Atmospheric Pressure and Wind

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Atmospheric Pressureand Wind

• Atmospheric Circulation
• Key Factors Affecting Wind
• Winds Resulting from Key Factors
• Global Distribution of Pressure
• Chapters 6.1 6.2 7.0 7.1

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Atmospheric Circulation
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• The general circulation serves to redistribute
  latitudinal imbalances of energy and moisture,
  and provides our winds

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Atmospheric Circulation
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• Winds are designated according to the compass
  point from which the wind comes
• An east wind comes from the east, but the air is
  moving westward

Not in Book
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Key Factors Affecting Wind
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• Pressure Gradient Force
• Coriolis Effect
• Friction
• These factors affect the wind speed and direction

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Pressure Gradient Force
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• A force that arises from spatial variation in
  pressure. Acting alone, the pressure gradient
  force would cause air to blow from an area of
  high pressure toward an area of low pressure
• Initiates air flow

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Pressure Gradient Force
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Not in Book
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Pressure Gradient Force
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Not in Book
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Coriolis Effect
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• The deflective effect of the Earths rotation on
  all free-moving objects, including the atmosphere
  and oceans
• Deflection is to the right in the Northern
  Hemisphere
• Deflection is to the left in the Southern
  Hemisphere

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Coriolis Effecton a southward moving object
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Relates to Figure 6.4
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Coriolis Effecton an eastward moving object
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Relates to Figure 6.4
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Coriolis Effecton an eastward moving object
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Relates to Figure 6.4
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Coriolis Effect
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• This effect is always directed at right angles to
  the direction of airflow
• Affects only wind direction, not speed
• Is affected by wind speed (the stronger the wind,
  the greater the deflection)
• Is strongest at the poles, and weakens equatorward

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Coriolis Effect
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Not in Book
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Friction
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• A force that acts to slow wind, but does not
  change its direction on its own
• Friction changes wind direction by affecting the
  Coriolis effect (Coriolis effect is a function of
  wind speed)

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Winds Resulting from Key Factors
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• Pressure Gradient Force (PGF) Alone
• PGF and Coriolis Effect (upper air)
• PGF, Coriolis Effect, and Friction (surface)
• Surface and Upper-Air Pressure Maps

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Pressure Gradient Force Alone
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• High pressure at the surface is associated with
  air subsiding from aloft and diverging at the
  surface
• Low pressure at the surface is associated with
  air converging at the surface and ascending

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Not in Book
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PGF and Coriolis Effect (Upper Air)
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• There is an equilibrium between the pressure
  gradient force and the coriolis effect
• Results in geostrophic wind, which blows parallel
  to the isobars

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PGF and Coriolis Effect (Upper Air)
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Figure 6.6
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PGF, Coriolis, and Friction (Surface)
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• Friction slows down the wind speed, which reduces
  the coriolis effect
• With a reduced coriolis effect, the wind crosses
  the isobars at an angle

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PGF, Coriolis, and Friction (Surface)
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Figure 6.8
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Resultant Winds
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• Surface winds
• Upper-air winds

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Surface Winds
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Not in Book
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Surface Winds
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Not in Book
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Upper-Air Winds
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Atmospheric Circulation
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• With an understanding of the factors influencing
  wind speed and direction, we can now look at the
  general circulation of the atmosphere

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