Abstract
Oceanic eddies, fluctuations on scales on the order of one km to hundreds of km, derive their energy primarily from baroclinic instability processes. Currently, climate models do not incorporate the space and time variability of the effects of eddies and sub-mesoscale processes in an energy-consistent way. Eddy diffusivities are specified without connection to the energy budget and, more fundamentally, it is unclear to what extent, where and on what scales the downgradient eddy diffusion model is appropriate at all. Rotational components of the eddy fluxes associated with the advective terms in the eddy variance equation are generally large, so that production and dissipation of eddy energy do not balance locally. We will review here the current understanding of the spatial and temporal variability of eddy diffusivities and eddy–mean flow interactions that have been inferred in both observations and eddying ocean models. A focus will be on Lagrangian particle statistics as an ideal tool to describe the effects of eddies on a time mean transport and to assess the limits and validities of the eddy diffusion model. Eddy diffusivity diagnostics and the current state of eddy parameterizations in ocean models will be discussed as well as prospects for energy-consistent parameterizations.
Published Version
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