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Keywords: current; channel of Sardinia; PRIMO-1.

The channel of Sardinia is one of the less-known areas of the Western Mediterranean sea. The paths of the Levantine Intermediate Water ŽLIW., the Tyrrhenian Dense Water ŽTDW. and the Western Mediterranean Deep Water ŽWMDW. mainly, in this wide passage, are still debated. Two major aims of the PRIMO-1 ŽProgramme de Recherche International en Mediterrane ́e Occidentale. experiment were to specify the mean circulation paths of these intermediate and deep waters there and to verify hypotheses about the migration of mesoscale eddies from Algeria to Sardinia and their effect on the circulation paths of all the water masses. Despite an important loss of moored instruments, current time series have been collected from November 1993 to October 1994 at four different locations and two CTD cross-sections have been performed. Current meters on the Sardinian slope indicate, during 1 year, an almost permanent alongslope flow toward the northwest in the intermediate and deep layers. Currents recorded on the African slope are always directed alongslope eastward down to 2500 m. Coherently, in the mid-western part of the channel, the bottom flow is northward along the isobaths, while the 200-m flow is southward due to the influence of anticyclonic eddies. At the bottom in the central part of the channel, the current is low and changing: episodes of northeast current along the orientation of the deepest channel axis alternate with westward flows. No seasonal variations have been clearly detected, but the mesoscale variability is large and has a deep signature in the western part of the channel.

The objective of this work is to evaluate the patterns of the ocean-atmosphere coupling in the Mediterranean sea using the statistical analysis of the time series of the three satellite measured variables: wind stress curl computed from the surface wind velocities measured by the European Remote Sensing Satellite-ERS1, sea level anomalies from the emerged ERS1-TOPEX/POSEIDON altimetric data and the sea surface temperature from the NOAA/NASA Pathfinder AVRR Oceans Project. This study examines the ocean-atmosphere coupling patterns in time and space through a canonical correlation analysis of the fields. The wide and exhaustive coverage of the oceanic and atmospheric fields from satellites (such as TOPEX/POSEIDON and ERS1) allow a potential detailed inspection of the coupling. In this study we assess the role of the wind stress and/or sea surface temperature space/time variations as forcing mechanisms of the sea level variability for the total 440 day duration (from October 1992 to December 1993) of the three satellite data sets in the different Mediterranean sub-basins. The linear barotropic vorticity equation is computed in order to estimate id the Mediterranean Sea level response to wind forcing is barotropic. Results indicate that except for the Strait of Sicily and the Adriatic Sea the barotropic response is not dominant. From the canonical correlation analysis, a correlation of 0.57 for the first mode between the sea level anomaly and the wind stress curl indicates a significant local coupling between them, especially in areas of the Eastern Mediterranean. Two uncoupled annual cycles are found in the sea surface temperature data.

The circulation and upwelling processes that control the phytoplankton distribution in the Alboran sea (western Mediterranean) are examined from a climatological perspective for the first time. To characterize the annual cycle of the near-surface phytoplankton patterns, we analyze the monthly distributions of pigments from the Coastal Zone Color Scanner (CZCS). Two regimes occur: a fall-to-winter bloom occurs. The newest ocean color data set available today from the Sea-viewing Wide Field-of-view Sensor (SeaWiFs) and the Ocean Color and Temperature Scanner (OCTS) fall within this annual progression. The combined interaction of seasonal stratification, coastal and gyre-induced upwelling, and horizontal advection control the near-surface pigment distribution in Alboran, while light availability does not determine the seasonal cycle of pigments.

Straits in the Mediterranean Sea form an important network from which one can determine the characteristics of the water exchange between all the constituent sub-basins. This includes the definition of water masses and water transport and their time variability. From 1994, all the major straits in the Mediterranean Sea (Gibraltar, Sicily, Otranto, Balearic Sea Straits, Cretan Arc Straits and Corsica) were subject to long term observations as part of various research projects. Besides adding new elements to the knowledge of internal strait conditions, the data sets collected allow us to propose a fairly consistent representation of the Mediter- ranean circulation and budgets in key points within the basin. The amplitude of the annual water transport measured at these straits was about 1 Sv and it appears to be modulated by a significant low-frequency and seasonal variability. For the first time, a seasonal component was identified at Gibraltar, thus raising new questions on the actual state of the Mediterranean. Also, the very likely existence of a significant interannual component was documented. In the Corsica Channel, this component was found to be related to the interannual variability of the North Atlantic Oscillation. The observations in the Cretan Arc Straits have provided a more comprehensive representation of the recent changes in the Eastern Mediterranean thermohaline cell. It is noteworthy that the effects of these changes have been observed both in the Otranto and Sicily Straits, and are now affecting the adjacent sea regions. The presence of a stream of Modified Atlantic Water in the Balearic Sea Channels indicates that part of the Atlantic inflow may be diverted directly into the northern region of the Western Mediterranean. Finally, data gathered in the Sardinia Channel indicate that the central Mediterranean region plays a critical role in controlling exchanges between the Eastern and the Western Mediterranean, while it is emphasized that the Tyrrhenian Sea area plays a role in strongly modifying some of the water masses that contribute to the large scale basin circulation. Their mixing creates new water types which modify the currently known pattern and composition of the Mediter- ranean circulation.

The Mediterranean Sea has been investigated intensively since the early nineties, using modern techniques and collaborative approaches. This overview summarizes some of the resulting advances that were made concerning the physical oceanography of the western Medit- erranean. The water mass formation processes are now much better understood and have been quantified to a large extent. The boundary conditions of the system in terms of surface fluxes and strait transports can be determined with improved accuracy, thus enabling future investi- gation of interannual variability. The dynamics of the surface and intermediate layers have revealed a variety of eddy and mesoscale processes that are important for the circulation and spreading of water masses. The deep circulation is being investigated with Lagrangian tech- niques (tracers and floats). First results show a large component of the deep water originating from the Tyrrhenian Sea and intense cyclonic and anticyclonic eddy flows.

SMOS, a European satellite mission, will provide for the first time global coverage of Sea Salinity for climàtic and general circulation studies from year 2005. The measurement will be done by low frequency microwave radiometry, and the data are expected to have a resolution similar to the standard climatilogies presently used for other ocean variables

This paper addresses the problem of motion estimation in sequences of remotely sensed images of the sea. When the temporal sampling period is low the estimation of the velocity field can be done by finding the correspondence between structures detected in the images. The scale space aproximation of these structures using the wavelet multiressolution is presented. The correspondence is solved using a simulated annealing technique which assures the convergence to high quality solutions.