1. Jet Stream Circulations
April 16, 2004

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

7. 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)

8. 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.

9. Convergence
From the above we can also say that mid-tropospheric downward motion has divergence below and convergence aloft and vice-versa
Divergence
Ground
Tropopause

10. 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

11. Vorticity & Vertical Motion
It has been stated that PVA increasing with height promotes rising motion

12. 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

14. Jet-Strm Divergence

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