The distribution and frequency of tropical storms and drought, and whether these have changed over time.
  • Outline the causes of the extreme weather conditions associated with tropical storms.
  • Outline the causes of the extreme weather conditions of El Niño/La Niña leading to drought.

a) When does extreme weather become a hazard?

  • Case studies of two contrasting natural weather hazard events arising from extreme weather conditions. The case studies must include a natural weather hazard from each bullet point below: There must be one UK based and one non-UK based natural weather hazard event
  • For each chosen hazard event, study the place specific causes (including the extreme weather conditions which led to the event), consequences of and responses to the hazard.

2.1 What evidence is there to suggest climate change is a natural process?

a) What evidence is there for climate change?

b) Is climate change a natural process?

  • Outline the causes of natural climate change including the theories of sun spots, volcanic eruptions and Milankovitch cycles.
  • Investigate the natural greenhouse effect and the impacts that humans have on the atmosphere, including the enhanced greenhouse effect.

c) Why is climate change a global issue?

  • Explore a range of social, economic and environmental impacts of climate change worldwide such as those resulting from sea level rise and extreme weather events. The impacts studied should relate to the 21st century.
  • Explore a range of social, economic and environmental impacts of climate change within the UK such as the impact on weather patterns, seasonal changes and changes in industry. The impacts studied should relate to the 21st century.

4.2 Why should tropical rainforests matter to us?

a) What biodiversity exists in tropical rainforests?

  • The distinctive characteristics of a tropical rainforest ecosystem, including the climate

4.3 Is there more to polar environments than ice?

a) What is it like in Antarctica and the Arctic?

  • Outline the distinctive characteristics of Antarctica and the Arctic, including climate

7.1 How is the UK changing in the 21st century?

a) What does the UK look like in the 21st century?

  • Overview of human and physical geographical characteristics of the UK, including population density, land use, rainfall and relief, and significant issues associated with these characteristics, including water stress and housing shortages.

8.1 Will we run out of natural resources?

a) How has increasing demand for resources affected our planet?

  • Outline the factors leading to demand outstripping supply of food, energy and water.

8.2 Can we feed nine billion people by 2050?

a) What does it mean to be food secure?

  • Understand the term ‘food security’ and the human and physical factors which influence this.

Global Atmospheric Circulation

One part of the Earth’s surface is always facing the Sun – it varies between the Tropic of Cancer at the June solstice to the Tropic of Capricorn at the December solstice.

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This latitude receives the most energy per unit surface area, and is known as the Inter-Tropical Convergence Zone or ITCZ. Here, the air rises, hits the top of the troposphere and spreads out towards the poles. The Coriolis Effect means that this poleward moving air is deflected ever more to the right, becoming westerly (remember we name winds by the direction they are blowing from) and eventually sinking in the sub-tropics and returning towards the ITCZ – this time becoming easterly and giving us the Trade Winds. The whole circulation is known as the Hadley Cell (Figure 1).

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Figure 1: A cross section through the atmosphere, showing air rising and forming deep clouds, at the InterTropical Convergence Zone and spreading polewards, and the Hadley, Ferrell and Polar cells.

Similarly, at the poles where the ground surface is coldest, the air sinks, spreads out towards the Tropics, is deflected to the right and eventually rises and completes a circulation – the Polar Cell.

In between, lies the ‘Ferrel cell’, characterised by surface westerlies and rising motion around 60°. This cell is actually the net product of all the mid-latitude weather systems. Figure 2 shows the 3-Dimensional circulation of the atmosphere.

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It’s worth noting that, if the Earth wasn’t rotating, we’d have just one ‘thermally direct’ cell with air rising at the ITCZ and sinking at the poles where the ground is coldest.

The polar and sub-tropical High pressure areas are the source regions for air masses.

Data and Image Sources

Take a look at the current air flow on the surface of the Earth, can you make out the Trade Winds? Do they tend to be stronger over land or ocean? Where is the ITCZ at the moment?

 

Coriolis Effect

As air blows from high to low pressure in the atmosphere, the Coriolis force diverts the air so that it follows the pressure contours. In the Northern Hemisphere, this means that air is blown around low pressure in an anticlockwise direction and around high pressure in a clockwise direction.

Think about a person standing at the Equator. In the course of a day, the planet rotates once, meaning that you travel a colossal 2π x R (the radius of the Earth – 6370km) = 40,000km through space – a speed of about 1700km/ hr. You don’t notice that you are travelling so fast, because the air around you is travelling at the same speed, so there is no wind. On the other hand, if you are standing at a Pole, all you do in the course of a day is turn around on the spot, you have no speed through space and similarly the air around you is stationary.

