Abstract
In May 1998 a big and deep open ocean anticyclonic eddy (AE 98-1) was sampled in the Algerian basin (western Mediterranean sea) in a region south of the Balearic islands. Fifteen surface Lagrangian buoys, tracked by satellite, were released across the eddy and were used for a few months to observe the continuity of the anticyclonic motion and the westward drift of the eddy. This kind of big and intense eddies in the Mediterranean can be detected by satellite altimeter radars. Using a new method, based on the Okubo-Weiss criterion, to identify mesoscale eddies in Sea Level Anomaly maps derived from measurements of the ERS and TOPEX/POSEIDON altimeters, an independent tracking of the same eddy was performed. There is a remarkable agreement between the two results despite the different nature of the information, mainly due to the fact that SLA maps contain interpolated and smoothed measurements while the drifter? trajectories are in situ data obtained from individual drifter fixes. The location of the eddy centre during two months with the two methods agrees within an average distance lower than the spatial resolution of the altimetric maps (0.2o). The size of the eddy, when it is possible to determine it, is also highly coincident in both cases (96.5% in diameter), and its average westwards translation speed is reasonably similar (24% lower from drifters). These results can be considered a good validation of the new tracking method in SLA maps in this specific case.
Highlights
The Mediterranean Sea circulation is characterised by the presence of three different scales
Using a new method, based on the Okubo-Weiss criterion, to identify mesoscale eddies in Sea Level Anomaly maps derived from measurements of the ERS and TOPEX/POSEIDON altimeters, an independent tracking of the same eddy was performed
There is a remarkable agreement between the two results despite the different nature of the information, mainly due to the fact that Sea Level Anomaly (SLA) maps contain interpolated and smoothed measurements while the drifters’ trajectories are in situ data obtained from individual drifter fixes
Summary
The Mediterranean Sea circulation is characterised by the presence of three different scales. At a regional scale the different meteorological and topographic characteristics configure specific circulation patTRACKING A MEDITERRANEAN EDDY 331. 1. – The Algerian basin (dashed-dotted line, area as in Fig. 7) in the western Mediterranean Sea. The dotted line indicates the region where the Lagrangian buoys were drifting 5 and 6) and the dashed line the area where the eddy tracking is analysed in this paper As was first pointed out by Millot (1987) from the observation of satellite infrared imagery, an important mesoscale variability gives rise to the generation of meanders, eddies, filaments and other structures that can greatly influence the circulation in some areas. The Algerian Basin, in the south of the western
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