Global Atmospheric Circulation

• Lines of latitude measure distance from equator
• 3 cells:

  • Hadley - either side of equator (clockwise)
  • Ferrel - inbetween (anticlockwise)
  • Polar - either side of poles (clockwise)
• Pressure:

  • High at poles and tropics
  • Low at equator and (ant)arctic circles
• Westerlies:

  • Winds moving from west to east
  • Between (ant)arctic circles and tropics
• Trade winds:

  • Winds moving from East to west
  • Between equator and tropics
• • (Ant)arctic circles are 60° north or south of the equator
  • Tropics are 30° north or South of the equator
• Hadley cells:

  1. Warm air rises away from earth's surface (low pressure)
  2. Atmosphere caps air and forces it towards poles
  3. Air cools and becomes denser
  4. Sunken air falls back to equator and heats up again (high pressure)
• Ferrel cells:

  • Not determined by temperature
  • Act like a cog helping to distribute GAC
• Polar cells:

  1. Cool, dense air descends
  2. Cool, dense air warms as it moves towards equator
  3. Now-warm air rises and moves back to poles, where it cools
• Low pressure areas:

  • Warm, less dense air that rises away from earth
  • This air cools, condenses and forms clouds
  • E.g UK, equator
• High pressure areas:

  • Cool, dense air that descends towards the earth
  • No clouds form
  • E.g sahara, (Ant)arctic
• Wimd is caused by the movement of air from high to low pressure
• Thermal gradient - different temperatures in different latitudes
• Why is there a Thermal Gradient?:

  • Due to the earth's curvature, sunlight is more concentrated in the equator and more spread out near the poles
  • Areas with no sunlight have a net loss of heat
  • Albedo effect in poles - white snow/clouds reflect sunlight and keep heat away