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Article

On the Structure and Kinematics of an Algerian Eddy in the Southwestern Mediterranean Sea

1
NATO Science and Technology Organization, Center for Maritime Research and Experimentation, 19126 La Spezia, Italy
2
Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA
3
Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149, USA
4
Mediterranean Institute for Advanced Studies, Spanish National Research Council and University of Balearic Islands, 07190 Esorles, Spain
5
National Institute of Oceanography and Experimental Geophysics, Oceanography Section, 34010 Sgonico, Italy
*
Author to whom correspondence should be addressed.
Academic Editor: Vladimir N. Kudryavtsev
Remote Sens. 2021, 13(15), 3039; https://doi.org/10.3390/rs13153039
Received: 3 July 2021 / Revised: 23 July 2021 / Accepted: 29 July 2021 / Published: 3 August 2021
An Algerian Eddy, anticyclonic vortex generated by the instability of the Algerian Current in the southwestern Mediterranean Sea, is studied using data provided by drifters (surface currents), Argo floats (temperature and salinity profiles), environmental satellites (absolute dynamic topography maps and ocean color images) and operational oceanography products. The eddy was generated in May 2018 and lasted as an isolated vortex until November 2018. Its morphology and kinematics are described in June–July 2018 when drifters were trapped in its core. During that period, the eddy was slowly moving to the NE (~2 km/day), with an overall diameter of about 200 km (slowly growing with time) and maximal surface swirl velocity of ~50 cm/s at a radius of ~50 km. Geostrophic currents derived from satellite altimetry data compare well with low-pass filtered drifter velocities, with only a slight overestimation, which is expected as its maximum vorticity corresponds to a small Rossby number of ~0.6. Satellite ocean color images and some drifters show that the eddy has an elliptical spiral structure. The looping tracks of the drifters trapped in the eddy were analyzed using two statistical methods: least-squares ellipse fitting and wavelet ridge analysis, revealing a typical eccentricity of about 0.5, a wide range of inclination and a rotation period between 3 and 10 days. Clusters of drifters on the northeastern limb of the eddy were also considered to estimate divergence and vorticity. The results indicate convergence (divergence) and downwelling (upwelling) at scales of 20–50 km near the northeastern (northwestern) edge of the eddy, in agreement with the quasi-geostrophic theory. Vertically, the eddy extends mostly down to 250 m depth, with a warm, low-salinity and low-density signature and with geostrophic currents near 50 cm/s in the top layer (down to ~80 m) reducing to less than 10 cm/s near 250 m. Near the surface, colder water is advected into it. View Full-Text
Keywords: southwestern Mediterranean Sea; Algerian eddy; satellite altimetry; drifters and floats southwestern Mediterranean Sea; Algerian eddy; satellite altimetry; drifters and floats
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MDPI and ACS Style

Poulain, P.-M.; Centurioni, L.; Özgökmen, T.; Tarry, D.; Pascual, A.; Ruiz, S.; Mauri, E.; Menna, M.; Notarstefano, G. On the Structure and Kinematics of an Algerian Eddy in the Southwestern Mediterranean Sea. Remote Sens. 2021, 13, 3039. https://doi.org/10.3390/rs13153039

AMA Style

Poulain P-M, Centurioni L, Özgökmen T, Tarry D, Pascual A, Ruiz S, Mauri E, Menna M, Notarstefano G. On the Structure and Kinematics of an Algerian Eddy in the Southwestern Mediterranean Sea. Remote Sensing. 2021; 13(15):3039. https://doi.org/10.3390/rs13153039

Chicago/Turabian Style

Poulain, Pierre-Marie, Luca Centurioni, Tamay Özgökmen, Daniel Tarry, Ananda Pascual, Simon Ruiz, Elena Mauri, Milena Menna, and Giulio Notarstefano. 2021. "On the Structure and Kinematics of an Algerian Eddy in the Southwestern Mediterranean Sea" Remote Sensing 13, no. 15: 3039. https://doi.org/10.3390/rs13153039

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