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What is the Jetstream?
Jet streams are currents of air
high above the Earth. They move
eastward at altitudes of about 8
to 15 kilometers (5 to 9 miles).
They form where large temperature
differences exist in the atmosphere.
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An air current is a flowing movement
of air within a larger body of air. Air
currents flow in the atmosphere, the
layers of air surrounding the Earth. They
form because the sun heats the Earth
unevenly. As the sun beams down on the
Earth, it warms some areas, particularly
the tropics, more than others, such
as the poles. As the Earth is heated, it
warms the air just above it. The warmed
air expands and becomes lighter than
the surrounding air. It rises, creating
a warm air current. Cooler, heavier air
then pushes in to replace the warm air,
forming a cool air current. Jet streams
are air currents in the highest part of
the atmosphere.
The Atmosphere
The atmosphere has a layered structure.
From the Earth upward, the layers are
the troposphere, the stratosphere, the
mesosphere, the thermosphere, and the
exosphere, which merges with thin gases
of space. The boundaries between the
layers are not sharply defined, and they
vary with latitude and season.
What is
the Jetstream?
Weather occurs in the troposphere. On
average, this layer extends to an altitude
of about 10 kilometers (6 miles),
ranging from less than 6 kilometers (4
miles) at the poles to about 20 kilometers
(12 miles) at the Equator. The top
of the troposphere is higher in summer
than in winter. Because the troposphere
contains most of the atmospheres water
vapor, clouds usually form in this layer.
Temperature decreases rapidly in the
troposphere as altitude increases.
The suns rays pass easily through the
troposphere. It is not heated directly by
the sun, but by the Earth. The troposphere
absorbs heat that is radiated from the
Earth into the atmosphere. Various gases
in the troposphere, such as carbon dioxide,
water vapor, and methane, trap this
radiated heat and dont let it escape into
space. The warming of the atmosphere
through this heat absorption is known
as the greenhouse effect.
The boundary between the turbulent troposphere
and the calm, cold stratosphere
is called the tropopause. Jet streams
travel in the tropopause..
Jet Stream
Jet streams are some of the strongest
winds in the atmosphere. Their speeds
usually range from 129 to 225 kilometers
per hour (80 to 140 miles per hour), but
they can reach more than 443 kilometers
per hour (275 miles per hour). They are
faster in winter when the temperature
At most times in the Northern and
Southern Hemispheres, there are two
jet streams: a subtropical jet stream
centered at about 30 degrees latitude
and a polar-front jet stream whose position
varies with the boundary between
polar and temperate air. A reverse jet
stream blows toward the west in tropical
high altitudes during the Northern
Hemispheres summer. It is associated
with the heating of the Asian continent
and may help bring summer monsoons
to the Indian Ocean.
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