Air Pressure

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Air Pressure

• Weight of the atmosphere per unit area.
• Atmosphere is made of gas molecules moving
  equally in all directions
• What causes air pressure to change?

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Why Does Air Pressure Change?

• 1.Constant Temperature Change
• Warm Air Low Pressure
• Cold Air High Pressure
• 2. Changing Humidity
• Water vapor is less than 1 of air
• Weighs less than N or O
• Humid Air Low Pressure

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COLD AIR
WARM AIR
High Pressure Low Pressure
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Air Pressure Units

• Millibar
• Isobars Lines that join areas of equal pressure
  at the same time

MILLIBAR
ISOBAR
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Highs Lows Pressure Gradients
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Pressure Gradient

• Strong Pressure Gradient
• Isobars are located close together
• Strong Wind
• Weak Pressure Gradient
• Isobars are far apart
• Weak Wind

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What Causes Winds?

• Wind results from differences in air pressure
• High Pressure Lots of air
• Low Pressure Not a lot of air
• Wind movement of air from high to low pressure

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Sea Breezes

• Occur during the day
• Land heats up faster than the ocean
• High Pressure on Ocean, Low pressure on Land
• The air moves from the high pressure (ocean) to
  the low pressure (land)

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SEA BREEZE
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Land Breeze

• Usually at night
• Land cools faster, making it colder than the sea
• High Pressure on Land, Low above Ocean
• This makes the air move from high pressure (land)
  to low pressure (ocean)

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Land Breeze
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The Coriolis Effect
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Global Wind Belts

• Unequal heating creates a giant transfer system.
• Moves warm air towards high altitudes and cool
  air towards the equator.
• Creating Wind Belts!

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Measuring Winds

• Wind Vein Determines wind direction
• Anemometer Speed is determined by the rotation
  of the cups on the anemometer
• Knot the unit used to measure wind speed
• 1 Knot 1.15 miles or 1.85 Kilometers