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• The Atmosphere
  • Composition
    • Vertical Structure
    • Layered temperature structure
    • Distribution of important gases
    • Physics responsible for layers
  • Winds
    • Zonal mean winds
    • Impact of rotation of the earth
• The Ocean
  • Composition
  • Wind driven circulation
  • Thermohaline circulation
    

The Atmosphere

• Depth of the atmosphere ~100 to 500km.
• 75% of the atmosphere’s mass below 10km

• At sea-level, the pressure due to the atmosphere above is ~1kg/cm² (14 lbs/in² or 1000mb or 1 atmosphere).

Composition of Atmosphere

• 78% Nitrogen
• 21% Oxygen
• 1% Argon
• 0.1% Water Vapour (highly variable)
• 0.037% Carbon Dioxide
• trace to .0008% Ozone
• trace Aerosols (fine particulate matter: dust, salt, ash ..)

The last four items are particularly environmentally important.

Atmospheric Temperature Profile

Details for lower atmosphere:

Note:

• Thermosphere heated internally (Oxygen)
• Mesosphere heated from below
• Stratosphere heated internally (Ozone)
• Troposphere heated from below

Aerosol Profile

Tropospheric Aerosols

Sources:

pollution	wave breaking	dust

Aerosols enhance cloud formation

Stratospheric Aerosols

Volcanic eruptions can send ash and sulfates into stratosphere

Winds in the Atmosphere

Zonal mean winds Northern Hemisphere Winter
Solid lines: Westerly wind Dashed lines: Easterly winds

Jet Stream in winter hemisphere stronger

What causes the wind to blow?

• Pressure gradient force (force due to horizontal variations in atmospheric pressure).
  
• The Earth is rotating and so there is another force (fictitious) that has an effect on the winds.
  
  Consider a ball thrown on a merry-go-round as observed from the ground (inertial frame) and from the merry-go-round (rotating frame)
• Wind motion on the Earth is the result of the balance between the pressure gradient and Coriolis forces.
  
• Around a low-pressure region winds circulate in the counter-clockwise (cyclonic) direction.
  Around a high-pressure region winds circulate in the clockwise (anti-cyclonic) direction

  
  

  The Coriolis force acts in an opposite sense in the two hemispheres

  	Winds circulate around low pressure systems in the opposite sense in the two hemispheres.
  	north hemisphere hurricane	south hemisphere extratropical cyclone

  Global distribution of winds

  
  

   

  The Ocean

  Covers 70% of the surface area of the Earth Most important reservoir for water (97%) Average depth ~3 km, Max depth ~11km Five main oceans (Atlantic, Pacific, Indian, Arctic and Southern) The Ocean

  Contains ~3.7% salt. As a result, density of sea water is a function of both temperature and salinity.

  Three main layers in the ocean:

  

   

  Surface currents are driven by surface winds

  	Ben Franklin’s map of the Gulf Stream

  Deep ocean currents are driven by sinking of water at high latitudes.

  Surface and deep ocean currents form the thermohaline circulation.

  The sinking motion (deep convection) that supplies the bottom water to the thermohaline circulation occurs in only a few locations and occurs sporadically in these locations. See: Pickart RS, Spall MA, Ribergaard MH, Moore GWK, Milliff RF, 2003. Deep convection in the Irminger Sea forced by the Greenland tip jet. Nature 424 (6945): 152-156. (UT privileged access to link)

  The sinking motion (deep convection) that supplies the bottom water to the thermohaline circulation occurs in only a few locations and occurs sporadically in these locations.