Atmosphere

• Why only around 50% of the solar energy reaching the edge of the atmosphere reaches the surface of the Earth

  1. Solar energy enters the atmosphere as short wave radiation

  2. Around 51% is absorbed by the Earth's surface

  3. Reflection and absorption by the atmosphere

  4. Clouds have a high albedo effect and cause 20% of solar energy to be reflected back to space

  5. Albedo effect describes how reflective a surface is with light coloured surfaces reflecting more energy than darker surfaces

  6. Around 6% of solar energy reaching atmosphere is scattered by atmospheric gases and dust

  7. Around 4% is reflected from the Earth's surface and travels directly back into space as long-wave radiation

  8. Clouds that absorb some of the energy can re-radiate this energy into the atmosphere
• Factors causing surplus/deficit of energy

  1. Earth is curved

  2. Sun's rays spread out over larger area at poles, smaller area at tropics

  3. Energy more concentrated at tropics making it warmer

  4. In tropics sun high in sky year-round providing maximum insolation, at poles angle of sun low for 6 months so less heating

  5. Poles have lighter icecaps reflecting a lot of sun's energy, tropics have darker forests absorbing energy (albedo effect)

  6. Sun's rays have less atmosphere to pass through at tropics than poles, less absorption and reflection by clouds and gases so more energy reaches surface
• Three Cell Model

  Transfers warm air from the Equator to higher (and cooler) latitudes and cold air from the Poles to lower (and warmer) latitudes
• Due to the Coriolis effect

  Winds are deflected to the right in the Northern hemisphere and the left in the Southern hemisphere
• What are the three cells called AND are they thermally direct OR indirect

  • Hadley Cell - Thermally Direct
  • Ferrel Cell - Thermally Indirect
  • Polar Cell - Thermally Direct
• Hadley Cell

  1. Intense solar insolation over the equator causes the air to rise resulting in low pressure

  2. The rising air travels polewards in the upper atmosphere, to approximately 30°N, cools and sinks resulting in high pressure

  3. At ground level the air returns to the equator forming the North East trade winds to replace the air that is rising
• Polar Cell

  1. Cold air over the poles sinks resulting in high pressure and moves towards the equator forming the polar easterlies

  2. At around 60°N this air has warmed and therefore rises

  3. As it rises it cools creating an area of low pressure bringing clouds and rain

  4. Some of the air that has risen moves back to the poles to replace the air that is sinking
• Ferrell Cell

  1. At 60°N the warm air rises due to friction from the air in the polar cell

  2. This air travels in the upper atmosphere to 30°N where it sinks due to friction from the air in the Hadley cell

  3. The sinking air creates an area of high pressure bringing no clouds and no rain

  4. The air then moves back to 60°N forming the prevailing westerlies to replace the air that is rising
• Ocean currents

  Transfer energy across the earth moving surplus energy from the tropics towards the poles
• Ocean currents

  • Follow loops or gyres flowing clockwise in the Northern hemisphere and anti-clockwise in the Southern hemisphere
• Cold currents


  Ocean currents flowing from the poles to the equator
• Warm currents

  Ocean currents flowing from the equator to the poles
• Ocean current patterns

  • Affected by the prevailing winds on the surface which create friction with the surface water
  • The trade winds drive the pattern between 0° and 30° North and South
  • The Westerlies create the pattern between 30° and 60° North and South
• Ocean currents

  • Don't flow due North or due South due to the Coriolis force caused by the earth's rotation
  • Deflected to the right in the Northern hemisphere and to the left in the Southern hemisphere
• Land masses may also deflect the movement of ocean currents e.g. North America
• Differential heating of water

  • Produces density differences in the oceans
  • Cold dense polar water sinks, and then spreads towards the equator where it warms up and rises back to the surface
  • This is called the great ocean conveyor
• The ITCZ

  The ITCZ is a band of low pressure which migrates NORTH in the summer and SOUTH in the winter.