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2.6 Air Circulation
1
NASA
Winds are created primarily because of
uneven solar heating of the earth,
which creates giant convection cells of
warm air rising and cool air falling.
Warm, moist air rises
from the equator and
cooler, dryer air falls
near the poles.
NASA
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There are three different convection cell between the equator and
each pole.
NASA
These are due to the rotation of the earth and the combined effect of
gravitational pull and the Coriolis Effect. They deflect matter to the right
in the northern hemisphere and to the left in the southern Hemisphere.
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Cloud cover and rainfall are associated with the low pressure
systems of the equator and at the subpolar region at 60o N and S
latitude, whereas cooler, dry air is found at 30o N and S. These areas
are often associated with desert biomes and are referred to at the
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Horse Latitudes.
Major wind patterns develop in association with the convection
cells at approximately every 30 degrees.
newmediastudio.org
Image used with permission
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”
NASA
Identification
Prevailing Westerlies
Doldrums
Easterlies
a. Trade winds
b. Polar
Direction
West to East
Little/no wind
East to West
Latitude
30-60o
0
0-30o
above 60o
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A major high altitude westerly
wind in the northern hemisphere
that helps control weather
patterns is called the jet stream.
NASA
It often brings cooler air from
northern latitudes and pushes
warm air in front of it.
NASA
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Weather fronts are associated with different temperature air masses.
Where warm, moist air interacts with colder air, cloud cover is likely
and precipitation will occur as a result of condensation.
Bands of rain showers and snow
are often observed at these
weather interfaces.
NASA
Low pressure systems can also create more rain, as seen in tropical
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cyclones or hurricanes.
Tropical cyclones form over warm water and travel with the Trade
Winds from east to west. In the Atlantic Ocean, they are called
hurricanes; typhoons in the Pacific and cyclones in the Indian
Ocean.
NASA
All of these storms are formed when warm moist air over the oceans
rises and creates convection cells. The warmer the ocean water
below, the stronger the convection becomes. This creates a “heat
engine” for the developing storm and miles of clouds begin to form
and winds are generated around the eye wall in a counterclockwise
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direction.
The upward flow of warm air
and downward flow of cooler air
produces the rain bands.
The Trade Winds provide the
force to push the storm
towards the west.
The storm’s direction is controlled by upper atmospheric
conditions such as the prevailing westerlies and the jet stream
as well as other stationary high and low pressure systems.
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NASA
Atlantic hurricanes form off the west coast of Africa and move
towards the eastern US. The hurricane season is from June 1November 1, but hurricanes can develop whenever the ocean
temperatures are above 80 degrees F.
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These storms usually begin as a low pressure system, then a
tropical depression and eventually become a tropical storm when
winds reach 39-73 mph at which time the storm is named. As the
barometric pressure continues to fall, the wind intensifies. The
Saffir-Simpson scale is used to measure hurricane strength.
US Army
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In this image of Hurricane Katrina, a distinct eye-wall is surrounded
by rain bands extending for hundreds of miles. The cyclonic flow is
clearly counterclockwise. As a result, the most damaging winds are
in the northeast quadrant of the storm where it approaches shore.
NASA
The area or distance of ocean covered by the storm is called the
fetch. In 1989, Hurricane Hugo hit South Carolina with a fetch of
over 1500 miles, making it the largest hurricane on record.
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NASA
Military and NOAA aircraft fly
into hurricanes and other
storms to determine the
intensity of the winds and
make projections about the
storm track.
Category of the hurricane is
given by a number.
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