Saturation of Ocean Surface Wave Slopes Observed During Hurricanes

Abstract

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 () at moderate winds and a saturation tail () 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.

In Situ Observations at the Air‐Sea Interface by Expendable Air‐Deployed Drifters Under Hurricane Michael (2018)

“…Several studies have compared hurricane wave observations to wind‐driven wave models (e.g., Moon et al., 2004a, 2004b; Moon, Hara, et al., 2004; Fan et al., 2009; Holthuijsen et al., 2012; Montoya et al., 2013; Tamizi et al., 2021; Chen et al., 2022; Zhou et al., 2022), and examined wave growth under hurricanes using self‐similar wave growth theory (Hu & Chen, 2011; Hwang, 2016; Kudryavtsev et al., 2015; Tamizi & Young, 2020; Young, 1998, 2003, 2006). The influence of the wave field on the surface drag coefficient continues to be explored (e.g., Black et al., 2007; Davis et al., 2023; Drennan et al., 2003; Moon et al., 2004b), particularly the importance of the angle between wind, waves and surface stress (Holthuijsen et al., 2012; J. Hsu, 2023; J.‐Y. Hsu et al., 2019; Moon et al., 2004a; Zhou et al., 2022).…”