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Chapter 19
The Atmosphere in Motion
19.1
Air Pressure and Wind
What is Air Pressure?
• Force exerted by the weight of
the air above.
• Weight of the air at sea
level.
• 14.7 pounds per square
inch
• 1 kilogram per
square centimeter
• Decreases with
increasing
altitude.
Measuring Air Pressure
• Units of measurement
• Millibar (mb) – standard sea level pressure
is 1013.2 mb
• Inches of mercury – standard sea level
pressure is 29.92 inches of mercury
• Instruments for measuring
• Barometer
• Mercury barometer
• Invented by Torricelli
in 1643
• Uses a glass tube filled
with mercury
Mercury
barometer
• Aneroid barometer
• "Without liquid"
• Uses an expanding
chamber
Recording Air Pressure
• Barograph
Continuously records the air pressure…
A recording aneroid barometer
Why Does Air Pressure Change?
• As air is warmed by the sun
it expands, cold air shrinks.
• Because of this, areas of higher and
lower pressure develop all over the
world.
• Pressure gradient force
• Isobars – lines of equal air pressure
• Pressure gradient – pressure change over
distance
Pressure Map Activity
Answer to Map Activity
What Makes the Wind Blow?
• Horizontal movement of air
• Out of areas of high pressure
• Into areas of low pressure
• Strong winds.
Measuring Surface Wind Direction
and Speed
• A wind vane shows wind
direction.
• Wind speed is measured with an
anemometer.
Quiz
1. Air pressure can be measured with a device called a
2. A barograph is an aneroid barometer that
continuously records air _________ day to day.
3. T / F Isobars are lines of equal air pressure.
4. Pressure gradient shows us how pressure changes
over __________
5. The horizontal movement of air out of high pressure
areas into low pressure areas is called _________
19.2
Factors Affecting Winds
Coriolis effect
• Apparent deflection in the wind direction due to
Earth's rotation.
• Deflection is to the
• right in the Northern Hemisphere
• & to the left in the Southern Hemisphere.
The Coriolis effect
• In our northern hemisphere, any
• High Pressure object in motion appears
to move right
• compared to our rotating earth.
Coriolis effect in the Northern
Hemisphere
Highs and Lows in the Northern
Hemisphere
Friction
• Near the surface,
winds are slowed
by friction
(mountains and
trees)
• At higher
altitudes, winds
are able to reach
very
• high speeds.
Jet
stream
Know the Standards
5b Students know the relationship between the
rotation of Earth and the circular motions of
ocean currents and air in pressure centers.
Quiz
1. Apparent deflection in the wind direction due to
Earth's rotation is due to the ________ effect.
2. Northern hemisphere, anything in motion appears to
move (right/left) compared to our rotating earth.
3. Where we are, winds spiral ________ wise out of a
high pressure area.
4. Near the surface, winds are slowed by __________
(mountains and trees)
5. At higher altitudes, _______ are able to reach very
high speeds.
19.3
Global Wind Patterns
Show video below and write
observations in Section Summary
http://www.youtube.com/watch?v=m2Gy8V0Dv78
Winds on a non-rotating Earth
Idealized global circulation
Weakness of the three-celled model
•
•
•
•
•
It does not take into effect the
continents or the seasons.
It is based only on upper level winds.
It does not take into account the
changing high and low pressure
systems that move across
the mid-latitudes.
• The continents heat up and cool faster than
the oceans causing the pressure belts to
break apart. Why?
• Finally, most of the upper level winds are
westerly (moving toward the East).
Strengths of the Three-celled Model
• Outside of the mid-latitudes, the model does a
good job of representing the
• surface winds and pressures.
• For the most part, the model fits well enough
for climate studies.
Description of Wind and Pressure Belts
•
•
•
•
•
Most of the sun’s energy warms the
equatorial areas or tropics.
This warm moist
raising air, produces little wind.
Due to this calm, sailing ships called these areas
the “Doldrums” or horse latitudes.
• Because of raising air in the tropics, winds
from the easterlies moved towards the tropics.
• This creates the “Intertropical Convergence
Zone” or ITCZ.
ITCZ in July
• At 30 degrees north and south of the equator
the air descends.
• This dry sinking air causes the Earth’s great
deserts like the Sahara, Gobi, and Australian.
Know the Standards
5a Students know how differential heating of Earth
results in circulation patterns in the atmosphere
and oceans that globally distribute the heat.
5e Students know rain forests and deserts on Earth
are distributed in bands at specific latitudes.
Quiz
1. The 3 celled model does not take into effect the
continents or the __________
2. It also does not take into account the changing high
and low pressure systems that move across the ______
3. Due to only raising air at the equator, the calm
winds came to be know as the __________
4. Because of raising air in the tropics, winds from the
easterlies move towards the tropics creating the _____
5. T / F At 30 degrees north and south of the equator,
air descends, creating the Earth’s great deserts.
19.4
Continental and Local Winds
Effects of Seasons and Continents
• In the summer,
• continents warm faster than the
. surrounding water.
This warmer air is less dense
• and creates
• low pressure
• areas over
• land
• In the winter the opposite happens.
• The cold
• continental air is
• dense and creates a
• high pressure area
•
•
•
•
over land
and low pressure
over most
of the oceans.
Monsoon
• Seasonal change in wind direction.
• Occur over continents.
• During warm months…
- Air flows onto land
- Warm, moist ocean air
• Winter months…
- Air flows off the land
- Dry, continental air
Local Winds
• These small scale winds are produced from local
temperature differences.
• Most common types are land and sea breezes.
Land and sea breeze
• Sea breeze, air moves onto
• land during the day.
• Land breeze, air move out to sea at night.
Quiz
1. In the summer, continents warm faster than the
surrounding _________
2. Winter the opposite happens, the cold continental air
is dense and creates a ______ pressure area over land.
3. A monsoon is a seasonal change in _____ direction.
4. Sea breeze, air moves onto ______ during the day.
5. Land breeze, air move out to sea at __________
End