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Probing the Hurricane Boundary Layer using NOAA’s Research Aircraft Jun Zhang University of Miami/RSMAS &  NOAA/AOML/Hurri...
<ul><li>Why is the boundary layer so important in hurricanes? </li></ul><ul><li>Where is the top of the atmospheric bounda...
Depiction of the ABL processes http://www.esrl.noaa.gov/research/themes/pbl/ ------- Boundary layer height
Outflow (“Exhaust”) Ocean (“Fuel”) Energy Release (“Cylinders”) Nature's great heat engine... The Hurricane  Courtesy of C...
<ul><li>Emanuel (1986,1995): </li></ul><ul><li>Axisymmetric model </li></ul><ul><li>Slab boundary layer </li></ul><ul><li>...
 
MM5 simulation of Hurricane Bob (1991) Braun and Tao, 2000 Sensitivity of hurricane simulations to boundary-layer paramete...
WRF Simulation of Hurricane Isabel Nolan, Zhang and Stern 2009 MWR
<ul><li>Where is the top of the hurricane boundary layer ? </li></ul>
<ul><li>“ The boundary layer is defined as part of the troposphere that is directly influenced by the presence of the eart...
Prior to 2003, the only boundary layer in-situ turbulence structure measurement was conducted by Moss (1978) in the periph...
Defining the boundary layer depth in numerical models <ul><li>Deardorff (1972) :  h = c u * /f </li></ul><ul><li>Troen and...
Aircraft observations of the mean hurricane boundary layer structure
GPS dropsonde
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 ...
Data distribution Zhang et al. 2011
Methodology The data are grouped as a function of the radius to the storm center (r) that is normalized by the radius of t...
Total wind speed (m/s) Zhang et al. 2011
Tangential and radial wind speed (m/s) x Zhang et al. 2011
Θ v  (K)
Θ v  -  Θ v150  (K) Black line shows the mixed layer depth defined as the constant 0.5 K contour
d Θ v  / dz (K/km) Black line shows the mixed layer depth defined as constant 3 K/km contour
Bulk Richardson number Black line shows the 0.25 constant contour
A schematic diagram of the characteristic height scales of the hurricane boundary layer Zhang et al. 2011, MWR in press
Aircraft observations of the turbulence structure of the hurricane boundary layer
Turbulent Fluxes and Parameterizations
2002: 3 Test flights in Hurricanes Edouard, Isidore, and Lili 2003: 6 flights in Hurricanes Fabian and Isabel 2004: Flight...
<ul><li>N43RF flux instrumentation   </li></ul><ul><li>-  BAT (“Best Aircraft Turbulence”) probe on boom  </li></ul><ul><l...
CBLAST STEPPED DESCENTS Black lines represent the flux runs Typical length of a flux run is 24 km
Dual aircraft mission
Vertical profiles of Mean Flow (Data are from measurements during Sept. 12th 2003) z i To Eye
pitch Time series for a typical flux run  (40 Hz data) u altitude roll heading humidity, q w v pitch
Spectral Analysis
EC Data from 8 field experiments : AGILE, AWE, ETCH,GASEX,HEXOS,RASEX, SHOWEX, SWADE, WAVES (4322 pts).  —   Smith (1980) ...
--------  COARE 3.0 Fairall et al. 2003 --------  Emanuel’s threshold COARE-3  --- COARE 2.5  — Either energy needs to be ...
Vertical Structure of Momentum flux  – —  Moss (1978) Zhang et al. 2009 JAS
Vertical Structure of humidity and sensible heat fluxes
Turbulent Kinetic Energy Budget I :  Shear production II:  Buoyancy III: Turbulent transport IV: Pressure transport V:  Ra...
Turbulent Kinetic Energy Budget Nicholls (1985)  Lenschow et al. (1980)  Zhang et al. 2009 JAS
Theory: dissipative heating The above theoretical method has been firstly used by Bister and Emanuel (1998). Since then, d...
Zhang, 2010
The theoretical  method would significantly overestimate the magnitude of dissipative heating by a factor of three.  It is...
