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Air Pressure and Wind
5th Grade Science
Changes in Air Pressure
• Volume
• Elevation
• Humidity
– Water vapor molecules weigh less than oxygen
– Moist air has less pressure than dry air
• Temperature
– Hot air molecules speed up and spread out
– Hot air weighs less and has less pressure than cold air
– WARM AIR RISES
High Pressure, Low Pressure, Isobars,
oh my!
• Isobars: areas of equal air
pressure on a weather map
(white lines)
• High Pressure (H) center of
the storm has a higher
pressure, winds blow
outward from the center in
a clockwise pattern
• Low Pressure (L) the center
of the storm has a lower
pressure, winds blow
toward the center in a
counterclockwise pattern
Weather Station Model
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•
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Temperature
Wind speed
Wind direction
Air pressure changes
Air pressure
What causes wind?
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•
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Wind is named for where it comes from
Air that moves horizontally is wind
Air that rises is an updraft
Air that sinks is a downdraft
Convection cell
– WARM AIR RISES
– Unequal heating and cooling
Updraft
Downdraft
Land and Sea Breezes
• Land heats and cools faster than water
• Wind that blows from the sea towards land is
called a sea breeze (Day)
• Wind that blows from the land towards the
sea is called a land breeze (Night)
• Valleys and Mountains: Valley breeze during
the day and mountain breeze at night
Coriolis Effect
• Earth’s rotation causes
the wind to curve
• Northern hemisphere
curves to the right
• Southern hemisphere
curves to the left
Global Wind Patterns
• Coriolis Effect +
convection cells = global
wind patterns
• We live in the prevailing
westerlies
• This means our weather
moves from WEST to
EAST across the U.S.