atmosphere

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Higher Geography Core UnitHigher Geography Core UnitATMOSPHEREATMOSPHERE

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By the end of this topic you should be able to:

explain with the aid of an annotated diagram, why Tropical latitudes receive more of thesun’s energy than Polar regions

explain why there is a net gain of solar region in the Tropical latitudes and a net loss towards the poles

describe the role of atmospheric circulation in the redistribution of energy over the globe

describe and explain the earth’s energy exchanges shown on a diagram

describe the factors which affect the amount of sunlight reflected from the earth’s surface

describe and account for the generalised pattern of atmospheric circulation and globalwinds, or ocean currents shown on a world map

describe the variations in world temperature for the last 100 years (shown eg. on a graph)and suggest both physical and human reasons for these variations

describe and explain the origin, nature and weather characteristics of Tropical Maritime (mT)and Tropical Continental (cT) air masses which affect West Africa

with reference to the Inter-Tropical Convergence Zone and the movement of air masses,describe and account for the variations in West African rainfall.

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GMTs

describe and interpret climate maps, diagrams and graphs

construct and analyse climate graphs

describe and explain climate graphs

comment on the accuracy of statements which describe climate patternsshown on maps etc.

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The Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by the Earth's gravity.

This mixture of gases is commonly known as air.

The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.

For tomorrow’s lesson…

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ATMOSPHERIC GASES

Nitrogen - 78%Oxygen - 21%

Carbon dioxide - 0.036% …...and rising!! Water vapour - variable - up to 4% over tropical oceans.(as humidity increases the relative amounts of othergases decrease).

Inert gases, dust and pollutants make up the rest of the atmosphere.

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Troposphere

• The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its water vapor and aerosols.

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Tropopause

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Stratosphere

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Mesosphere

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Thermosphere

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Thermosphere

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Troposphere = main zone of weather and climate.

lapse rate

= decrease in temperature with altitude

= 6.4ºC for every 1000metres

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Mt Everest (8800metres)Calculate the difference in temperature between sea level and the summit of the mountain.

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Global extremes of Temperature

58ºCSan Luis

Potosi, MexicoAl Aziziyah,

Libya

-88ºCVostok

Antarctica In the absence of an atmosphere the Earth would average about 30ºC

less than it does at present. Life (as we now know it) could not exist.

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absorbed by clouds and dust, water vapour and other gases in the atmosphere

absorbed by surface

reflected by clouds and dust, water vapour and other gases

in the atmosphere

reflected by surface

100%

18%

26%

56%

6%

50%

SOLAR INSOLATION

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absorbed by surface

reflected by atmosphere

reflected by surface

100%

18%

26%

56%

6%

50%

absorbed by atmosphere

solar insolation

reaches surface

TOTAL ALBEDO = 26 + 6= 32%

TOTAL ABSORPTION = 18 + 50= 68%

SOLAR INSOLATION

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In the previous lesson…• You learn the different players of atmosphere

which is categorized by using two variables: temperature and altitude.

• You also learnt about the global heat budget. In this section it is important to remember that:

1. % on your diagram tend to vary a bit from book to book, so do not be alarmed by slight variations.

2. This model does not take into account the global variation due to different locations. i.e. as you move away from the equator towards the Poles there is a latitudinal variation in the heat budget.

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In case you are not sure…

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The proportion of radiation reflected or absorbed depends on the object's reflectivity or albedo, respectively.

An ideal white body has an albedo of 100% and an ideal black body, 0%.

TOTAL ALBEDO = 26 + 6= 32%

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Albedo works on a smaller scale, too. People who wear dark clothes in the summertime put themselves at a greater risk of heatstroke than those who wear lighter color clothes

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Earth as a natural system (long wave radiation)

… is neither getting colder nor warmer.

Out of the 50% of solar energy absorbed by the Earth.

7% is re-radiated directly back into space and 43% is absorbed by greenhouse gases (Carbon dioxide, methane, water vapour)

TOTAL ABSORPTION = 18 (by atmosphere) + 50 (by earth’s surface)

= 68%

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The Earth's atmosphere is put into motion because of the differential heating of the Earth’s

surface by solar insolation.