Hurricane Boundary Layer Rolls Morrison et al., 2005; Foster 2005
RADARSAT SAR imagery during Hurricane Isidore   Zhang et al. 2008 BLM
<ul><li>Boundary Layer Flight in Hurricane Isidore </li></ul>
Wavelet Analysis
Momentum Flux ----- alongwind leg ───  crosswind leg Wavelength ~ 950 m ───  leg A ---------  legs B C D leg E Zhang et al...
Sensible Heat Flux ───  leg A ---------  legs B C D leg E Zhang et al. 2008 BLM
Summary <ul><li>1 .   Direct measurements of momentum and enthalpy fluxes were achieved in near hurricane force wind regim...
On-going and Future work <ul><li>1.Further explore the mean and turbulence structure of the hurricane boundary layer using...
Acknowledgements: Support of National Research Council  Associate Fellowship Award  Support of NOAA/HFIP Office of Naval R...
List of References <ul><li>  </li></ul><ul><li>Black, P. G., E. A. D’Asaro, W. M. Drennan, J. R. French, P. P. Niiler, T. ...
End Thanks!
Future Possible Hurricane Boundary Layer Turbulence and flux Observations <ul><li>P3 aircraft flying low again?  </li></ul...
Low-level eyewall penetration of Hurricane Hugo (1989)  Marks et al. 2008; Zhang et al. 2011
Low-level eyewall penetration of Hurricane Allen (1980)  Marks 1985
An Estimation of turbulent characteristics in the low level region of intense Hurricane Allen (1980) and Hugo (1989) Zhang...
TKE and momentum fluxes Zhang et al. 2011 MWR o Frances +  Hugo x  Allen
Exchange coefficients in HWRF Bender et al. 2007
Win Retrieval
Calibrations of the turbulent gust probe and BAT probe
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Probing the Hurricane Boundary Layer using NOAA's Research Aircraft

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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.

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Probing the Hurricane Boundary Layer using NOAA's Research Aircraft

  1. 1. Probing the Hurricane Boundary Layer using NOAA’s Research Aircraft Jun Zhang University of Miami/RSMAS & NOAA/AOML/Hurricane Research Division
  2. 2. <ul><li>Why is the boundary layer so important in hurricanes? </li></ul><ul><li>Where is the top of the atmospheric boundary layer in hurricanes? </li></ul><ul><li>What do we know about the mean and turbulence structure of the hurricane boundary layer from observations? </li></ul><ul><li>How to directly measure air-sea fluxes and boundary layer structure in hurricanes using research aircraft? </li></ul>Questions
  3. 3. Depiction of the ABL processes http://www.esrl.noaa.gov/research/themes/pbl/ ------- Boundary layer height
  4. 4. Outflow (“Exhaust”) Ocean (“Fuel”) Energy Release (“Cylinders”) Nature's great heat engine... The Hurricane Courtesy of Chris Landsea
  5. 5. <ul><li>Emanuel (1986,1995): </li></ul><ul><li>Axisymmetric model </li></ul><ul><li>Slab boundary layer </li></ul><ul><li>Use gradient wind </li></ul><ul><li>Bulk BL parameterization </li></ul><ul><li>C D drag coefficient (momentum) </li></ul><ul><li>C K enthalpy coefficient </li></ul>C K /C D ~ 1.2 – 1.5 C K /C D > 0.75
  6. 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.
  7. 8. WRF Simulation of Hurricane Isabel Nolan, Zhang and Stern 2009 MWR
  8. 9. <ul><li>Where is the top of the hurricane boundary layer ? </li></ul>
  9. 10. <ul><li>“ The boundary layer is defined as part of the troposphere that is directly influenced by the presence of the earth’s surface, and responds to surface forcings with a timescale of about an hour or less.” </li></ul><ul><li>Stull, 1988: An Introduction to Boundary Layer Meteorology </li></ul><ul><li>From this definition, the boundary layer height can be defined as the height where turbulent fluxes are negligible (~0). </li></ul>
  10. 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
  11. 12. Defining the boundary layer depth in numerical models <ul><li>Deardorff (1972) : h = c u * /f </li></ul><ul><li>Troen and Mahrt (1986) : Critical Richardson number method </li></ul><ul><li>Eliassen and Lystad (1977), Kepert (2001): </li></ul><ul><li>, </li></ul><ul><li>Emanuel (1986, 1995) : Slab boundary layer, constant boundary layer depth (mixed layer/height of the maximum wind) </li></ul><ul><li>Bryan and Rotunno (2009): Height of the maximum wind speed (~ 1km) following Emanuel’s definition </li></ul><ul><li>Smith et al. 2009: strong inflow layer (agradient wind balance) </li></ul>
  12. 13. Aircraft observations of the mean hurricane boundary layer structure
  13. 14. GPS dropsonde
  14. 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
  15. 16. Data distribution Zhang et al. 2011
  16. 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.
