Detecting microscale breaking waves

Microscale breaking waves are short wind waves that break without entraining air. Experiments have shown that microscale breaking waves are on average steeper than non-breaking waves, that they generate warm turbulent wakes that are visible in infrared (IR) images and that they have high values of vorticity in their crests. Based on this knowledge, we compared three independent methods for detecting microscale breaking waves. The three methods identify or detect microscale breaking waves when a threshold value is exceeded. The wave slope, areal extent of the thermal wake and the variance of the vorticity in the crest region are the threshold parameters that are used by the three detection methods. Comparison of the breaking percentages predicted by the different methods indicates that the method that utilizes the variance of the vorticity is the most accurate. It predicts that at a fetch of 5.5 m the percentages of microscale breaking waves are 9%, 78% and 90% at wind speeds of 4.5, 7.4 and 11 m s-1, respectively.