Measurements and Modeling of the Kinematics and Dynamics of Surface-Wave Breaking in Directional Wave Fields

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This project will use a high resolution scanning LIDAR along with visible and infrared imaging to measure the directional distributions of the surface wave field and wave breaking, and use this data to test and develop models of wave evolution and dissipation. The novelty is that it will give the directional wavenumber spectra of the surface waves from the scale of the swell, O(100) m, down to the scale of gravity- capillary waves, O(0.01)m. Similarly, it will give corresponding directional distributions of breaking across the same range of scales. These broadband data are expected to support a greatly improved understanding of the statistical description of wave breaking first proposed by Phillips (1985), based on the length of breaking fronts per unit area of ocean surface moving at around the phase velocity. The measurements of breaking front length in the literature are very limited and have a unimodal structure that is not understood. This program, including the analysis of field data, high-resolution wave breaking kinematics and directional wave measurements from the Scripps Institution of Oceanography (SIO) Per and airborne measurements during a R/P FLIP experiment and Santa Ana wind events offshore Southern California and Baja California, will allow more thorough testing of the current dissipation source function models in numerical wind wave models and development new models based on an analysis of the data constrained by the radiative transfer equation for the wave field. The data will also permit quantitative exploration of the transition from air-entraining whitecapping to microscale breaking, and the relationship between the kinematics and dynamics of breaking.Broader ImpactWhile the funded effort is focused on investigating hitherto inaccessible aspects of surface wave kinematics and dynamics, improvements in surface-wave and wave-breaking models will have a significant impact on coupled atmosphere-ocean models used for weather and climate prediction. The momentum and energy fluxes from the atmosphere to the ocean are a function of the directional wave spectra and wave breaking distributions. The air-sea transfer of greenhouse and other gases depend on air entrainment due to breaking.The SIO Pier experiments will be used as a hands-on teaching opportunity in graduate and undergraduate classes at SIO, UCSD. Currently, PI Melville uses the laboratory to provide demonstrations and hands-on experience for students taking classes in fluid mechanics and wave mechanics. The pier experiment will extend this experience for the students from the controlled environment of the laboratory to the uncontrolled environment of the field, thus providing a broader and qualitatively different experience for the students.This project will provide research experiences for undergraduate students at UCSD during the academic year and for fellowship programs during the summer sessions. From personal experience during his own undergraduate career, Melville understands the value of these programs in shaping careers and has worked to continue these programs in his laboratory.The results of this research and related material will be posted to Melville?s research web site (http://airsea.ucsd.edu).