Now, think about really fast moving, Tropical air which is being pulled towards the poles by a pressure gradient. As it travels polewards, it moves over ground which is rotating more slowly, and so it overtakes the ground, and looks like it is moving from west to east. Similarly, slow moving polar air will be left behind by the rotating Earth and look like it is moving from east to west if it is pulled equatorward by a pressure difference.

In general, moving air in the Northern hemisphere is deflected to the right by the Coriolis Effect.

As the air blows from high to low pressure the Coriolis force acts on it, diverting it, and we end up with air following the pressure contours and blowing around low pressure in an anticlockwise direction and around high pressure in a clockwise direction (both true only for the Northern Hemisphere).

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Figure 1:Schematic representation of flow around a low pressure area. Pressure gradient force represented by blue arrows. The Coriolis force, always perpendicular to the velocity, by red arrows. © SVG version, Roland Geider (Ogre), of the original PNG, (Cleontuni)

In this diagram, the black arrows show the direction the air is moving in. The Coriolis force pulls the air to the right (red arrows). As the air is being pulled in to the depression by the pressure gradient (blue arrows), it is continuously deflected by the Coriolis Force. When the air moves in a circle around the depression, the Coriolis force (red arrows) is balanced by the pressure gradient force (blue arrows).

In summary, for the Northern Hemisphere:

  • Low pressure is called a cyclone and has anticlockwise winds blowing around it.
  • High pressure is called an anticyclone and has clockwise winds blowing around it.
  • The wind tends to blow along the pressure contours.
  • We name winds by the direction they are blowing from.
  • Buys Ballot’s Law states that “In the Northern Hemisphere, if you stand with your back to the wind then the lower pressure will be on your left”
  • Alternatively, some people find the rule ‘righty tighty, lefty loosey’ a useful reminder of the direction of rotation – high pressure is like tightening a screw (righty tighty) and low pressure like loosening a screw (lefty loosey) (Figure 2).

depressions_hemispheres

Figure 2: Air blows around a low pressure in an anticlockwise direction and around a high pressure in a clockwise direction in the Northern Hemisphere © RMetS

What about the Southern Hemisphere?

In the Southern Hemisphere, winds blow around a high pressure in an anticlockwise direction and around a low pressure in a clockwise direction.

The simplest way of visualising why this is the case is to take a ball (or an apple or orange, or anything spherical!). Mark on the poles and the equator, and then mark a spot in the ‘northern hemisphere’ and the ‘southern hemisphere’ of your sphere. Rotate your sphere. Keeping it rotating, tilt your sphere so that you are looking at it from the North Pole – your northern hemisphere spot should be going round in an anticlockwise direction. Now, making sure you keep rotating your sphere in the same direction, tilt it so that you are looking at the ‘south pole’. Your southern hemisphere spot should be rotating in a clockwise direction. This demonstration doesn’t explain the Coriolis effect, but it does show how things can be seen differently in the two hemispheres of the same planet.

Data and Image Sources

For an example of wind blowing along pressure contours, see the BBC website.

http://www.metlink.org/wp-content/uploads/2013/11/media/video/coriolis.mov

Air Masses

An air mass is a large body of air with relatively uniform characteristics (temperature and humidity). Air masses are classified according to their source region and track.

There are six air masses (Figure 1) which can affect the weather in the UK – Polar Maritime is the most common, but we can also experience Polar Continental, Tropical Maritime, Tropical Continental, Arctic Maritime and Returning Polar Maritime air.

The source regions tend to be semi-permanent anticyclones (associated with the sinking regions of the global atmospheric circulation) in the sub-tropics and polar regions (‘tropical’ or ‘polar’ air). Air masses acquire their characteristics by contact with the underlying surface in the source region.

The UK sometimes also get Arctic air, which has travelled straight south from the Arctic. Returning polar air is polar air which changed direction over the Atlantic, hitting the UK from the west or even south of west, but still polar in nature.

A map showing the directions the 6 air masses that hit the UK . Artic Maritime air comes from the north, Polar Continental air comes from the northeast, Tropical Continental air comes from the south, Tropical Maritime air comes from the southwest, Polar Maritime comes from the northwest with the returning Polar Maritime air hitting the UK from the west.

Figure 1: The 6 air masses which can affect the weather in the UK

Southward moving air is warmed from below as it passes over warmer land and water and becomes more unstable, eventually rising and producing convective cloud – eg puffy cumulus clouds. When you look at these clouds you can sometimes watch the air rising and the cloud bubbling up. In contrast, northward flowing air is cooled from below and becomes more stable.

