1. Therapy for the cyclone with an identity crisis… “Subtropical Gustav” 9 Sep 2002

2. Quiz: Separate the 5 tropical cyclones from the 5 extratropical. Images courtesy NCDC

3. Some relevant questions… What makes a cyclone warm or cold-core? If all low pressure areas result from a column of air that is on average warmer than its environment, how can there be cold-core cyclones? What are the hydrostatic consequences of this thermodynamic structure & the resulting profile of cyclone “strength”? What about existence of mixed phase cyclones? Why the fuss? 60 knots is 60 knots!

4. Classic warm-core cyclone: TC Low pressure results from column of air on average warmer than environment, with the anomalous warmth in the troposphere Source: Advanced Microwave Sounder (AMSU) Temperature Anomaly Image courtesy Mark DeMaria, CIRA/CSU www.cira.colostate.edu/ramm/tropic/amsustrm.asp Hurricane Bonnie (1998) Temperature Anomaly 12km 6km 1km - +

5. Classic warm-core cyclone: TC TC Height Field (m) from hydrostatic balance Warm: expansion of surfaces Cold: contraction of height surface

6. Classic warm-core cyclone: TC Height anomaly from zonal mean shaded Height perturbation increases with altitude in troposphere

7. Classic warm-core cyclone: TC Intensifies through: sustained convection, surface fluxes. Cyclone strength greatest near the top of the PBL  Gradient wind balance in a convective environ. L WarmWarm Cold Z Troposphere Stratosphere Height perturbation - +

8. Classic cold-core cyclone: Extratropical L 2.5 NCAR/NCEP reanalysis Low pressure results from column of air on average warmer than environment, with the anomalous warmth in the stratosphere Cleveland Superbomb Temperature Anomaly

9. Classic cold-core cyclone: Extratropical Height anomaly from zonal mean shaded Height perturbation decreases with altitude in troposphere

10. Classic cold-core cyclone: Extratropical Intensifies through: baroclinic development, tropopause lowering. Cyclone strength greatest near tropopause  QG balance in a minimally convective environ L Cold Warm Z Troposphere Stratosphere Height perturbation - + Warm Cold

11. Hybrid (non-conventional) cyclone Troposphere Stratosphere Colder Warmer Z L Height perturbation - + What if an occluded extratropical cyclone moves over warm water? Characteristics of tropical and extratropical cyclones.

12. Examples of nonconventional cyclones: Past research Tannehill (1938):1938 New England Hurricane Pierce (1939):1938 New England Hurricane Knox (1955):Hurricane Hazel Palmén (1958):Hurricane Hazel Simpson (1972):“Neutercanes” Hebert & Poteat (1975):Subtropical cyclones Kornegay & Vincent (1976):T.C. Candy Bosart (1981):President’s Day Snowstorm DiMego & Bosart (1982):Hurricane Agnes Gyakum (1983):QE2 Storm Shapiro & Keyser (1990):Warm seclusion extratropical Bosart & Lackmann (1995):Hurricane David Beven (1997):Cyclone diagram, Hybrid cyclones, Mediterranean Miner et al. (2000):Hurricane “Huron” Thorncroft & Jones (2000):Hurricanes Iris & Felix

13. Non-conventional cyclones: Examples 1938 New England Hurricane ? 940hPa Pierce 1939 Began as intense tropical cyclone Rapid transformation into an intense hybrid cyclone over New England (left) Enormous damage ($3.5 billion adjusted to 1990). 10% of trees downed in New England. 600+ lives lost. Basic theories do not explain a frontal hurricane

14. Non-conventional cyclones: Examples Christmas 1994 Hybrid New England Storm NCDC Gulf of Mexico extratropical cyclone that acquired partial tropical characteristics A partial eye was observed when the cyclone was just east of Long Island Wind gusts of 50-100mph observed across southern New England Largest U.S. power outage (350,000) since Andrew in 1992 Forecast 6hr earlier: chance of light rain, winds of 5-15mph.

