Quantifying Energy Dissipation From Breaking Waves Using Time-Varying Properties of Whitecap Foam

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The goal of the proposed research is to develop a remote sensing technique to quantify the energy lost by breaking waves. The work is motivated by the fundamental role that wave breaking plays in enhancing the exchange of heat, mass, momentum and energy across the air-sea interface. Furthermore, existing remote sensing techniques remain highly uncertain due to large variations in the breaking strength parameter, motivating the need to develop alternative remote sensing techniques. It is anticipated that the proposed remote sensing technique will help enhance our fundamental knowledge of wave breaking and energy dissipation, which is important for the understanding of aerosol production and gas exchange. Furthermore, the remote new sensing technique implicitly accounts for both wave scale and breaking intensity on a wave-by-wave basis, which can provide valuable information for detailed modeling of ocean waves. The impact of the study will be further broadened by the participation of undergraduate interns in the laboratory experiments to help with data collection and preliminary analysis. The project team will participate in the public outreach lecture series hosted by the Birch Aquarium.The remote sensing technique will utilize high-speed and high resolution digital images of the time-varying properties of whitecap foam during active wave breaking and will be validated against a series of well-controlled laboratory experiments using seawater and breaking wave packets. Present remote-sensing techniques rely on measuring breaking wave speed to estimate breaking wave energy dissipation, but, critically, there is a lack of consensus in the literature regarding the most appropriate way to measure breaking wave speed. This has direct implications for estimates of the breaking strength parameter, which has been reported to vary by 4 orders of magnitude. Development of a new remote sensing technique will offer a parallel approach to the present methodology. Answers to the following key questions will be sought: 1) Can high-resolution and high-speed digital photography be used to quantify energy dissipation during wave breaking on a wave-by-wave basis? 2) Can the new remote sensing technique, developed using breaking waves generated by linear wave superposition, be applied to wind-driven breaking waves? 3) Using existing datasets of sea surface images, can the new remote sensing technique be applied to breaking waves in wind-driven seas? The proposed research will involve a combination of laboratory experiments and analysis of an existing database of sea surface images to begin to estimate energy dissipation for individual breaking waves. The laboratory experiments will be based on observations of breaking waves in both the 33 meter glass wave channel and the 40 meter wind-wave channel at the Scripps Institution of Oceanography. Importantly, the use of these two wave channels will ensure breaking waves are generated across a wide range of scales and with different forcing mechanisms (wave-wave interaction and wind shear stress). Whitecap foam, bubble plume and wave energetics will be monitored for spilling through plunging breakers using a downward looking camera to monitor the surface whitecap properties, a sideward looking camera to monitor bubble plume characteristics and wave gauges to accurately characterize energy dissipation due to breaking. This comprehensive experimental approach will provide the necessary data to develop the remote sensing technique for use in future-planned field studies.