1. Potential Vorticity

2. President’s Day

3. Positive PV Anomaly Near Trop

4. Negative PV Anomaly Near Trop

5. Surface +PV Anomaly

6. Piecewise PV Inversion

8. Stoelinga MWR. 124,5 1996: Overheads

9. Stoelinga 96
Intense case of western Atlantic baroclinic cyclogeneis: the Scamp storm
Four approaches:
Full physics mesoscale simulation
Partitioned PV integration (temporally integrates accumulation of PV from various processes, e.g., explicit and parameterized LH)
Piecewise inversion of particular PV anomalies to yield their direct contributions to the total circulation.
Sensitivity experiments: No LH

10. Results
Latent heat produces a large positive PV anomaly above surface warm/bent back fronts
Explains about 70% of the non-divergent circulation a low levels
Circulation associated with LH PV also enhanced vertical coupling between surface and upper level waves

11. Results
Latent heating enhanced upper level divergence and developmet of downstream ridge.
Cyclogenesis still occurred with LH-generated PV, but was much weaker (still had upper level PV)
Friction was much smaller player.

12. Lee Troughing and PV

13. Conservation of potential vorticity
conserved for adiabatic frictionless motion
Ratio of absolute vorticity and depth of vortex
Ertel Potential Vorticity
(Holton 2004, p. 96)

14. Conservation of potential vorticity
for a homogeneous incompressible fluid
z evaluated at constant height
Potential Vorticity
(Holton 2004, p. 96)

15. Conservation of potential vorticity
When the depth of the vortex changes following motion, its absolute vorticity must change to maintain conservation of potential vorticity
(Holton 2004, p. 98)

16. Conservation of potential vorticity
(b)
(c)
(d)
(e)
Conservation of potential vorticity
For westerly flow impinging on an infinitely long mountain range…
(a) upstream, zonal flow is uniform (du/dy = 0, v=0), z = 0
(b) deflection of upper q surface upstream of barrier  increases h  absolute vorticity must increase  air column turns cyclonically
(Holton 2004, p. 98)

17. ATMS 316- Background Conservation of potential vorticity
For westerly flow impinging on an infinitely long mountain range…
poleward drift in (b) also causes increase in f
(c) as column crosses mountain, h decreases  absolute vorticity must decrease  z becomes negative  air column drifts equatorward
(Holton 2004, p. 98)

18. Conservation of potential vorticity
(b)
(c)
(d)
(e)
Conservation of potential vorticity
For westerly flow impinging on an infinitely long mountain range…
equatorward drift in (c) also causes decrease in f
(d) as column crosses mountain, h increases  absolute vorticity must increase  z becomes positive  air column drifts poleward

19. ATMS 316- Background Conservation of potential vorticity
For westerly flow impinging on an infinitely long mountain range…
(e) alternating series of ridges and troughs downstream of mountain range
cyclonic flow pattern immediately to the east of the mountains (lee side trough)

20. (Ahrens 2005, p. 222)

24. Alps and Smaller Ranges More Complicated With All Kinds of Baroclinic Effects
Lee cyclogenesis
Preferred regions of cyclogenesis
Alps
Narrow mountain range
Theory that applies to Alps lee cyclogenesis is modifed from that used to describe lee cyclogenesis of the Rockies
Ageostrophic effects dominate and the modification of baroclinic instability by the Alps is more difficult to analyze

25. Tropopause +PV anomalies often apparent in water vapor imagery

28. Trop Pressure

29. Terminology: PV Streamer
A PV-streamer is an elongated band of potential vorticity, generally in the upper troposphere. It is mesoscale in width and synoptic scale in length.
In the upper troposphere, they are associated with stratospheric–tropospheric mass exchange, particularly in the area where the tropopause folds.

32. Wavebreaking

34. The End