scholarly journals Detecting and tracking eddies in oceanic flow fields: A vorticity based Euler-Lagrangian method

2016 ◽  
Author(s):  
Rahel Vortmeyer-Kley ◽  
Ulf Gräwe ◽  
Ulrike Feudel
Keyword(s):  
Fixed Point ◽  
Coherent Structures ◽  
Flow Fields ◽  
Lagrangian Method ◽  
Velocity Fields ◽  
Vortex Street ◽  
Lagrangian Coherent Structures ◽  
Convection Flow ◽  
Synthetic Vortex ◽  
Eddy Detection

Abstract. Since eddies play a major role in the dynamics of oceanic flows, it is of great interest to detect them and gain information about their tracks, their lifetimes and their shapes. We develop a vorticity based heuristic Euler-Lagrangian descriptor utilizing the idea of Lagrangian coherent structures. In our approach we define an eddy as a region around an elliptic fixed point (eddy core) surrounded by manifolds (eddy boundaries). We test the performance of an eddy tracking tool based on this Euler-Lagrangian descriptor using an convection flow of four eddies, a synthetic vortex street and an eddy seeded model. The results for eddy lifetime and eddy shape are compared to the results obtained with the Okubo-Weiss parameter, the modulus of vorticity and an eddy tracking tool used in oceanography. We show that the Euler-Lagrangian descriptor estimates lifetimes closer to the analytical results than any other method. Furthermore we demonstrate that eddy tracking based on this descriptor is robust with respect to certain types of noise which makes it a suitable tool for eddy detection in velocity fields obtained from observation.

scholarly journals Detecting and tracking eddies in oceanic flow fields: a Lagrangian descriptor based on the modulus of vorticity

2016 ◽  
Vol 23 (4) ◽  
pp. 159-173 ◽  
Author(s):  
Rahel Vortmeyer-Kley ◽  
Ulf Gräwe ◽  
Ulrike Feudel
Keyword(s):  
Velocity Field ◽  
Baltic Sea ◽  
Local Maximum ◽  
Velocity Fields ◽  
Vortex Street ◽  
Suitable Method ◽  
Convection Flow ◽  
Hyperbolic Trajectories ◽  
Synthetic Vortex ◽  
Eddy Detection

Abstract. Since eddies play a major role in the dynamics of oceanic flows, it is of great interest to detect them and gain information about their tracks, their lifetimes and their shapes. We present a Lagrangian descriptor based on the modulus of vorticity to construct an eddy tracking tool. In our approach we denote an eddy as a rotating region in the flow possessing an eddy core corresponding to a local maximum of the Lagrangian descriptor and enclosed by pieces of manifolds of distinguished hyperbolic trajectories (eddy boundary). We test the performance of the eddy tracking tool based on this Lagrangian descriptor using an convection flow of four eddies, a synthetic vortex street and a velocity field of the western Baltic Sea. The results for eddy lifetime and eddy shape are compared to the results obtained with the Okubo–Weiss parameter, the modulus of vorticity and an eddy tracking tool used in oceanography. We show that the vorticity-based Lagrangian descriptor estimates lifetimes closer to the analytical results than any other method. Furthermore we demonstrate that eddy tracking based on this descriptor is robust with respect to certain types of noise, which makes it a suitable method for eddy detection in velocity fields obtained from observation.

Persistency of debris accumulation in tidal estuaries using Lagrangian coherent structures

2021 ◽  
pp. 146808
Author(s):  
Anusmriti Ghosh ◽  
Kabir Suara ◽  
Scott W. McCue ◽  
Yingying Yu ◽  
Tarmo Soomere ◽  
...  
Keyword(s):  
Coherent Structures ◽  
Lagrangian Coherent Structures ◽  
Debris Accumulation ◽  
Tidal Estuaries

Lagrangian coherent structures deduced from HF radar measurements

2015 ◽  
Author(s):  
Francesco Enrile ◽  
Giovanni Besio ◽  
Marcello G. Magaldi ◽  
Carlo Mantovani ◽  
Simone Cosoli ◽  
...  
Keyword(s):  
Coherent Structures ◽  
Hf Radar ◽  
Lagrangian Coherent Structures ◽  
Radar Measurements

scholarly journals Fine-scale structures as spots of increased fish concentration in the open ocean

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Alberto Baudena ◽  
Enrico Ser-Giacomi ◽  
Donatella D’Onofrio ◽  
Xavier Capet ◽  
Cedric Cotté ◽  
...  
Keyword(s):  
Coherent Structures ◽  
Trophic Levels ◽  
Fish Distribution ◽  
Lagrangian Coherent Structures ◽  
Mesopelagic Fish ◽  
Fine Scale ◽  
Conservation Policies ◽  
Top Predators ◽  
Frontal Zones ◽  
Spatio Temporal

AbstractOceanic frontal zones have been shown to deeply influence the distribution of primary producers and, at the other extreme of the trophic web, top predators. However, the relationship between these structures and intermediate trophic levels is much more obscure. In this paper we address this knowledge gap by comparing acoustic measurements of mesopelagic fish concentrations to satellite-derived fine-scale Lagrangian Coherent Structures in the Indian sector of the Southern Ocean. First, we demonstrate that higher fish concentrations occur more frequently in correspondence with strong Lagrangian Coherent Structures. Secondly, we illustrate that, while increased fish densities are more likely to be observed over these structures, the presence of a fine-scale feature does not imply a concomitant fish accumulation, as other factors affect fish distribution. Thirdly, we show that, when only chlorophyll-rich waters are considered, front intensity modulates significantly more the local fish concentration. Finally, we discuss a model representing fish movement along Lagrangian features, specifically built for mid-trophic levels. Its results, obtained with realistic parameters, are qualitatively consistent with the observations and the spatio-temporal scales analysed. Overall, these findings may help to integrate intermediate trophic levels in trophic models, which can ultimately support management and conservation policies.

Lower thermospheric material transport via Lagrangian coherent structures

2021 ◽  
Author(s):  
S. Datta‐Barua ◽  
N. Pedatella ◽  
K. R. Greer ◽  
N. Wang ◽  
L. Nutter ◽  
...  
Keyword(s):  
Coherent Structures ◽  
Lagrangian Coherent Structures ◽  
Material Transport
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