PowerPoint Presentation

							EAS 100 Global atmospheric circulation


      Key points
      • global distribution of solar energy
      • buoyancy of air
      • convection
      • convergence and divergence
      • Hadley circulation
      • Coriolis effect
      • Intertropical Convergence Zone
      • westerlies and trades
      • subtropical highs
• Incoming solar energy flux (W/m2) decreases with latitude
• Energy is continuously redistributed from regions of surplus energy
to ones of net deficit; this is the origin of atmospheric circulation
• Heated air tends to rise (buoyancy),
since volume (and hence density) are related to temperature
PV=nRT (Ideal gas Law)

• Greatest heating occurs in the tropics, leading to rising air masses

• The decreased mass of this air results in low atmospheric pressure

• Air flows from zones of high to low pressure
Hadley circulation: convective cells ultimately fuelled by the
excess solar energy received in the tropics (InterTropical
Convergence Zone - ITCZ)
Idealized view
What’s missing?
The Earth rotates




Where drag and friction are minimal, and over large distances,
the Earth’s rotation imparts a deviation from linear trajectories
of movement: the Coriolis effect
Putting it all together
 North America




      ITCZ



     Subtropical highs



 Westerlies and
subpolar low
Africa
         Subtropical highs


            ITCZ


             Subtropical highs




             Westerlies and
            subpolar low
A final consideration: seasonal migration of the ITCZ due to the
tilt of the Earth’s axis (23.5˚ from vertical)
The ITCZ migrates 10-20˚ north and south of the Equator on a
seasonal basis, closely reflecting the zone of maximum solar energy
receipt, and dictating important weather phenomena (monsoons, etc.)
SUMMARY

• The driving force of atmospheric circulation is the global
distribution of solar energy

• Due to the incident angle of incoming solar radiation, there is
more solar energy in the tropics, resulting in an equator-to-pole
temperature gradient

• High temperatures produce buoyant air and hence low pressure

• Air flows from high to low pressure, resulting in winds

• Winds are subjected to the Coriolis effect from Earth’s rotation

• Global circulation redistributes available thermal energy from hot
to cold areas, thus providing a negative feedback against runaway
heating of the tropics, and cooling of the poles