Saturation of Ocean Surface Wave Slopes Observed During Hurricanes

Drifting buoy observations of ocean surface waves in hurricanes are combined with modeled surface wind speeds. The observations include targeted aerial deployments into Hurricane Ian (2022) and opportunistic measurements from the Sofar Ocean Spotter global network in Hurricane Fiona (2022). Analysis focuses on the slope of the waves, as quantified by the spectral mean square slope. At low-to-moderate wind speeds (<15 m s(-1)), slopes increase linearly with wind speed. At higher winds (>15 m s(-1)), slopes continue to increase, but at a reduced rate. At extreme winds (>30 m s(-1)), slopes asymptote. The mean square slopes are directly related to the wave spectral shapes, which over the resolved frequency range (0.03-0.5 Hz) are characterized by an equilibrium tail (f(-4)) at moderate winds and a saturation tail (f(-5)) at higher winds. The asymptotic behavior of wave slope as a function of wind speed could contribute to the reduction of surface drag at high wind speeds.

Automated summary

Drifting buoy observations and modeled surface wind speeds were used to study ocean surface waves in hurricanes. The analysis found that wave slopes increase linearly with wind speed at low-to-moderate winds, but the rate of increase reduces at higher winds and eventually reaches an asymptote at extreme winds. The findings suggest that the behavior of wave slope could contribute to the reduction of surface drag at high wind speeds.