Atmosphere
Higher Geography: Physical
Environments
Introduction
Skin cancers
Acid rain
Global warming
Atmosphere
in the news
Hole in the
ozone layer
Greenhouse
gases
CFC’s
Climate change
Although considered a difficult topic, this is the most up-to-date
of the basic units!
What we will learn
Atmosphere for Higher Geography is being able
to say how energy is moved around the world:
– in the air (air circulation)
– and the sea (ocean circulation)
What is the atmosphere?
The atmosphere is the gases that surround
our planet. They are held in place by gravity.
Atmosphere is made up of several gases.
Without it there would be no life on Earth!
Structure of our Atmosphere
The atmosphere is divided into four main layers,
each with a characteristic mixture of gases and a
range of temperatures.
You will need to know the order these layers come
in and their names.
Note that between each layer is a junction called a
‘pause’.
Layers of the Atmosphere
Global Heat Budget
The amount of energy the Earth gets from the
sun and how it is used / absorbed or reflected.
Insolation = Energy coming into our atmosphere
(input)
Radiation = Energy coming out of the
atmosphere (output)
Activity
Global heat budget bingo!
You have 5 minutes to read your statement
cards and number them according to where you
think they go on the blank global heat budget.
We will then see who got it right!
2
3
4
12
1
8
11
7
10
6
9
5
This would only apply in a perfect
world…but we have an imbalance.
Why do the
poles get less
energy?
Why does the
equator get
more energy?
Latitude
Thickness of Atmosphere
Extra Notes…
In Polar regions, there is a greater amount of atmosphere
to pass through, so more risk of it being deflected away.
Because of the angle of the rays, there is more Polar land
to share the heat than at the Tropics, so it averages cooler
temperatures.
Light coloured surfaces- like snow- reflect heat back into
the atmosphere. Forests- like rainforests- are dark and
absorb heat.
Throughout the year, Polar areas get less time in the Sun
than do Tropical areas due to the tilt of the Earth and the
orbit around the Sun.
Starter
On your show me boards, answer the following
questions:
1. What is the name given to energy entering the
Earth from the Sun.
2. Draw a diagram to show the 4 pauses of the
atmosphere.
3. What percentage of solar insolation is reflected
by the atmosphere?
4. Give two reasons why it gets colder as you move
further from the equator.
Aims of the lesson
• To learn about the formation of the 3 cells
that exist in our atmosphere.
• To learn about the pressure belts associated
with each cell.
• To learn about the wind patterns associated
with these cells.
Formation of the Hadley Cell
Insolation in tropical areas
causes warm air to rise and
spread polewards, carrying
heat energy.
INSOLATION
SOLAR ENERY
19
Air cools and begins to
fall at about 30ºN and
30ºS of Equator.
Cooled air returns to the
Equator.
NORTHERN HADLEY CELL.
SOLAR ENERGY
Heat energy is therefore
transferred from the Equator to
sub-tropical latitudes.
SOUTHERN HADLEY CELL.
Formation of the Polar Cell
Intensely cold, dense
air sinks at the poles,
then blows as surface
winds towards the
Equator.
21
At about 60ºN and 60 ºS, the
cold polar air is warmed in
contact with the earth’s surface.
NORTHERN POLAR CELLS.
This warmed air rises and
returns polewards, carrying heat
energy.
This circular motion is called the
POLAR CELL.
SOUTHERN POLAR CELLS.
Formation of the Ferrel Cell
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.
The Polar Cell causes an uplift
at about 60ºN and S. )
23
THE THREE CELLS
TOGETHER
Polar Cell
Ferrel Cell
Hadley Cell
Hadley Cell
Ferrel Cell
Polar Cell
24
Cells
It is well worth making sure that you can see the
rising and falling pattern of these cells.
The next section uses this to work out wind
directions on the surface of the earth.
ASSOCIATED PRESSURE BELTS
Rising air at the equator causes
the equatorial belt of low
pressure
Descending air at about 30ºN
and 30ºS causes the subtropical belt of high pressure
Polar high pressure
Mid latitude low pressure
Sub-tropical high pressure
Equatorial low pressure
Rising air at about 60ºN and
60ºS causes a mid-latitude
belt of low pressure
Sub-tropical high pressure
Mid latitude low pressure
Descending air at the poles
causes the polar high
pressure areas
Polar high pressure
26
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.
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)
Polar high pressure
Mid latitude low pressure
Sub-tropical high pressure
Equatorial low pressure
Sub-tropical high pressure
Mid latitude low pressure
Polar high pressure
Explain how circulation cells in the atmosphere and the
associated surface winds assist in the transfer of energy
between areas of surplus and deficit. 8 Marks
This question is asking you
to explain:
- How cold air is
transferred southwards
towards the equator
- How warm air is
transferred northwards
towards the poles
- The winds that are
created because of the
moving air.
