Comparison between Eulerian diagnostics and finite-size Lyapunov exponents computed from altimetry in the Algerian basin

Abstract

Transport and mixing properties of surface currents can be detected from altimetric data by both Eulerian and Lagrangian diagnostics. In contrast with Eulerian diagnostics, Lagrangian tools like the local Lyapunov exponents have the advantage of exploiting both spatial and temporal variability of the velocity field and are in principle able to unveil subgrid filaments generated by chaotic stirring. However, one may wonder whether this theoretical advantage is of practical interest in real-data, mesoscale and submesoscale analysis, because of the uncertainties and resolution of altimetric products, and the non-passive nature of biogeochemical tracers. Here we compare the ability of standard Eulerian diagnostics and the finite-size Lyapunov exponent in detecting instantaneaous and climatological transport and mixing properties. By comparing with sea-surface temperature patterns, we find that the two diagnostics provide similar results for slowly evolving eddies like the first Alboran gyre. However, the Lyapunov exponent is also able to predict the (sub-)mesoscale filamentary process occuring along the Algerian current and above the Balearic Abyssal Plain. Such filaments are also observed, with some mismatch, in sea-surface temperature patterns. Climatologies of Lyapunov exponents do not show any compact relation with other Eulerian diagnostics, unveiling a different structure even at the basin scale. We conclude that filamentation dynamics can be detected by reprocessing available altimetric data with Lagrangian tools, giving insight into (sub-)mesoscale stirring processes relevant to tracer observations and complementing traditional Eulerian diagnostics.

References in corpus (7)

• Predictability in the large: an extension of the concept of Lyapunov exponent
• Mixing structures in the Mediterranean Sea from Finite-Size Lyapunov Exponents
• Dispersion of passive tracers in closed basins: beyond the diffusion coefficient
• Detecting barriers to transport: A review of different techniques
• Chaotic stirring by a mesoscale surface-ocean flow
• Chaotic advection of reacting substances: Plankton dynamics on a meandering jet
• Leaking method approach to surface transport in the Mediterranean Sea from a numerical ocean model

Cited by in corpus (19)

• Top marine predators track Lagrangian coherent structures
• How reliable are Finite-Size Lyapunov Exponents for the assessment of ocean dynamics?
• Boundaries of the Peruvian Oxygen Minimum Zone shaped by coherent mesoscale dynamics
• Lagrangian study of transport and mixing in a mesoscale eddy street
• Oceanic three-dimensional Lagrangian Coherent Structures: A study of a mesoscale eddy in the Benguela ocean region
• Submesoscale circulation in the Northern Gulf of Mexico: Deep phenomena and dispersion over the continental slope
• Seasonal and regional characterization of horizontal stirring in the global ocean
• The reduction of plankton biomass induced by mesoscale stirring: a modeling study in the Benguela upwelling
• The Lagrangian description of aperiodic flows: a case study of the Kuroshio Current
• Characterization of coherent structures in three-dimensional flows using the finite-size Lyapunov exponent
• Characterization of the structure and cross-shore transport properties of a coastal upwelling filament using three-dimensional finite-size Lyapunov exponents
• New Lagrangian diagnostics for characterizing fluid flow mixing
• Lagrangian coherent structures in nonlinear dynamos
• Impact of mesoscale eddies on water transport between the Pacific Ocean and the Bering Sea
• Lagrangian transport in a microtidal coastal area: the Bay of Palma, island of Mallorca, Spain
• Lagrangian surface signatures reveal upper-ocean vertical displacement conduits near oceanic density fronts
• Three dimensional chaotic advection by mixed layer baroclinic instabilities
• On finite-size Lyapunov exponents in multiscale systems
• Identifying Lagrangian fronts with favourable fishery conditions