On the Interaction between Wind Stress and Waves: Wave Growth and Statistical Properties of Large Waves

Abstract

AbstractStatistical properties and development of wave fields with different wind forcings are investigated through parametric laboratory experiments. Thirty different, random sea states simulated using a JONSWAP spectrum are mechanically generated in deep-water conditions. Each of the random simulated sea states is exactly repeated but subjected to a range of different wind speeds to study the interaction between wind stress and the existing random sea state waves, especially the isolated effect of the wind stress on the largest waves. Wave crest distributions are sensitive to the wind at the extreme end such that there is an observed deviation from second-order theory for the largest (lowest probability) waves at high wind speed. Because the local wave steepness increases with wind speed, eventually reaching a breaking point, the growth of extreme waves (relative to the significant wave height) due to wind stress is shown to be limited by wave breaking. Even when large waves are breaking, the data reveal that amplitude modulation of wave groups is enhanced substantially as the wind speed increases due to the difference in growth rates between the highest and the lowest wave crests in a wave group. However, there is no evidence of an increase in modulation instability with the wind speed, suggesting that the wind–wave interaction under strong wind forcing dominates the wave growth mechanism over nonlinear wave interactions in a broadband wave field.