HIGHER GEOGRAPHY

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HIGHER GEOGRAPHY PHYSICAL ENVIRONMENTS
ATMOSPHERE
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By the end of this topic you should be able to
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GMTs
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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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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 other gases
decrease).
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Global extremes of Temperature
58ºC San Luis Potosi, Mexico Al Aziziyah, Libya
-88ºC Vostok 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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SOLAR INSOLATION
reflected by clouds and dust, water vapour and
other gases in the atmosphere
100
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absorbed by clouds and dust, water vapour and
other gases in the atmosphere
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reflected by surface
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absorbed by surface
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SOLAR INSOLATION
100
solar insolation
reflected by atmosphere
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TOTAL ALBEDO 26 6 32
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absorbed by atmosphere
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reaches surface
TOTAL ABSORPTION 18 50 68
reflected by surface
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absorbed by surface
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ENERGY SURPLUS and DEFICIT

The Earth's atmosphere is put into motion
because of the differential heating of the
Earths surface by solar insolation.
The Poles receive less heat than the Tropics
because
1. Insolation has to pass through more of the
Earths atmosphere
2. the angle of incidence of insolation
and 3. higher levels of surface albedo.
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2
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Insolation has to pass through more of the
Earths atmosphere
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The angle of incidence of insolation - energy is
spread out over a larger area because the suns
rays strike the surface at a lower angle.
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Higher levels of surface albedo - the ice-cap
reflects more solar insolation, and vegetation at
the equator reflects far less.
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In theory an imbalance in energy receipt could
result in 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 CIRCULATION and 2. OCEAN
CURRENTS
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DEFICIT
1. ATMOSPHERIC CIRCULATION 2. OCEAN CURRENTS
SURPLUS
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SINGLE CELL MODEL

• 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.

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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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NO! not directly
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TRANSFER of ENERGY by ATMOSPHERIC CIRCULATION
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THREE CELL MODEL
Polar Cell
Hadley Cell
Ferrel Cell
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ENERGY TRANSFER
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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ENERGY TRANSFER
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.
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TRANSFER of ENERGY by OCEAN CURRENTS
90º Pole
0º Equator
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SINGLE CELL MODEL
The single cell model of atmospheric
circulation was developed to explain the transfer
of energy from the Tropics to the Poles.
This was later improved and a three cell
model was developed.
Today the three cell model is also considered to
be an oversimplification of reality.
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HADLEY CELL
ITCZ
ITCZ Inter-tropical convergence Zone (Low
Pressure) STH Sub-tropical High (High Pressure)
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WINDS
divergence
divergence
convergence
convergence
LP HP LP
HP
winds blow from high pressure zones to low
pressure zones
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CONVERGENCE and DIVERGENCE
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PLANETARY WIND SYSTEM
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Coriolis occurs because the Earth rotates.
Earth rotates about its axis every 24 hours.
Distance around the equator is 25,000 miles
the earth is travelling east at 1,000 miles
per hour. 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.
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
CORIOLIS
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PLANETARY WINDS
High Pressure
Coriolis effect
WIND
pressure gradient force
Low Pressure
Winds are named by the direction from which they
blow.
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WIND BELTS
Polar easterlies
South westerlies
NE Trades
SE Trades
North westerlies
Polar easterlies
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WIND BELTS
Polar easterlies
South westerlies
NE Trades
SE Trades
North westerlies
Polar easterlies
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WIND BELTS
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
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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 Hemisphere Acts to the ?
of direction of motion in the Southern
Hemisphere Major wind belts of the Earth
surface 0 to 30ºN ? ?
? Southeast Trades
30 to 60ºN/S ? 60 to 90ºN/S
Polar ?
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Series of High and Low pressure centres approx.
every 30º latitude High 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
Hemisphere Acts to the Left of direction of
motion in the Southern Hemisphere Major wind
belts of the Earth surface 0 to 30ºN Northeast
Trades 0 to 30ºS Southeast Trades
30 to 60ºN/S Westerlies 60 to 90ºN/S
Polar easterlies
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INTER-TROPICAL CONVERGENCE ZONE (ITCZ)
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23?º
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.
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23½ºN TROPIC of CANCER
June Summer Solstice
0º EQUATOR
September Autumn Equinox
March Spring Equinox
December Winter Solstice
23½ºS TROPIC of CAPRICORN
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The location of the ITCZ varies throughout the
year The ITCZ over land moves farther north or
south than the ITCZ over the oceans due to the
variation in land temperatures.
ITCZ JANUARY
ITCZ JULY
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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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THE ITCZ AND PRECIPITATION IN SUMMER
South
North
Heaviest rainfall
Occasional rainfall
ITCZ
Moist unstable mT air now reaches far inland,
bringing rain to about 17ºN
GULF OF GUINEA
5ºN
20ºN
15ºN
10ºN
Based on a diagram from Core Themes in
Geography, by Broadley Cunningham
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THE ITCZ AND PRECIPITATION IN WINTER
North
South
mT air right at the ITCZ is prevented from rising
by stable cT air
ITCZ
Warm land surface makes the mT air unstable. It
rises and rain falls a short way behind the ITCZ
GULF OF GUINEA
5ºN
20ºN
15ºN
10ºN
Based on a diagram from Core Themes in
Geography, by Broadley Cunningham
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DESERT
dry all year
SAVANNA
dry winter wet summer
RAINFOREST
wet all year
ITCZ moves north in summer
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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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GUINEA SAVANNA
SAHEL SAVANNA
DESERT
RAINFOREST
rainfall decreases
seasonality increases
variability increases
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savanna parkland
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OCEAN CURRENTS
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• 3 forces
• solar heating
• surface winds
• Coriolis effect
• result in a clockwise circulation of
• water in the Northern hemisphere and an
  anticlockwise circulation in the Southern
  hemisphere.

This circulation is known as a GYRE.
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OCEAN CURRENTS IN THE NORTH ATLANTIC
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NORTH EQUATORIAL CURRENT
90º Pole
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GULF STREAM
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NORTH ATLANTIC DRIFT
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NORTH ATLANTIC DRIFT
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2
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LABRADOR CURRENT
1
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CANARIES CURRENT
0º Equator
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GLOBAL WARMING
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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 effect is the name given to
an expected increase in the magnitude of the
greenhouse effect, whereby the surface of the
Earth will amost 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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1 Carbon Dioxide gt fossil fuels, vehicle
emissions, forest clearance 2 Methane gt rice
cultivation, biomass burning, digestive
fermentation, termites, sewage, landfill,
natural gas production 3 CFCs gt aerosol
propellants, refrigerants, foaming agents 4
Nitrous oxide gt nitrogen fertilisers, industrial
pollution
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CONCENTRATION CHANGES SINCE 1750
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
BUT
CFCs c10,000 x effect of CO2
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C Temperature anomalies from the period
1961-1990