Global atmospheric circulation = worldwide system of winds → transports heat from tropical to polar latitudes
(hot → cold areas)
○ Helps explain the locations of world climate zones and distribution of weather hazards
○ Redistributes warm air across the surface of the Earth
○ Winds move from areas of high pressure → low pressure
● Most important influence on variations in climate is due to latitude (west → east)
○ Earth’s curved surface causes:
■ Equator receives high insolation ( low latitude)
■ Polar latitudes receive low insolation ( high latitude)
● Insolation = amount of solar radiation /sunlight an area receives (over a given time)
● Latitude = how far it is from the equator
○ Parallel rays of sunlight spread thinly at high latitudes
■ Solar energy strikes the ground at low angles → is spread over a large area
■ Each area receives little sunlight
○ Sunlight is highly concentrated at low latitudes
Air at equator is heated strongly
○ Air becomes less dense and rises to a high altitude
○ Creates a global climate zone of low pressure = equatorial zone
○ After rising → air spreads out/flows towards North/South poles
● Air at polar latitudes is not heated much
○ Air is much colder and denser
○ High pressure
○ Air sinks down towards ground level → spreads out and flows
towards equator
● Air at tropics regions
○ Areas of high pressure
■ Air sinks towards the ground , and warms
■ Results in high pressure and hot, dry desert conditions
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Convection cells:
Convection cell = differences in air temperature lead to the formation of areas of high/low air pressure
○ They become linked together by flows of warmer/cooler air
○ Low pressure belt at equator and high pressure belt at N/S poles → allows convection cells to operate
● Global circulation involves 3 cells because of Earth’s rotation
○ Hadley cell (equator regions)
■ Largest cells
■ Warm, less dense air rises
● Easterly winds (blow from NE and SE)
○ Ferrel cell (tropic regions)
■ Not driven by temperature
■ Move the opposite way to hadley/polar cells
■ Transports heat from the equator to the poles
■ Result in semi-permanent areas of high and low
pressure
● Westerly winds (blow from NW and SW)
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Polar cell (polar regions)
■ Smallest cells
■ Cold, dense air descends in polar regions
■ When the air leaves the polar regions → it starts to warm and rise
● Trade winds (blow towards the equator)
● Process of global atmospheric circulation:
1. Sun warms up the Earth at the equator → transfers heat to the air and causes it to rise
○ Creates a low pressure belt at the equator
2. Air rises and spreads out 30° north/south of the equator
○ Cool air sinks due to less heat → creates a high pressure belt
3. Cool air reaches ground and moves as surface winds either:
○ Back to the equator (trade winds)
■ Trade winds meet at the equator and are heated up again to rise and form clouds
○ Towards the N/S poles (westerlies)
4. Westerlies travel 60° north/south from the equator and meet cold air from the poles (low insolation)
○ Warm air of westerlies rises above cold air of poles → creates a low pressure belt
○ Some air moves back to equator as trade winds
○ Some air moves to the N/S poles
5. At the poles → cool air sinks and creates a high pPolar cell (polar regions)
■ Smallest cells
■ Cold, dense air descends in polar regions
■ When the air leaves the polar regions → it starts to warm and rise
● Trade winds (blow towards the equator)
● Process of global atmospheric circulation:
1. Sun warms up the Earth at the equator → transfers heat to the air and causes it to rise
○ Creates a low pressure belt at the equator
2. Air rises and spreads out 30° north/south of the equator
○ Cool air sinks due to less heat → creates a high pressure belt
3. Cool air reaches ground and moves as surface winds either:
○ Back to the equator (trade winds)
■ Trade winds meet at the equator and are heated up again to rise and form clouds
○ Towards the N/S poles (westerlies)
4. Westerlies travel 60° north/south from the equator and meet cold air from the poles (low insolation)
○ Warm air of westerlies rises above cold air of poles → creates a low pressure belt
○ Some air moves back to equator as trade winds
○ Some air moves to the N/S poles
5. At the poles → cool air sinks and creates a high pressure belt
○ Cool air is drawn back to equator as surface wind
● Exact position of jet streams/convection cells varies seasonally
○ Seasons arise due to Earth’s tilt on its axis
■ Jet streams = fast flowing current of air (200 km/hr) that circles the planet at a height of 10k
grows a wave of low pressure → results in tropical storms
○ Rainfall is higher in coastal areas in Western Europe
■ Due to movement of jet stream over Atlantic
■ Weather systems known as depressions (cloudy/wet) follow the jet stream
■ Bring stormy conditions to the UK’s west coast
○ Rainfall is very low around Tropics of Capricorn/Cancer
■ Areas of high pressure
■ Dry air descends as part of Hadley cell
■ Results in dry conditions
○ Precipitation is very low in polar regions
■ Falls mostly as snow
■ Cold air has limited ability to hold water vapour