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Ocean Science An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/os-2017-93
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
15 Jan 2018
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Ocean Science (OS).
Mesoscale Eddies in the Algerian Basin: do they differ as a function of their formation site?
Federica Pessini1, Antonio Olita1, Yuri Cotroneo2, and Angelo Perilli1 1IAMC CNR di Oristano, Oristano, Italy
2Università degli Studi di Napoli Parthenope, Napoli, Italy
Abstract. The circulation of the Western Mediterranean Sea (WMED) is dominated by highly variable and heterogeneous mesoscale circulation, strongly driven by the formation and propagation of eddies (cyclonic and anticyclonic) mainly acting in the Algerian Basin. Anticyclones are characterized by longer life, so potentially contributing to a large extent to the mesoscale characterization of the basin. Hereafter we will take into account only anticyclonic structures. In order to investigate the spatial and temporal distribution of eddy generation and their respective paths in the Algerian Basin, the most energetic WMED portion, we use an automated detection and tracking hybrid method (modified to fill the gaps in single eddy tracks) applied to 22 years of Sea Level Anomaly (SLA) data. The method is based on the computation of the Okubo–Weiss parameter in SLA closed loops.

We find that anticyclonic short-life eddies mostly occur in the northern portion of the domain, north of 39° N, along the North Balearic Front (NBF). We refer to all the structures formed in that area as Frontal Anticyclonic Eddies (FAEs). Such short-life eddies are characterized by low translational velocity and a highly variable direction of propagation. We found a weak seasonality in their formation, with maxima in fall and winter. By contrast, anticyclonic longer-life eddies tend to arise in the southern part of the basin, along the Algerian Current, with a clear maximum in spring. All the structures originating along the Algerian Current are known as Algerian Eddies (AEs).

According to previous studies, we observe that AEs mainly form east of 6.5° E and move eastward along the African coast to the Sardinia Channel, where they detach from the coast, continuing offshore and following the cyclonic intermediate circulation. We detect a region where such eddies tend to converge and terminate their life.

Finally, the analysis suggests that the Algerian Basin can be separated in two parts, southern and northern one as function of the eddy properties like formation site, path, number, energy and lifetime. The only connection in terms of eddy tracks between the two areas is represented by a few FAEs moving southward and being entrapped in the southern cyclonic circulation.

Citation: Pessini, F., Olita, A., Cotroneo, Y., and Perilli, A.: Mesoscale Eddies in the Algerian Basin: do they differ as a function of their formation site?, Ocean Sci. Discuss., https://doi.org/10.5194/os-2017-93, in review, 2018.
Federica Pessini et al.
Federica Pessini et al.
Federica Pessini et al.

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Short summary
The Algerian Basin plays a key role in the WMed and in particular the formation and propagation of mesoscale structures strongly influence its circulation. They transport water masses, heat, salts and other properties and also have an impact on chloriphyll and fisheries. We investigated the spatial and temporal distribution of the anticyclones applying a detection and tracking method to altimetry data. The results show mesoscale structures with different origins, behaviours and energies.
The Algerian Basin plays a key role in the WMed and in particular the formation and propagation...
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