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 Sept. 9 Vertical velocity 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 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

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 !