Jet%20Stream%20Circulations

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Jet Stream Circulations

• April 16, 2004

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• Tools
• Vorticity advection
• Thermal advection
• Jet stream ageostrophic circulation
• Isentropic lift
• To begin to discuss cyclogenesis, we have to
  define divergence and convergence

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Divergence

• Divergence is the horizontal spreading out of
  air.
• Convergence is the horizontal shrinking of air.
• By conservation of mass, we know that vertical
  stretching (shrinking) occurs with horizontal
  convergence (divergence)

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Vertical Velocity Divergence

• If we consider the atmosphere to have fixed
  boundaries at the bottom (ground) and top
  (tropopause), we can associate vertical motions
  with divergence and convergence as shown on the
  next slide.

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Divergence and Vertical motion

• From everything we have just discussed, you could
  be justified in saying that as long as we can
  measure divergence, we should be able to measure
  vertical motion and therefore regions of cyclone
  development (Cyclogenesis).
• Unfortunately this is not straightforward, but we
  can find a connection between divergence and
  something that is relatively easy to
  measure.VORTICITY

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Vorticity Vertical Motion

• It has been stated that PVA increasing with
  height promotes rising motion

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Jestreams and Cyclogenesis

• Putting this all together gives us the following
  Upper Convergent/Divergent pattern.
• A Convergent area ? Sfc Divergence
• B Divergent area ? Sfc Convergence
  Favourable for weather development
• C Divergent area ? Sfc Convergence
  Favourable for weather development
• D Convergent area ? Sfc Divergence

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Jet-Strm Divergence
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Jet-Strm Divergence
PVA increasing w/ height
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