On the occurrence of wave breaking

The practicality of common wave breaking criteria is reviewed. Video recordings of the sea surface taken from aboard R/P FLIP are used to extract breaking wave properties. The key quantity is Λ(c)dc, the length of breaking crests per unit area propagating with speeds in the range (c, c+ dc). Independent of wave field development, Λ(c) is found to peak at intermediate wave scales and to drop off sharply at larger and smaller scales. For young waves, breakers occur at a wide range of scales corresponding to phase speeds of about 0.1-1.0 cp, but in developed seas breaking is hardly observed at scales corresponding to phase speeds >0.5 cp. The phase speed of the most frequent breakers shifts from 0.4 cp to 0.2 cp as the wave field develops. The relative distribution of breaker scale increases the likelihood of rogue waves in developed seas compared to young seas. The overall breaking rate correlates well with the fraction of steep waves.