A patch in time saves nine: Methods for the identification of localised dynamical behaviour and lifespans of coherent structures

Blachut, Chantelle; González-Tokman, Cecilia; Hernández-Dueñas, Gerardo

doi:10.48550/arxiv.2109.09970

Cited by 2 publications

(2 citation statements)

References 28 publications

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“…Recent studies have used telescoping windows to investigate their effect on the geometry of finite-time coherent sets [33], to determine the life expectancy of an ocean eddy [6], and to find a maximal coherence timescale of a finitetime coherent which minimizes the rate of mass loss per unit window length through the boundary of the coherent set [19]. A sliding sequence of windows have been used to study the decay of an ocean eddy [29,19], to investigate the Lagrangian pathways of convective heat transfer in turbulent Rayleigh-Bénard convection flows, and to find structural changes in coherent features (such as merging or splitting) [12,13,52]. An alternative approach used to determine when a coherent set is born or dies was developed in [32], which removes the need for multiple sliding and telescoping computations by considering an inflated dynamic Laplace operator on a time-expanded domain.…”

Section: Tracking Sequences Of Finite-time Coherent Sets and Fronts F...mentioning

confidence: 99%

Bathymetry imposes a global pattern of cross-front transport in the Southern Ocean

Denes¹,

R²,

Froyland³

2023

Preprint

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The Southern Ocean plays an integral role in the global climate system, exchanging heat, salt, and carbon throughout the major ocean basins via the deep, fast-flowing Antarctic Circumpolar Current. The Antarctic Circumpolar Current is bounded by spatially and temporally varying fronts that partition distinct water masses. Locating and quantifying cross-front transport is crucial for understanding global patterns of inter-basin exchange; however, this is challenging because fronts are typically defined by hydrographic properties, such as temperature or salinity, which are subject to external sources and sinks, rather than by properties of the flow itself. Here we show that, when characterized by material contours that minimize deformation and cross-contour mixing, Southern Ocean fronts exhibit a global pattern of alternating poleward and equatorward transport caused by frontal meandering, which, in turn is influenced by prominent sea-floor obstacles. These results highlight the importance of bathymetric features in controlling Southern Ocean dynamics and inter-basin exchange.

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Section: Tracking Sequences Of Finite-time Coherent Sets and Fronts F...mentioning

confidence: 99%

Bathymetry imposes a global pattern of cross-front transport in the Southern Ocean

Denes¹,

R²,

Froyland³

2023

Preprint

View full text Add to dashboard Cite

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“…More recently, [54] used a sliding sequence of windows to study the Lagrangian pathways of convective heat transfer in turbulent Rayleigh-Bénard convection flows. Sliding sequences of windows have also been used to find structural changes in coherent features [13,14,49], such as merging or splitting. The effect of telescoping windows on the geometry of finite-time coherent sets was investigated in [34] and [3] have recently used a telescoping sequence of windows to determine the life expectancy of an ocean eddy by finding the largest window length that successfully identified a coherent vortex.…”

Section: Sequences Of Coherent Setsmentioning

confidence: 99%

Persistence and material coherence of a mesoscale ocean eddy

Denes¹,

Froyland²,

Keating³

2021

Preprint

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Ocean eddies play an important role in the transport and mixing processes of the ocean due to their ability to transport material, heat, salt, and other tracers across large distances. They exhibit at least two timescales; an Eulerian lifetime associated with persistent identifiable signatures in gridded fields such as vorticity or sea-surface height, and multiple Lagrangian or material coherence timescales that are typically much shorter. We propose a method to study the multi-timescale material transport, leakage, and entrainment by eddies with their surroundings by constructing sequences of finite-time coherent sets, computed as superlevel sets of dominant eigenfunctions of dynamic Laplace operators. The dominant eigenvalues of dynamic Laplace operators defined on time intervals of varying length allows us to identify a maximal coherence timescale that minimizes the rate of mass loss over a domain, per unit flow time. We apply the method to examine the persistence and material coherence of an Agulhas ring, an ocean eddy in the South Atlantic ocean, using particle trajectories derived from a 0.1 • global numerical ocean simulation. Using a sequence of sliding windows, the method is able to identify and track a persistent eddy feature for a time much longer than the maximal coherence timescale, and with considerably larger material transport than the corresponding eddy feature identified from purely Eulerian information. Furthermore, the median residence times of fluid in the identified feature far exceed the timescale over which fully material motion is guaranteed. Through residence time calculations, we find that this particular eddy does not exhibit a long-lived coherent inner core and that the bulk of material transport is performed by the quasi-coherent outer ring of the eddy.

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A patch in time saves nine: Methods for the identification of localised dynamical behaviour and lifespans of coherent structures

Cited by 2 publications

References 28 publications

Bathymetry imposes a global pattern of cross-front transport in the Southern Ocean

Bathymetry imposes a global pattern of cross-front transport in the Southern Ocean

Persistence and material coherence of a mesoscale ocean eddy

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