Publication details.


Author(s):P.-M. Poulain, L. Centurioni, T. Özgökmen, D. Tarry, A. Pascual, S. Ruiz, E. Mauri, M. Menna, G. Notarstefano
Title:On the Structure and Kinematics of an Algerian Eddy in the Southwestern Mediterranean Sea
Journal:Remote Sensing

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.

Related staff

  • Ananda Pascual Ascaso
  • Simón Ruiz Valero
  • Daniel Rodriguez Tarry
  • Related departments

  • Oceanography and Global Change
  • Related projects

  • WHOI (139.8)
  • Related research groups

  • Marine Technologies, Operational and Coastal Oceanography