- You should be
mentioning:
- Deficit at poles
- Surplus at equator
- Creating a balance
• The Equator is an area of surplus energy, the
poles are an area of deficit.
• The Hadley cells form above the equator.
• Warm air transfers the energy upwards into the
atmosphere. It then moves northwards and
southwards toward 30 degrees North and south
of the equator.
• The warm air cools and begins to drop at 30 N
and 30 S, transferring warmer air northwards and
southwards.
• The cool air then travels back towards the
equator. This creates the trade winds which
assist in energy transfer.
• Above the poles we find the polar cells. Cold air is
pushed downwards towards the earth and travels
down towards 60 N and S of the equator.
• This movement creates the Easterlies winds which
transfers cooler air to warmer latitudes.
• As it travels over the land it warms and then begins to
rise at 60 N and S allowing for warm air to be
redirected back to the poles.
• The Ferrel cells form between the Hadley and Polar
cells and energy moves because of friction created.
• These movements allow for warm air to redistribute
the surplus energy from the equator to the poles.
This question is asking you about the reasons why there is an
imbalance in the global heat budget.
You should mention:
• Impact of latitude
• Thickness of the atmosphere
• Distance from the sun
• Albedo effect.
Include diagrams!
Marking Scheme
Describe the pattern of ocean currents in the North Atlantic
Ocean, and explain how they help maintain the global energy
balance.
6 Marks
Answer could include:
• Where cold currents
travel from + named
example
• Where warm currents
travel from + named
example
• How land masses
deflect currents
• What is happening to
the surplus energy and
deficit energy at
equator/poles
• How salt content effects
currents
• How winds / friction
affect the direction of
currents
• The coriolis effect
• There is an energy surplus at the equator and a deficit
at the poles.
• There are warm currents directed northwards fro the
equator known as the gulf stream and north Atlantic
current.
• There are cold currents directed southwards from the
poles one is called the east Greenland current.
• Often ocean currents are deflected by land masses and
circular shaped loops of water form called gyres.
• This means that surplus energy often does not reach
the poles.
• In the N Atlantic ocean currents travel in a clockwise
direction because of the coriolis force.
• They also move in the direction of the prevailing winds
due to friction.
Mark Scheme
•
Description and Explanation might include:
currents follow loops or gyres – clockwise in the North Atlantic. In the
Northern Hemisphere the clockwise loop or gyre is formed with warm water
from the Gulf of Mexico (Gulf Stream/North Atlantic Drift) travelling
northwards and colder water moving southwards eg the Canaries Current.
currents from the Poles to the Equator are cold currents whilst those from the
Equator to the Poles are warm currents. Cold water moves southwards from
Polar latitudes – the Labrador Current. This movement of warm and cold
water thus helps to maintain the energy balance.
ocean currents are greatly influenced by the prevailing winds, with energy
being transferred by friction to the ocean currents and then affected by the
Coriolis effect, and the configuration of land masses which deflect the ocean
currents. Due to differential heating, density differences occur in water
masses, resulting in chilled polar water sinking, spreading towards the Equator
and displacing upwards the less dense warmer water
Aims of the Lesson:
• Revise air masses
• Look at how the boundary of two conflicting
air masses effect the climate in Africa.
• Understand this conflict as the ITCZ (Inter Tropical
Convergence Zone)
Air Masses
An air mass is a large volume of air with uniform characteristics of
temperature and humidity, acquired from its source region (where
it comes from).
The characteristics of the air mass are determined by the climate of
the place where it originated.
• Air masses which form over oceans are termed “MARITIME”.
These will bring wet weather.
• Air masses which form over land are called “CONTINENTAL”
These will bring dry weather.
• Air masses are also called POLAR, TROPICAL or ARCTIC
depending on where they formed.
Air masses in Africa and the ITCZ
• The main air masses influencing the climate of
Africa are Tropical Continental and Tropical
Maritime.
• Their meeting place (where they converge) is
known as the Inter Tropical Convergence Zone
(ITCZ).
Tropical Continental
cT
AFRICA
ITCZ
A warm, dry air mass given its
origin over the tropical Sahara
Desert. Brings warm, dry stable
air. Extremely warm
temperatures. No rainfall or
cloud. Also brings a warm, dry
Harmattan wind. Weather
conditions are monotonous.