The Poles receive less heat than the Tropics because:

1. Insolation has to pass through more of the Earth’s atmosphere

2. the angle of incidence of insolation

and 3. higher levels of surface albedo.

ENERGY SURPLUS and DEFICIT

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So why is Alaska so cold???

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Places at the equator or between the tropics are always hotter than places at higher latitudes.

This is because the earth is a sphere and the sun’s rays strike the area around the centre of the sky at right angles. (high in the sky)

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In polar areas the radiation has to pass through a greater depth of atmosphere (more scope for absorption, scattering or reflecting). Compared the width of XY and AB.

At higher latitude the rays strike the surface at a wider angle.

Similar amounts of solar radiation cover a greater area at the Poles. Compare the areas XY with AB.

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As you move from the Tropics to the Poles, there is variation and decrease in the time the sun releases solar radiation over the surface.

i.e…

We see the sun less or more depending on the position of over head sun.

Also know was seasons.

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Absorption at the surface is dependent upon the ‘albedo’ effect (whether the surface reflects more or less radiation).

For example, a dark surface (a forest) has low reflection, and a light surface (snow, ice, sand, water) has high reflection.

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Other variables include increased sunspot activity, an increased in atmospheric dust (after a volcanic eruption), and the tilt of the Earth’s axis and the varying distance of the Earth’s orbit around the sun.

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3

1

2

3

Insolation has to pass through more of the Earth’s atmosphere

The angle of incidence of insolation -energy is spread out over a larger area becausethe sun’s rays strike the surface at a lower angle.

Higher levels of surface albedo - the ice-cap reflects more solar insolation

SQA

Explain why tropical latitudes receive more solar radiation than polar latitudes. (8)

Textbook page 6-7 “Energy Receipt and Latitude”

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23º

The most intense heating of the sun, occurring at the so-called thermal equator, annually moves

between the tropics.

On or around June 20th each year the sun is overhead at 23½ºN, the Tropic of Cancer.

On or around December 20th the the sun is at overhead at 23½ºS, the Tropic of Capricorn.

These two dates are the solstices.

Twice a year, at the equinoxes, on or around March 20th and September 20th the overhead

sun crosses the equator.

This annual north to south and back again "shift" of the thermal equator shifts the belts of

planetary winds and pressure systems to the north and to the south as the year turns.

48http://msnbcmedia3.msn.com/j/msnbc/319000/319772.hlarge.jpg

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2008

Spring Equinox Mar 20 2008

Summer Solstice Jun 20 2008

Autumnal Equinox

Sep 22 2008

Winter Solstice Dec 21 2008

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In theory an imbalance in energy receipt could resultin lower latitudes becoming warmer and higher

latitudes becoming even colder.

In reality energy is transferred from lower latitudes (areas of surplus)to higher latitudes (areas of deficit)

BY

1. ATMOSPHERIC CIRCULATIONand

2. OCEAN CURRENTS

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0º Equator

90º Pole

SURPLUS

DEFICIT

1. ATMOSPHERIC CIRCULATION

2. OCEAN CURRENTS

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0º Equator 90º Pole

surplus deficit

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TRANSFER of ENERGY by ATMOSPHERIC CIRCULATION

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TRANSFER of ENERGY by OCEAN CURRENTS

0º Equator

90º Pole

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LP HP

At the Equator the atmosphere is heated Air becomes less dense and rises. Rising air creates low pressure at the equator. Air cools as it rises because of the lapse rate. Air spreads. As air mass cools it increases in density and descends. Descending air creates high pressure at the Poles. Surface winds blow from HP to LP.

SINGLE CELL MODEL

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warm air is less dense therefore lighter air rises in the Tropics this creates a zone of LOW PRESSURE air spreads N and S of the Equator air cools and sinks over the Poles this is a zone of HIGH PRESSURE air returns as surface WINDS to the Tropics

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This was later improved and a three cell modelwas developed.

The single cell model of atmospheric circulationwas developed to explain the transfer of energy

from the Tropics to the Poles.

SINGLE CELL MODEL

Today the three cell model is also considered to bean oversimplification of reality.