Air travelling over the sea is moistened and we refer to this as ‘maritime’ air, whereas the moisture in air with a continental track hardly changes and so this is known as ‘continental’ air.

Looking at Figure 1, it’s easy to think that the North East of the UK always experiences Polar Continental air, whilst the South West always experiences Tropical Maritime air etc, but this is not the case. Usually, the whole country experiences the same air mass at the same time. A front is where two air masses meet.

The table below which summarises what is happening to the air from the four major air masses as they approach the UK.

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The satellite image in Figure 1, shows Tropical Continental air over much of continental Europe and the UK. Although there is a front coming in from the west, before it arrives much of the UK is cloud free and sunny. However, it’s worth noting those small, puffy blobs of cloud over the centre of Spain and France. In small areas, the sun has warmed the ground enough to make the air there rise and form localised summer thunderstorms.

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In Figure 2 you can see a typical satellite image showing Polar Continental air. Air blowing off Scandinavia is initially very cold and dry, giving a clear band of sky in the east North Sea and Baltic. However, as it travels over the water it picks up moisture and eventually cloud forms – over the western North Sea and the first bit of the UK it reaches – the east coast.

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Figure 3, shows a very characteristic winter satellite image, as Polar Maritime air dominates UK weather. In the winter, the ocean is warmer than the land as well as being the moisture source – most of the convection (warm air rising) and rainfall occurs there. You can see the small blobs of convective cloud – puffy, cumulus clouds. The first bit of land the air reaches will be the west coast of Ireland, Wales, Scotland and England. As the air rises over the land, it cools further and more cloud, and rain, form.

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In Tropical Maritime air (Figure 4), the air is cooling as it travels North, so the cumulus clouds associated with convection don’t form. However, the air is cooling without rising, so cloud can still form – this time in large horizontal sheets of stratus cloud. Again, the water source is the ocean, so the cloud mainly forms there. This cloud won’t produce rainfall as heavy as that associated with polar air, but might give a steady drizzle.

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Teaching Resources

http://www.metlink.org/wp-content/uploads/2013/06/Air-Masses-Human-Board-Game.pdf

http://www.metlink.org/secondary/key-stage-4/airmasses-2/

http://www.metoffice.gov.uk/learning/learn-about-the-weather/how-weather-works/air-masses

http://www.metlink.org/secondary/key-stage-4/airmasses/

Case studies of UK air masses (November 2010, November 2011 and the end of September 2010) with answers for teachers and a case study of arctic maritime air (Jan/ Feb 2015) can be found on our case studies page.

Data and Image Sources

Take a look at the current surface air flow on earth.nullschool.net. Which air mass is affecting the UK now?

The followingYouTube clip from the BBC programme, The Great British Weather gives a great introduction to air masses.

Climate Zones

Climate zones.

Some introductory ideas on Climate Zones

 

Teaching Resources

http://www.metlink.org/wp-content/uploads/2013/11/work_schemes/lesson3_pritchard.pdf

Data and Image Sources

http://www.viewsoftheworld.net/wp-content/uploads/2014/12/AnnualPrecipitationAnimation.gif

 

El Nino/ La Nina

Every few years a very noticeable change comes about in the temperature of the equatorial Pacific Ocean. The eastern side, which is usually the coolest part, warms up considerably, particularly in the ‘tongue’ of cold water in the equatorial east Pacific seen in Figure 1, whilst temperatures in the west decrease a little.

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Figure 1: Annual mean sea surface temperature (degrees C), averaged from 1971-2000. Note the very warm water in the tropical west Pacific and the cold “tongue” along the equator in the east Pacific.© US Climate Prediction Center

The result of this is that the gradient of temperature from east to west decreases. The atmosphere responds to this change with the heaviest rainfall moving out into the centre of the equatorial Pacific and the eastern side of the ocean also becomes much wetter. This shift has a big impact on land regions bordering the equatorial Pacific. Northeast Australia and Indonesia/Papua new Guinea become much drier whilst coastal parts of Peru and northern Chile, which are usually rather dry, experience much more rain.

