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0º Equator. 90º Pole. LP HP. SINGLE CELL MODEL. At the Equator the atmosphere is heated Air becomes less dense and rises. Rising air creates low pressure at the equator. - PowerPoint PPT Presentation
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0º Equator 90º PoleLP 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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ITCZ = Inter-tropical convergence Zone (Low Pressure)
STH = Sub-tropical High (High Pressure)
HADLEY CELL ITCZ
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0º Equator 90º Pole30º 60ºLP HP LP HP
Hadley Cell
Polar Cell
Ferrel Cell
THREE CELL MODEL
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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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0º Equator 90º Pole30º 60ºLP 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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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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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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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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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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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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4 forces: solar heating surface winds 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
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2
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45
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1
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NORTH EQUATORIAL CURRENT
GULF STREAM
NORTH ATLANTIC DRIFT
LABRADOR CURRENT
CANARIES CURRENT
NORTH ATLANTIC DRIFT
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