Blowing in the Wind
By Patti Hutchison
Imagine you are outside working on a hot summer
day. You would give anything for just a little breeze. That
would help you cool off. What makes the wind blow? The
short answer is that differences in temperature and
pressure cause wind. But wind is a little more complicated
than that. There are global wind systems that have a huge
effect on our weather.
1
Wind is moving air. Warm air rises. Cold, dense air
rushes in to take its place. This causes wind.
2
The rotation of the earth from west to east causes the Coriolis Effect. This
means that particles of air are turned to the right in the northern hemisphere. The
earth is hot in some places and cold in others. Together, the Coriolis Effect and the
uneven heating of the earth produce global wind systems. These systems move
warm air to cold places and cooler air to warm areas. This helps to keep the climate
zones in balance. No one place can keep on getting hotter or colder.
3
One wind system is known as the trade winds. These winds blow between 30
degrees north latitude and 30 degrees south latitude. At 30 degrees either north or
south of the equator, cool air sinks and then moves toward the equator. There it
warms and rises, moving back towards 30 degrees. Then it cools and sinks and
starts all over again. At 30 degrees, the sinking air creates high pressure that
produces very light winds. At the equator, there is also very little wind but a lot of
rain. This is the cause of the rain forests there.
4
A second wind system is called the prevailing westerlies. These blow between
30 and 60 degrees latitude. In this zone, the winds blow toward the poles in an
easterly direction. (Winds are named by the direction they are flowing from; that is
why they are called prevailing westerlies.) These winds cause most of the weather
movement across the United States.
5
The third wind system is the polar easterlies. This wind zone is between 60
degrees latitude and the poles. These winds flow from the northeast to the
southwest. They usually bring cold air with them.
6
Jet streams occur at the boundaries between these wind systems. There is a big
difference in temperature and pressure at the upper levels. This causes winds that
blow as fast as 185 km/hr high above the earth. They blow from west to east. The
7
polar jet stream separates the polar easterlies from the prevailing westerlies. The
subtropical jet stream is located where the trade winds meet the prevailing
westerlies.
Disturbances sometimes form along the jet streams. These produce large
weather systems that move cold and warm air around. The jet stream can move in a
northerly or southerly direction. It can even split into two branches. Whichever
way it moves, weather systems move along the jet stream. Even though it is high in
the air, the jet stream impacts the weather greatly.
8
Wind can make a big difference in the feeling of the air. It can cool the air on a
hot day. It can blow in clouds and precipitation. Without these major wind
systems, the temperature in the atmosphere would be out of control. The equator
would keep getting hotter, and the poles would keep getting colder. A breeze on a
hot summer day keeps your body's climate in balance. The major wind systems
keep the earth's climate in balance, also.
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Blowing in the Wind
1. What causes wind?
2. Where do the trade winds blow?
Between 30 degrees north and
30 degrees south latitude
Between 30 and 60 degrees
latitude
Between 60 degrees N latitude
and the poles
3. Winds that blow between 30 and 60
degrees latitude are called:
Trade winds
Prevailing westerlies
Polar easterlies
5. Where do jet streams occur?
4. Polar easterlies bring what kind of
air with them?
Cold
Wet
Warm
6. How fast do the winds blow along
the jet stream?
185 mph
185 km/h
65 mph
Name _____________________________
Date ___________________
Blowing in the Wind
Explain how the jet stream causes changes in the weather.