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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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