atmosphere

• layers of the atmosphere


  troposphere - most atmospheric moisture and 75% of all air, water vapour and dust, temperature decreases with altitude, most weather develops here.

  stratosphere - dry, temperatures rise, lots of ozone gases, filters out suns harmful UV rays.

  mesosphere - meteors burn up as shooting stars, temperatures fall to 100°c.

  thermosphere - northern lights, temperatures up to 1,000°c, satellites orbit.

  exosphere - outermost layer
• functions of the atmosphere


  • helps support plant and animal life on earth
  • provides us with gas balance which we can breathe in
  • acts as a filter of solar radiation
  • retains heat that would be lost in space
  • moves heat around the planet
  • reduces diurnal temperature radiation
• reasons for differences in energy balance


  • the further N/S from the equator, the same amount of energy is spread over a larger area
  • sun rays have less distance to the equator so less atmospheric absorption occurs
  • sun rays are more focused at the equator and less so N/S
  • high albedo from polar ice, low albedo from dense tropical vegetation
  • earth's tilt means the sun is higher in the sky between the tropics focusing energy
  • no solar radiation at winter solstices meaning long periods of no sunlight
• global heat budget

  
• single cell model


  hot air rises at the equator creating low pressure

  air descends at the poles giving high pressure

  the air returns to the equator through surface level winds

  a convection cell is created, this is when warmer parts move up and cooler parts move down
• Hadley cell


  thermally direct cell

  convection cells/single cell model does not reach the poles

  only reach to 30° north and south of the equator (the tropics)

  • heat from the sun is concentrated at the equator
  • warm air rises due to the intense heat from the sun, low pressure
  • as the warm air rises it cools and sinks over the tropics, high pressure
• polar cell


  thermally direct cell

  cold air sinks at the poles (90°) creating high pressure

  • at about 60° north and south, the cold polar air comes in contact with the earth's surface and warms
  • this warm air rises and returns toward the poles carrying heat energy
• Ferrell cell


  thermally indirect cell, response to the 2 other cells

  occurs between 30° and 60° north and south of the equator

  caused by friction in between the 2 cells

  • as the air falls (30°) in the Hadley cell, it pulls down the air beside it due to friction
  • as the air rises (60°) in the polar cell, it uses friction to pull the air beside it up