Direct Measurements of Momentum and Enthalpy Fluxes in the Hurricane Force Wind Regime

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Direct Measurements of Momentum and Enthalpy
Fluxes in the Hurricane Force Wind Regime
Jun Zhang NOAA/AOML/HRD William Drennan Univ. of
Miami/ RSMAS Jeffrey French Univ. of
Wyoming Peter Black NOAA/AOML/HRD (Currently NRL)
AMS 89th Annual Meeting, Paper 10.2Phoenix, 14
January, 2009
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• Emanuel (1995)
• Axisymmetric model
• Slab boundary layer
• Use gradient wind
• Bulk BL parameterization
• CD drag coefficient (momentum)
• CK enthalpy coefficient

CK/CD 1.2 1.5 CK/CD gt 0.75
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MM5 simulation of Hurricane Bob (1991)
Braun and Tao, 2000
Sensitivity to boundary-layer parameterization
? Skillful prediction of intensity change
requires an accurate representation of the
boundary layer and parameterization of surface
fluxes.
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EC Data from 8 field experiments AGILE, AWE,
ETCH,GASEX,HEXOS,RASEX, SHOWEX, SWADE, WAVES
(4322 pts). Smith (1980)
Consensus (pre-2003) - CDN increases
linearly with wind speed from 5
to 20 m/s. - Scatter due to wave age and
swell - No direct measurements of drag
coefficients for U gt 23 m/s
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)
COARE-3 --- COARE 2.5
- CEN constant (or nearly so) with
wind speed from 5 to 20 m/s. - No direct
measurements of exchange coefficient of heat flux
for U gt 20 m/s
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Powell et al. 2003
Cd leveling off at wind speed higher than 30-40
m/s
Donelan et al. 2004
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The Coupled Boundary Layer Air-sea Transfer
(CBLAST) Hurricane Experiment
Six flights in two hurricanes in 2003 3
Hurricane Fabian 3 Hurricane Isabel Two
flights in two hurricanes in 2004
1 Hurricane Frances 1 Hurricane
Jeanne Black et al. 2007 BAMSDrennan et al.
2007 JASFrench et al. 2007 JAS Zhang et al. 2008
GRL
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• N43RF Flux instrumentation
• - BAT (Best Aircraft Turbulence) probe on boom
  
• - Rosemount Gust probes in radome and fuselage
• - Inertial navigation, GPS systems in fuselage
• - LICOR LI-7500 hygrometer (modified)
• - Rosemount temperature sensors
• - PRT5 radiometer for sea surface temperature
• - Stepped Frequency Microwave radiometer (SFMR)

? BAT
?LICOR head
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Vertical profiles of Mean Flow(Data are from
measurements during Sept. 12th 2003)
To Eye
zi
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Drag Coefficients
Smith (1992) ------ Large and Pond (1980) ------
Smith (1980) ------- COARE 3.0 CBLAST LOW
(o) Powell et al. (2003) --- Donelan et al.
(2004) ----
CBLAST Data LF (?) RF (?) LR (X) RR()
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Dalton Numbers
CE10N ltw'q'gt/U10N(qsat-q10N)
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Stanton Numbers
? CBLAST X HEXOS
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CK/CD 0.63 lt 0.75

• Can we explain the disagreement between the
  CBLAST data against Emanuels theory?
• Budget study of Emanuel (2006 Hurricane
  Conference) suggests that the ratio may increase
  significantly for intense hurricane conditions
• Strong air-sea interaction inward from the
  eyewall transports extra entropy through
  mesovortices was a key reason to get a cat 5
  hurricane in Isabel case (Montgomery et
  al.,2006)
• Emanuels model ignores the dynamics of the
  boundary layer
• We need measurements of turbulent fluxes,
  especially enthalpy fluxes, at higher wind
  speeds.

? CBLAST X HEXOS
-------- COARE 3.0 .. Emanuels threshold
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Fk (W m-2)
u (m s-1)
Cdx1000
Ckx1000
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Summary

• 1. Direct measurements of turbulent fluxes were
  made in the boundary layer of major hurricanes
  Bulk parameterizations of momentum and enthalpy
  fluxes were extended up to near hurricane force
• 2. Drag coefficients level off at around 22-25
  m/s, slightly lower than the that found from
  previous studies
• 3. Exchange coefficients of sensible heat and
  latent heat, as well as enthalpy are nearly
  constant with wind speed up to 30 m/s
• 4. The ratio of Ck/CD is significantly lower than
  the threshold used in the hurricane potential
  intensity theory, indicating that the enthalpy
  flux required for hurricane development may come
  from sources other than turbulent fluxes, or it
  demands a re-evaluation of the theoretical models
  used to derive the threshold.

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Acknowledgements
Office of Naval Research (ONR) CBLAST Hurricane
Program NOAA Hurricane Research Division OAR
USWRP NOAA/OMAO Aircraft Operations
Center Support of National Research Council
Fellowship