Jun Zhang presented this work during his short visit at NCAR in June 2011. Below is the abstract of this talk: The boundary layer is known to play an important role in the energy transport processes of a hurricane, regulating the radial and vertical distribution of momentum and enthalpy that are closely related to storm development and intensification. However, the hurricane boundary layer is the least observed part of a storm till now. In particular, there is a lack of turbulence observation due to instrumentation limitation and safety constraint. This talk will present aircraft observations of the atmospheric boundary layer structure in intense hurricanes. Turbulence data presented are related to topics of air-sea exchange of turbulent fluxes, turbulent kinetic energy budget, dissipative heating, and vertical mixing in the boundary layer. The question of how to define the top of the hurricane boundary layer is also discussed.

1. Probing the Hurricane Boundary Layer using NOAA’s Research Aircraft Jun Zhang University of Miami/RSMAS & NOAA/AOML/Hurricane Research Division

3. Depiction of the ABL processes http://www.esrl.noaa.gov/research/themes/pbl/ ------- Boundary layer height

4. Outflow (“Exhaust”) Ocean (“Fuel”) Energy Release (“Cylinders”) Nature's great heat engine... The Hurricane Courtesy of Chris Landsea

7. MM5 simulation of Hurricane Bob (1991) Braun and Tao, 2000 Sensitivity of hurricane simulations to boundary-layer parameterization  Skillful prediction of intensity change requires an accurate representation of the boundary layer and parameterization of surface fluxes.

8. WRF Simulation of Hurricane Isabel Nolan, Zhang and Stern 2009 MWR

11. Prior to 2003, the only boundary layer in-situ turbulence structure measurement was conducted by Moss (1978) in the periphery of marginal hurricane Eloise (1975) at surface wind speed of about 20 m/s. Moss (1978) Z i

13. Aircraft observations of the mean hurricane boundary layer structure

14. GPS dropsonde

15. Dropsonde dataset Zhang et al. 2011 MWR in press A total of 2231 data have been analyzed, and 790 of them are used in the final analysis. Storm name Year Storm Intensity range (kt) Number of sondes Erika 1997 83 – 110 40 Bonnie 1998 68 - 93 76 Georges 1998 66 - 78 39 Mitch 1999 145 - 155 28 Bret 1999 75 - 90 33 Dennis 1999 65 - 70 7 Floyd 1999 80 - 110 40 Fabian 2003 68 - 120 131 Isabel 2003 85 - 140 162 Frances 2004 68 - 83 62 Ivan 2004 65 - 135 123 Dennis 2005 65 - 70 7 Katrina 2005 68 - 100 46

16. Data distribution Zhang et al. 2011

17. Methodology The data are grouped as a function of the radius to the storm center (r) that is normalized by the radius of the maximum wind speed (RMW), i.e., r * = r / RMW. The center positions have been determined using the flight-level data to fix the storm center using the algorithm developed by Willoughby and Chelmow (1982). Values of RMW are mainly determined using the Doppler radar data from the tangential winds at 2 km. When there is no radar data available, the RMW is determined from the flight-level data. When compositing the data, the radial bin width is 0.2 r * for r * < 2, and 0.4 r * for r * > 2. The data are also bin-averaged vertically at 10 m resolution.

18. Total wind speed (m/s) Zhang et al. 2011

19. Tangential and radial wind speed (m/s) x Zhang et al. 2011

20. Θ v (K)

21. Θ v - Θ v150 (K) Black line shows the mixed layer depth defined as the constant 0.5 K contour

22. d Θ v / dz (K/km) Black line shows the mixed layer depth defined as constant 3 K/km contour

23. Bulk Richardson number Black line shows the 0.25 constant contour

24. A schematic diagram of the characteristic height scales of the hurricane boundary layer Zhang et al. 2011, MWR in press

25. Aircraft observations of the turbulence structure of the hurricane boundary layer

26. Turbulent Fluxes and Parameterizations

27. 2002: 3 Test flights in Hurricanes Edouard, Isidore, and Lili 2003: 6 flights in Hurricanes Fabian and Isabel 2004: Flights at top of boundary layer, only 2 flux flights in Hurricanes Frances and Jeanne Black et al. 2007 BAMS Drennan et al. 2007 JAS French et al. 2007 JAS Zhang et al. 2008 GRL Zhang et al. 2009 JAS Zhang 2010 QJ The Coupled Boundary Layer Air-sea Transfer Experiment (CBLAST)

