General Atmospheric Circulation

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General Atmospheric Circulation
V1003 - Science and Society
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Take away concepts and ideas

• The Earth is heated unevenly.
• Why there are seasons.
• Global-scale wind patterns.
• Geostrophic flow Balance of forces that act on
  atmospheric flow (Pressure gradients gravity
  balanced by Coriolis force)
• Wind belts and climate zones.
• Monsoonal climate.

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As a sphere, the Earth is unevenly
heated,equator to poles
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2. As a tilted sphere, the Earth has seasons
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Seasonal changes in solar energy
winter summer
winter
summer winter
summer
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The equation of state (air)

• Atmospheric Pressure is a function of temperature
  and density
• Ideal Gas Law P ? R T
• if pressure is constant, then what happens to
  ?? as T increases?

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Concept of horizontal motionSea Breeze
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Pressure imbalance flow

• 1. Pressure imbalance is a FORCE
• (F m x a)
• 2. Law of mass continuity (empty spaces not
  tolerated in fluids)

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Earths uneven radiation

• Earth is a sphere (uneven radiation)
• Tilted (there are seasons)
• Sphere means equator gets more radiation than
  poles.
• Tilt mean the amount of radiation at one location
  changes with time (seasons).

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Incoming (and outgoing) radiation
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Heating imbalance (?T) Pressure imbalance (?P)
Winds
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Q1 Knowing uneven heating and P ??R T

• Poles have low pressure, equator has high
  pressure?
• b) Equator has low pressure, poles have high
  pressure?

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BUT - The Earth rotates

• Apparent (inertial) forces control the flow of
  air in response to these pressure gradients.

Centripedal force is the force acting on body by
string Centrifugal force is the opposite force
acted on by the ball (by its own inertia)
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Imagine a satellite in orbit

• Centripetal force Gravity
• Centrifugal force mass and acceleration of
  satellite
• Exact balance sets the angular velocity of the
  satellite

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The Coriolis Force

• Artifact of Earths rotation
• An apparent force which acts on motion on the
  earths surface
• Conservation of angular momentum
• Fcoriolis 0 on equator, increases poleward

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Coriolis Force Cons. of Angular Momentum
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Geostrophic Balance

• the pressure gradient force (?P) is balanced by
  Coriolis force.
• Applies to atmosphere and ocean circulation where
  friction can be ignored.

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Geostrophic balanceBalance between pressure and
coriolis forces
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Geostrophic Balance
NORTHERN HEMISPHERE
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Geostrophic flow in the Northern Hemisphere
Counter-clockwise around low pressure cells
Clockwise around high pressure cells
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Opposite Coriolis deflection for opposite
hemispheres
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An example of Geostrophic flow
Low
High
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Q2 What direction is the wind coming FROM in
Burlington, VT today?

• North
• East
• West
• South

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Application to Earth
Geostrophic flow gives rise to banded circulation
zones
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Trade Winds and the Intertropical Convergence
Zone (ITCZ)
ITCZ
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Hadley Cell Tropical convection cells
westerlies
Trade winds
Hadley Cell
Trade winds
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Global vegetation patterns

• Rising limb of Hadley Cell (ITCZ) Rainforest
• Descending limb of Hadley Cell Deserts

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Global Vegetation
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Incoming (and outgoing) radiation