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0º Equator 90º Pole30º 60º

LP HP LP HP

Hadley Cell

Polar Cell

Ferrel Cell

THREE CELL MODEL

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Hadley Cell- see your notes on “single cell model”

• Warm air rises at the equator: Inter-Tropical Convergence Zone.

• The rising warm air carries a lot of moisture which cools, resulting in tall tower of cumulo-nimbus clouds and heavy precipitation.

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• Equatorial air flows to ≈ 30°N then sinks to the surface (HP) and returns as a surface wind to the equator.

• Some of this wind heads to the other LP point northwards.

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ITCZ = Inter-tropical convergence Zone (Low Pressure)

STH = Sub-tropical High (High Pressure)

HADLEY CELL ITCZ

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Ferrel Cell (Thermally indirect cell- powered by other two cells)

• At 30 °N some of the air heads towards the North Pole as wind.

• This wind is usually known as mid-latitude westerlies, which is warm and moist.

• At 60 °N the warm mid-latitude westerlies meets the cold air from the polar cell.

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• The warm air rises over the cold air and travels higher into the atmosphere.

• Here the air cools down and spread out.

• The air which spread out back south towards the equator completes this Ferrel cell circulation.

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Polar Cell

• At the North Pole (90°N) the air is very cold and dense it sinks down creating a HP.

• It then flows southwards towards 60°N and is warmed by the land and ocean it rises up into the atmosphere to completes it’s circulation.

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Warm air rises at the Equator - Inter-Tropical Convergence Zone (ITCZ).

Equatorial air flows to ~30º N then sinks to the surface and returns as a surface flow to the tropics.

This is the Hadley cell. Cold air sinks at the North Pole. It flows S at the surface

and is warmed by contact with land/ocean, by ~60º N it rises into the atmosphere.

This the Polar cell.

Between 60º N and 30º N there is another circulation cell. This is the Ferrel cell.

The Hadley cell and the Polar cell are thermally direct cells.The Ferrel cell is a thermally indirect cell.

ENERGY TRANSFER

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ENERGY TRANSFER

Hadley Cell

Polar Cell

Ferrel Cell

Heat energy is transferred from the Hadley Cell to the Ferrel Cell and from the Ferrel Cell to the Polar Cell.

In this way heat is transferred from the Equator where there is an energy surplus

to the Poles where there is an energy deficit.

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Hadley Cell.Warm air rises at the equator: Inter-Tropical Convergence Zone. The rising warm air carries a lot of moisture which cools, resulting in tall tower of cumulo-nimbus clouds and heavy precipitation.Equatorial air flows to ≈ 30°N then sinks to the surface (HP) and returns as a surface wind to the equator.Some of this wind heads to the other LP point northwards. Ferrel Cell. At 30 °N some of the air heads towards the North Pole as wind. This wind is usually known as mid-latitude westerlies, which is warm and moist. At 60 °N the warm mid-latitude westerlies meets the cold air from the polar cell.The warm air rises over the cold air and travels higher into the atmosphere. Here the air cools down and spread out. The air which spread out back south towards the equator completes this Ferrel cell circulation.Polar Cell At the North Pole (90°N) the air is very cold and dense it sinks down creating a HP.It then flows southwards towards 60°N and is warmed by the land and ocean it rises up into the atmosphere to completes it’s circulation.

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Basic Principle

1. Hot air rises low pressure.

2. Cold air sinks high pressure.

3. Air moves from high to low pressure.

4. Air is deflected by the spinning of the Earth Coriolis effect.

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0º Equator 90º Pole30º 60º

LP HP LP HP

conv

erge

nce

dive

rgen

ce

conv

erge

nce

dive

rgen

ce

winds blow from high pressure zones to low pressure zones

WINDS

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Coriolis effect occurs because the Earth rotates.

• Earth rotates about its axis every 24 hours. • Distance around the equator is ~25,000

miles (40 233.6 km)• the earth is travelling east at ~ 1,041 miles

per hour. (1675km)

• Distance around the Earth at 40ºN ~19,000 miles

• the earth is travelling east at ~800mph.

