ST. ANDREW’S HIGH SCHOOL

transcript

GEOGRAPHY DEPARTMENT

HIGHER GEOGRAPHY

Higher GeographyAtmosphere

INTRODUCTION

Atmosphere in the news

Global warming

Hole in the ozone layer Climate

change

Skin cancers

Acid rain

Greenhouse gases

CFC’s

Although considered a difficult topic, this is the most up-to-date of the basic units!

Atmosphere

In this unit we will be covering the following topics:

Topic 1: Global Insolation Topic 2: Atmospheric Circulation Topic 3: Oceanic Circulation Topic 4: Air Masses Topic 5: Climatic Change

Atmosphere

Today we are going to find out:

What the atmosphere is and why it is important.What global insolation and the heat budget are.Why variations in insolation occur.

Atmosphere

What is the atmosphere? Originally formed as the earth cooled, the atmosphere is a blanket of gases which contains solid material, such as volcanic dust and blown soils, and is attached to earth by the force of gravity.

Atmosphere

This atmosphere is a mixture of oxygen (21%), nitrogen (78%), carbon dioxide (0.037%) and other gases such as hydrogen, helium, argon, neon, krypton, xenon and ozone. It also contains water vapour.

These gases are densest at the Earth's surface and get less dense with increasing height. Around 90% of the atmosphere by weight lies in the lowest 15 km (9 miles) above the surface and it is only a very thin skin of air that keeps all life on Earth alive.

Atmosphere

1) The troposphere contains approximately 75% of the atmosphere's mass, and has an average

depth of about 16 km. The troposphere is is where weather systems develop.

There are five main layers in the atmosphere. Atmosphere

2) The stratosphere 16-50km is dry with rising temperatures. It contains large amounts of ozone gas which protects life on earth by filtering out most of the Sun’s harmful rays. 3) Many rock fragments from space burn up in the mesosphere 50-90km (middle sphere). As it lies between the maximum altitude for aircraft and the minimum altitude for orbital spacecraft, this is the most poorly understood part of the atmosphere.

Atmosphere

4) The thermosphere is directly above the mesosphere. Within this layer, ultraviolet radiation causes ionization. The thermosphere, named from the Greek (thermos) for heat, begins about 80 km above the earth and can experience temperatures of 2,500°C.

Atmosphere

5) The upper limit of our atmosphere is the exosphere. The main gases within the exosphere are the lightest gases, mainly hydrogen, with some helium, carbon dioxide, and atomic oxygen.

Atmosphere

Topic 1: Global Insolation

Insolation: incoming solar energy Less than half the incoming solar energy actually penetrates to the surface of the earth. The rest is lost in a variety of ways.

Atmosphere

The Global Heat BudgetIncoming heat being absorbed by the Earth, and outgoing heat escaping the Earth in the form of radiation are both perfectly balanced.

If they were not balanced, then Earth would be getting either progressively warmer, or progressively cooler with each passing year. This balance between incoming and outgoing heat is known as Earth’s heat budget.

Atmosphere

As the sun’s rays pass through the atmosphere, some are reflected, some absorbed and some pass through to reach the earth’s surface.

Atmosphere

Variations in Insolation Because the earth is a sphere, there are variations in the amounts of insolation received in different places.

Both bands of solar radiation are of the same strength.

The band near the north pole though has to heat a large area (D-E) due the curve of the earth.

The band at the equator can concentrate its heat in a smaller area A-B

AGAIN, COPY AND MEMORISE THIS

DIAGRAM!

Atmosphere

Latitudinal Variations in insolationAtmosphere

Radiation Budget We can also compare energy received by the earth (insolation) with energy lost by radiation (terrestrial radiation).

Insolation: solar energy received by the earth. Terrestrial radiation: solar energy lost by

radiation. At the equator: insolation is greater than terrestrial

radiation (due to darker forest material and higher land concentration), leading to a surplus in energy.

At the polar zones, insolation is weak and terrestrial radiation is high (due to lighter light-reflecting snow + lower land concentration), leading to an energy deficit.

