Air pressure and winds

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Air pressure and winds

• Chapter 8

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Atmospheric Pressure

• What causes air pressure to change in the
  horizontal?
• Why does the air pressure change at the surface?

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Atmospheric Pressure

• Horizontal Pressure Variations
• It takes a shorter column of dense, cold air to
  exert the same pressure as a taller column of
  less dense, warm air
• A Warm air column is normally associated with a
  low surface pressure
• A Cold air column is normally associated with a
  High surface pressure
• At surface, horizontal difference in temperature
  horizontal pressure in pressure wind

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Atmospheric Pressure

• Special Topic Gas Law
• P is proportional to T x ?
• P pressure
• T temperature
• ? density

http//www.youtube.com/watch?v17wGIdMvJfM
(youtube video of gas law)
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Atmospheric Pressure

• Daily Pressure Variations
• Thermal tides in the tropics
• Mid-latitude pressure variation driven by
  transitory pressure cells
• Pressure Measurements
• Barometer, barometric pressure
• Standard atmospheric pressure 1013.25mb
• Aneroid barometers
• Altimeter, barograph

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Atmospheric Pressure

• Pressure Readings
• Instrument error temperature, surface tension
• Altitude corrections high altitude add pressure,
  10mb/100m above sea level

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To get sea level pressure Add 10 mb
(elevation/ 100 m) to the station pressure
measurement. Example A station at 700 meters
elevation records a pressure of 940 mb. The sea
level pressure for this station would be 940 mb
70 mb 1010 mb
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Surface and Upper Level Charts

• Sea-level pressure chart constant height
• Upper level or isobaric chart constant pressure
  surface (i.e. 500mb)
• High heights correspond to higher than normal
  pressures at a given latitude and vice versa

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