Download Where are the major global wind belts located?

Chapter 12
Section 6
Wind
Essential Questions Ch 12 S6
1. What causes winds?
2. How do local winds and
global winds differ?
3. Where are the major global
wind belts located?
Because air is a fluid, it can move
easily from place to place.
Differences in air pressure causes
the air to move.
What is Wind?
Wind is the horizontal movement
of air from an area of high pressure
to an area of lower pressure.
What causes wind?
The horizontal movement of air (wind) is
caused by differences in air pressure.
Most differences in air pressure are
caused by the unequal heating of the
atmosphere. Convection currents form
when an area of the Earth's surface is
heated by the sun’s rays.
Air over a heated surface expands (becomes
less dense) and the air pressure decreases. If
the air in a nearby area is not heated as
much, it is cooler (denser) and the air
pressure is higher. The cooler, denser air
flows underneath the warmer, less dense air.
This forces the warm air to rise.
area of high pressure
area of low pressure
Wind blows from areas of high pressure
toward areas of low pressure.
Measuring Wind
•Winds are described by their direction and
speed.
•Wind direction is determined with a wind
vane.
•The name of a wind tells you where the
wind is coming from.
•A south wind blows toward the north.
•A north wind blows toward the south.
•Wind speed can be measured with an
anemometer.
See page 419 figure 19
Wind-Chill Factor
• A cool breeze on a warm day feels good, but on
cold days the same breeze can make you feel
colder.
• The wind blowing over your skin removes the
body heat.
• The stronger the wind, the colder you feel.
The increased cooling a wind can cause is called the
wind-chill factor.
Local Winds…
• are winds that blow over short distances.
• are caused by the unequal heating of the Earth’s
surface within a small area.
• form only when large-scale winds are weak.
Sea Breeze… (day time)
• or lake breeze is a local wind that blows from an
ocean or a lake. (water takes longer to heat and
takes longer to lose its heat) See page 420
Land Breeze… (night time)
• is the flow of air from land to a body of water.
(land heats faster and cools faster) See page 42o
Global Winds…
* are winds that blow steadily from specific
directions over long distances.
* are created by the unequal heating of the Earth’s
surface. (like local winds)
* occur over a
large area.
(unlike local
winds)
Global Convection Currents
• Temperature differences between the equator and
the poles produce giant convection currents in
the atmosphere
The Coriolis Effect
• If the Earth did not rotate, the winds would blow
in a straight line from the poles toward the
equator.
• Earth's rotation causes long distance winds to
curve.
The way Earth’s rotation makes winds
curve is called the Coriolis Effect.
• causes the winds in the Northern Hemisphere to
turn to the right.
• causes the winds in the Southern Hemisphere to
turn to the left.
Global Wind Belts
• Global convection currents and other factors
combine to produce a pattern of calm areas and
wind belts.
• The calm areas include the doldrums and horse
latitudes.
Major Wind Belts
• Trade Winds
• Polar Easterlies
• Prevailing Westerlies
• Regions near the equator with little or no wind
are called the doldrums.
• At about 30 degrees north or south latitudes, the
air stops moving toward the poles and forms
another belt of calm air. Long ago sailors ran out
of food for their horses in this area so they threw
the horses overboard. This area is called the
horse latitude.
Trade winds
Winds in the Northern Hemisphere between 30
degrees north latitude and the equator generally
blow from the northeast. In the southern
hemisphere the winds between 30 degrees south
latitude and the equator blow from the southeast.
Long ago sailors relied on these winds to carry
cargo from Europe to the West Indies and South
America. As a result of this, the steady easterly
winds are called the trade winds.
Prevailing Westerlies
In the mid-latitudes, between 30 degrees and 60
degrees north and south, winds that blow toward
the poles are turned toward the east. Because
they blow from the west to the east, they are
called prevailing westerlies. They play an
important part in the weather of the U.S.
Polar Easterlies
Cold air near the poles sinks and flows toward the
lower latitudes and the Coriolis effect shifts the
polar winds to the west. This produces the polar
easterlies. The polar easterlies meet the
prevailing westerlies at about 60 degrees north
latitude and 6o degrees south latitude, along the
polar front. The mixing of the warm and cold air
along the polar front has a major effect on
weather in the U.S.
Jet streams
• A wind that flows in the upper troposphere from
west to east over vast distances at great speeds.
• about 10 kilometers above the surface
• hundreds of kilometers wide but only a few
kilometers deep
• blow at speeds of 200 to 400 kilometers per
hour
• Wander north and south along a wavy path
1.
2.
Quiz
________ are caused by differences in air pressure.
_________are caused by the unequal heating of
Earth’s surface within a small area.
3. _________ are created by the unequal heating of
earth’s surface over a large area.
4. Major global wind belts are the ____________, the
______________, and the _______________.
Word Bank
Global winds
prevailing westerlies
winds
trade winds
local winds
polar easterlies
Essential Questions Answered
Ch 12 S6
1. What causes winds?
Differences in air pressure,
which are caused by unequal
heating of the atmosphere.
E Q Answered Ch 12 S6
2. How do local winds and
global winds differ?
Local winds involve a small area
and develop only when global
winds are weak. Global winds
happen over a large area.
EQ Answered Ch 12 S6
3. Where are the major global
wind belts located?
Trade winds: between the equator and 30°
N and S;
prevailing westerlies: between 30 ° and 60 °
N and S;
polar easterlies: 60 ° N and 60 ° S to the
poles.