Gac

• Winds


  The movement of air on a large scale. The air is made up of gases.
• What causes winds?


  Differences in air pressure cause winds.
• What causes differences in air pressure?

  Different temperatures cause movement, like with convection currents. The equator is warmer than the North Pole or the South Pole, and this difference causes different air pressures.
• How does air pressure affect winds?

  Winds move from high-pressure areas of the Earth to lower-pressure areas of the Earth.
• Global atmospheric circulation cells

  • Cool sinking air forms high-pressure belts of wind
  • Warm rising air forms low-pressure belts of wind
• Global atmospheric circulation cells

  • Hadley cells
  • Ferrel cells
  • Polar cells
• Global Atmospheric Circulation Model

  Describes how air circulates between low and high-pressure belts as a result of differing conditions at different latitudes. This involves the transfer of heat via circulation cells.
• What happens at the equator?

  1. The Earth's surface is warmed by the Sun at the equator

  2. The Earth transmits this heat to the nearby air

  3. The air gets hotter and rises

  4. The rising, hot air forms a low-pressure belt

  5. The rising air cools and moves away from the equator towards 30° north and 30° south
• What happens at 30° north and south?


  1. The air is further from the equator and the cool air falls

  2. This results in a high-pressure belt with minimal rainfall and no clouds

  3. The cool air reaches the Earth's surface, surface winds blow the cool air either towards the equator, or away from the equator towards the Poles
• What happens at 60° north and south?


  1. Cold air blown from the poles meets warm air surface winds

  2. The warmer air is less dense, it rises and forms a low-pressure belt

  3. The air splits, with some returning back towards the equator and the rest heading to the poles
• What happens at the poles?

  1. Cool air will sink, forming a high-pressure belt

  2. This high-pressure belt will move back towards the Earth's equator as a surface wind
• 90 - 60


  polar easterlies
• 30 - 60

  westerlies
• Equator to 30 


  Northeast or southeast trade winds
• Coriolis force 


  circulating air is deflected toward the right in the Northern Hemisphere and toward the left in the Southern Hemisphere