Eddy Detection in HF Radar-Derived Surface Currents in the Gulf of Naples
Abstract
:1. Introduction
2. Materials
2.1. Dataset
2.2. Dynamical Parameters Characterizing Recirculations
2.2.1. Okubo–Weiss and Local Okubo–Weiss Parameters
2.2.2. Local Normalized Angular Momentum and Momentum Flux Fields
3. Methods
3.1. Eddy Detection Algorithms
3.2. Ameda
- 1.
- Identifies grid points which are local extrema of satisfying and , for a chosen threshold ;
- 2.
- Verifies the existence of at least one closed streamline around each extremum.
- 2’.
- Confirms that the velocity field constantly rotates along the perimeter of the square domain of edge and centered at the extremum, for a chosen distance b.
3.3. Neal
- 1.
- Identifies couples of adjacent grid points such that the meridional component of the velocity field changes sign going westward along the zonal segment of length , centered at , and increases its magnitude away from this point. This computation also provides the expected sign of rotation;
- 2.
- Verifies that, at any such grid point , the zonal component of the velocity field changes sign going northward along the meridional segment of length , centered at , and increases its magnitude away from this point. This change must be compatible with the expected rotation;
- 3.
- Identifies the (kinetic energy) local minima inside a square domain of edge , centered at , which are global minima in a square neighborhood of the same size;
- 4.
- Confirms that the velocity field constantly rotates along the perimeter .
3.4. Yada
- 1.
- Identifies the local extrema of a dynamical field like , or ;
- 2.
- Analyzes the streamline geometry within some neighborhood of each extremum, ensuring the existence of either bounded hyperbolic orbits (characterizing eddies with sink-like cores) or elliptic orbits (in presence of eddies having stable orbits).
3.5. Tuning Strategy
4. Results
4.1. Ameda Tuning and Results
- 3.
- Discards those extrema satisfying .
4.2. Neal Tuning and Results
4.3. Yada Tuning and Results
- (1)
- The end points belong to the square domain (that is: they stay away from the boundary of the reference domain);
- (2)
- Each streamline completes at least one revolution.
4.4. Eddy Boundaries
4.4.1. Sink-Like Cores
4.4.2. Eddies Having Elliptic Orbits
5. Discussion
5.1. Detected Eddies
5.2. Equivalent Radii
5.3. Spatial Distribution
6. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
Appendix A. the Hausdorff Distance
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Bagaglini, L.; Falco, P.; Zambianchi, E. Eddy Detection in HF Radar-Derived Surface Currents in the Gulf of Naples. Remote Sens. 2020, 12, 97. https://doi.org/10.3390/rs12010097
Bagaglini L, Falco P, Zambianchi E. Eddy Detection in HF Radar-Derived Surface Currents in the Gulf of Naples. Remote Sensing. 2020; 12(1):97. https://doi.org/10.3390/rs12010097
Chicago/Turabian StyleBagaglini, Leonardo, Pierpaolo Falco, and Enrico Zambianchi. 2020. "Eddy Detection in HF Radar-Derived Surface Currents in the Gulf of Naples" Remote Sensing 12, no. 1: 97. https://doi.org/10.3390/rs12010097