Understanding Whitecap Foam Decay using Shipboard Infrared Remote Sensing

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This work is motivated by the need to improve parameterization of the fractional coverage of whitecaps on the ocean surface. Whitecaps, which are created during wave breaking (stage A) and linger on the surface afterwards (stage B), have considerable influence on the boundary layer and climate. For example, they are critical to the exchange of heat, mass, and momentum, the production of aerosols, upper-ocean mixing, gas diffusion, and tropical storm intensity. Whitecap coverage is used expansively to estimate these and other processes, yet the routinely employed wind speed dependence has orders of magnitude uncertainty that is, in large part, due to large variations in stage B lifetime. In order to understand the factors influencing foam lifetime, a ship-based field study of whitecaps will be conducted with infrared imagery, acoustic characterization of bubble plumes and additional oceanographic and meteorological measurements. The data will be analyzed statistically to yield a model that will predict stage B lifetime in various environments leading to more accurate estimates of whitecap coverage and the surface processes they infer. Whitecaps are used during satellite remote sensing to estimate surface winds and surface albedo both of which are initializing variables in climate models. A more robust knowledge of whitecaps will therefore improve these models. Furthermore, whitecaps must be accounted for when using satellites to retrieve ocean color and primary production estimates. This will also be more accurate as a result of this research. A great deal of anthropogenic CO2 is sequestered into the ocean and exchanged across the air-sea interface, in part, through whitecap air entrainment and bubble bursting. Small droplets produced when whitecap bubbles burst scatter solar radiation and act as cloud condensation nuclei, affecting cloud albedo. Understanding the complex interactions at the air-sea interface that influence whitecaps in the contemporary ocean will enable researchers to construct better informed models of the impact whitecaps have on climate and may be used to predict the role of whitecaps in the future Earth system. Deaf and Hard of Hearing (HoH) students from Texas A&M University will be recruited to work on this project. These high impact learning experiences will provide Deaf and HoH students from other disciplines the opportunity to participate in STEM research which may otherwise not be available. It is expected that this will lead to more Deaf and HoH students earning undergraduate degrees in STEM fields leading to graduate degrees and STEM careers. A graduate student will be supported through this research and receive training in physical oceanography. Science majors from across the Texas A&M University campus will be offered an opportunity for hands-on research experience in oceanography, and several undergraduate students will become active partners in the research by conducting individual research projects. Results from the research will primarily be disseminated through peer-reviewed publications and presentations at scientific meetings, with students playing an active role at all stages in the dissemination process.The objective of this project is to develop a parametric model that can predict stage B whitecap lifetime. The model will be created using data from shipboard infrared images of whitecaps captured simultaneously with measurements of meteorological and oceanographic conditions at the air-sea interface. Infrared remote sensing will be used because it provides clear, unambiguous separation of whitecap stages not afforded by other remote sensing techniques. These data will be analyzed using a principle component analysis to determine each parameter's relative contribution to the lifetime of stage B whitecaps and to develop the model. Infrared images will be recorded in the Gulf of Mexico during multiple cruises in order to capture a wide variety of conditions that will lend strength to the model. Shipboard data will be supplemented with wave information taken from existing buoy networks. This research is a collaboration between the Naval Research Laboratory (NRL) in Washington, D.C. and the Department of Oceanography at Texas A&M University. Both institutions bring equipment that the other does not have, leading to collaboration much greater than its parts. This project may cultivate a longstanding academic-government partnership.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.