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Variability of the MAW vein branching, in the Central Mediterranean, estimated by altimetric data

Slim Gana(1)

(1) Institut National Agronomique de Tunisie, 43, Avenue Charles Nicolle, 1082 Tunis- Mahrajene, Tunisia

Abstract

Three years of JASON-1 altimetric data (2002-2004) are analysed to shed lights on spatio-temporal variability of mesoscale structures that occurs in the Central Mediterranean, off the Tunisian coasts. This region is considered as a key area for the whole Mediterranean Sea dynamics (Astraldi, 1999). It includes the Sardinia Channel, the Strait of Sicily and the Gulf of Gabes, particularly known for the relatively high amplitude of its tides. In this study, attention is specially paid to the branching of the Modified Atlantic Water (MAW) vein, east of the Sardinia Channel. The classical scheme of the circulation is this area (called T2S: Tunisia- Sardinia-Sicily) consists on the separation of this MAW vein into two branches: one is flowing northward into the Tyrrhenian Sea, the other is crossing the Sicily Strait to flow into the Eastern Mediterranean (Astraldi et al., 1996, Herbaut et al., 1998). The latter branch is variable in time and space and seems to be itself subject to additional branching. Recent studies (Lermussiaux and Robinson, 2001, Molcard et al., 2002, Mercator Group) are often referring to two sub-branches: the Atlantic Tunisian Current (ATC) flowing along the Tunisian shelf and the Atlantic Ionian Stream (AIS) reaching the Sicilian shelf, north of Malta, and then flowing towards the Ionian Sea. However, because the lack of a dedicated monitoring, several questions remains concerning the dynamical behaviour, the path, the spatial extension, the temporal scale involved in the variability of these two branches, that, furthermore, have not been pointed out in previous studies using altimetric data (Ayoub et al., 1998, Larnicol et al., 2002). We show that JASON1 along-tracks Sea Level Anomaly data are very suitable to address some of these remaining questions, especially concerning the ATC and the AIS. The analysis allows us to obtain a more accurate identification of these mesoscale structures, a quantification of the branches strength, variability and spatial extension and to suggest some hypothesis on the dynamical equilibrium involved in.

References

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                 Last modified: 07.10.03