• The Coriolis effect results from this difference in velocity.

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Coriolis occurs because the Earth rotates.

In the Northern hemisphere the Coriolis effect deflects movement to the right.

In the Southern hemisphere Coriolis effect deflects movement to the left.

The combination of atmospheric cells and Coriolis effect lead to the wind belts.

Wind belts drive surface ocean circulation

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Rossby wave and the Jet Stream

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Happens ≈30º~ 60º N/S

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Cold air is transferred southwards and warm air to the north

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Rossby waves in the atmosphere are easy to observe as (usually 4-6) large-scale meanders of the jet stream.

When these loops become very pronounced, they detach the masses of cold, or warm, air that become cyclones and anticyclones and are responsible for day-to-day weather patterns at mid-latitudes.

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CONVERGENCE and …………DIVERGENCE

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Coriolis effect occurs because the Earth rotates.

• Earth rotates about its axis every 24 hours. • Distance around the equator is ~25,000

miles (40 233.6 km)• the earth is travelling east at ~ 1,041 miles

per hour. (1675km)

• Distance around the Earth at 40ºN ~19,000 miles

• the earth is travelling east at ~800mph.

• The Coriolis effect results from this difference in velocity.

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Coriolis occurs because the Earth rotates.

In the Northern hemisphere the Coriolis effect deflects movement to the right.

In the Southern hemisphere Coriolis effect deflects movement to the left.

The combination of atmospheric cells and Coriolis effect lead to the wind belts.

Wind belts drive surface ocean circulation

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WIND

Coriolis effect

High Pressure

Low Pressure

pressure gradient force

Winds are named by the direction they blow from.

PLANETARY WINDS

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Be very, very careful what you put that head, because you will never, ever get it out.

Thomas Cardinal Wolsey (1471-1530)

The water in a sink rotates one way as it drains in the northern hemisphere and the other way in the southern hemisphere. Called the Coriolis Effect, it is caused by the rotation of the Earth.

This is NOT true!

The Coriolis force is so small, that it plays no role in determining The Coriolis force is so small, that it plays no role in determining the direction of rotation of a draining sink anymore than it doesthe direction of rotation of a draining sink anymore than it doesthe direction of a spinning CD.the direction of a spinning CD.

CORIOLIS

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90ºS

90ºN

0º Equatorial Low - Doldrums LP

30ºNSub-tropical High - Horse Latitudes HP

30ºSSub-tropical High - Horse Latitudes HP

60ºSTemperate Low LP

60ºN Temperate Low LP

Polar easterlies

South westerlies

NE Trades

Polar easterlies

North westerlies

SE Trades

WIND BELTS

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Homework for Monday 15th Sept

• What is the Inter-tropical Convergence Zone (Doldrums Doldrums)? – where is it found? What conditions? What happens?

(4)

• Explain why at the equator (Doldrums) we have very calm condition? – why do we have very little wind at the birth place of wind???

(5)

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Home work answer• ITCZ or otherwise known as

the Doldrums is found between 0-10º north and south of the equator.

• Since is it close to the equator it receives the strongest solar radiation. This creates a hot and humid condition.

• The intense sun heats the atmosphere and ocean hot air rises strong upwards convection current the air becomes heavy with moisture.

• We usually find massive rain clouds like cumulus nimbus.

• Atmospheric condition is usually very calm at ITCZ because… due to the strong overhead sun the air is being convected upwards.

• Main movement of air is upwards.

• This creates an area of low pressure. Wind travels from high pressure to low pressure. So by the time Trade winds have made it back to the equator it has weakened.

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90ºS

Polar easterlies

South westerlies

NE Trades

Polar easterlies

North westerlies

SE Trades

0º convergence Inter-tropical convergence zone LP

30ºSdivergence Sub-tropical High HP

30ºNdivergence Sub-tropical High HP

60ºN convergence LP

60ºSconvergence LP

WIND BELTS

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WIND BELTS

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Northern Hemisphere

Polar Easterlies Blowing from the Polar High Pressure zone to about 60ºN

Westerlies Blowing from Sub-Tropical High Pressure zone to about 60ºN

Northeast Trade Winds Blowing from Sub-Tropical High Pressure zone to Equatorial Low Pressure zone.

