2. 1 IPV and the Dynamic Tropopause John W. Nielsen-Gammon Texas A&M University 979-862-2248 n-g@tamu.edu

3. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon2 Outline PV basics Seeing the world through PV Waves and vortices Nonconservation Forecasting applications –Short-range forecasting –Tracking disturbances over the Rockies –Understanding the range of possibilities

4. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon3 Mathematical Definitions of PV Rossby: Vorticity divided by theta surface spacing : Relative vorticity in isentropic coordinates Minus sign: makes PV positive since pressure decreases upward

5. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon4 Mathematical Definitions of PV Rossby: Ertel: Vorticity times static stability

6. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon5 Units of Potential Vorticity 1 PVU equals…you don’t want to know Midlatitude Troposphere: -0.2 to 3.0 PVU –Typical value: 0.6 PVU Midlatitude Stratosphere: 1.5 to 10.0 PVU –Typical value: 5.0 PVU

7. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon6 PV Cross Section Pole to Pole at 80W

8. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon7 PV and Westerlies (m/s)

9. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon8 PV and Absolute Vorticity (*10 -5 s -1 )

10. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon9 PV and Potential Temperature (K) 280 310 330 350 380

11. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon10 What do PV gradients imply? Steep PV gradients –Jet streams High PV to left of jet –Vorticity gradients Same sign as PV gradients –Stratification gradients High stratification where PV is large –Vertical tropopause Flat PV gradients –Boring –No wind or vorticity variations –Stratification high where PV is large –Flat tropopause

12. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon11 PV Contours: 0, 0.25, 0.5, 1, 2, 4, 8

13. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon12

14. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon13

15. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon14 PV Contours: 0, 0.25, 0.5, 1, 2, 4, 8

16. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon15

17. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon16

18. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon17 Strong PV gradients matter; PV maxes and mins are inconsequential Jet stream follows PV gradients Waves in the PV field correspond to waves in the jet stream PV extrema bounded by strong gradients could mean short waves or cutoffs High PV = trough; Low PV = ridge

19. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon18 Forget PV! The Traditional Geopotential Height Maps Work Fine! Advantages of Height Identification and assessment of features Inference of wind and vorticity Inference of vertical motion? Disadvantages of Height Gravity waves and topography Inference of evolution and intensification Role of diabatic processes is obscure Need 300 & 500 mb

20. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon19 What’s PV Got that Traditional Maps Haven’t Got? Advantages of PV PV is conserved PV unaffected by gravity waves and topography PV at one level gives you heights at many levels Easy to diagnose Dynamics Disadvantages of PV Unfamiliar Not as easily available Not easy to eyeball significant features Qualitative inference of wind and vorticity Hard to diagnose vertical motion?

21. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon20 DYNAMICS? A given PV distribution implies a given wind and height distribution If the PV changes, the winds and heights change If you know how the PV is changing, you can infer everything else And PV changes only by advection!

22. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon21 The PV Conundrum Maps of mean PV between pressure surfaces –Encapsulates the PV distribution –Cannot diagnose evolution or dynamics

23. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon22 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

24. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon23 The PV Solution: Tropopause Maps Pick a PV contour that lies within the (critical) tropopause PV gradient Overlay this particular contour from all the different isentropic layers (or interpolate to that PV value) Result: one map showing the location of the important PV gradients at all levels Contours advected by horizontal wind

25. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon24 The 1.5 PVU contour on the 320 K isentropic surface is…

26. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon25 …identical to the 320 K contour on the 1.5 PVU (tropopause) surface!

27. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon26 Color Fill Version of Tropopause Map

28. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon27 Tropopause Map with Jet Streams

29. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon28 Tropopause Map, hour 00

30. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon29 Tropopause Map, hour 06

31. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon30 Tropopause Map, hour 12

32. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon31 Tropopause Map, hour 18

33. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon32 Tropopause Map, hour 24

34. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon33 Tropopause Map, hour 30

35. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon34 Tropopause Map, hour 36

36. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon35 Tropopause Map, hour 42

37. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon36 Tropopause Map, hour 48

38. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon37 Tropopause Map, hour 48, with jets

39. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon38 Midway Point Play with some PV Watch a movie

40. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon39 PV Dynamics: The Short Course High PV / Stratosphere / Low Theta on Tropopause Low PV / Troposphere / High Theta on Tropopause

41. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon40 Superposition PV field –Basic state –Anomalies Associated wind field –Basic state wind –Winds associated with each anomaly Add ‘em all up to get the total wind/PV

42. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon41 PV Anomaly: A Wave on the Tropopause +

43. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon42 PV Anomaly: Anomalous Winds + Think of each PV anomaly as a cyclonic or anticyclonic vortex

44. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon43 PV Wind Rules (for Northern Hemisphere) Positive anomalies have cyclonic winds Negative anomalies have anticyclonic winds Winds strongest near anomaly Winds decrease with horizontal distance Winds decrease with vertical distance

45. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon44 PV Anomaly: What will the total wind field be? + + Short Wave Planetary Wave

46. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon45 Wave Propagation Individual waves propagate upstream Short waves move slower than jet Long waves actually retrogress ++

47. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon46 The Making of a Rossby Wave Packet ++ Trough amplifies downstream ridge Ridge amplifies downstream trough, weakens upstream trough Wave packet propagates downstream - + - +

48. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon47 Intensification: Two Ways Increase the size of the PV anomaly –“Amplification” Increase the amount of PV (or number of PV anomalies) within a small area –“Superposition”

49. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon48 Tropopause, Feb. 10, 2001, 00Z Superposition? Amplification

50. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon49 Tropopause, Feb. 10, 2001, 06Z

51. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon50 Tropopause, Feb. 10, 2001, 12Z

52. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon51 Tropopause, Feb. 10, 2001, 18Z

53. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon52 Tropopause, Feb. 11, 2001, 00Z

54. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon53 500 mb, Feb. 10, 2001, 00Z

55. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon54 500 mb, Feb. 10, 2001, 06Z

56. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon55 500 mb, Feb. 10, 2001, 12Z

57. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon56 500 mb, Feb. 10, 2001, 18Z

58. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon57 500 mb, Feb. 11, 2001, 00Z

59. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon58 Low-Level Potential Temperature Acts like upper-level PV –Locally high potential temperature = cyclonic circulation –Locally low potential temperature = anticyclonic circulation But gradient is backwards –Winds from north intensify upper-level PV –Winds from south intensify low-level warm anomaly

60. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon59 MSLP (mb), 950 mb theta-e (K), 700- 950 mb PV, 300 K 1.5 PV contour

61. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon60 Surface, Feb. 10, 2001, 06Z

62. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon61 Surface, Feb. 10, 2001, 12Z

63. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon62 Surface, Feb. 10, 2001, 18Z

64. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon63 Surface, Feb. 11, 2001, 00Z

65. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon64 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

66. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon65 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

67. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon66 Diabatic Processes: Diagnosis Low-level PV increases Upper-level PV decreases Tropopause potential temperature increases

68. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon67 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

69. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon68 Forecasting Applications (1): Evolution Can directly diagnose evolution –Motion of upper-level systems –Intensification and weakening –Formation of new troughs and ridges downstream

70. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon69 Forecasting Applications (2): Model Correction Can correct forecast for poor analyses or short-range deviation –Where’s the real trough? –How will it affect the things around it? –How will its surroundings affect its evolution?

71. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon70 Forecasting Applications (3): The Rockies Can track systems over topography –Vorticity is altered by stretching and shrinking as parcels go over mountains –Potential vorticity is conserved on isentropic surfaces –PV shows you what the trough will look like once it leaves the mountains –Better forecasts, better comparison with observations

72. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon71 Forecasting Applications (4): Uncertainty Can understand the range of possibilities –Could this trough intensify? –Could a downstream wave be triggered? –How many “objects” must be simulated correctly for the forecast to be accurate?

73. COMET Feb. 20, 2002 IPV and the Dynamic Tropopause John W. Nielsen-Gammon72 Summary Definition of PV IPV maps and tropopause maps Diagnosis of evolution using PV Dynamics using PV Forecasting applications of PV