Where the air masses
converge
Tropical Maritime
mT
A warm, wet air mass given its origin
over tropical oceans (the Atlantic).
Brings moist, unstable air causing rainfall
and thunderstorms. Temperatures can
be hot and weather patterns vary.
Sahara Desert
Sahel, semi
desert
South of Africa,
Rainforest over
equator, grasslands
as you go south.
How does the ITCZ and its associated air masses
influence the climate of Africa?
The ITCZ shifts position throughout the year in relation to the
apparent movement of the sun because of the way the earth
sits on its axis.
In July
The sun is directly overhead the Tropic of Cancer due to the
tilt of the earth. The ITCZ migrates northwards and is
positioned over the Tropic of Cancer.
ITCZ is positioned at
the Tropic of Cancer
ITCZ
23 ½ºN
0º
23½ºS
This means that Africa is dominated by the Tropical Maritime
air mass, bringing with it warm,wet and generally unstable
conditions. This explains why July is Africa’s wet season.
cT
ITCZ
mT
ITCZ
positioned at
Tropic of
Cancer
Warm moist
unstable Tropical
Maritime Air
dominates most
of Africa.
In January
The sun is directly overhead the Tropic of Capricorn due to
the tilt of the earth. Therefore the ITCZ migrates south and is
positioned over the Tropic of Capricorn.
ITCZ
23 ½ºN
0º
23½ºS
ITCZ is positioned at the
Tropic of Capricorn
This means that much of Africa is influenced by Tropical
Continental air, bringing with it warm, dry stable conditions
and the warm, drying Harmattan wind. This explains why
most of Africa experiences its dry season at this time of year.
ITCZ
mT
cT
Warm, dry
stable Tropical
Continental Air
dominates
most of Africa.
ITCZ
positioned
at Tropic of
Capricorn
• Some western and southern parts of Africa remain
under the influence of Tropical Maritime air because
the Tropical Continental air mass (above the ITCZ) is
not strong enough to push against the Tropical
Maritime air mass which is moving into the land from
the sea.
• In March and September the sun sits directly overhead
the Equator, so at these times of year the ITCZ is
positioned over the Equator.
Problems with the ITCZ in recent years
In recent years the ITCZ has not migrated as far north as it should
do in July. It has only shifted position to 14ºN of the Equator. This
means that the Tropical Maritime (warm, wet) air does not reach
the Sahel region of Africa. Instead, this part of Africa is dominated
by Tropical Continental air, resulting in hot dry conditions and a
summer drought.
In Winter (January) the ITCZ migrates to its position at the Tropic of
Capricorn so the Sahel region remains dominated by the warm, dry
Tropical Continental Air. This means that for most of the year the
Sahel region of Africa is influenced by extreme heat and dry
conditions, causing drought, soil erosion, desertification and land
degradation.
Task Time!
Use your notes on the ITCZ to answer the
following questions:
1)
2)
3)
4)
5)
6)
7)
8)
9)
Write a definition for the ITCZ.
Why does the ITCZ appear to migrate to different positions throughout the
year?
Where is the ITCZ positioned in a) July b) January c) September?
Explain why most of Africa experiences warm, wet weather in July.
Explain why most of Africa experiences its dry season in January.
Why do some parts of western and southern Africa always experience
Tropical Maritime air?
What has happened to the movement of the ITCZ in recent years?
Describe the consequences of this movement on the Sahel region of
Africa.
Have a go at ACTIVITY 6 on page 7 of the Higher Geography textbook
Example exam question (1)
From Paper 1 2007:
Study reference diagrams Q1A and Q1B. Identify air masses A and B,
and describe their origin and nature. (6)
How to answer
Air mass A is Tropical Continental or cT. It originates over the
Sahara Desert in tropical latitudes, hence its name, tropical
continental. It brings warm, dry stable air and extremely warm
temperatures to the areas over which it passes. There is a
lack of rainfall or cloud.
Air mass B is Tropical Maritime or Mt. It originates over the
Atlantic ocean in tropical latitudes. It brings warm, moist
unstable air, causing rainfall and thunderstorms.
Example exam question (2): Homework
Describe and explain the varying rainfall patterns shown in reference
diagram Q1B. (12)
How to answer
Timbuktu has on average very little rainfall (only 250mm per annum). It
has no rainfall at all in January, February November and December. Jos
too has distinct wet and dry seasons, experiencing 1000mm of rainfall
per annum, a peak of 300mm in July and minimal rainfall in November,
December, January and February. In contrast, Lagos has markedly
more rainfall throughout the year, with up to 2000mm per annum, and
rainfall peaking twice in the year. (June at 475mm and October at
200mm). It also has no dry months at all.
