Global Climatic Controls.

Global Climatic Controls.

1. The Atmospheric Heat Budget.

   • Looks at the distribution of heat energy which the Earth receives from the sun. It is the balance between the incoming solar radiation and outgoing radiation from the planet.
   • 51% of the incoming solar radiation reaches the Earths surface.
     • The rest of the incoming solar radiation is reflected back or absorbed by either the clouds, atmosphere or the Earth's surface.

2. The Structure of the Atmosphere.

   • The structure of the atmosphere is determined by temperature changes with height. 99% of the atmosphere is nitrogen and oxygen but there is also water vapour, ozone and carbon dioxide.
     • According to the Environmental Lapse Rate temperatures decrease by 6.5C with every 1000m upwards.

3. The Effects of Latitude.

   • Latitude effects the climate in 2 ways:
     • The angle of the sun.
     • The length of daylight. The longer the daylight, the greater in insolation.
     • In the tropics, the length of daylight is constant at 12 hours. At the poles in their winter virtually no sunlight reaches them so there is nearly 24 hours of darkness - this reduces temperatures significantly. However in summer, they have long days and short night meaning relatively more direct heat (however it still isn't warm due to the oblique angle of the sun.)

4. General Atmospheric Circulation.

   • A redistribution of heat energy must constantly take place so that the equator and the tropics don't get warmer and the poles don't get colder.
     • The Hadley Cells.
   • The Tricellular Model.
     • In addition to the Hadley cells there are two more cells that operate in a similar way. The Ferrel Cell and the Polar Cell.
   • The Jet Stream.
     • There are four jet streams. Two in the northern hemisphere and two in the southern hemisphere.
     • The currents are fast flowing (over 100mph) and flow from West to East.
       • They flow in the Troposphere.
     • The waves in the Jet stream are known as Rossby Waves.

5. Planetary Surface Winds.

   • Planetary surface winds form when low air rises in the ITCZ. Cool air then sinks as they allow the sinking air to replace the rising air. The surface winds are equalising the pressure differences.

6. Ocean Currents and Circulation.

   • Ocean currents are set in motion by the prevailing winds blowing over the surface of the ocean.
     • The are vital in transferring heat from the equator to the poles.
       • The Gulf Stream.
         • Part of the Thermohaline circulation.
         • The gulf stream carries warm, less dense waters on the surface towards the UK. Then once it reaches Greenland there is a sinking zone, this happens because colder, denser water which is very salty drags the warm water down. This then moves subsurface back towards the Gulf of Mexico.
     • The main ocean currents follow circular routes (gyres).
       • In the northern hemisphere rotation is clockwise and in the southern hemisphere rotation is anticlockwise.
   • Distance from Sea.
     • Continental areas warm up in summer very quickly and cool down quickly in winter due to a low specific heat capacity. This creates an extreme continental climate with large temperature range. Whereas coastal areas, heat up slower but also cool down much slower. This creats a smaller temperature range and a maritime climate.
   • La Nina/El Nino.

7. The Effect of Altitude.

   • The effect of altitude on climate is more useful for explaining local variations in climate.
   • In the Uk Relief rainfall occurs when moist air is forced to rise over the mountains.
   • The impacts of altitude on temperature.
     • ELR states that with every 1000m upwards the temperature decreases by 6.5C