CAREER: Ready to Resolve: Subgridscale Physics for Mesoscale Ocean Large Eddy Simulations

Brown University, Providence RI

Investigators

Abstract

Climate models are a key tool in understanding our world and our role in it. Much of the memory of these models, from seasons to centuries, is the oceanic component, and the majority of the subsurface ocean energy is held in mesoscale eddies. These eddies transport energy, momentum, salinity, and other tracers, and thereby affect the climate. Yet, it is only now that computational capabilities have made it possible to run climate models at sufficient resolution to permit or resolve larger eddies, avoiding many uncertain parameters approximating the influence of eddies at unresolved (subgrid) scales. This new class of models called by the PI "Mesoscale Ocean Large Eddy Simulations (MOLES)" will be with us for decades to come, yet few experts are trained to understand and improve them. Even in MOLES, some phenomena are unresolved. Thus, a form of subgrid modeling is still required, but the old approaches designed when no eddies were resolved will not perform well when some eddies are resolved and some are not. Prototype models show even MOLES are somewhat sensitive to choice of subgrid models, so care is required. This project, expanding on the proven subgrid model of Fox-Kemper and Menemenlis (2008), will build and train a new team to implement and evaluate subgrid models appropriate for the improving resolution of modern simulations. The subgrid models for MOLES will combine the advantages of past eddy subgrid models developed for coarse resolution use (water mass preservation, systematic extraction of potential energy, advective and diffusive transport, and neutral physics) with the key advantages of Large Eddy Simulation subgrid models; self-adjusting magnitude, scale-awareness, robust numerical stability, convergence with increasing resolution, and avoidance of double-counting. Intellectual Merit: The PI is already evaluating MOLES subgrid models in idealized settings, and suggests a viable pathway to implementation in realistic models. The subgrid model to be further developed seems to combine all features mentioned above. This CAREER research will take on these two tasks, using a team of undergraduate, graduate, and postdoctoral researchers: 1) New diagnostic approaches will be used to evaluate and differentiate the subgrid models' behavior. These diagnoses offer clues for global budgets of energy and potential vorticity as well. 2) The primary deliverable is this new class of subgrid models, greatly needed for the present and future generations of ocean circulation modeling, which will be evaluated, enhanced, and implemented during the course of this award. Broader Impacts To build and train this team of future scientists, a new suite of courses will be developed to educate students from Brown University's departments of geology (including geophysics), physics, engineering, and applied mathematics. One early-career faculty member, one graduate student, one postdoc, and a group of STEM and non-STEM undergraduate researchers will be supported though the lifetime of the award. This effort will reintroduce physical oceanography to Brown, missing since the 1950s. Outreach activities to the public and K-12 audiences in conjunction with Save the Bay will educate about climate modeling globally and in Rhode Island. Save The Bay educators will be trained and supplied with teaching materials developed by the PI and group, in collaboration with a group of non-STEM Brown & Rhode Island School of Design undergraduates. The fundamentals of the next generation of climate models will be evaluated and improved.