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JETSTREAM
The jetstream is a belt
of high-speed winds which flow in the upper levels of the troposphere. These
narrow filaments or "rivers" of air exist between 10,000 and 40,000
feet above the surface of the Earth. They move in a general west to east direction
at high velocities with individual jets or "jetstreaks" joining each
other to form a great river of rushing air which sweeps around the Earth in
a wavy course between the Arctic Circle and the Tropic of Cancer. Jetstream
wind speeds generally range from 150 to 300 mph with some speeds reported to
near 400 mph.
Jetstreams develop when
a strong temperature difference exists between two air masses in the upper atmosphere.
Around the globe, these two air masses would be the polar air and tropical air.
The temperature differences lead to pressure differences which enhance the wind
speed. In general, the twists and turns of jetstreams follow the boundary between
warm and cold air. These streams of rapidly moving air tend to wander northward
during the summer, and southward during the winter.
The mid-latitudes in the
Northern Hemisphere range from the Arctic Circle to the Tropic of Cancer, and
weather on this part of the globe varies due to the jetstream. The jetstream
does not directly produce the changing weather on the surface of the Earth.
Instead, it plays an important role in the steering and formation of high and
low pressure systems in the lower layers of the atmosphere which influence our
local weather.
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