numerical simulations and observations of surface wave fields under an extreme tropical cyclone

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Numerical Simulations and Numerical Simulations and Observations of Surface Wave Observations of Surface Wave Fields Under an Extreme Tropical Fields Under an Extreme Tropical Cyclone Cyclone Yalin Fan Yalin Fan Isaac Ginis Isaac Ginis University of Rhode Island University of Rhode Island ollaborators: etsu Hara (URI), Wayne Wright (NASA), Edward Walsh (NASA)

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Numerical Simulations and Observations of Surface Wave Fields Under an Extreme Tropical Cyclone. Yalin Fan Isaac Ginis University of Rhode Island. Collaborators: Tetsu Hara (URI), Wayne Wright (NASA), Edward Walsh (NASA). Wind-Wave-Current Interaction in Tropical Cyclones. Wind. - PowerPoint PPT Presentation

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Page 1: Numerical Simulations and Observations of Surface Wave Fields Under an Extreme Tropical Cyclone

Numerical Simulations and Numerical Simulations and Observations of Surface Wave Observations of Surface Wave

Fields Under an Extreme Tropical Fields Under an Extreme Tropical CycloneCyclone

Numerical Simulations and Numerical Simulations and Observations of Surface Wave Observations of Surface Wave

Fields Under an Extreme Tropical Fields Under an Extreme Tropical CycloneCyclone

Yalin FanYalin Fan

Isaac GinisIsaac Ginis

University of Rhode IslandUniversity of Rhode Island

Yalin FanYalin Fan

Isaac GinisIsaac Ginis

University of Rhode IslandUniversity of Rhode Island

Collaborators:Tetsu Hara (URI), Wayne Wright (NASA), Edward Walsh (NASA)Collaborators:Tetsu Hara (URI), Wayne Wright (NASA), Edward Walsh (NASA)

Page 2: Numerical Simulations and Observations of Surface Wave Fields Under an Extreme Tropical Cyclone

WindWind

Ocean currentsOcean currents

Surface wavesSurface waves

AtmosphereAtmosphere

OceanOcean

Wind-Wave-Current Interaction in Tropical Cyclones

airτrairτrWave informationWave information

cτr

CurrentCurrent

CurrentCurrent

cair ττ rr≠

Page 3: Numerical Simulations and Observations of Surface Wave Fields Under an Extreme Tropical Cyclone

Observations under hurricane IvanObservations under hurricane Ivan

Envisat-1 ERS-2

Page 4: Numerical Simulations and Observations of Surface Wave Fields Under an Extreme Tropical Cyclone

WindWind

Ocean currentsOcean currents

Surface wavesSurface waves

AtmosphereAtmosphere

OceanOcean

Experiments

airτrairτr

Wave informationWave informationCurrentCurrent

CurrentCurrent

Exp. A B CWAVEWATCH III

+Wave Bounary Layer Model

+Princeton Ocean Model

Exp. A: WAVEWATCH III wave model (operational model)Exp. B: Coupled wind-wave model (accounts for sea state)Exp. C: Coupled wind-wave-current model

Page 5: Numerical Simulations and Observations of Surface Wave Fields Under an Extreme Tropical Cyclone

Significant Wave Height SwathsExp. A Exp B

Exp C

Exp. A: WAVEWATCH III wave model (operational model)Exp. B: Coupled wind-wave model (accounts for sea state)Exp. C: Coupled wind-wave-current model

Wave PredictionsWave Predictions

Exp A - Exp C

Page 6: Numerical Simulations and Observations of Surface Wave Fields Under an Extreme Tropical Cyclone

Dominant Wave Length Significant Wave Height

Wave Direction

Wave parameter comparisons between model and SRA data

SRA

SRA data number

SRA data number SRA data number

Vertical velocity

Wave PredictionsWave Predictions

Sept. 9

Page 7: Numerical Simulations and Observations of Surface Wave Fields Under an Extreme Tropical Cyclone

Wave parameter comparisons between model and SRA data

Wave PredictionsWave Predictions

- Sept. 9 - Sept. 12 -

Sept. 14-15

Exp. A Exp. B Exp. C

SRA Hs (m) SRA Hs (m) SRA Hs (m)

Model Hs (m)

Page 8: Numerical Simulations and Observations of Surface Wave Fields Under an Extreme Tropical Cyclone

Comparison with Satellite measurements (Exp. C)

Wave PredictionsWave Predictions

Envisat-1 Sept. 15, 3:38 UTCERS-2 Sept. 15, 4:06 UTC

Sept. 1422:00 UTC

Sept. 154:00 UTC

Sept. 152:00 UTC

SRA

Page 9: Numerical Simulations and Observations of Surface Wave Fields Under an Extreme Tropical Cyclone

Comparison with NDBC Buoy measurements

Wave PredictionsWave Predictions

Page 10: Numerical Simulations and Observations of Surface Wave Fields Under an Extreme Tropical Cyclone

Current Effect on Wave Prediction

Wave PredictionsWave Predictions

∂N

∂t+∇x ⋅

r U c +

r C g( ) N[ ]−

∂k

r k ⋅

∂r

U c∂s

N ⎛

⎝ ⎜

⎠ ⎟+

∂θ

1

k

r k ⋅

∂r

U c∂m

N ⎛

⎝ ⎜

⎠ ⎟= F

Wave Action Equation

N = / ------ wave action spectrum,

Cg ------ group velocity vector,

------ wave number vector,

k ------ wave number, ------ wave direction,

s ------ a coordinate in the wave direction,

m ------ coordinate perpendicular to s,

F ------ forcing, ------ ocean current

rk

rU c

Exp D

Page 11: Numerical Simulations and Observations of Surface Wave Fields Under an Extreme Tropical Cyclone

Reduction of significant wave height by current

Wave PredictionsWave Predictions

Sept. 9 Wave Field Hs difference (Exp C -Exp D)

Hs difference (Exp D -Exp B)

Current Field

∂N

∂sUc +Cg − Ut( ) − k

∂N

∂k

∂Uc

∂s= F

∂N0

∂sCg − Ut( ) = F0

∂( N0 − N )

∂sCg − Ut( ) = −k

∂N

∂k

∂Uc

∂s+

∂N

∂sUc + F0 − F( )

Exp C

Exp D

C - D

Page 12: Numerical Simulations and Observations of Surface Wave Fields Under an Extreme Tropical Cyclone

Main ConclusionsMain Conclusions

1. The original WAVEWATCH III drag parameterization tends to overestimate the significant wave height, and wave energy under very strong wind forcing.

2. The improved stress parameterization, together with including the wave-current interaction, is shown to improve forecast of significant wave height and wave energy.

3. The hurricane induced ocean current tends to reduce the significant wave height mainly because it increases the advection speed of the wave packet. The strong shear of the current field widens the directional spreading of the wave spectrum.

Page 13: Numerical Simulations and Observations of Surface Wave Fields Under an Extreme Tropical Cyclone

Acknowledgement:

U.S. National Science Foundation.

U.S. Office of Naval Research (CBLAST program).

NASA - Physical Oceanography Program

NOAA - Hurricane Research Division