A hybrid identification and tracking of Lagrangian mesoscale eddies

Aouni, Anass El

doi:10.1063/5.0038761

Cited by 7 publications

(6 citation statements)

References 45 publications

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“…Moreover, a Lagrangian point of view has been used to detect Coherent Lagrangian Vortices. Different methodologies were developed to detect mesoscale eddies through direct considerations on advected fields or particles evolving together in time, in particular to reduce the number of thresholds commonly used in Eulerian methods (Abernathey and Haller, 2018;Beron-Vera et al, 2008;El Aouni, 2021;Haller, 2016).…”

Section: Introductionmentioning

confidence: 99%

META3.1exp: a new global mesoscale eddy trajectory atlas derived from altimetry

Pegliasco

Delepoulle

Mason

et al. 2022

Earth Syst. Sci. Data

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Abstract. This paper presents the new global Mesoscale Eddy Trajectory Atlases (META3.1exp DT all-satellites, https://doi.org/10.24400/527896/a01-2021.001, Pegliasco et al., 2021a; and META3.1exp DT two-satellites, https://doi.org/10.24400/527896/a01-2021.002, Pegliasco et al., 2021b), composed of eddy identifications and trajectories produced with altimetric maps. The detection method used is inherited from the py-eddy-tracker (PET) algorithm developed by Mason et al. (2014), and is optimized to efficiently manage large datasets, and thus long time series. These products are an improvement on the earlier META2.0 product, which was produced by SSALTO/DUACS and distributed by AVISO+ (https://aviso.altimetry.fr, last access: 8 March 2022) with support from CNES, in collaboration with Oregon State University and support from NASA, and based on the Chelton et al. (2011) code. META3.1exp provides supplementary eddy information, such as eddy shapes, eddy edges, maximum speed contours, and mean eddy speed profiles from the center to the periphery. The tracking algorithm is based on overlapping contours, includes virtual observations, and acts as a filter with respect to the shortest trajectories. The absolute dynamic topography (ADT) field is now used for eddy detection, instead of the previous sea level anomaly (SLA) maps, in order to better represent the dynamics in the more energetic oceanic regions and in the vicinity of coasts and islands. To evaluate the impact of the changes from META2.0 to META3.1exp, a comparison methodology has been applied. The similarity coefficient (SC) is based on the ratio of the eddy overlaps to their cumulative area, and allows for extensive comparison of the different datasets in terms of geographic distribution, statistics on the main physical characteristics, changes in the lifetimes of the trajectories, etc. After evaluating the impact of each change separately, we conclude that the major differences between META3.1exp and META2.0 are due to the change in the detection algorithm. META3.1exp contains smaller eddies and trajectories lasting at least 10 d; these were not available in the META2.0 product. Nevertheless, 55 % of the structures in META2.0 are similar to META3.1exp, thereby ensuring continuity between the two products and their physical characteristics. Geographically, the eddy distributions differ mainly in the strong current regions, where the mean dynamic topography (MDT) gradients are sharp. The additional information on the eddy contours allows for more accurate collocation of mesoscale structures with data from other sources, and so META3.1exp is recommended for multi-disciplinary application.

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Section: Introductionmentioning

confidence: 99%

META3.1exp: a new global mesoscale eddy trajectory atlas derived from altimetry

Pegliasco

Delepoulle

Mason

et al. 2022

Earth Syst. Sci. Data

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“…Several previous studies have investigated lifetimes in the context of ocean eddies, for example, Froyland et al [20] first identified a suitable timescale and then carried out a series of FTCS computations on time windows sliding forward in time, Andrade et al [3] exhaustively search a discretised twoparameter space (𝑡, 𝑇) where 𝑡 is the initial time and 𝑇 is the flow duration, using these pairs as variable inputs to many separate LCS computations. El Aouni [14] identifies the timespans of local rotational motion during each Lagrangian trajectory and then defines an eddy as those trajectories that are close at the beginning and the end of their respective timespans.…”

