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Peer-Reviewed Research

Saturation of Ocean Surface Wave Slopes Observed During Hurricanes

Sofar Ocean

This paper was written by J. R. Davis, J. Thomson, I. A. Houghton, J. D. Doyle, W. A. Komaromi, C. W. Fairall, E. J. Thompson, and J. R. Moskaitis.

Abstract

Drifting buoy observations of ocean surface waves in Hurricanes Ian and Fiona (2022) are combined with modeled wind speed to explore the evolution of the sea surface from moderate to extreme winds (up to 54 m s −1). The sea surface is characterized using the physical slope of the waves, or the ratio of a wave's height to its length, which has previously only been well-understood up to moderate wind speeds of 15–20 m s −1. At lower wind speeds, the average slopes increase proportional to the wind speed, meaning the waves continually steepen as the wind strengthens. At higher winds, the slopes continue to increase, but at a reduced rate. The slopes eventually reach a maximum value at the most extreme winds (i.e., the slopes saturate). This phenomenon is accompanied by a change in sea surface character from one that is patterned by occasional wave breaking to one that is almost entirely covered by whitecaps and foam. Using wave slope as a measure of the roughness of the ocean surface, the observed wave slope saturation could help to explain the relative reduction in wind surface forcing at extreme wind speeds.

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