Atmosphere

Seasonal Insolation Not only does insolation vary with latitude, it

also varies with season.

Because of the earth’s tilt, during the northern summer the sun is overhead at the Tropic of Cancer, and the Artic regions receive insolation 24 hours per day.

However, in the northern winter, the sun does not shine on the Artic, so there is no insolation at all.

Atmosphere

Factors Affecting Insolation

The Green House Effect

Atmosphere

What were the key points for ‘Variations in Isolation’

Albedo Affect◦ Equator’s surface – low reflection (high insolation)◦ Pole’s surface – high reflection (high terrestrial radiation)◦ (land cover)

Earth’s tilt◦ Earth’s orbit around the sun◦ Winter solstice – polar region – no solar insolation◦ Tropics – yearly solar insolation

Earth is a sphere◦ Concentrated rays at equator◦ Intensity from vertical rays

Atmosphere

Topic 2 Atmospheric CirculationThis diagram

shows how heat from the Equatorial area is transferred to the polar regions by the circulation of the atmosphere in the Northern Hemisphere.

Atmosphere

Insolation in tropical areas causes warm air to rise and spread polewards, carrying heat energy.

CELLS AND HEAT TRANSFER

The 3 CELL MODEL: The Formation of a Hadley Cell

SOLAR ENERY

INSOLATION

Nb; lots of new terms to learn!

Atmosphere

SOLAR ENERGY

Air cools and begins to fall at about 30ºN and 30ºS of Equator. Cooled air returns to the Equator.

Heat energy is therefore transferred from the Equator to sub-tropical latitudes.

NORTHERN HADLEY CELL

SOUTHERN HADLEY CELL.

Atmosphere

FORMATION OF THE POLAR CELL

Intensely cold, dense air sinks at the poles, then blows as surface winds towards the Equator.

Atmosphere

This circular motion is called the POLAR CELL.

At about 60ºN and 60 ºS, the cold polar air is warmed in contact with the earth’s surface. This warmed air rises and returns polewards, carrying heat energy.

NORTHERN POLAR CELLS.

SOUTHERN POLAR CELLS.

Atmosphere

FORMATION OF THE FERREL CELL

The Polar Cell causes an uplift at about 60ºN and S. )

Unlike the Hadley and Polar Cells, the Ferrel Cell is not driven by differences in heat energy.The Ferrel Cell is caused by friction where air is in contact with the other two cells.(The Hadley Cell drags air down at about 30ºN and S.

Atmosphere

THE THREE CELLS

TOGETHER Ferrel Cell

Polar Cell

Hadley Cell

Polar Cell

Ferrel Cell

Hadley Cell

Atmosphere

ASSOCIATED PRESSURE BELTS

Rising air at the equator causes the equatorial belt of low pressureDescending air at about 30ºN and 30ºS causes the sub-tropical belt of high pressureRising air at about 60ºN and 60ºS causes a mid-latitude belt of low pressure Descending air at the poles causes the polar high pressure areas

Mid latitude low pressure

Equatorial low pressure

Sub-tropical high pressure

Polar high pressure

Atmosphere

ASSOCIATED SURFACE WIND PATTERNS

Winds always blow from high pressure to low pressure.They are deflected because of the Coriolis Force which come about because of the rotation of the earth. ( see later slide)Winds in Northern Hemisphere are deflected to the right.

Winds in the southern hemisphere are deflected to the left.

These wind belts shift seasonally. (See next section)

Equatorial low pressure

Polar high pressure

Atmosphere

Answer these questions fully in sentences.

Q1. What kind of pressure has rising air?A.Low pressure has rising air.

Q2. What kind of pressure has falling air?B.High pressure has falling air.

Q3. Name two latitudes with rising air.C.The Equator and 60 degrees N/S have rising

Q4. Name two latitudes with falling air.D.30 degrees N/S and the Poles have falling air.

Atmosphere

Q5. Explain the two factors that make the NE trade winds blow in the direction they do.

