Numerical Simulations and Observations of Surface Wave Fields Under an Extreme Tropical Cyclone
description
Transcript of 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)
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≠
Observations under hurricane IvanObservations under hurricane Ivan
Envisat-1 ERS-2
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
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
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
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)
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
Comparison with NDBC Buoy measurements
Wave PredictionsWave Predictions
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
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
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.
Acknowledgement:
U.S. National Science Foundation.
U.S. Office of Naval Research (CBLAST program).
NASA - Physical Oceanography Program
NOAA - Hurricane Research Division