Identifying the breaking point of waves

As a wave propagates through water, its smooth form becomes steeper until it can no longer maintain itself. A bulge forms on the leading edge of the wave, disrupting the smoothness. The bulge can move forward, creating a large plunging breaker, or roll down the leading face of the wave to create a smaller spiller breaker.

Research into wave breaking is important for coastal operations, shipping safety, offshore rigs, and climate change monitoring. All wave forecasting models incorporate a threshold for wave steepness to determine wave breaking and redistribution of their energy.

Knobler et al. examined the dependence of wave breaking probability on steepness in laboratory and open sea data. Their recently introduced technique measured instantaneous surface elevation fluctuations and used pattern recognition to identify the frequency signature of a breaking wave.

The team searched for breaking waves in data from a wind wave tunnel, which contained small scale waves, and in open sea data to see if there were differences in the breaking probabilities.

“Because in the lab we can do such accurate measurements of the waves in general, we could produce these accurate statistics of breaking probability versus wave steepness, which basically tells you when we see breaking and non-breaking waves and at what steepness,” said author Dan Liberzon.

The breaking probabilities were very similar in the laboratory and ocean data, an accurate comparison made possible by the new detection method. Interestingly, the group did not find a steepness threshold, a result which would greatly impact models if it holds true. They hope to use their method on more data sets in the future.

Source: “Wave breaking probabilities under wind forcing in open sea and laboratory,” by Sagi Knobler, Ewelina Winiarska, Alexander Babanin, and Dan Liberzon, Physics of Fluids (2022). The article can be accessed at https://doi.org/10.1063/5.0084276 .