15. Model interpretation: What type of development? P MIN =1009hPaP MIN =1001hPa P MIN =1003hPa P MIN =1005hPa

16. Why is the phase of a cyclone important? Predictability is a function of cyclone phase Model interpretation/trust is a function of phase It is often not at first apparent what the model is forecasting, or the nature of cyclone development MPI is a function of cyclone phase

17. Impact is a function of structural evolution and interaction Analysis courtesy NOAA/NWS/NHC Fran (1996):No transition Floyd (1999): Transition from pos. tilt trough Analysis courtesy NCAR/NCEP Reanalysis-2 Hazel (1954): Transition from a neg. tilt trough Analysis courtesy Jim Abraham, CHC

18. Significance: Classification Better understanding of the current state Applying conceptual models The type/extent of expected impact/damage Quantifying potential for intensity change and its uncertainty –Scales of motion dependence –Maximum intensity How can intensity change be forecast if there is great structural uncertainty? Amount of intrinsic (mis)trust of numerical model forecasts  Need a diagnosis of basic cyclone structure that is more flexible than only tropical or extratropical

19. Goal: A more flexible approach to cyclone characterization  To describe the basic structure of tropical, extratropical, and hybrid cyclones simultaneously using a cyclone phase space. Phase Space Parameter A Parameter B Parameter C

20. Cyclone Parameter 1: Vertical structure -V T : Thermal Wind [Warm vs. Cold Core] Height perturbation - + - + - + Warm coreHybridCold Core 300mb 600mb 900mb

21. Cyclone Parameter -V T : Thermal Wind Warm-core example: Hurricane Floyd 14 Sep 1999 ZZ ZZ ZZ ZZ ZZ ZZ ZZ ZZ ZZ Two layers of interest Vertical profile of Z MAX -Z MIN is proportional to thermal wind (V T ).

22. Cyclone Parameter -V T : Thermal Wind Cold-core example: Cleveland Superbomb 26 Jan 1978

23. Cyclone Parameter 2: Horizontal structure B: Thermal Asymmetry SymmetricHybridAsymmetric

24. Defined using storm-relative 900-600hPa mean thickness field (shaded) asymmetry within 500km radius: B >> 0:FrontalB  0:Nonfrontal Cyclone Parameter B: Thermal Asymmetry 3160m 3260m L Cold Warm

25. Cyclone Parameter B: Thermal Asymmetry LLL DevelopingMature Occlusion B >> 0 B > 0 B  0 Conventional Extratropical cyclone: B varies LLL FormingMatureDecay Conventional Tropical cyclone: B  0

26. Constructing Phase Space

27. Constructing 3-D phase space from cyclone parameters: B, -V T L, -V T U A trajectory within 3-D generally too complex to visualize in an operational setting  Take two cross sections (slices) : B -V T L -V T U -V T L

28. Hurricane Mitch (1998) Case of symmetric, warm-core development and decay Classic tropical cyclone

29. Symmetric warm-core evolution: Hurricane Mitch (1998) Slice 1: B Vs. -V T L

31. Symmetric warm-core evolution: Hurricane Mitch (1998) Slice 2: -V T L Vs. -V T U Upward warm core development maturity, and decay. With landfall, warm-core weakens more rapidly in lower troposphere than upper.

32. Symmetric warm-core evolution: Hurricane Mitch (1998) Slice 2: -V T L Vs. -V T U Upward warm core development maturity, and decay. With landfall, warm-core weakens more rapidly in lower troposphere than upper.

33. December 1987 Extratropical Cyclone Case of asymmetric, cold-core development and decay Classic occlusion of an extratropical cyclone

34. Asymmetric cold-core evolution: Extratropical Cyclone Slice 1: B Vs. -V T L

36. Asymmetric cold-core evolution: Extratropical Cyclone Slice 2: -V T L Vs. –V T U

38. Hurricane Floyd (1999) Multiple phase evolution: Case of extratropical transition of a tropical cyclone

39. Warm-to-cold core transition: Extratropical Transition of Hurricane Floyd (1999): B Vs. -V T L -V T L B 12 3 4 5 1 2 3 4 5

40. Warm-to-cold core transition: Extratropical Transition of Hurricane Floyd (1999) B Vs. -V T L  Provides for objective indicators of extratropical transition lifecycle. Extratropical transition begins when B=10m Extratropical transition ends when –V T L < 0 -V T L B

41. Spaghetti Plot of 34 Cyclone Phase Trajectories based upon Navy NOGAPS operational analyses B -V T L 960hPa970hPa980hPa990hPa1000hPa1010hPa Symmetric Warm Core Asymmetric Warm- core Symmetric Cold-core Asymmetric Cold-Core

42. TETE T E +24h T E +48h TBTB T MID T B -24h T B -48h 34-Cyclone Composite Mean Phase NOGAPS-analysis based Trajectory with key milestones labeled Composite Mean ET Structural Evolution Summary T B -72h T E +72h

43. Boxes represent the calculated one standard deviation spread about the 34-cyclone consensus mean trajectory for each time Variability About the Composite Mean Considerable variability about mean once transition completed=> posttropical phase can take many forms….

