Diagnosing Lateral Mixing in the Upper Ocean with Virtual Tracers: Spatial and Temporal Resolution Dependence

Keating, Shane R.; Smith, K. Shafer; Kramer, Peter R.

doi:10.1175/2011jpo4580.1

Cited by 52 publications

(56 citation statements)

References 72 publications

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“…Oceanogr. ), there are reasons to expect that eddy-induced transport is dominated by eddies with spatial scales longer than 8Rd 1 and time scales longer than week-this is in accord with our study (see also Keating et al 2011). We also investigate the effects of the Ekman velocities on particle dispersion by adding to the altimetric fields the Ekman velocities obtained from National Aeronautics and Space Administration (NASA)'s Quick Scatterometer (QuikSCAT) wind stresses.…”

Section: B Datasetssupporting

confidence: 82%

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Eddy-Induced Particle Dispersion in the Near-Surface North Atlantic

Rypina

Kamenkovich

Berloff

et al. 2012

Journal of Physical Oceanography

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This study investigates the anisotropic properties of the eddy-induced material transport in the near-surface North Atlantic from two independent datasets, one simulated from the sea surface height altimetry and one derived from real-ocean surface drifters, and systematically examines the interactions between the mean-and eddy-induced material transport in the region. The Lagrangian particle dispersion, which is widely used to characterize the eddy-induced tracer fluxes, is quantified by constructing the ''spreading ellipses.'' The analysis consistently demonstrates that this dispersion is spatially inhomogeneous and strongly anisotropic. The spreading is larger and more anisotropic in the subtropical than in the subpolar gyre, and the largest ellipses occur in the Gulf Stream vicinity. Even at times longer than half a year, the spreading exhibits significant nondiffusive behavior in some parts of the domain. The eddies in this study are defined as deviations from the long-term time-mean. The contributions from the climatological annual cycle, interannual, and subannual (shorter than one year) variability are investigated, and the latter is shown to have the strongest effect on the anisotropy of particle spreading. The influence of the mean advection on the eddy-induced particle spreading is investigated using the ''eddy-following-full-trajectories'' technique and is found to be significant. The role of the Ekman advection is, however, secondary. The pronounced anisotropy of particle dispersion is expected to have important implications for distributing oceanic tracers, and for parameterizing eddy-induced tracer transfer in non-eddy-resolving models.

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Section: B Datasetssupporting

confidence: 82%

“…Oceanogr.) and Keating et al (2011) suggest that eddies on these scales play the dominant role in the particle dispersion by geostrophic currents. The results of our study are presented in terms of the ''spreading ellipses''-a convenient way of portraying properties of the particle dispersion.…”

Section: Discussionmentioning

confidence: 98%

Eddy-Induced Particle Dispersion in the Near-Surface North Atlantic

Rypina

Kamenkovich

Berloff

et al. 2012

Journal of Physical Oceanography

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“…25 , its effective resolution is much lower ($1 ). 21 To better estimate how remotely observed rings decay, it would be interesting to compare the present calculation against a new altimetric dataset recently reprocessed by Aviso to improve its spatial resolution. Comparing the newer and former products, Ref.…”

Section: Discussionmentioning

confidence: 99%

Studying an Agulhas ring's long-term pathway and decay with finite-time coherent sets

Froyland

Horenkamp

Rossi

et al. 2015

Chaos: An Interdisciplinary Journal of Nonlinear Science

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Coherent sets in dynamical systems are regions in phase space that optimally "carry mass" with them under the system's evolution, so that these regions experience minimal leakage. The dominant tool for determining coherent sets is the transfer operator, which provides a complete description of Lagrangian mass transport. In this work, we combine existing transfer operator methods with a windowing scheme to study the spatial and temporal evolution of a so-called Agulhas ring: a large anticyclonic mesoscale eddy playing a key role in inter-ocean exchange of climate-relevant properties. Our focus is on ring decay over time and the windowing scheme enables us to study how the most coherent region (our estimate of the ring) varies in position and size over a period of more than two years. We compare the eddy-like structure and its spatio-temporal changes as revealed by our method and by a classical Eulerian approach. Finite-time coherent sets are determined by assembling gridded Lagrangian trajectories into a grid-to-grid transition matrix and computing dominant singular vectors of this matrix. We introduce a new combination of transfer operator based coherent set techniques with an overlapping window scheme, which enables ring size to vary over time, and follow an Agulhas ring's west-north-westward pathway across the southern Atlantic Ocean for over more than 2 years. We describe the evolution of the ring during this long journey and draw relationships between various dynamical and physical quantities associated with the ring and its decay. The advantage of the transfer operator method is that mass loss from rings is explicitly minimised over moderate periods of time using Lagrangian trajectory information. Our overlapping window approach readily accommodates the decay of rings over longer timespans during which part of the fluid is expelled from the structure. The ring boundary obtained by our method can then be used to explicitly study ring decay in both Eulerian and Lagrangian senses.

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“…A new generation of global climate models have eddy-resolving oceans, but output fields on monthly frequency, which can introduce large errors to particle trajectories [Keating et al, 2011]. Also, Lagrangian experiments are computationally expensive.…”

Section: Introductionmentioning

confidence: 99%

A new Eulerian method to estimate “spicy” Agulhas leakage in climate models

Putrasahan

Beal

Kirtman

2015

Geophysical Research Letters

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The Agulhas leakage brings warm and saline water from the Indian Ocean into the South Atlantic, forming part of the returning branch of the global thermohaline circulation, an important component of climate. We develop a new method using the passive tracer spice, to estimate Agulhas leakage transport in an ocean eddy‐resolving climate model that properly captures Agulhas Retroflection and leakage. We identify Agulhas leakage waters as positive spice anomalies (≥ +0.1) and are able to trace leakage to depths greater than 1000 m. Spice‐based Eulerian Agulhas leakage captures spikes in Lagrangian leakage transport which coincide with the passage of Agulhas rings, yielding a statistically significant correlation (0.47). On interannual times scales, differences between Eulerian and Lagrangian transports are reduced and correlation increases to 0.77. We obtain a mean spice‐based Eulerian Agulhas leakage of 17 ± 4 sverdrup (Sv) and Lagrangian Agulhas leakage of 18 ± 2 Sv, which are within the range of observational estimates.

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Diagnosing Lateral Mixing in the Upper Ocean with Virtual Tracers: Spatial and Temporal Resolution Dependence

Cited by 52 publications

References 72 publications

Eddy-Induced Particle Dispersion in the Near-Surface North Atlantic

Eddy-Induced Particle Dispersion in the Near-Surface North Atlantic

Studying an Agulhas ring's long-term pathway and decay with finite-time coherent sets

A new Eulerian method to estimate “spicy” Agulhas leakage in climate models

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