( You will need to be able to do this for any of the winds in diagram 13 !)

i) Air is flowing from a high pressure area at 30 degrees north towards a low pressure area at the Equator.ii). The winds are being deflected by the

Coriolis force/ effect to the right as the area is in the northern hemisphere.

Atmosphere

Rossby waves and the Jet StreamNot far above our heads in the northern UK is where the Ferrel and Polar cells meet.

Here is where powerful waves of turbulence occur called Rossby waves.

This turbulence is mainly responsible for the series of depressions and anticyclones that happen over Britain.

Atmosphere

What are Rossby waves and jet streams?

Rossby waves are high altitude, fast moving westerly winds, which often follow an irregular path. The path that they take changes throughout seasons, as shown in the diagram below:

See the website for more information onRossby Waves and the Jet Stream.

THE CORIOLIS EFFECT

What happens when you set off in a plane to fly to somewhere?The earth turns beneath you, and you have to keep adjusting your direction ! Watch……….

Atmosphere

destination

Destinationhas moved

Direction of Earth-spin

direction

Twenty minutes in

Thirty minutes in

Got the idea? Note the runners path is curved!

Initial direction

Ten minutes in

Atmosphere

Watch Episode 1 of ORBIT

Atmosphere

Ocean CurrentsAtmosphere

Ocean CurrentsYou need to know how the ocean currents work in one ocean. The Atlantic will do.You need to remember the names of the currents and the directions in which they travel. You must know whether they are hot or cold.Note how the ocean currents also obey the Coriolis Force Laws.

Atmosphere

AtmosphereAtmospheric Circulation

So far, we have concentrated on the circulation of the air throughout the depth of the atmosphere.Now it is time to look in detail at air movements near the earth’s surface.It is easier to understand and remember this movement if we start with the global pressure belts.In theory, the global pressure belts are perfectly balanced north and south of the Equator.

Atmosphere

The Main Global Pressure Belts

There is a band of Low Pressure at the equator.There are two bands of High Pressure between 300 and 400 north and south of the Equator.There are two bands of Low Pressure around 600 north and south of the Equator.

There are two bands of High Pressure over the North and South Poles.

Atmosphere

OCEAN CURRENTS and HEAT TRANSFER

Water heats up and cools down very slowly.But once it has stored it, it holds on to that temperature for a long time. As currents move, they transport heat and cold around the globe.

Copy this

The pattern of ocean currents is linked to the pressure belts and wind patterns.Land masses disrupt an otherwise straight-forward water flow pattern.Winds blowing over currents assist them in transferring heat from warm to cool areas and vice versa.Winds deflected by the Coriolis force help to create the currents.The nature of the current affects the land masses it flows beside.

CASE STUDY AREA- the ITCZ in AFRICA

You will need to be able to give very detailed answers to a question on this area in an assessment.

This case study shows the way that the movement of the wind belts between their summer and winter positions has a profound effect on the lives – indeed the very survival- of people who live in the Sahel zone of northern Africa.

You will need an atlas for most of this section. Get one now.

The ITCZ is an area where two air masses meet- it brings heavy rain to the areas it passes over. It happens all round the world between the Equator and about 20 degrees N/S. Its full name is the Inter Tropical Convergence Zone. It is part of the Hadley convection cells, and has the Doldrums within its boundary.

Copy text

The ITCZ does not stay in the same area all year round but migrates to the north and then back south again.It is this movement that matters so much to the people and animals of the area.

The AFRICAN ITCZ REGION

Discuss this diagram

The trade winds ( mT air mass) come into the zone from cooler areas in the southern mid- latitudes and have travelled over oceans; they are therefore carrying a lot of moisture. This is their position in January. Once in the hotter latitudes, they are energised into huge towering cumulo-nimbus thunderclouds. These can be anything up to 10kms across, and groups of clouds can form covering 1000kms. In between the clusters are often sunny cloud-free areas. The clusters are particularly found over land, not sea.

