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Jet Stream Populations
Name: Heather W.
Status: student
Age: 14
Location: N/A
Country: N/A
Date: 2001
Question:
where and how many jet streams occur in each hemisphere
in the earth?
Replies:
Heather,
There are generally two jet streams on each continental area
of the Earth, whether northern or southern hemisphere, although
the positions and existence of these vary with season and shape
of landmass. However, there are some other jets, such as the
weak Polar Night Jet that forms high in the Stratosphere
during the polar winter in both hemispheres (caused by extreme
cooling during the pronged period of constant darkness) and the
weak Tropical Easterly Jet over Africa, India, and Southeast Asia
during the summer which is associated with the onset of the
monsoon season.
For the North American continent, the Polar Front Jet (5 to 12
kilometers altitude) usually sits near the Canada/USA border
and the Subtropical Jet (8 to 15 kilometers altitude) sits near
the southern boundary of the USA. During winter these jets are
larger and faster than during the summer because the north to
south temperature difference is greater in the winter. Also,
during an arctic outbreak of very cold air in winter, the Polar
Front Jet can dive down into the southern part of the USA and
combine with the Subtropical Jet to form one large jet (this is
happening right now - see the jet stream maps at:
squall.sfsu.edu/gif/jetstream_norhem_00.gif and
www.wunderground.com/US/Region/US/JetStream.htm).
When the jet stream flow is "split", in other words when both
jet streams exist separately, very cold air is prevented from
reaching deep into the USA and the temperatures in much of the
eastern part of the country can be quite warm, especially if
the Subtropical Jet is weak.
s
During the summer, the Subtropical Jet can almost disappear,
leaving only a weak Polar Front Jet to bottle hot air up south
of it, giving us some very hot weather in the heart of summer.
David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory
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Update: June 2012
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