Transcript No Slide Title

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
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HADLEY CELL
ITCZ
ITCZ = Inter-tropical convergence Zone (Low Pressure)
STH = Sub-tropical High (High Pressure)
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THREE CELL MODEL
Hadley
Cell
0º Equator
LP
Polar
Cell
Ferrel
Cell
30º
HP
60º
LP
90º Pole
HP
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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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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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convergence
divergence
convergence
divergence
WINDS
0º Equator
LP
30º
HP
60º
LP
90º Pole
HP
winds blow from high pressure zones to low pressure zones
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CONVERGENCE and …………DIVERGENCE
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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
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PLANETARY WINDS
High Pressure
Coriolis effect
WIND
pressure gradient force
Low Pressure
Winds are named by the direction they blow from.
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90ºN
WIND BELTS
Polar easterlies
Temperate Low
LP
60ºN
South westerlies
Sub-tropical High - Horse Latitudes
HP
30ºN
NE Trades
Equatorial Low - Doldrums
LP 0º
SE Trades
Sub-tropical High - Horse Latitudes
HP
30ºS
North westerlies
Temperate Low
LP
60ºS
Polar easterlies
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90ºS
WIND BELTS
Polar easterlies
convergence
LP
60ºN
South westerlies
divergence
Sub-tropical High
HP
30ºN
NE Trades
convergence
Inter-tropical convergence zone
LP
0º
SE Trades
divergence
HP 30ºS
Sub-tropical High
North westerlies
convergence
LP
60ºS
Polar easterlies
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90ºS
WIND BELTS
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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 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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4 forces:
 solar heating
 surface winds
 Coriolis effect
 and surface winds
result 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
90º Pole
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NORTH EQUATORIAL CURRENT
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2
GULF STREAM
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NORTH ATLANTIC DRIFT
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NORTH ATLANTIC DRIFT
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LABRADOR CURRENT
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CANARIES CURRENT
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3
6
2
1
0º Equator
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