  17. 18. Total wind speed (m/s) Zhang et al. 2011
  18. 19. Tangential and radial wind speed (m/s) x Zhang et al. 2011
  19. 20. Θ v (K)
  20. 21. Θ v - Θ v150 (K) Black line shows the mixed layer depth defined as the constant 0.5 K contour
  21. 22. d Θ v / dz (K/km) Black line shows the mixed layer depth defined as constant 3 K/km contour
  22. 23. Bulk Richardson number Black line shows the 0.25 constant contour
  23. 24. A schematic diagram of the characteristic height scales of the hurricane boundary layer Zhang et al. 2011, MWR in press
  24. 25. Aircraft observations of the turbulence structure of the hurricane boundary layer
  25. 26. Turbulent Fluxes and Parameterizations
  26. 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)
  27. 28. <ul><li>N43RF flux instrumentation </li></ul><ul><li>- BAT (“Best Aircraft Turbulence”) probe on boom </li></ul><ul><li>- Rosemount Gust probes in radome and fuselage </li></ul><ul><li>- Inertial navigation, GPS systems in fuselage </li></ul><ul><li>- LICOR LI-7500 hygrometer (modified) </li></ul><ul><li>- Rosemount temperature sensors </li></ul><ul><li>- PRT5 radiometer for sea surface temperature </li></ul><ul><li>- Stepped Frequency Microwave Radiometer (SFMR) </li></ul>← LICOR head ↓ BAT
  28. 29. CBLAST STEPPED DESCENTS Black lines represent the flux runs Typical length of a flux run is 24 km
  29. 30. Dual aircraft mission
  30. 31. Vertical profiles of Mean Flow (Data are from measurements during Sept. 12th 2003) z i To Eye
  31. 32. pitch Time series for a typical flux run (40 Hz data) u altitude roll heading humidity, q w v pitch
  32. 33. Spectral Analysis
  33. 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
  34. 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)
  35. 36. Vertical Structure of Momentum flux – — Moss (1978) Zhang et al. 2009 JAS
  36. 37. Vertical Structure of humidity and sensible heat fluxes
  37. 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:
  38. 39. Turbulent Kinetic Energy Budget Nicholls (1985) Lenschow et al. (1980) Zhang et al. 2009 JAS
  39. 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
  40. 41. Zhang, 2010
  41. 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
  42. 43. Hurricane Boundary Layer Rolls Morrison et al., 2005; Foster 2005
  43. 44. RADARSAT SAR imagery during Hurricane Isidore Zhang et al. 2008 BLM
  44. 45. <ul><li>Boundary Layer Flight in Hurricane Isidore </li></ul>
  45. 46. Wavelet Analysis
  46. 47. Momentum Flux ----- alongwind leg ─── crosswind leg Wavelength ~ 950 m ─── leg A --------- legs B C D leg E Zhang et al. 2008 BLM
  47. 48. Sensible Heat Flux ─── leg A --------- legs B C D leg E Zhang et al. 2008 BLM
  48. 49. Summary <ul><li>1 . Direct measurements of momentum and enthalpy fluxes were achieved in near hurricane force wind regime. </li></ul><ul><li>2.Turbulent kinetic energy budget indicates that the advection term is important in the hurricane boundary layer dynamics. </li></ul><ul><li>Boundary layer rolls tend to enhance the momentum flux but rescale the sensible heat flux transport. </li></ul><ul><li>The formulation of drag coefficient multiplying the cubic of surface wind speed would significantly overestimate the magnitude of dissipative heating. </li></ul><ul><li>There are several types of height scales that may represent the top of the hurricane boundary layer; the inflow layer depth may be a good representation of the hurricane boundary layer top according to vertical flux profiles in the outer core. </li></ul>