Southern Hemisphere

Southeast Trade Winds Blowing from Sub-Tropical High Pressure zone to Equatorial Low Pressure zone.

Westerlies Blowing from Sub-Tropical High Pressure zone to about 60ºS

Polar Easterlies Blowing from the Polar High Pressure zone to about 60ºS

WIND BELTS

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Once you have finished…

Try drawing the global wind circulation diagram from memory.

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Series of High and Low pressure centres approx. every ? latitude ? pressure zones associated with descending air ( ? ) Low pressure zones associated with ? air (convergence)

? circulation cells in each hemisphere: ? ? direct ? thermally indirect Polar Cell thermally direct

Wind is the horizontal movement of air arising from differences in ? . Very little wind at the Equator ( ? ) because air is being convected ? .Little wind at 30ºN and S (Horse Latitudes) because direction of air movement is down.

Winds always blow from an area of ? Pressure to ? Pressure.

Winds are affected by the ? Effect.Coriolis is a consequence of motion on a rotating sphere. Acts to the ? of direction of motion in Northern HemisphereActs to the ? of direction of motion in the Southern Hemisphere

Major wind belts of the Earth surface0 to 30ºN ? ?

? Southeast Trades 30 to 60ºN/S ?

60 to 90ºN/S Polar ?

SLIDE 37

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Series of High and Low pressure centres approx. every 30º latitudeHigh pressure zones associated with descending air (divergence) Low pressure zones associated with rising air (convergence)

Three circulation cells in each hemisphere: Hadley Cell thermally direct Ferrel Cell thermally indirect Polar Cell thermally direct

Wind is the horizontal movement of air arising from differences in pressure. Very little wind at the Equator (Doldrums) because air is being convected upward.Little wind at 30ºN and S (Horse Latitudes) because direction of air movement is down.

Winds always blow from an area of High Pressure to Low Pressure.

Winds are affected by the Coriolis Effect.Coriolis is a consequence of motion on a rotating sphere. Acts to the Right of direction of motion in Northern HemisphereActs to the Left of direction of motion in the Southern Hemisphere

Major wind belts of the Earth surface0 to 30ºN Northeast Trades

0 to 30ºS Southeast Trades 30 to 60ºN/S Westerlies 60 to 90ºN/S Polar easterlies

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23º

The most intense heating of the sun, occurring at the so-called thermal equator, annually moves

between the tropics.

On or around June 20th each year the sun is overhead at 23½ºN, the Tropic of Cancer.

On or around December 20th the the sun is at overhead at 23½ºS, the Tropic of Capricorn.

These two dates are the solstices.

Twice a year, at the equinoxes, on or around March 20th and September 20th the overhead

sun crosses the equator.

This annual north to south and back again "shift" of the thermal equator shifts the belts of

planetary winds and pressure systems to the north and to the south as the year turns.

110http://msnbcmedia3.msn.com/j/msnbc/319000/319772.hlarge.jpg

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2008

Spring Equinox Mar 20 2008

Summer Solstice Jun 20 2008

Autumnal Equinox

Sep 22 2008

Winter Solstice Dec 21 2008

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Land or Ocean- Which one stays warmer???

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Answer • In winter the continental cool down more

quickly than oceans and so they have a lower pressure.

• In summer the continents heat up more quickly and so have lower pressure.

Summer: Land / Ocean

Winter: Land / Ocean

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Inter-tropical Convergence Zone (ITCZ)

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0ºEQUATOR

23½ºNTROPIC of CANCER

23½ºSTROPIC of CAPRICORN

December Winter Solstice

September Autumn Equinox

June Summer Solstice

March Spring Equinox

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Where is it?

• Near the equator, from about 5° north and 5° south. the northeast trade winds and southeast trade winds converge in a low pressure zone known as the ITCZ.

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How does it work?

• ITCZ is formed by the vertical ascent (rise) of warm moist air from the latitudes north and south of the equator.

• The air is drawn into the inter-tropical convergence zone by the action of the Hadley cell.

