Air Pressure

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Air Pressure

• Objectives
• - determine the effect altitude has on air
  pressure
• -describe the weather conditions associated with
  high and low pressure

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Who has heard of the expression light as air?
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What is air pressure?

• The weight of the atmosphere as it pushes down on
  the Earths surface
• Air pressure decreases as altitude increases. Ex
  airplane
• Air pressure is most noticeable when you are
  rapidly ascending (going up) or when you are
  rapidly descending

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Air pressure decreases as altitude increases
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Air Pressure in Weather

• Changes in elevation are not the only changes in
  air pressure
• In general, air pressure decreases as temperature
  increases
• As air gets warmer, the molecules move faster and
  get farther apart and there are less molecules
  than in an equal volume of cold air

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Air Pressure in Weather

• Changes in humidity also cause changes in air
  pressure
• The more water there is in the air (Humidity),
  the lighter the air is, which causes lower air
  pressure

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Air Pressure in Weather

• Air pressure changes give us a simple way of
  forecasting weather
• A decrease in air pressure means warmer more
  humid air is coming, along with rain or snow
• An increase in air pressure means cooler air,
  drier, and more fair weather is coming

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Analyzing Changes in Air Pressure

• Meteorologists analyze pressure changes using
  isobars on weather maps
• An isobar is a line that joins points that have
  the same air pressure
• The area defined by an isobar is called a high
  pressure area (high) or a low pressure area (low)

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Air Pressure

• Wind always moves from high pressure to low
  pressure. (think bicycle tire with a hole?-wind
  moves from inside (high), out (low)

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Coriolis Effect

• Because of the earths ROTATION, wind traveling
  from the north/south pole gets DEFLECTED (put off
  course).