29. CBLAST STEPPED DESCENTS Black lines represent the flux runs Typical length of a flux run is 24 km

30. Dual aircraft mission

31. Vertical profiles of Mean Flow (Data are from measurements during Sept. 12th 2003) z i To Eye

32. pitch Time series for a typical flux run (40 Hz data) u altitude roll heading humidity, q w v pitch

33. Spectral Analysis

34. EC Data from 8 field experiments : AGILE, AWE, ETCH,GASEX,HEXOS,RASEX, SHOWEX, SWADE, WAVES (4322 pts). — Smith (1980) Drag coefficients Smith (1992) ------ Large and Pond (1980) ------ Smith (1980) ------- COARE 3.0 — CBLAST LOW (o) Edson et al. 2007 Powell et al. (2003) −∙−−∙ Donelan et al. (2004) −−∙−∙− CBLAST Data * LF ( ◊ ) RF ( □ ) LR (X) RR(+) Zhang 2007; Black et al. 2007

35. -------- COARE 3.0 Fairall et al. 2003 -------- Emanuel’s threshold COARE-3 --- COARE 2.5 — Either energy needs to be from other sources or the theory needs to be re-evaluated. Zhang et al. 2008 GRL Exchange coefficients for Enthalpy Transfer O AGILE (Donelan & Drennan 1995) X HEXOS (DeCosmo et al 1996) ◊ GASEX (McGillis et al 2004) SOWEX (Banner et al 1999) □ SWADE (Katsaros et al 1993) Δ CBLAST (Drennan et al. 2007)

36. Vertical Structure of Momentum flux – — Moss (1978) Zhang et al. 2009 JAS

37. Vertical Structure of humidity and sensible heat fluxes

38. Turbulent Kinetic Energy Budget I : Shear production II: Buoyancy III: Turbulent transport IV: Pressure transport V: Rate of dissipation I II III IV V TKE:

39. Turbulent Kinetic Energy Budget Nicholls (1985) Lenschow et al. (1980) Zhang et al. 2009 JAS

40. Theory: dissipative heating The above theoretical method has been firstly used by Bister and Emanuel (1998). Since then, dissipative heating has been included in a number of theoretical and numerical models simulating hurricanes. Surface layer similarity theory : Zhang, 2010 JAS

41. Zhang, 2010

42. The theoretical method would significantly overestimate the magnitude of dissipative heating by a factor of three. It is crucial to understand the physical processes related to dissipative heating in the hurricane boundary layer while implementing it into hurricane models. Zhang, 2010

43. Hurricane Boundary Layer Rolls Morrison et al., 2005; Foster 2005

44. RADARSAT SAR imagery during Hurricane Isidore Zhang et al. 2008 BLM

46. Wavelet Analysis

47. Momentum Flux ----- alongwind leg ─── crosswind leg Wavelength ~ 950 m ─── leg A --------- legs B C D leg E Zhang et al. 2008 BLM

48. Sensible Heat Flux ─── leg A --------- legs B C D leg E Zhang et al. 2008 BLM

51. Acknowledgements: Support of National Research Council Associate Fellowship Award Support of NOAA/HFIP Office of Naval Research (ONR) CBLAST Hurricane Program NOAA Hurricane Research Division NOAA/OMAO Aircraft Operations Center

53. End Thanks!

55. Low-level eyewall penetration of Hurricane Hugo (1989) Marks et al. 2008; Zhang et al. 2011

56. Low-level eyewall penetration of Hurricane Allen (1980) Marks 1985

57. An Estimation of turbulent characteristics in the low level region of intense Hurricane Allen (1980) and Hugo (1989) Zhang, Marks, Montgomery, Lorsolo, 2011 MWR Vertical eddy diffusivity

58. TKE and momentum fluxes Zhang et al. 2011 MWR o Frances + Hugo x Allen

59. Exchange coefficients in HWRF Bender et al. 2007

60. Win Retrieval

61. Calibrations of the turbulent gust probe and BAT probe