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Name: Peter E.
Status: educator
Age: 60s
Location: N/A
Country: N/A
Date: 2001


Question:
Dear Dr.R.Cook.

I have read your archival info re "Jet Streams" and in my studies have realized that this complex 3-D system (according to some authors) BEGINS with the temp/press gradients at a low level, influencing mid level winds moving either cyclonically or anticyclonically;add the intrusion of high level winds and the Coriolis Effect; plus the effect of the pressure gradient at the 300mb. level and the position of the Polar Front == THE PATTERN for the Jet Stream.

1] in this simplification have I left out an important "factor"?

2]does the system BEGIN at the temp/press gradient at a LOW level?

3]or perhaps, there is a causality which begins with the jet stream and works its way down to the surface?

I appreciate your time and effort in this section and would be very grateful if you could enlighten me on the above questions.

Sincerely Peter E.


Replies:



Peter,

The strength of the polar jet stream is largely determined by the strength of the temperature and pressure gradients at the surface. That is why the polar front is so important. Strong temperature gradients (and pressure gradients secondarily) at the surface are amplified to stronger gradients with increasing altitude, thereby resulting in large horizontal wind shear at about 300-500 mb (depending on the time of year and latitude of the polar front) and strong winds (the jet stream) at that level. The fastest winds of the jet stream are restricted to just below the Tropopause, the boundary between the Troposphere and Stratosphere. The stable stratification of the Stratosphere prevents intrusion of the jet stream into it. The high level winds and pressure gradient at 300 mb are more affected by the polar jet than the jet is by the high level winds and pressure gradient at 300 mb.

This system is complex! A good place to see the complex structure of the polar front, polar jet, subtropical front, and subtropical jet (the latter two existing only during the warm half of the year) is a diagram (with a description of the jet stream before it) at the Univ. of Oregon site at

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

Another interesting site is one from Lyndon State College showing the Northern Hemisphere jets. Pick "Northern Hemisphere Jet Stream with MSL Pressure" at

apollo.lsc.vsc.edu/textonly/weather/hemis.html

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


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