Wet warm mT air

HEAVY RAINS

Gulf of Guinea

Coastal areas- equatorial climate

Inland areas- savanna climate type

Sahara- Desert climate type

Moves this way

Hot dry cT air

‘Harmattan’ wind

IN JANUARYCopy diagram

In January, the sun is overhead near the Tropic of Capricorn, in the southern hemisphere.The ITCZ zone of meeting air lies well to the south, as seen here.The rains brought by the zone are confined to the very coastal areas of Nigeria, Togo, Ghana and their neighbours.

ITCZ JANUARY

Case study area

AtmosphereThe Inter Tropical Convergence Zone- The ITCZ

The movement of the ITCZ and its effects on rainfall can be best understood by examining the situation in Africa.

23.50N

Equator

Warm, Moist Winds (mT)

Warm, Dry Winds (cT) 23.50N

23.50S

Equator

January

The ITCZ in Africa In January

The ITCZ in Africa In July

Warm, Dry Winds

23.50S

SE Trade Winds

NE Trade Winds

Warm, Moist Winds

AtmosphereThe Changing ITCZ

The ITCZ moves north and south over Africa to “follow the sun”. However, the ITCZ sticks over the land areas since the land is warmer than the sea causing lower pressure over he land than over the area.

July September

November

ITCZITCZ

AtmosphereThe Changing ITCZ

The ITCZ moves north and south over Africa to “follow the sun”. However, the ITCZ sticks over the land areas since the land is warmer than the sea causing lower pressure over he land than over the area.

January March May

ITCZ ITCZ

ATMOSPHERE

Here, the moist warm mT air from the Atlantic Ocean meets the hot dry cT air coming out of the Sahara Desert. Note that the desert is an area of HIGH pressure in winter and particularly strong winds blow AWAY from such areas.

The cT wind is called the HARMATTAN and is extremely hot, dry and dusty. Of course, the Harmattan cannot bring any rain to the area it travels over, and all the northern part of Africa is influenced totally by it. No crops can grow.

In the south, however, the wet moist winds from the sea are forced upwards over the land where they drench the land in life-giving torrential rains. Here crops can be easily grown, providing the soil is fertile enough and not washed away.

ATMOSPHERE

During the spring, the ITCZ moves slowly northwards, the Harmattan losing its dominance over the land bit by bit.

Places further and further inland get the rains that they so desperately need for people, crops and animals alike. The slight drawback is that the further the ITCZ travels north, the less water it can bring to the rainy area, so crops to the north get less than those to the south.

By mid spring, places like northern Ghana, northern Benin and central Nigeria are getting the rains. The wells are re-filled, the grass for feeding animals starts to grow and farmers can start off their crops.

ATMOSPHERE

Gulf of Guinea

Coastal areas- equatorial climate

Inland areas- savanna climate type

Sahara- Desert climate type

Wet warm mT air

Hot dry cT air

‘Harmattan’ wind

IN JULY

Moves this way

HEAVY RAINS LIGHT RAINS

Copy diagram

Compare the January and July diagrams.

ATMOSPHERE

There is a handout illustrating the two main climate types mentioned on the previous slide, affected by the ITCZ.

You will need to be able to recognise the differences between them in an exam question.

ATMOSPHERE

By July the ITCZ has reached as far north as it will go, reaching central Mali, northern Niger and northern Chad. There the Harmattan is confined to the very edges of the Sahara desert, the weakest it gets all year. This is the Sahel zone, the area most prone to DESERTIFICATION that you learned about in Standard Grade. Without these rains most years, the desert will take over yet more land, forcing poverty-stricken, hungry people to migrate southwards into other peoples’ territory, with their thirsty cattle and goats.

ITCZ JULY

ATMOSPHERE

After July, the belt moves back down south again, giving a second rainy spell to the lucky areas in its path. No more rain will fall this far inland until next year! The people rely on these rains that arrive within a week or two of the same time every year.Recently, there have been several years where the rain has not got as far inland as normal ! What do you think has been the result of this?

ATMOSPHERE

Read the article on the handout which highlights the human consequences of the failure of this pattern of rainfall.

Answer the 12 questions in your jotters.

