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Name: Kevin H.
Status: educator
Age:  20s
Location: N/A
Country: N/A
Date: Wednesday, June 26, 2002


Question:
I have read the responses to other questions regarding jet streams, but I still do not know why they form and how they do so. Could you please explain this? Also, why are they so narrow vertically and horizontally? Thank you.


Replies:
The jet is normally narrow vertically because of being at the tropopause transition zone; vertical gradients of temperature and pressure are usually considerably greater than horizontal gradients. The jet can be much wider horizontally, especially if there is a large horizontal extent of consistently large gradients of pressure and temperature. I have seen the jet become up to 500 miles wide, although that is unusual. The strength of the pressure and temperature differences and the distance over which those conditions exist determine the width of the jet vertically and horizontally.


Replies:
Kevin,

The jet stream results from latitudinally and vertically large gradients of temperature and pressure at the intersection of a colder air mass from the north with a warmer air mass from the south. Just as high winds are seen behind a strong cold front (because of large gradients of temperature and pressure near the surface), the same happens in the middle atmosphere at the jet. The jet tends to occur at about the height of the tropopause, the transition from the troposphere (where temperature decreases with height) to the stratosphere (where temperature increases with height). The combination of these differences in air mass, plus some help from the coriolis force (coriolis acceleration to use precise terminology) creates the acceleration of winds into the jet stream.

David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory


Dear Kevin-

Here are some links that discuss jet streams...

Jet Stream description - basic...

http://www.usatoday.com/weather/wpjet.htm

Jet Stream description - more detailed

http://www.wrh.noaa.gov/missoula/jet1.html

Jet Stream description - more technical

http://zebu.uoregon.edu/~js/glossary/jet_streams.html

(also nice graphic depicting location of jet streams relative to weather fronts)

If you do a search in one of the popular search engines, such as Google, you will find LOTS of information on this subject. Some of it will be very basic, and some very technical. Good Luck..!

Wendell Bechtold, meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO


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