Atmosphere

Atmosphere

1. Atmosphere

   • The mixture of gases surrounding the Earth

2. Different layers of the atmosphere

   • Stratosphere (Stratopause
     • The layer of the atmosphere above the troposhere
     • Temperature does not decrease with increasing altitude
     • Free of cloud and dust, ozone absorbs and filters out UV radiation
   • Thermosphere
     • The outermost layer of the Earths surface
     • Temperature falls with increasing altitude
   • Mesosphere
     • The layer of atmosphere above the stratosphere to an altitude of about 80km above the surface of the Earth
   • Troposphere (Tropopause)
     • Layer extending approx. 8- 17km upwards from Earths surface
     • Temperature decreases with increasing height
       • Temp usually decreases at av. 6.5C per km
     • Most of our climae and weather processes happen here

3. Atmospheric heat budget

   • depends on the balance between incoming solar radiation (insolation) and outgoing radiation from the planet

4. Planteray surface winds

   • Wind is the horizontal movement of air on the Earth's surface
   • Winds result in differences in air pressure - always blow from high to low
     • If temp. increases in a place the air expands and rises, which reduces air pressure
       • If temp. decreases in a place the air becomes denser and sinks which increases air pressure.
   • Surface winds change seasonally and are affected by land and sea

5. Atmospheric pressure and winds

   • The pressure exerted by the weight of the air in the atmosphere at the surface of the Earth
   • Av. pressure at sea level is 1,013mb.
   • Ground surface has greatest weight acting upon them - so pressure is greatest here.
   • High pressure - air is descending and associated with dry weather
   • Low pressure - air is rising and associated with precipitation and windy conditions. As it ascends air cools and cannot hold as much water vapour - so condenses and become clouds and condensation level.

6. General atmospheric circulation system

   • The differential heating of the Earth's surface by the sun is sufficient to create a pattern of pressure cells.
     • Movement within each cell is usually circular and responsible for the transfer of surplus energy from equatorial regions to other parts of the Earth
   • Rossby waves - A series of large waves that occur in the westerlies in the mid-latitudes in both Northern and Southern hemispheres
   • Hadley Cells - form the basis of tropical air circulation, and are responsible for seasonal changes in climate
     • Between the 2 Hadley cells there is an area of low pressure known as the Inter Tropical Convergence Zone (ITCZ
       • Sun is always high, ground heated rapidly by day and lots of surface evaporation. Hot air rises in convection currents and area of low pressure develops
         • This rising air cools and water vapour condenses giving heavy rainfall
     • At high altitudes the air moves polewards - usually circulating as upper westerly wind as a result of the Coriolis
   • Ferrel and Polar cells