Transcript Atmosphere 3 - Global Transfer of Energy

Energy Receipt and Latitude
Recap
Tasks:
1. Study figure 2.3 (page 7) describe the
areas of energy surplus and deficit.
2. Using page 6 give 3 reasons why there is
a net gain of energy in the low tropics.
3. Find 3 reasons why the poles are an area
of energy deficit.
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Exam Question - 2002
With the aid of an annotated diagram of the earth, describe
and explain the latitudinal variation of the Earth’s energy
balance?
Use Figure 2.3 on page 7 to help
What is this question asking?
1.
DESCRIBE the variation in solar energy at different latitudes – notably
the tropics and polar regions
2.
EXPLAIN why this variation occurs – i.e. why does what you are saying
to the first part of the question actually happen
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Global Transfer of Energy
1.
What is the global transfer of energy?
2.
How does this happen?
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Single cell model of atmospheric circulation
Three cell Ferrel model
‘Tropical latitudes receive more solar energy than Polar
latitudes. The atmosphere and oceans help to redistribute this
energy to maintain a global energy balance.’
Source: Question 1, Higher Geography Paper 1 - 2004
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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).
How?
1. Atmospheric circulation (80% of heat
transfer).
2. Ocean Currents.
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Global Transfer of Energy
Why do we have transfer of energy?
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Areas above 38° latitude receive less solar energy than
those between these latitudes.
At higher latitudes more energy is emitted from the
surface than is absorbed.
Deficit in energy above 38°.
Surplus between 38° North and South.
If this were too remain the tropics would become much
hotter and higher latitudes much colder.
This does not occur as energy is moved from areas of
surplus to areas of deficit.
This process is known as atmospheric circulation.
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90º Pole
DEFICIT
1. ATMOSPHERIC CIRCULATION
2. OCEAN CURRENTS
SURPLUS
0º Equator
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surplus
0º Equator
deficit
90º Pole
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TRANSFER of ENERGY by ATMOSPHERIC CIRCULATION
0º Equator
90º Pole
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TRANSFER of ENERGY by OCEAN CURRENTS
90º Pole
0º Equator
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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.
0º Equator
LP
90º Pole
HP
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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
 air moves from areas
of low pressure to high
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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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THREE CELL MODEL
Hadley
Cell
0º Equator
LP
Polar
Cell
Ferrel
Cell
30º
HP
60º
LP
90º Pole
HP
BBC Clip - Global Circulation
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Hadley Cell
ITCZ
ITCZ = Inter-tropical convergence Zone (Low Pressure)
STH = Sub-tropical High (High Pressure)
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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. 16
The Ferrel cell is a thermally indirect cell.
ENERGY TRANSFER
Hadley
Cell
Ferrel
Cell
Polar
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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Task:
Answer questions 3 and 4 on page 32
Under the heading ‘Energy Transfer and the Atmosphere’
Answers can be found on pages 8  10
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Global Heat Budget
Atmospheric Circulation: Exam Style Question
Describe the role of atmospheric circulation in the redistribution
of energy over the globe.
Or
Explain how the circulation cells assist in the redistribution of
energy over the Earth.
PLAN:
Name the cells
Describe where they start / stop
Explain why they operate
Explain how air rises, falls
Describe the movement of air
Learn the concluding sentence – link back to the question.
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Global Heat Budget
Atmospheric Circulation: Exam Style Question
Energy is redistributed across the globe by 3 atmospheric cells – the Hadley, Ferrel and
Polar cells.
The Hadley cell is a thermally direct cell that moves energy polewards. Air rises at the
equator as it is an area of energy surplus. Air is heated, becomes less dense and begins to
rise. As it cools it spreads North and South from the equator. At approximately
30degrees N&S air cools and sinks to the ground. Some of the air is returned as surface
winds towards the equator for reheating.
The Polar cell is also thermally direct. Cold, dense air sinks at the poles and moves towards
the mid-latitudes as surface winds. At this point it meets air coming upwards from the
equator – this creates a zone of convergence and forces air to rise at appox 60degrees.
Some of this air returns to the Poles to complete the Polar cell. Some moves to the equator.
The Ferrel cell is thermally indirect and is driven by movement in the other two cells. It
allows warm air from the equator to move polewards and cold air from the Polar cell to
move towards the equator. It is in this way that the cells move energy from an area of
surplus to an area of deficit and redistribute energy across the globe.
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