Collaborative Research: Interaction of Eddies with Mixed Layers

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Parameterizations for the interaction of mesoscale eddies with turbulent mixing in the upper ocean will be derived and tested in climate models. Mesoscale parameterizations used in ocean general circulation models typically represent only the adiabatic release of available potential energy by eddies, as suggested by Gent and McWilliams. In the upper ocean, eddy fluxes develop a diabatic component because density is maintained vertically homogeneous by strong mixing while geostrophic motions are constrained to be horizontal near the boundary. Furthermore mesoscale strain interacts and modifies turbulent mixing at small scales. The dynamics of these diabatic surface eddy fluxes and their interactions with small-scale turbulence are not fully understood, and are not currently parameterized in the surface mixed layers of ocean models. Instead, tapering schemes are used to turn of the adiabatic eddy flux schemes at the surface. Coupled climate models are very sensitive to the choice of this tapering scheme. Here a new approach to eddy parameterizations, based on the Transformed Eulerian Mean is proposed. The new approach provides a unified framework for the treatment of eddy fluxes in the adiabatic interior and in the diabatic surface boundary layer.The project involves 1) analysis of observational data sets with key information on eddy transport in the upper ocean, 2) high resolution process models that explicitly resolve the full range of motions in the mixed layer, and 3) the derivation of new parameterization schemes based on a compromise between numerical efficiency and the theoretical information learned from observations and simulations. The main focus of the Team will be to implement and test the new parameterization schemes in the coupled climate models currently used in the modeling centers at GFDL, NCAR, and GSFC. This research is aimed at improving state of the art models of the atmosphere and ocean for study of the climate of the Earth and how it might change in the future. Thus it is of great societal impact. The project will also contribute to the education of a number of post-doctoral and graduate students bridging between observations, theory, and modeling.