The increase in ocean temperatures is known as an ‘El Niño’ event and has been known about for well over 100 years. The name, which means ‘the boy child’ in Spanish, derives from the fact that the warming tends to be strongest around Christmas time and was named by the fishermen of Peru. They noticed that, around Christmas every 3-7 years or so the fish stocks in the equatorial Pacific reduced as the water warmed. The opposite phenomenon often occurs the following year when the eastern equatorial Pacific becomes even colder than normal and the west becomes even warmer. This leads to flooding in Indonesia and eastern Australia and drought conditions in Peru and Northern Chile. This state of the ocean is known as ‘La Niña’, or the ‘girl child’.

Both El Niño and La Niña affect weather patterns far beyond the equatorial Pacific as the whole global pattern of winds and precipitation in the atmosphere adjusts to the changes in the Pacific. The southern USA tends to experience wetter winters during El Niño episodes whereas north-eastern Brazil and south-east Africa become drier than normal. Western Canada, south-east Asia and Japan all tend to be warmer than normal during an El Niño event and in fact the average temperature of the atmosphere averaged around the whole globe tends to be higher than normal in the months during and immediately following an El Niño event, as vast amounts of heat are transferred from the ocean into the atmosphere.

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The processes in the ocean and atmosphere that control the evolution of El Niño events are complex.

Teaching Resources

El Nino Southern Oscillation introduction

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/.

The US National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC) has an excellent web-based tutorial.

Data and Image Sources

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.

Food Security

http://www.metlink.org/ipcc-updates-geography-teachers/#9

Teaching Resources

Data and Image Sources

Water Security

http://www.metlink.org/climate/ipcc-updates-for-a-level-geography/security-of-water-supplies/

Teaching Resources

Data and Image Sources

Extreme Weather

Weather records will always be broken!

Further Information

http://www.metlink.org/other-weather/miscellaneous-weather/depth-extreme-weather-met-office/

Teaching Resources

What do we mean by Extreme Weather? Data analysis.

Community experience of extreme weather Fieldwork/ investigation

http://www.yourclimateyourlife.org.uk/a_extreme_weather_fieldwork.html

Work scheme on extreme weather including tropical storms

Data and Image Sources

 

UK Flash Flood Events

An introduction to flooding.

 

Other useful flooding links

Teaching Resources

A flooding worksheet (aimed at A level but easily adaptable).

resources from CEH to come

Data and Image Sources

National River Flow Archive http://nrfa.ceh.ac.uk/

Current UK river levels http://www.gaugemap.co.uk/

Tropical Storms

Teaching Resources

http://www.metlink.org/teachers/useful-links/#tropical

Work scheme on extreme weather including tropical storms.

http://www.metlink.org/wp-content/uploads/2013/11/work_schemes/lang_gis_hurricane_task.pdf

http://www.metlink.org/teachers/teacher-development/extreme-weather-2/

 

Data and Image Sources

Drought

http://www.metlink.org/other-weather/weather-hazards/drought/

Teaching Resources

Data and Image Sources

Heat Wave

A case study of the 2003 heat wave.

A case study of the 2013 heat wave.

Teaching Resources

Data and Image Sources

Past Climate Change

 

Teaching Resources

Past Climate Change teaching resources

Data and Image Sources

Tempest database

Climate Change

Considerably more information can be found at our Climate Change Updates for Geography Teachers pages and in our general past climate change resources/ section.

Teaching Resources

http://www.metlink.org/teachers/teacher-development/climate/

Climate Change Schools Project

Data and Image Sources

UK climate projections and associated teaching resources

Rainfall and Relief

Precipitation has been recorded in the British Isles for over 200 years. Through the dedication and enthusiasm of W R Symons, the mid-19th century saw the formation of the British Rainfall Organisation whose main objective was to establish a countrywide network of rain gauges where daily measurements were made. This network has grown to over 7,000 gauges today, including many that are automatic.

As most people in the British Isles know, precipitation can be extremely variable, both in intensity and duration. The spatial distribution of precipitation during an individual month is very uneven, just as it is on an individual day. Rainfall in Britain is associated with several distinct synoptic situations; all places may get rain from most such types, but some areas get more from some types than others. Therefore, it is not surprising that patterns of temporal variation of rainfall are complex.

Precipitation over the British Isles is the result of one or more, of three basic mechanisms.

1. Cyclonic, or frontal, rain associated with the passage of low-pressure systems. Bands of rain are associated with the passage of warm and cold fronts across the UK. These rain events are caused by the uplift and cooling of moist air parcels.

2. Convectional, with local showers and thunderstorms, caused by the localised thermal heating and overheating of the ground surface. Large towering cumulonimbus clouds may be generated, producing heavy rain.

