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Jet Streams and Climate
Name: Martin E.
Status: student
Age: 18
Location: N/A
Country: N/A
Date: Sunday, December 01, 2002
Question:
Dear sir/madam
First of all I would like to say how helpful this site is. A realgem.
My question relates to jet streams. I think I have a basic understanding
of how they are formed and behave (I use the term "understand" loosely)
but am trying to find out more about their importance in relation to an
understanding of global climate. I find bits on the Internet but nothing
giving a basic explanation, they seem to start half way through a subject,
which I find a little confusing. Any help would be gratefully appreciated.
Replies:
Martin,
You have probably seen the other answers about jet streams
on this site. The jet streams do have a strong influence on
weather patterns and thus short term climate (seasonal to annual
basis). They do this by steering weather systems, whether high
or low pressure systems, and by acting as effective blocks to
the movement of upper level moisture and energy from north to
south or vice versa. How they do this is quite complex and
you can see, by watching the weather for a few months, that the
jet streams can strengthen and weaken, change orientation, and
change elevation and depth, sometimes very rapidly, sometimes
more slowly.
At times a jet stream will remain nearly stationary for
weeks, resulting in nearly unchanging surface weather during
the period. You can see how this might affect seasonal climate,
by preventing Gulf air from penetrating into the plains and
midwest states or the southeastern states, causing drought
(a frequent occurrence), or by funneling moisture and energy
into those same areas to produce violent storms, flooding, etc.,
as has happened the past two days in the southeast.
When jet streams move eastward over the U.S. in a more
regular pattern, all areas tend to benefit from more consistent
rainfall, resulting in improved crop yields in most parts of
the country. This happened this year, except for part
of the southeast.
The affect of the jet streams on longer term (annual or longer)
climate is sometimes more difficult to assess, but is clearly
evident during an El Nino, which itself affects the positioning of the
jet stream over long periods of time. Severe drought in some
areas (southwest U.S.) and flooding in others (western South
America) occur during these periods, changing the climate
from what is normal over multiple seasons.
David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory
Dear Martin-
Generally speaking, jet streams are defined as "rivers of high-speed air in
the atmosphere." Jet streams form along the boundaries of global air masses
where there is a significant difference in atmospheric temperature. The jet
streams may be several hundred miles across and 1-2 miles deep at an
altitude of 8-12 miles. They generally move west to east, and are strongest
in the winter with core wind speeds as high as 250 mph. Changes in the jet
stream indicate changes in the motion of the atmosphere and weather.
Here are some links which describe the jet stream in general terms:
http://www.wrh.noaa.gov/Missoula/jet1.html
http://www.doc.mmu.ac.uk/aric/eae/Atmosphere/Older/Jet_Stream.html
And probably the BEST non-technical explanation and description of the jet
stream, and how it forms, with some great graphics, can be found at:
http://www.pbs.org/wgbh/nova/vanished/jetstream.html
I hope this helps you find the information you're seeking on this subject.
Wendell Bechtold, meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis MO
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Update: June 2012
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