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• Equatorial region experience precipitation up to 200 days each year, making the equatorial and ITCZ the wettest on the planet.

• The equatorial region lacks a dry season and is constantly hot and humid. (this is why the “rainforest” is found in the equatorial region)

What does it do?

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• The location of the ITCZ varies throughout the year and while it remains near the equator, the ITCZ over land ventures farther north or south than the ITCZ over the oceans due to the variation in land temperatures.

• The location of the ITCZ can vary- they usually travel within the latitude of 25° north or south of the equator based on the pattern of land and ocean.

Why is it important?

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ITCZ JULYITCZ

JANUARY

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Case Study of West Africa

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• Areas next to the Equator have high annual rainfall totals because of the continued uplift of air which results from the convergence of the Trade winds and strong convectional currents (upward movement of warm air).

• Further away from the equator the annual rainfall decreases and the length of the dry seasons increases.

(equator=2000mm/year, Sahara= 250mm/year)

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• The twin Hadley Cell structure means converging and ascending air near the Equator and descending and diverging air over the sub-tropical deserts.

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• The inner zone of convergent air is known as the Inter-Tropical Convergence Zone (ITCZ) which provides the source of the majority of rainfall.

• The Hadley Cells, the ITCZ and the Trade belts swing North and South, following the overhead sun, during the course of the year. This movement controls the seasonal rainfall and temperature- the maximum rainfall occurs 1-2 months after the passages of the overhead sun.

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• Between March and July the ITCZ moves northwards across West Africa bringing cloudy and humid conditions. As the moist Tropical Maritime (mT) air moves northwards heavy rainstorm develops.

• During the winter dry Tropical Continental air (cT) blows over the Sahara moving southwards to enable the dry north-east Trade winds to blow into the Sahel.

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Tropical Maritime (mT) air

•South-Western Monsoon winds

•High temperature

•High rainfall

Tropical Continental (cT) air

•North-East Trade winds

•High temperature

•Very low or no rainfall

136http://www.cpc.ncep.noaa.gov/products/fews/ITCZ/itcz.shtml

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http://www.cla.sc.edu/geog/faculty/carbone/modules/newmods/africa-itcz/

The blue shading on the map shows the areas of highest cloud reflectivity,

which correspond to the average monthly position of the ITCZ.

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The migration of the inter-tropical convergence zone (ITCZ) in Africa affects seasonal precipitation patterns across that continent.

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DESERT

SAVANNA

RAINFOREST

dry all year

ITCZ moves north in summer

dry ‘winter’wet ‘summer’

wet all year

DESERT

SAVANNA

RAINFOREST

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Tropical rainforest

savanna

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The further North of the Equator in tropical Africa:-

the lower the annual rainfall

the more the rainfall is concentrated in the summer months

the more variable the rainfall.

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0º 20ºN10ºN

RAINFORESTGUINEA

SAVANNASAHEL

SAVANNADESERT

rainfall decreases

seasonality increasesvariability increases

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LAGOS SOKOTO TIMBUKTU

A B C A B C A B C

JAN 27 28 65 20 0 13 22 0 22

FEB 29 41 69 22 0 13 24 0 19

MAR 29 96 72 31 0 11 28 2 18

APR 28 143 72 34 10 17 32 0 15

MAY 28 274 76 33 51 31 35 5 18

JUN 26 460 80 30 89 41 36 23 31

JUL 25 282 80 28 147 55 32 79 45

AUG 25 69 76 26 236 64 30 81 57

SEP 25 140 77 27 145 59 32 38 45

OCT 26 208 76 28 13 37 31 3 23

NOV 27 69 72 27 0 18 28 0 17

DEC 28 25 68 25 0 15 22 0 19

annual 27 1835 74 28 691 31 29 231 27

A = average monthly temperature C

B = mean monthly rainfall mmC = % relative humidity at midday

LAGOS

SOKOTO

TIMBUKTU

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savanna savanna climateclimate

tropical summer rain

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savanna savanna vegetationvegetation

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savanna ‘parkland’

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149


150baobab tree

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acacia tree

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acacia thorns

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desertification

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Responsible for ≈ 20% of redistribution of energy.

