Jet stream circulations
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Jet Stream Circulations. April 16, 2004. Tools Vorticity advection Thermal advection Jet stream ageostrophic circulation Isentropic lift To begin to discuss cyclogenesis, we have to define divergence and convergence. Divergence. Divergence is the horizontal spreading out of air.

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Jet Stream Circulations

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Jet stream circulations

Jet Stream Circulations

April 16, 2004


Jet stream circulations

  • Tools

    • Vorticity advection

    • Thermal advection

    • Jet stream ageostrophic circulation

    • Isentropic lift

      To begin to discuss cyclogenesis, we have to define divergence and convergence


Divergence

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)


Vertical velocity divergence

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.


Jet stream circulations

Tropopause

Convergence

Divergence

Ground

Divergence

Convergence

From the above we can also say that mid-tropospheric downward motion has divergence below and convergence aloft and vice-versa


Divergence and vertical motion

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


Vorticity vertical motion

Vorticity & Vertical Motion

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


Jestreams and cyclogenesis

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


Jet stream circulations

Jet-Strm Divergence


Jet stream circulations

Jet-Strm Divergence

PVA increasing w/ height


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