In the realm of oceanography and energy research, a team of scientists from the University of Washington and the University of California, Los Angeles, has made significant strides in understanding the complex interactions between waves and currents in the ocean. Led by Jeffrey J. Early, this group has developed a new framework to measure energy fluxes between waves and geostrophic features, which are large-scale ocean currents influenced by the Earth’s rotation. Their work, published in the Journal of Physical Oceanography, offers valuable insights that could enhance our understanding of ocean dynamics and improve energy predictions in the marine environment.
The researchers tackled a longstanding challenge in physical oceanography: quantifying the energy content of waves and balanced flows, and the fluxes that connect these energy reservoirs with their sources and sinks. Previous methodological limitations had hindered the decomposition of realistic flows with non-hydrostatic motions and variable stratification. The team addressed this by creating a framework that separates the flow into wave and geostrophic components, based on the principle that waves have no Eulerian available potential vorticity signature.
Starting with new expressions for available energy and potential vorticity conservation, the researchers constructed a basis of wave and geostrophic modes. These modes are complete and orthogonal with respect to quadratic approximations of the conserved quantities. Using the resulting non-hydrostatic projection operators, the nonlinear equations of motion were expressed as coupled wave and geostrophic equations. This allowed the team to quantify cascade and transfer fluxes of wave and geostrophic energy.
The researchers applied their method to non-hydrostatic mid-ocean simulations with geostrophic mean-flow, near-inertial, and tidal forcing. From these experiments, they constructed source-sink-reservoir diagrams for exact and quadratic fluxes, quantifying the fluxes between geostrophic and wave components. The simulations revealed a geostrophic inverse cascade, a forward wave cascade, and a direct transfer of geostrophic to wave energy, with no indication of a forward geostrophic cascade. The mean-flow-only simulation showed weak spontaneous wave emission during spin-up, which diminished to zero over time.
The team also evaluated the decomposition by comparing linearized and fully conserved available potential vorticity. They found that errors became significant at scales below 15 kilometers. This research provides a robust framework for understanding the complex energy dynamics in the ocean, which can be crucial for the energy sector, particularly in offshore wind and tidal energy projects. By improving our ability to predict and understand ocean currents and wave interactions, this work can contribute to more accurate energy assessments and better-informed decision-making in marine energy development.
In summary, the team’s innovative approach offers a clearer picture of the energy fluxes between waves and currents, enhancing our understanding of ocean dynamics. This knowledge is invaluable for the energy industry, particularly in the realm of marine renewable energy, where accurate predictions of ocean conditions are essential for efficient and sustainable energy production.
This article is based on research available at arXiv.