Energy Pathways and Scale Interactions in the Ocean

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Large-scale currents and eddies pervade the ocean and play a prime role in the general circulation and climate. The coupling between scales ranging from ten thousand kilometers to a millimeter presents a major difficulty in understanding, modeling, and predicting oceanic circulation and mixing. What are the power requirements to sustain turbulence and mixing in the ocean? What are its sources and sinks? What are the mechanisms to transfer such energy across scales? Due to the lack of rigorous quantitative methods for detecting and measuring energy transfer rates between scales in the ocean, our understanding of the oceanic energy budget is uncertain within at least a factor of two and possibly as large as ten. This poses serious limitations on our climate prediction capabilities. Using a novel mathematical scale-analysis framework, we propose to study the coupling between scales and map out the energy pathways from realistic ocean model data. The approach is very general, allows for probing the dynamics simultaneously in scale and in space, and is not restricted by the usual assumptions of homogeneity or isotropy, thus making it ideally suited for studying oceanic flows. A primary goal is to examine the extent to which the accepted geostrophic model for such pathways is valid in the ocean.The contribution of various nonlinear mechanisms to the transfer of energy across scales such as baroclinic and barotropic instabilities, barotropization, Rossby wave generation, and internal wave generation and breaking will be investigated. If successful, this research will provide oceanographers with a promising set of tools with which to analyze and interpret data from simulations, satellite measurements, and experiments.Intellectual Merit: Understanding and quantifying the oceanic energy pathways and balances as a function of scale is a challenging fundamental problem in oceanography. To this end, rigorous analytical tools will be further developed and to applied to data from global, regional, and idealized numerical simulations. The problem of understanding nonlinear interactions in the ocean is a major intellectual challenge and new techniques and ideas will be applied to better quantify the energetics of the ocean.Broader Impacts:Mapping and quantifying the energy pathways supplying and depleting the mesoscale flow will reduce the current uncertainty in the oceanic energy budget. The work also promises to provide insights into the scale-physics at play in the ocean, offer a priori constraints on parameter tuning of current parameterization schemes such as Gent-McWilliams, on proposed schemes that may be applied to eddy permitting ocean models, and will help in the development of a new class of ocean parameterizations that are a function of location and resolution.The work will support a junior scientist at the threshold of a promising career. Finally, the P.I. will be revising a general textbook that has been adopted by a number of universities for the teaching of atmospheric and oceanic dynamics. The book will help education in the geosciences broadly, and the research conducted under this project will provide context and examples for the students.