Advances in Coastal Altimetry over the Northwestern Mediterranean
Paolo Cipollini(1) , Stefano Vignudelli(2) , Laurent Roblou(3) , Florent Lyard(4) , Gian Pietro Gasparini(5) , Giuseppe Manzella(6) , and Mario Astraldi(7)
National Oceanography Centre, Southampton,
SO14 3ZH Southampton,
(2) Consiglio Nazionale delle Ricerche, Area della Ricerca CNR S. Cataldo, 56100 Pisa, Italy
(3) UMR CNRS/UPS, 14, Avenue Edouard Belin, F-31400 Toulouse, France
(4) LEGOS/CNRS, 18, Av. Edouard Belin, 31401 Toulouse Cedex 9, France
(5) CNR, Forte Santa Teresa, 19036 Pozzuolo di Lerici, Italy
(6) ENEA CRAM, Forte Santa Teresa, 19036 Pozzuolo di Lerici, Italy
(7) CNR , Forte Santa Teresa, 19036 Pozzuolo di Lerici, Italy
In this paper we describe the motivations and outcomes of 10 years of research into applications of altimetry to the area of the Corsica Channel in the Northwestern Mediterranean. This area is highly relevant from an oceanographic point of view, as the flow through the Channel links the overall circulation in the Ligurian and Tyrrhenian Seas, and its variations and trends play a key role in establishing the ocean dynamics in the two sub-basins.
The research activities had two specific and complementary purposes: a) to contribute to the oceanographic knowledge of the area and b) to assess the applicability of altimeter techniques in coastal/marginal systems. The Corsica Channel is a perfect site for such investigations, in virtue of the favourable location of altimetric tracks and cross-over points, combined with the availability of long-term in-situ observations from a number of instruments including currentmeters, tide gauges and bottom pressure recorders. As such, it has been chosen as a site of cal/val activities and hydrographic campaigns in the framework of the joint French-Italian ALBICOCCA (ALtimeter-Based Investigations in COrsica, Capraia and Contiguous Areas) project.
One important oceanographic issue that has been addressed with the help of altimetry is what drives the flow along the channel, which exhibits a marked seasonal and interannual variability. We describe how along-track Topex/Poseidon (T/P) data have confirmed that the contribution of the steric level difference between the two interconnected basins is predominant.
A significant part of the research activity has been devoted to assessing the extent to which altimetry data can be applied in the area, and devising any possible improvement in the data processing chain and in the retrieval of the geophysical parameters, which may increase the applicability of altimetry in coastal seas. A comparison between XBT data and T/P altimetry shows that the altimeter is capable to detect the overall spatial and seasonal pattern seen in the circulation; an ad hoc processing strategy based on local corrections has been attempted and the results compared against in situ sea level anomalies and surface velocity anomalies from moorings, showing a good level of agreement. We conclude by discussing further improvements on the processing scheme, including the use of 20 Hz data, which should allow a better match between altimetric and in situ observations, and hopefully promote the 15-year sea surface height from altimetry to the rank of operational record for the coastal areas.