3. Orographic, or relief rain, with precipitation increasing with altitude over upland areas. The mechanism for relief rain is the uplift and cooling of moist air over upland areas. The normal rate of cooling (environmental lapse rate) is 6.5 °C per 1,000 metres. Therefore, near the summit on the windward side of the hill or mountain, the air will have cooled sufficiently for thick cloud, rain and possibly snow to fall.

Air will descend and warm on the leeward side, so there is little or no rain on this leeward side of the hill or mountain. This is called a rain shadow, and sometimes there are warm winds in these sheltered areas as the air, now much drier than during its ascent, descends quickly and warms up. This is called a föhn effect, and the warm winds are called föhn winds.

Rain forms when air cools, the rate of condensation becomes faster than the rate at which water is evaporating and cloud droplets form. If these get big enough, they form as rain – or snow, sleet or hail.
There are various ways in which the air can cool to form rain – three common types which are often talked about are frontal, orographic or relief and convective rain.
Frontal Rain
This is found where warm air meets cold at the cold and warm fronts in a depression.
front
Convective Rain
Convection is the term given to warm air rising. Convection is normally marked by cumulus clouds which billow upwards as the air rises. The base of such clouds is usually flat, marking the level where temperatures are cold enough for more condensation to be going on than evaporation.
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Image copyright RMetS
Extreme convection can be found in thunder clouds – towering cumulonimbus, which can reach all the way up to the top of the troposphere – the lowest 10km or so of the atmosphere in which our weather is found. As air can’t rise into the stratosphere above, the top of the cumulonimbus cloud spreads out, giving it a characteristic ‘anvil’ shaped top. Such convection can occur where the ground has become particularly warm, heating the air above it. It is particularly associated with the Tropics, characteristically giving heavy rain in the late afternoon.
Cumulonimbus clouds can give heavy rain, hail, thunder lightning and sometimes tornadoes.
Cb_Kettering
Cumulonimbus cloud over Kettering, UK, August 2014
Image copyright Sylvia Knight

Orographic or Relief Rain
When air is forced to rise over land, particularly higher ground such as hills and mountains, it cools as the pressure falls. Dry air cools at 9.8°C per 1000m it rises. Eventually, the air can cool enough for cloud to form.
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Orographic cloud forming upstream of the Matterhorn
Image copyright RMetS
The cloud droplets may get big enough to fall as rain on the upstream side of the mountain. If that happens, then, when the air has passed over the top of the mountain and starts to descend, and warm, on the far side, there will be less water to evaporate back into the air. The air will end up drier than it was on the upstream side of the mountain.
This can produce ‘rain shadow’ – an area of land downstream from some mountains (for the prevailing wind direction, in the UK, this would be to the east) where there is noticeably less rainfall. The Gobi desert in Mongolia and China is so dry because it is in the rain shadow of the Himalayas.
Orography can enhance frontal or convective rain; for example, we have explored how polar maritime air, our prevailing air mass, brings convective rain to the Atlantic. As the air reaches the UK and rises over the land, the precipitation is increased.
UK_precip
A precipitation map showing the rainfall ‘climate’ (averaged over 30 years) of the UK. With prevailing westerly winds, there is clearly more rain on the western side of the country, enhanced by the mountains of Wales and Scotland and the English Pennines.
As well as being drier on the downwind side of the mountains, it can also be warmer. Remember that water releases heat into the atmosphere as it condenses and takes it up as it evaporates. If there is less water in the air on the downwind side, then there is less to evaporate and not all the heat that was released on the upwind side will be taken up again. This is known as the Föhn Effect.
The onset of a Föhn is generally sudden. For example, the temperature may rise more than 10°C in five minutes and the wind strength increase from almost calm to gale force just as quickly. Föhn winds occur quite often in the Alps (where the name originated) and in the Rockies (where the name chinook is used). They also occur in the Moray Firth and over eastern parts of New Zealand’s South Island. In addition, they occur over eastern Sri Lanka during the south-west monsoon.
Where there are steep snow-covered slopes, a Föhn  may cause avalanches from the sudden warming and blustery conditions. In Föhn conditions, the relative humidity may fall to less than 30%, causing vegetation and wooden buildings to dry out. This is a long-standing problem in Switzerland, where so many fires have occurred during Föhn conditions that fire-watching is obligatory when a Föhn is blowing.

Teaching Resources

A case study of orographic rainfall and Foehn winds in Scotland with images for students Image 1, Image 2, Image 3, Image 4, Image 5.

 

Data and Image Sources

UK climate data from the Met Office

 

Other useful links.

Further KS4 resources.

Link to OCR website for the full specification.