Section: Introductionmentioning

confidence: 99%

Detecting the birth and death of finite‐time coherent sets

Froyland

Koltai

2023

Comm Pure Appl Math

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Finite‐time coherent sets (FTCSs) are distinguished regions of phase space that resist mixing with the surrounding space for some finite period of time; physical manifestations include eddies and vortices in the ocean and atmosphere, respectively. The boundaries of FTCSs are examples of Lagrangian coherent structures (LCSs). The selection of the time duration over which FTCS and LCS computations are made in practice is crucial to their success. If this time is longer than the lifetime of coherence of individual objects then existing methods will fail to detect the shorter‐lived coherence. It is of clear practical interest to determine the full lifetime of coherent objects, but in complicated practical situations, for example a field of ocean eddies with varying lifetimes, this is impossible with existing approaches. Moreover, determining the timing of emergence and destruction of coherent sets is of significant scientific interest. In this work we introduce new constructions to address these issues. The key components are an inflated dynamic Laplace operator and the concept of semi‐material FTCSs. We make strong mathematical connections between the inflated dynamic Laplacian and the standard dynamic Laplacian, showing that the latter arises as a limit of the former. The spectrum and eigenfunctions of the inflated dynamic Laplacian directly provide information on the number, lifetimes, and evolution of coherent sets.

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“…Detailed comparisons show that all Eulerian methods have pros and cons, and none of them is superior to another (Souza et al, 2011;Escudier et al, 2016). Methods based on identifying Lagrangian coherent structures obey a much better mathematical foundation (Haller, 2015;Beron-Vera et al, 2018;Haller et al, 2018;El Aouni, 2021;Ryzhov and Berloff, 2022). However, they are computationally rather demanding and the (relatively low) spatial resolution of the input fields is a challenging aspect of them (Amores et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

“…1. Recent data evaluation of satellite observations suggests that eddy-rich regions exhibit a significant increase in mesoscale variability (thus EKE per unit volume), while the equatorial oceans show a decrease in EKE (Martínez-Moreno et al, 2019, 2021.…”

Section: Introductionmentioning

confidence: 99%

Global coarse-grained mesoscale eddy statistics based on integrated kinetic energy and enstrophy correlations

et al. 2022

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Abstract. Recently, Jánosi et al. (2019) introduced the concept of a “vortex proxy” based on an observation of strong correlations between integrated kinetic energy and integrated enstrophy over a large enough surface area. When mesoscale vortices are assumed to exhibit a Gaussian shape, the two spatial integrals have particularly simple functional forms, and a ratio of them defines an effective radius of a “proxy vortex”. In the original work, the idea was tested over a restricted area in the Californian Current System. Here we extend the analysis to global scale by means of 25 years of AVISO altimetry data covering the (ice-free) global ocean. The results are compared with a global vortex database containing over 64 million mesoscale eddies. We demonstrate that the proxy vortex representation of surface flow fields also works globally and provides a quick and reliable way to obtain coarse-grained vortex statistics. Estimated mean eddy sizes (effective radii) are extracted in very good agreement with the data from the vortex census. Recorded eddy amplitudes are directly used to infer the kinetic energy transported by the mesoscale vortices. The ratio of total and eddy kinetic energies is somewhat higher than found in previous studies. The characteristic westward drift velocities are evaluated by a time-lagged cross-correlation analysis of the kinetic energy fields. While zonal mean drift speeds are in good agreement with vortex trajectory evaluation in the latitude bands 30–5∘ S and 5–30∘ N, discrepancies are exhibited mostly at higher latitudes on both hemispheres. A plausible reason for somewhat different drift velocities obtained by eddy tracking and cross-correlation analysis is the fact that the drift of mesoscale eddies is only one component of the surface flow fields. Rossby wave activities, coherent currents, and other propagating features on the ocean surface apparently contribute to the zonal transport of kinetic energy.

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A hybrid identification and tracking of Lagrangian mesoscale eddies

Cited by 7 publications

References 45 publications

META3.1exp: a new global mesoscale eddy trajectory atlas derived from altimetry

META3.1exp: a new global mesoscale eddy trajectory atlas derived from altimetry

Detecting the birth and death of finite‐time coherent sets

Global coarse-grained mesoscale eddy statistics based on integrated kinetic energy and enstrophy correlations

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