Enduring Lagrangian coherence of a Loop Current ring assessed using independent observations

Area of Science:

• Oceanography
• Fluid Dynamics
• Dynamical Systems Theory

Background:

• Ocean currents are typically inferred from satellite altimetry, assuming geostrophic balance.
• Nonlinear dynamical systems reveal mesoscale eddies with persistent material boundaries, suggesting effective transport.
• Limitations in resolving submesoscale motions by altimetry may impede observed Lagrangian coherence.

Purpose of the Study:

• To provide observational evidence of enduring Lagrangian coherence in a Loop Current ring.
• To assess if data-assimilative models can reproduce observed Lagrangian coherence.
• To highlight the importance of Lagrangian metrics in evaluating ocean model performance.

Main Methods:

• Utilized combined satellite ocean color and surface drifter trajectory data.
• Analyzed a Loop Current ring detected via altimetry.
• Evaluated a data-assimilative model's simulated flow, including altimetry-emulating subsampling.

Main Results:

• Observed enduring Lagrangian coherence in a Loop Current ring using combined datasets.
• The data-assimilative model, despite reproducing dispersion statistics, failed to capture the observed long-lasting Lagrangian coherence.
• Simulated flows did not exhibit the same coherence as the observed ring.

Conclusions:

• The study provides observational evidence for long-lasting Lagrangian coherence in an ocean eddy.
• Current data-assimilative models may not fully capture complex coherent structures in ocean flows.
• Lagrangian coherence metrics are crucial for assessing the performance of ocean circulation models.