Ask A Scientist© Weather Archive

name         Arvid
status       other
age          60s

Question -   Please explain in detail how the jetstream contributes to
create low pressures at the surface.
(I have a unversity degree, so don't be afraid of refering to physics or
mathematics. I also have a basic knowledge of weather through my private
pilot license.)

Arvid,

You have asked a fascinating question.

First, there are two jets, normally, the polarfront
jet (in temperate latitudes) and the subtropical jet
(in subtropical regions well north the equator (it
commonly is found hugging the southern coastline of
the United States.  The polarfront jet
tends to vary in latitudinal location more than the
subtropical jet.  Sometimes, in the summer, only the
subtropical jet exists.

The jets form along tropopause breaks.  To the north
of the break the tropopause is low in the atmosphere
and to the south it is higher.  This discontinuity results
in high wind speeds, significant turbulence (often called
Clear Air Turbulence, which is normally found near the edges
of the jet), sometimes some rotation of the jet, and significant
instability as a result of the very different vertical gradients
of temperature of the two tropopauses.  Normally, temperatures
under the northern tropopause are lower than under the southern
tropopause.  Surface cold fronts form north of the jet and
low pressure areas often form north of the jet and just west of a
southern pointing V in the jet (which is where a trough of
lower pressure also exists).  The V enhances the instability
under the jet and results in low pressure areas (instability leads
to convection and air mass lifting, which when organized, produces
a low pressure area).

You can see this very well in the surface
(www.intellicast.com/LocalWeather/World/UnitedStates/SurfaceAnalysis)
and upper level maps
(www.intellicast.com/LocalWeather/World/UnitedStates/JetStream)
today (Dec. 6, 2000) at Intellicast weather on the Internet.


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