Eddy-mean flow interactions from the perspective of eddy geometry
Geophysical flows are richly nonlinear, with interactions between motions at all scales. Eddy-mean flow interactions is a term generically used to describe the two-way interactions between a larger-scale flow (the “mean”) and smaller-scale structures (the “eddies”). These interactions are important because they achieve the transfer of energy from large scales on which the ocean is forced to small scales where turbulence drives ocean mixing and dissipation. They also allow for small-scale circulation features to feedback onto the larger scale flow. In general, eddy-mean flow interaction processes remain poorly understood and, as a consequence, inadequately represented in Earth system models. This so-called eddy parameterization problem, which has numerous facets, has been one of the most challenging problems in theoretical oceanography in recent decades. It is also one of the most pressing, given the urgent need to improve the robustness of high-end numerical models used to study Earth’s climate and to project its future.
We study eddy-mean flow interactions from a theoretical perspective using idealized process models. In recent years, we have focused on a description of these interactions in terms of the properties of eddy ellipse geometry. Although these ideas are not new, in recent years they have been the subject of renewed interest as the basis for an eddy parameterization framework in the ocean modelling community. This geometric framework also has the potential to offer new theoretical insights into eddy-mean flow interactions by linking eddy effects to spatial patterns of eddy geometry that can suggest the mechanisms underpinning these effects, and further, by describing the eddy feedback in terms of a lower-order (less differentiated) description of the flow, be useful in the analysis of coarse resolution data. We work to develop geometric frameworks to describe eddy feedbacks, and we experiment with applying these frameworks to the description of eddy-mean flow interactions in idealized numerical models of oceanic flows to better understand the insights they can reveal. More recently, we have started to characterize eddy geometry in real and realistic ocean flows, using satellite observations and global general circulation ocean models. With this work, we aim to understand how these frameworks can give us new insights into eddy-mean flow feedbacks in the real ocean. |
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