Atmospheric Pressure and Winds

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Atmospheric Pressure and Winds

• Chapter 19

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Air Pressure

• The weight of the atmosphere per unit area.
• 1kg per cm² at sea level
• 14.7 lbs/in² at sea level
• Directed equally in all directions
• Barometer
• 76cm / 30in at sea level
• given in metric unit of millibars (mb)

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Barometer

• Instrument that measures air pressure
• Mercury Barometer
• Requires a tall column of mercury
• Aneroid Barometer
• Uses no liquid

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Mercury Barometer
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Air Pressure Records
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Why Air Pressure Changes

• Temperature Changes
• warm air is lighter than cold air
• Changing Humidity
• the more water vapor, the lighter the air
• water vapor pushes out heavier O2 and N2 of the
  dry air

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What Makes Wind Blow

• Pressure Gradient Force
• the difference in air pressures that cause winds
• Local Winds
• Sea Breeze daytime wind from sea, land heats
  faster than water and causes air to rise
• Land Breeze nighttime wind from land to sea,
  water is warmer than land

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Local Winds Sea Breeze
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Local Winds Land Breeze
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Earths Rotation and Weather Systems

• Coriolis Effect
• Turns wind to the right
• Clockwise
• Out of HIGH pressure
• Counterclockwise
• Into LOW pressure

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High Pressure Center
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Low Pressure Center
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Global Air Currents
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Air Masses and Fronts

• Chapter 20

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Air Masses

• Huge section of air that has the same weather
  throughout
• Take on the characteristics of the area they
  originated over
• maritime tropical mT
• continental tropical cT
• maritime polar mP
• continental polar - cP

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Air Mass Source Regions
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Fronts

• Boundary between 2 air masses
• Causes warm air to rise
• Where temperatures and humidity change

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Warm Front Map View

• Slow moving
• Long lasting rain
• Cirrus to stratus clouds, then nimbostratus

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Warm Front Side View
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Warm Front Side View
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Cold Front Map View

• Fast moving
• Unstable air
• Cumulus cumulonimbus clouds
• Thunderstorms
• Clears quickly and leaves clear skies

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Cold Front
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Cold Front
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Occluded Front Map View

• When a cold front overtakes a warm front
• Form low pressure systems

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Occluded Front Side View
Warm Air
Cold Air
Cold Air