Atmospheric Pressure and Winds

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Atmospheric Pressure and Winds
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Air Pressure

• The weight of the atmosphere per unit area
• Pressure is force per unit

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Mercury Barometer

• Air pressure is measured by this
• As pressure increases the mercury level rises

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Aneroid Barometer

• Measures pressure with a thin metal can
• As the pressure increases the spring (or similar
  device) moves the needle
• The needle moves as the can changes shapes

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Why does Air pressure Change

• Air Temperature
• Warmer air
• Lighter than cold air lowering the pressure
  readings on the barometer
• Humidity
• The more water vapor, the lighter the air is,
  lowering the air pressure
• This sounds backwards but it is not!
• When water vapor enters the atmosphere, it pushes
  out dry air, mainly containing N Othe water
  vapor is lighter than the N O combined

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Highs and Lows???
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Winds

• What makes them blow?
• Uneven heating and cooling of the atmosphere
• Pressure gradient force
• The change between the ocean and the land
• Wind moves from high pressure to low pressure

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Pressure belts and winds
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Jet stream pattern

• See how the weather changes from one day to the
  next Wed (67) Thurs (85)