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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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