Observations of the Scale and Occurrence of Breaking Surface Waves

Abstract

Breaking of surface waves was monitored with conductivity measurements at wind speeds up to 18 m s?1. This method of wave breaking detection is well defined but excludes microbreakers and breaking of very short gravity waves. Observations in both fetch limited and open ocean conditions reveal that wind speed or wave age are insufficient to characterize breaking activity. A scaling of the breaking frequency based on wind energy input is proposed. This scaling collapses the authors? diverse datasets, consistent with energy dissipation being determined primarily by the high frequency tail of the wave spectrum. Breaking waves with significant air entrainment were observed to have wavelengths between ?0.1 of the dominant waves and that of the largest wind waves. The median value of the period of breaking waves is approximately half the period of the dominant waves and the mean height of breaking waves is ?0.7 times the significant wave height. Less than 10% of observed breaking events resulted in deeply penetrating air entrainment (>0.2 m), suggesting the predominance of spilling breakers.