Variability of the MAW vein branching, in the Central Mediterranean, estimated by altimetric data
Institut National Agronomique de Tunisie,
43, Avenue Charles Nicolle,
1082 Tunis- Mahrajene,
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.
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