On the Thermal Signature of the Residual Foam in Breaking Waves

Abstract

Wave breaking plays a critical role in air-sea interaction processes in both the open ocean and the surf zone. The energy transferred from the atmosphere to the ocean through wind-wave generation is ultimately dissipated by wave breaking. Therefore, quantifying the energy dissipation due to wave breaking is directly relevant to wave prediction models used for operational sea-state forecasting and the impact of waves on coastal regions. At high-wind speeds, bubbles generated by large scale breaking waves are the primary mechanism for gas transfer and dominate the energy dissipation due to breaking (Lamarre & Melville, 1991). Bubbles generated by breaking waves also contribute to marine aerosol formation through spray droplets produced when foam bubbles burst at the surface (Erinin et al., 2019; Veron, 2015, and references therein). Foam generated by wave breaking has increased reflectivity of solar radiation that can affect the earth's albedo (Evans et al., 2010; Gordon & Jacobs, 1977) and the enhanced microwave emissivity of foam impacts space-borne radiometer measurements of wind speed. In short, wave breaking is an important mechanism for fluxes of momentum, gas, and heat across the air-water interface and for global ocean remote sensing applications. Here we focus on breaking waves that produce visible foam.

Laboratory Heat Flux Estimates of Seawater Foam for Low Wind Speeds

“…The brightness temperature of the residual foam was found by [27] to be as much as 0.3 K below the brightness temperature of the surrounding surface water. The cooling foam phenomenon was recently exploited by [28] to study energy dissipation due to breaking waves.…”

A Novel Method to Discriminate Active from Residual Whitecaps Using Particle Image Velocimetry

“…The first is the potential non-uniform breaking velocity across an individual whitecap that results in zero average before the breaking front stops advancing. The second is that whitecap cooling is delayed due to the inequity in rates of foam cooling and renewal as identified by Masnadi et al (2020) [43]. This would have implication for breaking wave mechanics such as bubble penetration depth and degassing time.…”

“…The foam temperature showed no observable decrease until the foam remained on the surface for some time after the bubble generator had been turned off. Masnadi et al (2020) [43] found that cooling of surface foam is delayed until the rate of renewal of the foam by rising bubbles is less than the foam cooling rate. The same mechanism is likely responsible for the delayed cooling observed in the lab and supports the theory that whitecaps observed in IR remain in stage A briefly after breaking velocity reaches zero due to bubble plume dynamics.…”

Large-scale particle shadow tracking and orientation measurement with collimated light

“…Experiments are performed in the Washington Air-Sea Interaction Facility (WASIRF) (Long, 1992;Masnadi et al, 2021), a long wave tank in which wind blows over the surface of the water (figure 7). The test section of the tank is 12.2 m long and 0.91 m wide, and is filled with tap water to a depth of 0.6 m, leaving 0.6 m of headspace for airflow.…”