Lesley MonkBalfron High School

Session 2005/6

ATMOSPHERE

GLOBAL WARMING – ARE WE TO BLAME ?

This is one of the most frequently asked environmental questions in recent times.

That the planet’s climate is changing, there is no doubt. But who or what is the reason for this is a hotly debated point.We shall put the evidence in front of you and let you decide!

So what is the answer ?

We really don’t know !

ATMOSPHERE

Graph 1 shows the temperature of the Earth over 1 million years. Note the line showing today’s average temperatures, and the arrow to the last Ice Age.Graph 2 is a close-up from the last few years of the Ice Age till today. Graph 3 shows the time since the Vikings began raiding Britain.

ATMOSPHERE

WHAT EVIDENCE IS THERE OF GLOBAL WARMING ?

1. ICE CORE ANALYSIS-Air trapped in ancient snow- now ice- can show what the atmosphere was like millions of years ago.

2. TREE RING ANALYSIS-Tree rings record good and bad years for tree growth and can go back to prehistoric times.

4. POLLEN ANALYSIS-This will show the types of plants that were growing in an area millions of years ago, and we can work out the likely conditions from comparison with today’s plant needs.

Copy text3. OCEAN FLOOR

SEDIMENTS-The mud in the ocean deep has been there for millennia and can be analysed for oxygen isotopes.

ATMOSPHERE

So you can see that our planet hasn’t exactly had a stable climate !

But are we responsible for the changes, or is it natural forces at work?

Read pages 25 and 26 of the booklet. You will need to be able to discuss each of these factors in a way that shows you appreciate their potential importance.

ATMOSPHERE

Physical Factors

• Solar variation• Volcanic activity• Ocean currents• Milankovitch

cycles

Human Factors

Burning fossil fuels Increased output of methane etc.

Deforestation

There are different possible causes of these raised temperatures. They fall into two categories- Physical and Human.

Let’s look at each in turn.

ATMOSPHERE

PHYSICAL 1 - SOLAR VARIATIONSunspots: an increase in sunspot activity may lead to a very slight increase in the sun’s output and a temporary warming of the earth.

Sunspot activity follows 11 and 22 year cycles.

The Little Ice Age of 1450-1700 may have been linked to periods of very low sunspot activity.

ATMOSPHEREPHYSICAL 2 - VOLCANIC ERUPTIONS

• Eruptions of volcanoes can throw millions of tonnes of ash,dust and sulphur dioxide into the atmosphere.

• This produces aerosols that can reduce the amount of sunlight reaching the earth.

• This can lead to a temporary cooling of the earth.

ATMOSPHERE

VOLCANIC ERUPTIONS 2

• Major eruptions in the past which have been linked to short periods of global cooling include;-

• Tambora (1815), • Krakatoa (1883), • Mt. St Helens (1980) • Pinatubo (1991)

ATMOSPHEREPHYSICAL 3 – OCEAN CURRENTS

A longer term example would be the North Atlantic Drift, which may change position every few thousand years.

Changes in the pattern and strength of ocean currents may lead to changes in the distribution of heat around the planet. A short term example would be El Niño, which appears every few years.

ATMOSPHEREENSO - the El Niño Southern Oscillation

A La Niña year An El Niño year

The “normal” conditions, with cool surface water off the coast of Peru.

Every 2-7 years the western Pacific becomes much warmer, disrupting weather patterns - possibly on a global scale.

ATMOSPHERE

One theory suggests that global warming will increase the number of icebergs in the Atlantic, cooling the sea and switching off the North Atlantic Drift / Atlantic Conveyor system. This would be bad news for us!

ATMOSPHEREPHYSICAL 4 - MILANKOVITCH CYCLES

•Milankovitch cycles are three variations in the earth’s orbit. Although they may be linked to very long term changes in the climate, their effect would not be noticed on a scale of a few hundred years.

ATMOSPHERE

HUMAN FACTORS THE ENHANCED GREENHOUSE EFFECT.

ATMOSPHERE

These are the main greenhouse gases

See how they have increased over the years of industrial activity.

