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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
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
Wind speed
Wind direction
Air pressure changes
Air pressure
What causes wind?
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
– Unequal heating and cooling
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
• This means our weather
moves from WEST to
EAST across the U.S.