These patterns can be attributed to the movement of the ITCZ and its
associated air masses. Lagos is under the influence of warm moist
Tropical Maritime air for most of the year, which explains its higher
annual rainfall amounts and lack of dry season. Its twin rainfall
peaks are caused by the ITCZ migrating northwards and southwards in
relation to the position of the sun. Timbuktu and Jos in contrast are
much further North than the ITCZ in January, which is positioned at the
Tropic of Capricorn. This will result in Timbuktu and Jos being influenced
by warm, dry Tropical Continental air, which explains why they have either
No or very little rainfall during these months.
In June and July Timbuktu and experiences its highest rainfall amounts
because the ITCZ has migrated northwards due to the position of the sun
overhead the Tropic of Cancer. This results in Timbuktu experiencing
Tropical Maritime air at these times, hence its this is when it gets the
majority of rainfall. Similarly, this is why Jos experiences its highest rainfall
totals (300mm and 275mm respectively) in July and August.
NOW YOU HAVE A GO – REMEMBER DON’T PANIC, THIS IS
DIFFICULT!!!
1)
2)
3)
Collect a copy of the TWO past paper questions.
Read each question carefully, then write a detailed answer to each.
Get your answers checked by your teacher.
Summary
So far we have…
• Learnt the definition of an air mass.
• Learnt how to describe the characteristics of air
masses.
• Learnt the definition of the ITCZ and the influence
of it on the winter and summer weather
conditions of Africa.
Aims of the lesson
• To learn about the human and physical factors
that may be causing global climate change.
• To discuss the possible consequences of
climate change.
Climate Change
Climate change is a
significant and lasting
change in the
statistical distribution
of weather patterns
over periods ranging
from decades to
millions of years.
The Greenhouse Effect
The Sun
The Earth
Mauna Loa Climate Graph
Temperature Variation over 800,000
Years
Physical & Human Factors
As we can see from the two graphs on the
previous slides global climate has always varied
naturally.
However, we are now 95% certain that current
climate change is being driven mainly by human
activity.
Physical & Human Factors
Physical:
• Solar variation
• Volcanic activity
• Ocean currents
• Milankovitch cycles
Human:
• Burning fossil fuels
• Increased output of
methane etc.
• Deforestation
Information Treasure Hunt
Working in pairs, you are
going to collect information
on each of these factors
affecting climate change.
Resources available:
• Library Computers (1
between 2)
• Library Reference Books
• B10 Reference Books
PHYSICAL 1 - SOLAR VARIATION
•Sunspots: 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.
PHYSICAL 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.
VOLCANIC ERUPTIONS 2
• Major eruptions in the past
which have been linked to short
periods of global cooling include
Mt. St Helens (1980)
When Mt. Pinatubo
erupted in 1991 an
estimated 22 million tons
of ash was thrown into
the atmosphere, cooling
the world’s climate by
about 1°C.
When Tambora erupted i
1815 it led to 1816 being
called “the year without
summer”, when summer
frosts and other major
weather problems were
experienced. It cooled th
global climate by 3°C.
PHYSICAL 3 - MILANKOVITCH CYCLES
• Stretch,
Wobble and
Roll!!!
• 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.
PHYSICAL 4 - OCEAN CURRENTS
• 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.
• A longer term example would be the
North Atlantic Drift, which may change
position every few thousand years.
ENSO - the El Niño Southern Oscillation
The “normal”
conditions, with cool
surface water off the
coast of Peru.
A La Niña year
Every 2-7 years the western
Pacific becomes much warmer,
disrupting weather patterns possibly on a global scale.
An El Niño year
- HUMAN FACTORS -
HUMAN 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).
BURNING FOSSIL FUELS
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.
BURNING FOSSIL FUELS
Power stations are one of the main producers of
greenhouse gases such as Carbon Dioxide.
Environmental campaigners
all over the world are
demanding cuts in CO2
emissions. Here Greenpeace
uses a light display to get its
message across.
HUMAN 1 - VEHICLE EXHAUSTS
Vehicle
exhausts
are the
main
source of
Nitrous
Oxides.
HUMAN 2 - INCREASED METHANE
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.
I am a ruminant - when I
digest grass, I produce
methane - lots of it!
HUMAN 2 - INCREASED METHANE
• 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.
HUMAN 3 - DEFORESTATION
Forests absorb CO2 and release oxygen:
...if they are cut down, atmospheric levels of CO2 must rise as a consequence.
HUMAN 3 - DEFORESTATION
• 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.
What are the consequences?
In your groups, create a spider diagram of all the
possible consequences of global climate change.