Coriolis Force

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Coriolis Force

• Or, why things rotate on earth
• Mean wind patterns
• Cyclonic rotation

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Coriolis calculation

• Where ? is the angular velocity of the earth
  (7.27x10-5 radians per second)
• ? is latitude
• v is velocity

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Coriolis effect
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Key Coriolis fact

• The Coriolis Effect is not a real physical force.
  It is an apparent acceleration or deflection due
  to our insistence upon using a moving frame of
  reference.

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Coriolis theme 1

• Coriolis is 3-dimensional in nature. However, the
  horizontal components are much larger than the
  vertical ones.

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Coriolis theme 2

• The apparent acceleration is small in actual
  value. Hence, the effect is only important for
  motions that occur over long time periods. In
  other words, it is critical for large-scale
  motions.

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Coriolis theme 3

• The magnitude of the apparent acceleration varies
  with latitude. It is zero at the equator and
  increases with the sin of the latitude. Hence, it
  has a maximum value at the poles.

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Coriolis theme 4

• The effect increases with increasing wind speed

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Coriolis theme 5

• The apparent deflection is always to the right in
  the Northern Hemisphere, and to the left in the
  Southern Hemisphere.

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Consequently, the patterns of global surface
winds for the non-rotating earth we defined last
time
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Must now be deflected according to the Coriolis
effect!
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Low pressure systems (cyclonic)

• Air moves into converging low pressure systems
  and rises, causing cloud formation and storm
  activity.
• In the northern hemisphere, the deflection is to
  the right

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• And in the southern hemisphere to the left

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High pressure systems

• High pressure systems are associated with
  diverging warm dry air and thus cannot usually be
  detected from space.
• The same deflection patterns occur right in the
  northern hemisphere, left in the southern

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Northern hemisphere high pressure
1100
1000
900
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Southern hemisphere high pressure
H
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1000
900
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Example of Coriolis effect for 100 meters
traveled in 50 and 2 seconds at 45N
So, even though the Coriolis acceleration is
higher in the fast moving object, it is
experiencing this acceleration for a shorter
time. Thus it is deflected less. If both
experience their acceleration for the same amount
of time, the faster moving object would be
deflected more.