Recent progress on predicting breaking onset for water waves and modelling wave breaking influence in sea state forecast models

Abstract: 

Breaking waves have challenged mariners since the earliest days of seafaring, with scientific and engineering interest increasing rapidly following the publication of Stokes’ remarkable mathematical theory of water waves in 1847. Yet, despite transformative advances in computational capabilities, wave breaking has resisted a compelling understanding of what actually underpins its onset and whether it is generic across diverse breaking onset scenarios – group-mediated, bottom-induced, opposing current, amongst others.

This talk highlights exciting results from our numerical study that elucidate key aspects of this historically elusive topic and likely have broader application to other natural dispersive wave systems. Of particular interest are refinements on wave geometry/kinematics in unsteady 2D and 3D wave packet evolution, involving crest (and trough) leaning modes which appreciably modify wave crest (and trough) speeds. This underpins new insights on wave breaking onset, including a unified breaking threshold for 2D and 3D wave packets for a wide range of depth/wavelength conditions. This result is closely supported by observations.

I will also overview our recent advances on the allied topic of representing wave breaking in spectral ocean wave forecast models, with the challenge of how best to model the turbulent kinetic energy dissipation rate from wave breaking across the spectrum. Our effort has improved the accuracy of standard sea state model output especially in severe states. It also extends present forecasting capabilities to key geophysical properties that depend on wave breaking as well as the wind speed, including whitecap cover and sea spray flux. These advances underpin the next refinement of the TOGA-COARE air-sea flux parameterisations.