Spray generation by collective bubble bursting

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Bubbles in the ocean are formed after a breaking wave has entrained air below the sea surface. Sea spray drops created by bubble bursting affect the exchange between the ocean and atmosphere by transporting water, heat, dissolved gases, salts, surfactants, and biological materials, and are major players in weather prediction and hurricane intensification. Large uncertainties in sea spray production predictions remain despite long standing efforts; this is attributed to the lack of knowledge in the original distribution of sea spray drop sizes and velocities. The research will span all scales relevant to the problem, from individual bubbles to wave statistics at the ocean surface; it will include detailed studies of the impact of key variables such as the concentration of surfactants, temperature, turbulence within a single experimental and numerical framework. A better understanding and improved parameterizations of sea spray production are necessary to improve the exchange between ocean-atmosphere of heat, moisture and aerosols, key elements of climate and weather models and forecast. Sea spray aerosols serve as cloud condensation nuclei and a better understanding of clouds generation and growth is seen by many as one of the biggest challenges in climate sciences. Sea spray is also related to health issues in coastal environments. When red tides are present, such as the Gulf of Mexico, blooms of harmful algae release toxins that can be transported as aerosols up to urban communities. The upscaling approach used in this study to connect the small scale, detailed processes to the larger scales of the ocean is general and could be used to improve the modeling of other ocean-atmosphere interactions as well. Through this project, undergraduate and graduate students at Princeton will be exposed to critical environmental challenges that require research on fundamental multi-phase flows. The project will also promote the use of open source methods through workshops and teaching activities.The complex droplet formation process by collective bursting depends on multiple variables: the size and density of the bubbles rising in the turbulent upper ocean, the coalescence and foam formation at the surface and the physical-chemical properties of water. This project will fill gaps in our knowledge by conducting a comprehensive study that integrates high quality laboratory and numerical data to build models for the distribution of sizes and velocities of sea spray drops. Single bubble bursting will be studied with state of the art numerical simulations, developing a fundamental understanding at the bubble scale. The role physical and chemical variables, such as salinity, temperature and surfactant on the collective bubble bursting, foam aging and droplet formation will be investigated with laboratory experiments. Finally, an upscaling approach will be employed, going from one bubble plume entrained by a single breaking wave to the ocean scale by integrating the results over the breaking statistics, leading to a better parameterization of sea spray fluxes for numerical models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.