Computing Eddy-Driven Effective Diffusivity Using Lagrangian Particles

The climate of the global ocean is mediated by irreversible mixing induced by mesoscale ocean eddies. However, at present, a complete spatial and temporal quantification of this mixing from either observations or strongly eddying ocean models has yet to be performed. To this end we use the effective diffusivity metric, which is a Lagrangian measure of irreversible mixing within the fluid. Typical methods to compute effective diffusivity require evolution of multiple scalar fields and, consequently, are computationally expensive. To overcome this issue, we utilize Lagrangian In-situ Global High-performance particle Tracking (LIGHT) within the the Model for Prediction Across Scales Ocean (MPAS-O), which is able to routinely track the same number of particles as Eulerian cells. This Lagrangian-particle based approach to computing effective diffusivity is explored within the context a mid-latitude double gyre circulation and an idealized Southern Ocean re-entrant channel configuration. We then compare and contrast the estimates of irreversible mixing computed using effective diffusivity methods to traditional single- and multiple-particle methods for estimating diffusivities.