ATMOSPHEREHUMAN 1 - BURNING FOSSIL FUELS

The fossil fuels are:- COAL OIL NATURAL GAS

They are called fossil fuels because they are formed from the remains of ancient plants (coal) and marine animals (oil).

ATMOSPHERE

When we burn these fuels, we release millions of tonnes of Carbon Dioxide (CO2) into the atmosphere.

There has been an enormous increase in these greenhouse gases since the Industrial Revolution began about 200 years ago.

ATMOSPHERE

Power stations are one of the main producers of greenhouse gases such as

Carbon Dioxide.

ATMOSPHERE

Environmental campaigners all over the world are demanding cuts in CO2 emissions. Here Greenpeace uses a light display to get its message across.

ATMOSPHERE

Vehicle exhausts are the main source of Nitrous Oxides.

ATMOSPHERE

A cow can burp / fart about a quarter of a kg. of methane a day.

The number of cattle has doubled in the past 40 years. Sheep, goats and camels are also ruminants.

There are now 1.3 billion cattle, each burping / farting methane several times a minute!

The New Zealand government is proposing to bring in a “flatulence” tax on cattle farms.

I am a ruminant - when I digest grass, I produce methane - lots of

HUMAN 2 - INCREASED METHANE

ATMOSPHERE

The huge increase in world population and in the area of land given over to crops in general and to rice production in particular, has led to a rapid rise in global methane production. Farmland for rice has doubled in 45 years.

ATMOSPHERE

HUMAN 3 - DEFORESTATION

...if they are cut down, atmospheric levels of CO2 must rise as a consequence.

Forests absorb CO2 and release oxygen:

ATMOSPHERE

• Clearing forest by burning releases huge amounts of stored CO2 back into the atmosphere.

• The smoke from the fires also adds to global air pollution.

This is known as a double- whammy !

ATMOSPHEREKEY TERMS TO REMEMBER

Solar variation / Sunspots Volcanic eruptions /Sulphur dioxide /Aerosols Milankovitch cycles El Niño Enhanced Greenhouse effect Carbon Dioxide / Methane / Nitrous Oxides The Industrial Revolution / burning fossil fuels Padi fields / cattle / methane production Deforestation

CONGRATULATIONS !!

You have now finished the Higher Geography Course!

All that remains is to learn it all!

Lesley MonkBalfron High School

Session 2005/6

ATMOSPHERE REVISION

There are only a few types of questions they ask about;-

The principles of energy movement

around the planet

Energy budget diagramslike in slide 4

Cells and the way they move heat around-

not done for a few years !

The contribution made by ocean currents to

heat transfer.

ATMOSPHERE REVISION

The ITCZ and its effects

The principles explained

Data like maps and graphs described and

explained.

ATMOSPHERE REVISION

The causes and effects of climate change, including global warming.

World temperature fluctuation graph described

and explained

The human and physical causes of the greenhouse

effect named and explained.

These are often

combined!

ATMOSPHERE REVISION

Energy budget diagam-

Describe and explain the exchanges that result in only 50% of the potential Sun’s energy reaching the surface. (4)

ATMOSPHERE REVISION

Atmospheric winds circulation

diagram

Explain how the cells A,B and C, and their associated surface winds, help to distribute energy around the Earth. (4)

ATMOSPHERE REVISION

Ocean circulation diagram

Explain how the ocean currents operate to maintain an energy balance. (3 or 4 )This question has been known to focus on one ocean only to explain !

ATMOSPHERE REVISION

The principles of the ITCZ

Using the information on the maps and the graph, and referring to the characteristics of the two air masses shown, describe and account for the annual seasonal variations in rainfall in West Africa. (4)

ATMOSPHERE REVISION

Describe in detail and account for the pattern of annual rainfall shown in the diagrams. (5)

The effectsof the ITCZ

ATMOSPHERE REVISION

World temperature fluctuation graph

described and explained

Describe and give both human and physical reasons for the fluctuation in world temperatures shown in the graph. (5)

ST. ANDREW’S HIGH SCHOOL

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