Laboratory air‐entraining breaking waves: Imaging visible foam signatures to estimate energy dissipation

• Published in: Geophysical research letters Vol. 43; no. 21; pp. 11,320 - 11,328
• Main Authors: Callaghan, A. H., Deane, G. B., Stokes, M. D.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.11.2016
• Subjects: Air; Air-water exchanges; Atmosphere; Atmospheric models; Breaking; Breaking waves; Bubble barriers; Bubble Plume Depth; Bubbles; Climate; Climatology; Decay; Depth; Design engineering; Detection; Dissipation; Energy consumption; Energy Dissipation; Energy exchange; Entrainment; Estimates; Evolution; Exchanging; Foams; Imaging; Imaging techniques; Laboratories; Laboratory experiments; Marine; Marine engineering; Multiphase flow; Ocean engineering; Ocean models; Ocean-atmosphere system; Offshore engineering; Penetration depth; Plumes; Remote Sensing; Shipbuilding; Signatures; Statistical methods; Temperature (air-sea); Time; Two‐phase flow; Wave energy; Wave height; Wave power; Weather; Whitecap Foam
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2016GL071226

Oceanic air‐entraining breaking waves fundamentally influence weather and climate through bubble‐mediated ocean‐atmosphere exchanges, and influence marine engineering design by impacting statistics of wave heights, crest heights, and wave loading. However, estimating individual breaking wave energy dissipation in the field remains a fundamental problem. Using laboratory experiments, we introduce a new method to estimate energy dissipation by individual breaking waves using above‐water images of evolving foam. The data show the volume of the breaking wave two‐phase flow integrated in time during active breaking scales linearly with wave energy dissipated. To determine the volume time‐integral, above‐water images of surface foam provide the breaking wave timescale and horizontal extent of the submerged bubble plume, and the foam decay time provides an estimate of the bubble plume penetration depth. We anticipate that this novel remote sensing method will improve predictions of air‐sea exchanges, validate models of wave energy dissipation, and inform ocean engineering design. Key Points Bubble plume volume time‐integral scales linearly with breaking wave energy dissipation Foam evolution can be used to determine the bubble plume volume time‐integral Remote sensing of evolving foam area could estimate individual breaking wave energy dissipation