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Global Winds and Local Winds
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THINK ABOUT IT!
• We have learned that the Earth is heated from
the sun unevenly.
• Warm air is less dense (lighter), and exerts less
air pressure than cool air. Because of this,
warm air rises and cool air sinks. How do you
think this affects our weather locally and
globally?
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• Wind is moving air caused by differences in
air pressure. Air moves from areas of high
pressure to areas of low pressure. (This is why
your ears “pop” when you ascend in an
airplane – as the plane rises to where there is
less air pressure, the air in your ears balance
and you feel it as a “pop”) The greater the
pressure difference, the faster the air moves,
and the stronger the wind blows.
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• Most differences in air pressure are caused by
differences in air temperatures. Temperature
differences happen because some parts of the
Earth get more energy from the sun than
others. Since the sun shines more directly on
the equator than on the poles, the air is warmer
near the equator.
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• Since the air near the equator is less dense, it
rises forming areas of low pressure.
• The cold air near the poles sinks because it is
more dense, forming areas of high pressure.
• The air moves in large circular patterns called
convection cells.
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Chapter 15
Section 3 Global Winds and Local
Winds
Why Air Moves
• Air Rises at the Equator and Sinks at the Poles
As the cold air sinks, it creates areas of high pressure
around the poles. This cold polar air then flows toward
the equator.
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Chapter 15
Section 3 Global Winds and Local
Winds
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• Wind
• Pressure Belts and Convection Cells
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Chapter 15
Section 3 Global Winds and Local
Winds
Why Air Moves, continued
• The Coriolis Effect The apparent curving of the
path of currents due to the Earth’s rotation is called the
Coriolis effect; the deflection, or curving, of moving
objects from a straight path. Wind moving from the
poles to the equator is deflected to the west. Wind
moving from the equator to the poles is deflected to the
east. In the Northern Hemisphere the winds travel in a
clockwise direction, and in the Southern Hemisphere
the winds travel in a counter-clockwise direction.
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Chapter 15
Section 3 Global Winds and Local
Winds
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• Coriolis Effect
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Chapter 15
Section 3 Global Winds and Local
Winds
Global Winds
• Polar Easterlies are the wind belts that extend from the poles to
60° latitude in both hemispheres. They form as cold, sinking air
moves away from the poles. They can carry cold arctic air over
the U.S. which can produce snow and freezing weather.
• Westerlies are the wind belts found between 30° and 60°
latitude in both hemispheres. They blow toward the poles from
west to east. These winds can carry moist air of the U.S.
producing rain and snow.
• Trade Winds are the winds that blow from 30° latitude almost to
the equator in both hemispheres. They curve to the West as they
blow toward the equator.
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Chapter 15
Section 3 Global Winds and Local
Winds
Global Winds, continued
The Doldrums The trade winds of the Northern and Southern
Hemispheres meet in an area around the equator called the
doldrums. there is very little wind because the warm, rising air
creates an area of low pressure. The name doldrums means “dull”
or “sluggish.”
• The Horse Latitudes At about 30° north and 30° south latitude,
sinking air creates an area of high pressure called the horse
latitudes. According to legend, this name was given to these areas
when sailing ships carried horses from Europe to the Americas.
When the ships were stuck in this windless area, horses were
sometimes thrown overboard to save drinking water for the
sailors.
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• Jet Streams are narrow belts of high-speed
winds that blow in the upper troposphere and
lower stratosphere. Knowing the path of a jet
stream is important not only to pilots but also
to meteorologists. Because jet streams affect
the movement of storms, meteorologists can
track a storm if they know the location of a jet
stream.
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Chapter 15
Section 3 Global Winds and Local
Winds
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• Types of Wind
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Chapter 15
Section 3 Global Winds and Local
Winds
Local Winds
• Local winds generally move short distances and can
blow from any direction.
• Mountain and valley breezes are examples of local
winds caused by an area’s geography.
• Sea and land breezes are affected by temperature.
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• Local Winds
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Chapter 15
Section 3 Global Winds and Local
Winds
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