# Computing eddy-driven effective diffusivity using Lagrangian particles

## 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. We compute the effective diffusivity 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). Furthermore, 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.

- Authors:

- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

- Publication Date:

- Research Org.:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

- Sponsoring Org.:
- USDOE Office of Science (SC). Biological and Environmental Research (BER) (SC-23)

- OSTI Identifier:
- 1412853

- Report Number(s):
- LA-UR-16-28091

Journal ID: ISSN 1463-5003

- Grant/Contract Number:
- AC52-06NA25396

- Resource Type:
- Journal Article: Accepted Manuscript

- Journal Name:
- Ocean Modelling

- Additional Journal Information:
- Journal Volume: 118; Journal Issue: C; Journal ID: ISSN 1463-5003

- Publisher:
- Elsevier

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 54 ENVIRONMENTAL SCIENCES; 97 MATHEMATICS AND COMPUTING; Earth Sciences; effective diffusivity; Lagrangian particle tracking; online diagnostics; MPAS-O; LIGHT

### Citation Formats

```
Wolfram, Phillip J., and Ringler, Todd D.
```*Computing eddy-driven effective diffusivity using Lagrangian particles*. United States: N. p., 2017.
Web. doi:10.1016/j.ocemod.2017.08.008.

```
Wolfram, Phillip J., & Ringler, Todd D.
```*Computing eddy-driven effective diffusivity using Lagrangian particles*. United States. doi:10.1016/j.ocemod.2017.08.008.

```
Wolfram, Phillip J., and Ringler, Todd D. Mon .
"Computing eddy-driven effective diffusivity using Lagrangian particles". United States.
doi:10.1016/j.ocemod.2017.08.008. https://www.osti.gov/servlets/purl/1412853.
```

```
@article{osti_1412853,
```

title = {Computing eddy-driven effective diffusivity using Lagrangian particles},

author = {Wolfram, Phillip J. and Ringler, Todd D.},

abstractNote = {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. We compute the effective diffusivity 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). Furthermore, 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.},

doi = {10.1016/j.ocemod.2017.08.008},

journal = {Ocean Modelling},

number = C,

volume = 118,

place = {United States},

year = {Mon Aug 14 00:00:00 EDT 2017},

month = {Mon Aug 14 00:00:00 EDT 2017}

}

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