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

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


1
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)
2
Wind-Wave-Current Interaction in Tropical Cyclones
Wind
Wave information
Atmosphere
Current
Surface waves
Ocean
Current
Ocean currents
3
Observations under hurricane Ivan
Envisat-1 ERS-2
4
Experiments
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
5
Wave Predictions
  • 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
6
Wave Predictions
  • Wave parameter comparisons between model and
    SRA data

Vertical velocity
Sept. 9
Wave Direction
SRA
SRA data number
Dominant Wave Length
Significant Wave Height
SRA data number
SRA data number
7
Wave Predictions
  • 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)
8
Wave Predictions
  • Comparison with Satellite measurements (Exp. C)

Sept. 15 200 UTC
Envisat-1 Sept. 15, 338 UTC
ERS-2 Sept. 15, 406 UTC
Sept. 15 400 UTC
Sept. 14 2200 UTC
SRA
9
Wave Predictions
  • Comparison with NDBC Buoy measurements

10
Wave Predictions
  • 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
11
Wave Predictions
  • 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
12
Main Conclusions
  • 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.

13
Acknowledgement 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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