Computing eddy-driven effective diffusivity using Lagrangian particles. (October 2017)

• Record Type: Journal Article
• Authors: Wolfram, Phillip J.; Ringler, Todd D.
• Is Part Of: Ocean modelling. Volume 118(2017:Oct.)
• Page Start: 94
• Page End: 106
• Publication Date: 2017-10
• Subjects: Effective diffusivity -- Lagrangian particle tracking -- Scalar transport -- MPAS-O -- LIGHT; Oceanography -- Periodicals; Océanographie -- Périodiques; Oceanography; Periodicals; 551.46
• DOI: 10.1016/j.ocemod.2017.08.008
• Languages: English
• ISSNs: 1463-5003

Abstract

Highlights: A novel Lagrangian scalar transport and effective diffusivity method is presented. Lagrangian and Eulerian ICC (idealized circumpolar current) transport is similar. Effective and dispersion-based diffusivity are within a factor of 2 within the ICC. Abstract: A novel method to derive effective diffusivity from Lagrangian particle trajectory data sets is developed and then analyzed relative to particle-derived meridional diffusivity for eddy-driven mixing in an idealized circumpolar current. Quantitative standard dispersion- and transport-based mixing diagnostics are defined, compared and contrasted to motivate the computation and use of effective diffusivity derived from Lagrangian particles. The effective diffusivity is computed by first performing scalar transport on Lagrangian control areas using stored trajectories computed from online Lagrangian In-situ Global High-performance particle Tracking (LIGHT) using the Model for Prediction Across Scales Ocean (MPAS-O). The Lagrangian scalar transport scheme is compared against an Eulerian scalar transport scheme. Spatially-variable effective diffusivities are computed from resulting time-varying cumulative concentrations that vary as a function of cumulative area. The transport-based Eulerian and Lagrangian effective diffusivity diagnostics are found to be qualitatively consistent with the dispersion-based diffusivity. All diffusivity estimates show a region of increased subsurface diffusivity within the core of an idealized circumpolar current and results are within a factor of two of each other. The Eulerian and Lagrangian effective diffusivities are most similar; smaller and more spatially diffused values are obtained with the dispersion-based diffusivity computed with particle clusters.