Global atmospheric circulation

• Winds are large scale movements of air caused by differences in air pressure
• winds are a part of cells, which are loops that have warm rising air and cool falling air
• warm air —> rises —> low pressure (on earth)

  cool air —> falls —> high pressure (on earth)
• the sun heats the world unevenly. the equator and low latitudes get more heat, whereas the poles get less heat

  • this drives global atmospheric circulation
• Hadley cells (around the equator)

  • the sun warms the earth and this is transferred to the air above
  • Warm air —> rises —> low pressure
  • Creates clouds which condense
  • Rain is associated with low pressure
  • Lots of rain along the equator (rainforests)
• Ferrel cells (30-60 degrees N/S)

  • at 30 degrees the air cools and sinks, creating high pressure. here there are clear skies and desert climates
  • the air sinks and either moves back to the equator or towards the poles
  • at 60 degrees there is low pressure as warm air from the ferrel cell and cool air from polar cell mixes
  • lots of rain here
• polar cells (60-90 N/S)

  • at the poles cold air sinks, creating high pressure (clear skies, cool air)
  • cold air sinks and moves away from poles
• from the equator: pressure is

  • low (equator)
  • high (30 degrees = deserts)
  • low (90 degrees = uk)
  • high (poles)

  
• Wind

  Wind is air moving from areas of high to low pressure, which means that atmospheric circulation causes winds

  • this makes some parts of the world windier
  • Winds are weak in low pressure belts
  • Winds are strong between pressure belts
• precipitation

  Precipitation occurs when warm, wet air rises and cools, which causes the water vapour to condense

  • air rises in low pressure belts, so precipitation is often and intense in these areas
  • Rainforests are usually in low pressure belts
  • High pressure belts is where air sinks and precipitation is low, like deserts
• temperature

  the equator receives the most energy from the sun, whereas the poles receive the least