Dynamic tropopause analysis; What is the dynamic tropopause?

1. Dynamic tropopause analysis; What is the dynamic tropopause? • A level (not at a constant height or pressure) at which the gradients of potential vorticity on an isentropic surface are maximized • Large local changes in PV are determined by the advective wind • This level ranges from 1.5 to 3.0 Potential vorticity units (PVUs)

2. Consider the cross sections that we have been viewing: • Our focus is on the isentropic cross section seen below • the opposing slopes of the PV surfaces and the isentropes result in the gradients of PV being sharper along isentropic surfaces than along isobaric surfaces

5. Dynamic tropopause pressure: A Relatively high (low pressure) Tropopause in the subtropics, and a Relatively low (high pressure) Tropopause in the polar regions; a Steeply-sloping tropopause in the Middle latitudes

8. Tropopause potential temperatures (contour interval of 5K from 305 K to 350 K) at 12-h intervals (from Morgan and Nielsen-Gammon 1998) The appearance of the 330 K closed contour in panel c is produced by the large values of equivalent potential temperature ascending in moist convection and ventilated at the tropopause level; as discussed earlier, this is an excellent means of showing the effects of diabatic heating, and verifying models

9. the sounding shows a tropopause fold extending from 500 to 375 hPa at 1200 UTC, 5 Nov. 1988 for Centerville, AL, with tropospheric air above and extending to 150 hPa. The fold has descended into Charleston, SC by 0000 UTC, 6 November 1988 to the 600-500 hPa layer. The same isentropic levels are associated with each fold

10. Coupling index: Theta at the tropopause Minus the equivalent Potential temperature at Low levels (a poor man’s lifted index)

11. December 30-31, 1993 SLP And 925 hPa theta

18. An example illustrates the detail of the dynamic tropopause (1.5 potential vorticity units) that is lacking in a constant pressure analysis

19. 250 and 500-hPa analyses showing the respective subtropical and polar jets: 250-hPa z and winds 500-hPa z and winds

20. Dynamic tropopause map shows the properly-sharp troughs and ridges and full amplitudes of both the polar and subtropical jets

25. The dynamic tropopause animation during the 11 May 1999 hailstorm:

27. An animation of the dynamic tropopause for the period from December 1, 1998 through February 28, 1999:

29. The PV Conundrum • IPV (Isentropic Potential Vorticity) maps • Many isentropic surfaces have dynamically significant PV gradients • Hard to know which isentropic surfaces to look at

30. The 1.5 PVU contour on the 320 K isentropic surface is…

31. …identical to the 320 K contour on the 1.5 PVU (tropopause) surface!

32. Color Fill Version of Tropopause Map

33. Tropopause Map with Jet Streams

34. Tropopause Map, hour 00

35. Tropopause Map, hour 06

36. Tropopause Map, hour 12

37. Tropopause Map, hour 18

38. Tropopause Map, hour 24

39. Tropopause Map, hour 30

40. Tropopause Map, hour 36

41. Tropopause Map, hour 42

42. Tropopause Map, hour 48

43. Tropopause Map, hour 48, with jets

44. Cyclogenesis • Mutual Amplification • Southerlies assoc. w/ upper-level trough intensify surface frontal wave • Northerlies assoc. w/ surface frontal wave intensify upper-level trough • Superposition • Trough and frontal wave approach and occlude

45. Diabatic Processes • Latent heating max in mid-troposphere • PV increases below LH max • PV decreases above LH max • It’s as if PV is brought from aloft to low levels by latent heating • Strengthens the surface low and the upper-level downstream ridge

46. Diabatic Processes: Diagnosis • Low-level PV increases • Upper-level PV decreases • Tropopause potential temperature increases

47. Diabatic Processes: Prediction • Plot low-level equivalent potential temperature instead of potential temperature • Compare theta-e to the potential temperature of the tropopause • If theta-e is higher: • Deep tropospheric instability • Moist convection likely, rapid cyclogenesis