Eddy Tracking From In Situ and Satellite Observations

Creators: Erickson, Zachary K.; Fields, Erik; Johnson, Leah; Thompson, Andrew F.¹; Dove, Lilian A.¹; D'Asaro, Eric; Siegel, David A.

1. California Institute of Technology

Abstract

Mesoscale eddies are a dominant source of spatial variability in the surface ocean and play a major role in the biological marine carbon cycle. Satellite altimetry is often used to locate and track eddies, but this approach is rarely validated against in situ observations. Here we compare measurements of a small (under 25 km radius) mode water anticyclonic eddy over the Porcupine Abyssal Plain in the northeastern Atlantic Ocean using CTD and Acoustic Doppler Current Profiler (ADCP) measurements from three ships, two gliders, two profiling floats, and one Lagrangian float with those derived from sea level anomaly (SLA). In situ estimates of the eddy center were estimated from maps of the thickness of its central isopycnal layer, from ADCP velocities at a reference depth, and from the trajectory of the Lagrangian float. These were compared to three methods using altimetric SLA: one based on maximizing geostrophic rotation, one based on a constant SLA contour, and one which maximizes geostrophic velocity speed along the eddy boundary. All algorithms were used to select CTD profiles that were within the eddy. The in‐situ metrics agreed to 97%. The altimetry metrics showed only a small loss of accuracy, giving >90% agreement with the in situ results. This suggests that current satellite altimetry is adequate for understanding the spatial representation of even relatively small mesoscale eddies.

Copyright and License

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Acknowledgement

The authors would like to gratefully acknowledge the efforts of the captains and crews of the RRS Discovery, RRS James Cook, and R/V Sarmiento de Gamboa, as well as those of the entire EXPORTS science team. This field deployment was funded by the NASA Ocean Biology and Biogeochemistry program and the National Science Foundation Biological and Chemical Oceanography programs. Initial gliders deployments were performed by the RRS Discovery and the authors thank the Porcupine Abyssal Plain – Sustained Observatory of the Natural Environment Research Council (NERC, UK), which is principally funded through the Climate Linked Atlantic Sector Science (CLASS) project supported by NERC National Capability funding (NE/R015953/1) and by IFADO (Innovation in the Framework of the Atlantic Deep Ocean) EAPA_165/2016. Technical assistance with the Slocum glider deployment and quality control was provided by Filipa Carvalho (NOC) and Marine Autonomous Robotic Systems (NOC). Assistance and quality control of the Seagliders was provided by Geoff Shilling (UW) and Craig Lee (UW). Z.K. Erickson would like to thank Scott Martin (UW) for valuable conversations about satellite altimetry products.

Contributions

Author Contributions:

Conceptualization: Zachary K. Erickson, Leah Johnson, Andrew F. Thompson, Eric D’Asaro, David A. Siegel.
Data curation: Zachary K. Erickson, Erik Fields.
Formal analysis: Zachary K. Erickson.
Methodology: Zachary K. Erickson, Erik Fields, Leah Johnson, Andrew F. Thompson, Lilian A. Dove, Eric D’Asaro,
David A. Siegel.
Project Administration: David A. Siegel.
Software: Zachary K. Erickson, Erik Fields.
Validation: Zachary K. Erickson, Eric D’Asaro, David A. Siegel.
Visualization: Zachary K. Erickson.

Data Availability

The in situ data collected by the EXPORTS-NA project can be found at Siegel et al. (2021). Satellite altimetry was provided by Copernicus Climate Change Service (2018), and the META3.2 analysis was provided by AVISO (2022). Code to process ADCP measurements was provided by the University of Hawaii Data Acquisition System (UHDAS) (2021). Figures were made using Matplotlib version 3.7.1 (Hunter, 2007).

Additional Information

This is PMEL Contribution Number 5444.

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