Rühs, Siren , Zhurbas, Victor, Koszalka, Inga Monika , Durgadoo, Jonathan V. and Biastoch, Arne (2018) Eddy diffusivity estimates from Lagrangian trajectories simulated with ocean models and surface drifter data - a case study for the greater Agulhas system. Journal of Physical Oceanography, 48 . pp. 175-196. DOI 10.1175/JPO-D-17-0048.1.

Preview	Text jpo-d-17-0048.1.pdf - Published Version Available under License Creative Commons: Attribution 4.0. Download (2MB) | Preview
Preview	Text 10.1175_JPO-D-17-0048.s1.pdf - Supplemental Material Available under License Creative Commons: Attribution 4.0. Download (453kB) | Preview

Abstract

The Lagrangian analysis of sets of particles advected with the flow fields of ocean models are used to study connectivity, i.e. exchange pathways, timescales and volume transports, between distinct oceanic regions. One important factor influencing the dispersion of fluid particles and hence connectivity is the Lagrangian eddy diffusivity, which quantifies the influence of turbulent processes on the rate of particle dispersal. Due to spatial and temporal discretization, turbulence is not fully resolved in modelled velocities, and the concept of eddy diffusivity is used to parametrize the impact of unresolved processes. However, the relations between observational- and model-based Lagrangian eddy diffusivity estimates as well as eddy parameterizations are not clear.

This study presents an analysis of the spatially variable near-surface lateral eddy diffusivity estimates obtained from Lagrangian trajectories simulated with 5-day mean velocities from an eddy-resolving ocean model (INALT01) for the Agulhas system. INALT01 features diffusive regimes for dynamically different regions, some of which exhibit strong suppression of eddy mixing by mean flow, and is consistent with the pattern and magnitude of drifter-based eddy diffusivity estimates. Using monthly-mean velocities decreases the estimated diffusivities less than eddy kinetic energy, supporting the idea that large and persistent eddy features dominate eddy diffusivities. For a non-eddying ocean model (ORCA05), Lagrangian eddy diffusivities are greatly reduced, in particular when the Gent and McWilliams parameterization of mesoscale eddies is employed.

Actions (login required)

View Item