44. Floyd (1999): Non-intensifying cold-core development (  40%) Hugo (1989): Explosive cold-core development (  20%) Charley (1986): Schizophrenia (  20%) Keith (1988): Explosive warm- seclusion development (  15%) Dennis (1999): “ET-Interruptus”. (  5%)

45. Hurricane Olga (2001) Multiple phase evolution: Case of tropical transition of a cold-core cyclone

46. Cold-to-warm core transition: Tropical Transition of Hurricane Olga (2001) -V T U Vs. -V T L -V T L -V T U Tropical transition begins when –V T L > 0 (subtropical status) Tropical transition completes when –V T U > 0 (tropical status)

47. Summary of cyclone types within the phase space

48. ?Polar lows?

49. Phase space limitations Cyclone phase diagrams are dependent on the quality of the analyses upon which they are based. Three dimensions (B, -V T L, -V T U ) are not expected to explain all aspects of cyclone development Other potential dimensions: static stability, long-wave pattern, jet streak configuration, binary cyclone interaction, tropopause height/folds, surface moisture availability, surface roughness... However, the chosen three parameters represent a large percentage of the variance & explain the crucial structural changes.

50. Often model analysis representation is poor

51. Warm-Seclusion Dilemma: Hurricane Fabian (2003): NOGAPS Phase Verification

52. Hurricane Fabian (2003): Temperature anomaly (°C) from zonal mean At what point has extratropical transition occurred?

53. Cyclone Phase Forecasting

54. Real-time Cyclone Phase Analysis & Forecasting Phase diagrams produced in real-time for various operational and research models. Provides insight into cyclone evolution that may not be apparent from conventional analyses Web site: http://moe.met.fsu.edu/cyclonephasehttp://moe.met.fsu.edu/cyclonephase Also available a historical archive of CPS diagrams for nearly 100 cyclones

56. Example real-time cyclone availability for AVN

57. Example AVN forecast oceanic extratropical cyclone Forecast phase analysis Zoomed

58. Example AVN forecast oceanic extratropical cyclone Forecast phase analysis Zoomed

59. Example use of cyclone phase space for structural forecast  Subtropical to tropical Karen (2001)

60. Example: (Sub)tropical cyclogenesis or tropical transition Conventional forecast fields: [MSLP, T, PV,  E ] do not always provide sufficient insight into nature of cyclone development. This type of development is critical to both threat and expected predictability (model fallibility). Need to understand structural future before we can begin to anticipate intensity evolution Derived phase may be more valuable than the explicit numerical intensity forecast. Example: Hurricane Karen(2001)

61. Karen (2001) 1800 UTC 10 October 1800 UTC 11 October 1800 UTC 12 October1800 UTC 13 October

62. Forecast MSLP P MIN =1009hPaP MIN =1001hPa P MIN =1003hPaP MIN =1005hPa

63. 400hPa Temperature

64. Increasing thermal symmetry & lower tropospheric warm core

65. Warm core development at surface then building upward -V T L -V T U

66. Multiple model solutions: Measure of structural forecast uncertainty AVN NGP UKM

67. Cyclone phase trajectory ensembling

68. Other Past/Current CPS Uses Tropical cyclone genesis diagnosis/forecasting Subtropical cyclone genesis diagnosis/forecasting Timing of extratropical transition Timing of tropical transition Diagnosis of structural predictability Diagnosis of when to switch NEXRAD radars to tropical mode

69. 1999-2004 Model performance for phase forecasting –Nam:Does not analyze or generate shallow/deep warm-core cyclones –CMC:Does not analyze or generate deep warm-core cyclones –MM5:Rapid warm-core intensification, although highly CPS-dependent –GFDL:Best initial warm-core representation, although exaggerates warm- core depth & symmetry for hybrid systems. Shallow warm-core is unstable: rapid conversion of shallow-warm core to deep warm core; poorly handles extratropical transition –NGP:Best initial warm-core representation, although exaggerates warm- core depth & symmetry for hybrid systems. Synthetic bogus appears to delay onset of extratropical transition & produce overintensification thereafter [too frequent high latitude warm seclusions] –GFS, UKM:Both underestimate initial warm-core intensity & depth

70. A closing thought from “The Simpsons”… 1996, Episode “Hurricane Neddy” Homer:“Oh Lisa! There's no record of a hurricane ever hitting Springfield.“ Lisa : “Yes, but the records only go back to 1978 when the Hall of Records was mysteriously blown away!”

71. Quiz: Separate the 5 tropical cyclones from the 5 extratropical. Images courtesy NCDC

72. Separate the 5 tropical cyclones from the 5 extratropical. Images courtesy NCDC Noel (2001) Floyd (1999) Unnamed TC (1991) Gloria (1985) Michael (2000) President’s Day Blizzard (1979) “Perfect” Storm (1991) Superstorm of 1993 Extratropical Low