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Progress Towards Developing a Coupled Atmosphere-Wave-Ocean Framework for

Research and Operational Hurricane Models

Isaac GinisB. Thomas, R. Yablonsky, T. Hara

University of Rhode Island

J.-W. Bao, C. Fairall, L. BiancoNOAA/ESRL

Progress Towards Developing a Coupled Atmosphere-Wave-Ocean Framework for

Research and Operational Hurricane Models

Isaac GinisB. Thomas, R. Yablonsky, T. Hara

University of Rhode Island

J.-W. Bao, C. Fairall, L. BiancoNOAA/ESRL

Interdepartmental Hurricane Conference, 2011, Miami, FL

Wind-Wave-Current InteractionWind-Wave-Current Interaction

Image courtesy of Fabrice Veron

• Hurricane model: air-sea fluxes depend on sea state (Moon et al., 2007) and sea spray (Bao et al, 2011) and include surface current

• Wave model is forced by sea state dependent wind forcing and includes surface current (Fan et al. 2009)

• Ocean model is forced by wind stress that is modified by growing or decaying wave fields (Fan et al. 2010)

Coupled Atmosphere-Wave-Ocean FrameworkCoupled Atmosphere-Wave-Ocean Framework

Red - atmospheric parameters, Green – wave parameters, Blue - ocean parameters

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Effect of Wave Coupling on Wind Stress

Surface Roughness Drag Coefficient

Sea state dependence is parameterized based on Moon, Ginis & Hara (2007)

Wind, Waves and Drag Coefficient in the Experimental GFDL Coupled Hurricane-Wave-Ocean Model

Wind at 35 m

Drag Coeff. at 35 m

Wave phase speed

SignificantWaveheight

Wind and Current Vectors Near the Hurricane Center

Wind/current ratio is not in a proper scale

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⎝ ⎜

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- wind speed vector at a specific height

- wind speed vector at the surface (= ocean current vector)

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ru (0)

Effect of Ocean Current on Wind Stress

U* vs. Wind Speed at 35 m

Case Study: Hurricane Earl Initial Time: 00 UTC, 30 August, 2010

Effect of Ocean Current on Hurricane Intensity

Effect of Waves on Momentum Budget and Flux into Ocean

Wind stress

Wave Momentum flux

Momentum flux intoocean

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τocean

τ air

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τocean

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τair

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τwave

Momentum Flux Reduction due to Wave Coupling

Relative reduction of the momentum flux to ocean

depends on wind stress , which is not well constrained at high winds.

Uncertainty of drag coefficient

Upper bound: extrapolation of bulk parameterization

Blue: Moon et al. (2007) estimates from coupled wind-wave model

Lower bound: observations by Powell et al. (2007)

Upperbound of wind stress

Moon et al.(2007) estimate of wind stress

8% reduction

Lowerbound of wind Stress

15% reduction

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τocean

τ air

=τ air −τ diff

τ air

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τair

Fan et al. (2010)

Effect of Wave Momentum Budget on Hurricane IntensityCase Study: Hurricane Earl

Initial Time: 00 UTC, 30 August, 2010

Sensitivity experiments with experimentation GFDL hurricane-wave-ocean model:1.Without effect of current and wave momentum budget2. With effect of current, without effect of waves3.With effect of current, with effect of waves4.Without effect of current, with effect waves

Case Study: Hurricane Earl Initial Time: 00 UTC, 30 August, 2010

Spume production – water droplets are ripped from wave crests by the wind when surface wind exceeds about 7 ms-1.

Droplets range from ~40m to ~1mm in diameter.

Parameterization of Sea Spray EffectParameterization of Sea Spray Effect

NOAA/ESRL Sea Spray ParameterizationNOAA/ESRL Sea Spray Parameterization(Fairall et al. 2009, Bao et al. 2011)(Fairall et al. 2009, Bao et al. 2011)

Input parameters

Effect of Sea Spray on Momentum FluxEffect of Sea Spray on Momentum Flux

Sea Spray Effect on Drag CoefficientSea Spray Effect on Drag Coefficient

Wave model component - WAVEWATCH III

WAVEWATCH III can accurately reproduce observed hurricane surface wave fields if:

- Wind forcing is reduced at very high wind speeds. - Ocean current is explicitly included in the simulation.

WW3 significant wave height field (color) at Sept. 15 2:00 UTC. The thick gray line is the flight track.

Significant wave height comparison between SRA measurements (during this flight) and WW3 results from experiments A, B (with modified wind stress) and C (with modified wind stress and including ocean currents).

Comparison between modeled and measured significant wave heights from all flights.

Fan et al. (2009)

Extending WW3 to Finite/Shallow Water.

* Previous version of WAVEWATCH III (v2.2.2) did not work well for water depth less than 30m (grey area below)

•New version of WAVEWATCH III (v3.1.4) includes improved physics in shallower water.

* We are validating the WAVEWATCH III (v3.1.4) results in shallower water against observations (Scanning Radar Altimeter) in collaboration with Ed Walsh.

Hurricane Ivan (2004) significant wave height predictions

WW3 2.22 WW3 3.14

Difference

Extending the model to finite/shallow water

SRA aircraft track on 3 Oct 2002 during the landfall of Hurricane Lili (from Ed Walsh)

Future Evaluation of WW3 in Shallow Waters using SRA Measurements

Summary and Future Work

• Explicit representation of wind-wave-current interaction and sea spray indicate potential important effects on the air-sea momentum fluxes in hurricane conditions.

• Some components of the developed coupled atmosphere-wave-ocean interaction framework will be implemented into the HWRF and COAMPS-TC models for testing and evaluation in 2011.