Applied Mathematics Seminars: A New Gauge Invariant Method for Diagnosing Eddy Diffusivities
11 November 2016 14:00 in CM219
Numerical ocean models at mesoscale eddy permitting resolutions are generally prohibitively expensive for climate studies, as such the representation of the unresolved mesoscale eddy field remains an active area of research. In this talk the main focus will be on a technique for diagnosing eddy diffusivities directly from the eddy fluxes. Since it is the eddy flux divergence that appears in the mean equation, the eddy diffusivity is defined up to a rotational term. The technique proposed here removes this gauge freedom in the diffusivity via the definition of an eddy force function. An optimisation problem based on minimising the mismatch of the diagnosed eddy force function and eddy force function associated with the parameterisation results in a diffusivity that is uniquely defined with controlled smoothness. This technique is tested using data from multi-layer quasi-geostrophic double gyre simulations, employing the FEniCS system for solving the optimisation problem.
If time, recent work on a parameterisation variant that displays emergent eddy saturation at least in an idealised two-dimensional zonally averaged model is presented. A recipe for implementing this into a General Circulation Model is proposed.
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