Limits on Fluid Turbulence Oberved in Breaking Waves and Implications for Bubble Formation and Aerosol Production (Invited Presentation)

Experiments with seawater waves in a laboratory channel reveal bubble size distributions and time and space-resolved maps of turbulent dissipation rate inside breaking wave crests. Four wave types are studied, ranging from spilling through plunging with energy dissipation in the range 9.2 – 48 J/m of wave crest, corresponding to the smaller end of the breaking wave scale driven by 6 – 11 m/s winds. The results of this study suggest that turbulence in whitecaps saturates in the range 10 – 70 W/kg. Space and time averages of turbulence dissipation are lower, in the range 0.5 – 2 W/kg. One of the implications of this result is that the bubble Hinze scale – the scale of the largest bubble stable to fragmentation by fluid turbulence in the whitecap – is expected to be invariant over a range of wave scales. This expectation is consistent with observations of the Hinze scale made in breaking waves in the laboratory, the surf zone and the open ocean, which yield estimates of this scale in the range 1.3 - 1.6 mm. Invariance of the Hinze scale has important implications for the dependence of air-sea gas flux and aerosol production as a function of wind shear stress and breaking wave scale.