Quantifying mean-flow suppression of eddy-induced mixing in an idealized Southern Ocean simulation

Mixing by mesoscale eddies within the Southern Ocean mediates the ventilation and transport of heat and carbon throughout the global ocean. We employ an idealized Southern Ocean model to better understand the role of the mean flow in modulating the amplitude and structure of mesoscale eddy mixing. The mean flow is approximated by a low-pass filtered velocity. Lagrangian particle trajectories are computed along isopycnal surfaces using two velocity fields: total velocity and total minus mean-flow velocity. Particle-based calculations of diffusivity for these two velocity fields allows us to estimate the role of the mean flow in suppressing eddy-induced mixing. In addition, we employ a novel approach for computing effective diffusivity in order to evaluate the sensitivity of our findings to the underlying method.