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

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

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 Fields Under an Extreme Tropical Cyclone

Wind

Wave information

Atmosphere

Current

Surface waves

Ocean

Current

Ocean currents


Observations under hurricane Ivan Fields Under an Extreme Tropical Cyclone

Envisat-1

ERS-2


Experiments Fields Under an Extreme Tropical Cyclone

Exp.

A

B

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

WAVEWATCH III

+

Wave Bounary Layer Model

+

Princeton Ocean Model

Wind

Atmosphere

Wave information

Current

Surface waves

Ocean

Current

Ocean currents


Wave Predictions Fields Under an Extreme Tropical Cyclone

  • Significant Wave Height Swaths

Exp. A

Exp B

Exp C

Exp A - 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 Predictions Fields Under an Extreme Tropical Cyclone

  • Wave parameter comparisons between model and SRA data

Sept. 9

Vertical velocity

Wave Direction

SRA

SRA data number

Dominant Wave Length

Significant Wave Height

SRA data number

SRA data number


Wave Predictions Fields Under an Extreme Tropical Cyclone

  • Wave parameter comparisons between model and SRA data

- Sept. 9- Sept. 12 - Sept. 14-15

Exp. A

Exp. B

Exp. C

Model Hs (m)

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


Wave Predictions Fields Under an Extreme Tropical Cyclone

  • Comparison with Satellite measurements (Exp. C)

Sept. 15

2:00 UTC

Envisat-1

Sept. 15, 3:38 UTC

ERS-2

Sept. 15, 4:06 UTC

Sept. 15

4:00 UTC

Sept. 14

22:00 UTC

SRA


Wave Predictions Fields Under an Extreme Tropical Cyclone

  • Comparison with NDBC Buoy measurements


Wave Predictions Fields Under an Extreme Tropical Cyclone

  • Current Effect on Wave Prediction

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

Exp D


Wave Predictions Fields Under an Extreme Tropical Cyclone

  • Reduction of significant wave height by current

Hs difference (Exp C -Exp D)

Wave Field

Sept. 9

Hs difference (Exp D -Exp B)

Current Field

Exp C

Exp D

C - D


Main Conclusions Fields Under an Extreme Tropical Cyclone

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

  • 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.


Acknowledgement: Fields Under an Extreme Tropical Cyclone

U.S. National Science Foundation.

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

NASA - Physical Oceanography Program

NOAA - Hurricane Research Division

Thank You !


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