Probing the Hurricane Boundary Layer using NOAA’s Research

Aircraft

Jun Zhang

University of Miami/RSMAS & NOAA/AOML/Hurricane Research Division

• Why is the boundary layer so important in hurricanes?

• Where is the top of the atmospheric boundary layer in hurricanes?

• What do we know about the mean and turbulence structure of the hurricane boundary layer from observations?

• How to directly measure air-sea fluxes and boundary layer structure in hurricanes using research aircraft?

Questions

Depiction of the ABL processes

http://www.esrl.noaa.gov/research/themes/pbl/

------- Boundary layer height

Outflow (“Exhaust”)Outflow (“Exhaust”)

Ocean (“Fuel”)Ocean (“Fuel”)

Energy ReleaseEnergy Release(“Cylinders”)(“Cylinders”)

Courtesy of Chris Landsea

Emanuel (1986,1995):

•Axisymmetric model

•Slab boundary layer

•Use gradient wind

•Bulk BL parameterization CD drag coefficient (momentum) CK enthalpy coefficient

)( *0

0

02

max kkT

TT

C

CV s

D

k

qLTqcqck vlpd ])1([

CK/CD ~ 1.2 – 1.5

CK/CD > 0.75

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.

WRF Simulation of Hurricane IsabelNolan, Zhang and Stern 2009 MWR

Where is the top of the hurricane boundary layer ?

“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.”

Stull, 1988: An Introduction to Boundary Layer Meteorology

From this definition, the boundary layer height can be defined as the height where turbulent fluxes are negligible (~0).

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)

Zi

Defining the boundary layer depth in numerical models

• Deardorff (1972) : h = c u*/f

• Troen and Mahrt (1986) : Critical Richardson number method

• Eliassen and Lystad (1977), Kepert (2001):

, • Emanuel (1986, 1995) : Slab boundary layer, constant

boundary layer depth (mixed layer/height of the maximum wind)

• Bryan and Rotunno (2009): Height of the maximum wind speed (~ 1km) following Emanuel’s definition

• Smith et al. 2009: strong inflow layer (agradient wind balance)

2/1)/2( IKh )//)(/2(2 rVrVfrVfI

2)(

))()(/(

sH

svsvHvsb UU

zHgRi

Aircraft observations of the mean hurricane boundary

layer structure

GPS dropsonde

Dropsonde datasetZhang et al. 2011 MWR in press

Storm name YearStorm

Intensity range (kt)

Numberof sondes

Erika 1997 83 – 110 40Bonnie 1998 68 - 93 76Georges 1998 66 - 78 39Mitch 1999 145 - 155 28Bret 1999 75 - 90 33

Dennis 1999 65 - 70 7Floyd 1999 80 - 110 40Fabian 2003 68 - 120 131Isabel 2003 85 - 140 162

Frances 2004 68 - 83 62Ivan 2004 65 - 135 123

Dennis 2005 65 - 70 7Katrina 2005 68 - 100 46

A total of 2231 data have been analyzed, and 790 of them are used in the final analysis.

Data distribution

Zhang et al. 2011

MethodologyThe 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.

Total wind speed (m/s)

Zhang et al. 2011

Tangential and radial wind speed (m/s)

x

Zhang et al. 2011

Θv (K)

Θv - Θv150 (K)

Black line shows the mixed layer depth defined as the constant 0.5 K contour

dΘv / 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 2)(

))()(/(

sH

svsvHvsb UU

zHgRi

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

2)]0()([ UzUC zD

)]0()()][0()([ TzTUzUCcH zHps

)]0()()][0()([ qzqUzUCLH zEve

Turbulent Fluxes and Parameterizations

z

uKuwvwu m

2

*2/122

)''''(

zcKtucTwcH phpps

**''

z

qKquLqwLH qvve

**''

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 BAMSDrennan et al. 2007 JASFrench et al. 2007 JASZhang et al. 2008 GRLZhang et al. 2009 JASZhang 2010 QJ

The Coupled Boundary Layer Air-sea Transfer Experiment (CBLAST)

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)

←LICOR head

↓ BAT

CBLAST STEPPED DESCENTSCBLAST 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)

zi

To Eye

pitch

Time series for a typical flux run

ualtitude

roll

heading humidity, q

w

vpitch

(40 Hz data)