  49. 50. On-going and Future work <ul><li>1.Further explore the mean and turbulence structure of the hurricane boundary layer using the existing in-situ aircraft data; </li></ul><ul><li>2. Evaluation and improvement of the surface layer and planetary boundary layer (PBL) parameterization schemes in hurricane models using observations; </li></ul><ul><li>3. Design field experiments to measure turbulent fluxes in the high wind boundary layer </li></ul>
  50. 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
  51. 52. List of References <ul><li>  </li></ul><ul><li>Black, P. G., E. A. D’Asaro, W. M. Drennan, J. R. French, P. P. Niiler, T. B. Sanford, E. J. Terrill, E. J. Walsh, and J. A. Zhang, 2007: Air-Sea Exchange in Hurricanes: Synthesis of Observations from the Coupled Boundary Layer Air-Sea Transfer Experiment, Bulletin of American Meteorological Society, 88, 357-374. </li></ul><ul><li>Drennan, W. M., J. A. Zhang, J. R. French, and P. G. Black, 2007: Turbulent Fluxes in the Hurricane Boundary Layer, II. Latent Heat Flux, Journal of Atmospheric Science, 64, 1103-1115. </li></ul><ul><li>  French, J. R., W. M. Drennan, J. A. Zhang, and P. G. Black, 2007: Turbulent Fluxes in the Hurricane Boundary Layer, I. Momentum Flux, Journal of Atmospheric Science, 64, 1089-1102. </li></ul><ul><li>Zhang, J. A., 2010: Estimation of dissipative heating using low-level in-situ aircraft observations in the hurricane boundary layer. Journal of the Atmospheric Sciences, 67 , 1853-1862. </li></ul><ul><li>Zhang, J. A., 2010: Spectra characteristics of turbulence in the hurricane boundary layer. Quart. J. Roy. Meteor. Soc. , DOI:10.1002/qj.610. </li></ul><ul><li>  Zhang, J. A., P. G. Black, J. R. French, and W. M. Drennan, 2008: First direct measurements of enthalpy flux in the hurricane boundary layer: The CBLAST results. Geophysical Research Letters, 35(11):L14813, doi:10.1029/2008GL034374. </li></ul><ul><li>Zhang, J. A., W. M. Drennan, P. G. Black, and J. R. French, 2009: Turbulence structure of the hurricane boundary layer between the outer rain bands. Journal of Atmospheric Science, 66, 2455-2467. </li></ul><ul><li>Zhang, J. A., K. B. Katsaros, P. G. Black, S. Lehner, J. R. French, and W. M. Drennan, 2008: Effects of roll vortices on turbulent fluxes in the hurricane boundary layer. Boundary-Layer Meteorology, 128(2), 173-189. </li></ul><ul><li>Zhang, J.A., F.D. Marks, Jr., M.T. Montgomery, and S. Lorsolo, 2011b: An estimation of turbulent characteristics in the low-level region of intense Hurricanes Allen (1980) and Hugo (1989). Mon. Wea. Rev ., 139, 1447-1462. </li></ul><ul><li>Zhang, J. A., R. F. Rogers, D. S. Nolan, and F. D. Marks, 2011: On the characteristic height scales of the hurricane boundary layer. Monthly Weather Review , in press. </li></ul>
  52. 53. End Thanks!
  53. 54. Future Possible Hurricane Boundary Layer Turbulence and flux Observations <ul><li>P3 aircraft flying low again? </li></ul><ul><li>GPS dropsonde </li></ul><ul><li>Remote sensing (Radar, Lidar, etc.) </li></ul><ul><li>Aerosonde with turbulence instrumentation </li></ul><ul><li>Buoy designed to sustain hurricane force </li></ul>
  54. 55. Low-level eyewall penetration of Hurricane Hugo (1989) Marks et al. 2008; Zhang et al. 2011
  55. 56. Low-level eyewall penetration of Hurricane Allen (1980) Marks 1985
  56. 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
  57. 58. TKE and momentum fluxes Zhang et al. 2011 MWR o Frances + Hugo x Allen
  58. 59. Exchange coefficients in HWRF Bender et al. 2007
  59. 60. Win Retrieval
  60. 61. Calibrations of the turbulent gust probe and BAT probe

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