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What is it? • An ocean current is continuous, directed

movement of ocean water. Ocean currents are “rivers” of hot or cold water within the ocean. The currents are generated from the forces acting upon the water like the planet rotation, the wind, the temperature and salinity differences and the gravitation of the moon.

• Ocean currents play an important role in redistributing energy.

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Where is it?

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• Energy is redistributed in the oceans by ocean currents, this is called oceanic circulation.

• Ocean currents can flow for thousands of kilometers. They are very important in determining the climates of the continents, especially climate regions next to oceans.

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How does it work?

• Ocean currents are driven by thermohaline circulation.

Thermo= heat

Haline= salt

together they determine the density of sea water.

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How does it work?• Uneven heating of

surface water in high and low latitudes sets up convection currents which transfer energy.

• The water round the Poles is more dense than at the equator because it contains more salt. Salt does not freeze.

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How does it work?• Global Winds cause frictional drag on large

water surfaces.

• Ocean currents therefore tend (but not always) to follow prevailing wind directions.

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How does it work? • The Coriolis force winds are deflected to

the right in the northern hemisphere and to the left in the southern hemisphere.

• Ocean currents are also deflected in the same way.

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How does it work?

• Ocean currents direction is modified by the shape of the continents.

• Consequently the major oceanic basin have huge, roughly circular shaped loops of water called gyres.

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4 forces: solar heating salt Coriolis effect and surface windsresult in a clockwise circulation of water in the Northern hemisphere.

This circulation is known as a GYRE.

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OCEAN CURRENTS IN THE NORTH ATLANTIC

0º Equator

90º Pole

1

2

3

45

6

1

2

3

4

5

6

NORTH EQUATORIAL CURRENT

GULF STREAM

NORTH ATLANTIC DRIFT

LABRADOR CURRENT

CANARIES CURRENT

NORTH ATLANTIC DRIFT

• The greenhouse effect is the name applied to the process which causes the surface of the Earth to be warmer than it would have been in the absence of an atmosphere.

• Global warming or the enhanced greenhouse effectenhanced greenhouse effect is the name given to an expected increase in the magnitude of the greenhouse effect, whereby the surface of the Earth will almost inevitably become hotter than it is now.

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About 70% of the sun's energy is radiated back into space.

But some of the infrared radiation is trapped by greenhouse gases

and warms the atmosphere,

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Water vapour accounts for 98% of the natural Greenhouse effect.

Water vapour has lower ‘radiative forcing’ properties than some other atmospheric gases such as

carbon dioxide, methane and nitrous oxide which are naturally present in the atmosphere

in small quantities.

Since the Industrial Revolution the proportion of these gases has increased significantly.

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Enhanced Greenhouse Effect

164%

219%

311%

46%

CO2

CFCsN2O

CH4

1 Carbon Dioxide > fossil fuels, vehicle emissions, forest clearance2 Methane > rice cultivation, biomass burning, digestive fermentation,

termites, sewage, landfill, natural gas production3 CFCs > aerosol propellants, refrigerants, foaming agents4 Nitrous oxide > nitrogen fertilisers, industrial pollution

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Carbon Dioxide: 280 ppm 360 ppm (+30%)

Methane: 0.70 ppm 1.80 ppm (+145%)

Methane c25 x effect of CO2

CFCS (chlorofluorocarbons) recent significant decrease due to concern about OZONE LAYER

CFCs c10,000 x effect of CO2

BUT

CONCENTRATION CHANGES SINCE 1750

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°C Temperature anomalies from the period 1961-1990

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Solar energy Ocean Currents

Volcanic activities Astronomical changes

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http://delicious.com/MissTomitaka/atmosphere

192

• Watch a short clip from youtube called “geography seasons”

http://www.youtube.com/watch?v=taHTA7S_JGk

• Then answer the following question: Why do we have seasons? How does it work? (4 Marks)

• Then complete the “summer solstice” diagram by adding the latitude and length of daylight.

atmosphere

Education

atmosphere solar insolation

earths surface

solar energy

surface total albedo

ultraviolet solar radiation

layer of gases

mixture of gases

inert gases