Spectral Analysis

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. 2007Powell et al. (2003) −∙−−∙Donelan et al. (2004) −−∙−∙−

CBLAST Data *LF (◊) RF (□)LR (X) RR(+)

Zhang 2007; Black et al. 2007

-------- COARE 3.0 Fairall et al. 2003-------- Emanuel’s threshold

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)

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

Vertical Structure of Momentum flux

–— Moss (1978)

Zhang et al. 2009 JAS

Vertical Structure of humidity and sensible heat fluxes

Turbulent Kinetic Energy Budget

Z

pw

Z

ewqwgwg

Z

vwv

Z

uwu

Dt

De ''1'''61.0'')/(''''

2/32/3 )]([2

ffSU

fuuu

I : Shear production

II: Buoyancy

III: Turbulent transport

IV: Pressure transport

V: Rate of dissipation

I II III IV V

TKE: )'''(2

1 222 wvue

Turbulent Kinetic Energy Budget

Nicholls (1985)

Lenschow et al. (1980)

Zhang et al. 2009 JAS

Theory: dissipative heating

z

vwv

z

uwu ''''

z

u3*

)ln(0

13*

1 z

zuzeheatingDissipativ

)ln(0

1*

z

zuU

22

* UCu D

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:

3

0

13* )ln( UC

z

zueheatingDissipativ D

Zhang, 2010 JAS

)ˆ''ˆ''( jvwiuw

2/1* |)(|

u

2N10

2N10, UuCD

2/32/3 )]([2

ffSU

fuu

au

1zDH

3UCDH D

Zhang, 2010

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

Hurricane Boundary Layer RollsMorrison et al., 2005;

Foster 2005

RADARSAT SAR imageryduring Hurricane Isidore

Zhang et al. 2008 BLM

Boundary Layer Flight in Hurricane Isidore

Wavelet Analysis

Momentum Flux

----- alongwind leg

─── crosswind leg

Wavelength ~ 950 m

─── leg A --------- legs B C D leg E

Zhang et al. 2008 BLM

Sensible Heat Flux

─── leg A --------- legs B C D leg E

Zhang et al. 2008 BLM

1. Direct measurements of momentum and enthalpy fluxes were achieved in near hurricane force wind regime.

2.Turbulent kinetic energy budget indicates that the advection term is important in the hurricane boundary layer dynamics.

3. Boundary layer rolls tend to enhance the momentum flux but rescale the sensible heat flux transport.

4. The formulation of drag coefficient multiplying the cubic of surface wind speed would significantly overestimate the magnitude of dissipative heating.

5. 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.

Summary

On-going and Future work1.Further explore the mean and turbulence

structure of the hurricane boundary layer using the existing in-situ aircraft data;

2. Evaluation and improvement of the surface layer and planetary boundary layer (PBL) parameterization schemes in hurricane models using observations;

3. Design field experiments to measure turbulent fluxes in the high wind boundary layer

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/OMAOAircraft Operations Center

Acknowledgements:Acknowledgements:

List of References 

• 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.

• 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.

•  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.

• 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.

• Zhang, J. A., 2010: Spectra characteristics of turbulence in the hurricane boundary layer. Quart. J. Roy. Meteor. Soc., DOI:10.1002/qj.610.

•  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.

• 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.

• 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.

• 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.

• 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.

End

Thanks!

Future Possible Hurricane Boundary Layer Turbulence and flux Observations

• P3 aircraft flying low again?

• GPS dropsonde

• Remote sensing (Radar, Lidar, etc.)

• Aerosonde with turbulence instrumentation

• Buoy designed to sustain hurricane force

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, Marks, Montgomery, Lorsolo, 2011 MWR

Vertical eddy diffusivity

TKE and momentum fluxesZhang et al. 2011 MWR

o Frances+ Hugox Allen

Exchange coefficients in HWRFBender et al. 2007

Win Retrieval

dtLVVV ppa ][

,coscossinsin

]sincoscossinsintan

sinsinsincoscostancos[sin

L

DUuu ap

,sincoscossin

]sinsincossincostan

sinsincoscossintancos[cos

L

DUvv ap

,cos

]coscostansincostan[sin

L

DUww ap

22 tantan1 D

Calibrations of the turbulent gust probe and

BAT probe