Simulation of Wave-Current Interactions Under Hurricane Conditions Using an Unstructured-Grid Model: Impacts on Ocean Waves

The effect of wave-current interactions on ocean waves under hurricane conditions is investigated through application of the unstructured-grid finite-volume community ocean model (FVCOM) coupled to the unstructured-grid surface wave model (SWAVE) in the North Atlantic Ocean. We study wave-current interactions during the life cycles of extratropical hurricanes Juan (2003) and Bill (2009) as they propagate from subtropical waters to midlatitudes in the Northwest Atlantic. Simulations of wave parameters in each hurricane are shown to compare well with buoy and satellite altimeter observations, in terms of winds, significant wave heights, wave energy spectra, and wave directions. This is partially achieved by restricting the drag coefficient. It is well known that the maximum intensity of tropical cyclones depends on the ratio of the enthalpy coefficient to the drag coefficient. The latter increases with wind speed, levels off with category one hurricanes and may drop for even higher winds. In our study, we find that setting a limiting value on the drag coefficient improves the simulations of waves at peak storm intensities. Simulation of wave-current interactions is also shown to improve the simulation of the wave heights and wave energy spectra. This is notable at the peak of the storms, in comparisons with observations from buoys in areas of both deep water and relatively shallow water. The effect of currents on significant wave heights is shown to reach 0.4 m for hurricane Juan and 1.0 m for hurricane Bill, or as much as about 10% for wave heights distributed along the storm track.