Koszalka, Inga Monika (2018) Lagrangian diffusivity and its application to represent lateral eddy transport in models. [Talk] In: Ocean Science Meeting 2018. , 12.-16.02.2018, Portland, OR, USA .

Abstract

In recent years, a substantial effort has been placed on quantifying oceanic eddy trasport with Lagrangian diffusivity coefficients estimated either from surface and subsurface Lagrangian observations (drifters and floats) or from Lagrangian particle trajectories advected by velocity output from eddy-permitting/-resolving ocean models. A tantalizing aspect of these studies is a possible application of these Lagrangian diagnostics to parameterize eddy transport of tracers in global circulation models. The questions remain however regarding a large spread and high values of the Lagrangian diffusivity estimates and their practical implementation in model simulations.

I will address these questions by compiling my various studies, reflections and discussions on the topics of Lagrangian diffusivity and Lagrangian modeling. First, I will take up different factors associated with the calculation of Lagrangian diffusivities that may add onto the natural spatio-temporal variability of the eddy field and bias the estimated eddy diffusivity coefficients high. In the second part, I will consider implementation of Lagrangian diffusivities to represent eddy transport processes with cautious remarks on their usage as mixing (Redi) coefficients in global circulation models. I will discuss, and show examples of, an alternative approach employing Lagrangian (stochastic) modeling to represent lateral turbulent transport (eddy mixing) and remarking on specific applications ("to diffuse or not to diffuse"), the choice of the stochastic model, and the impact of spatial variability of the diffusivities.

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