Seasonal variability of the Algerian/Provençal basin circulation from historical data

The Algerian/Provençal and the Sardinian Channel are regions of intense dynamical processes both in the coastal and in the open ocean areas. The driving mechanisms of some oceanographic structures (surface fronts, underlaying upwelling and downwelling processes) and their response to the atmospheric forcing, which is an important factor for the Western Mediterranean basin dynamics, are not yet well known. By using the MODB (Mediterranean Oceanographic Data Base) historical hydrological data set, we extracted bottle station profiles and obtained mean temperature profiles, mean salinity profiles and high resolution maps where we analysed LIW signal. The analysis of this data set revealed the presence of three LIW branches off the western side of Sardinia, into the Algerian/Provençal basin. The first goes northward after Cape Teulada, the second goes towards the west, south-west off Cape Teulada with an intensity depending on seasonality. The third branch, called Algerian, shows highest salinity and temperature maximum in the subsurface with the possibility of compensation effects in the density equation. The analysis of the data also revealed interesting seasonal dynamics of mixing in the Sardinian Channel and the possibility of horizontal eddy dispersion due to the instability of the LIW current turning northward after Cape Teulada. The space and time scales of the structures will be also assessed from the NASA/JPL long satellite images time series (1982-1994) and from CZCS (Costal Zone Color Scanner) data. The atmospheric forcing parameters are taken from operational analysis of ECMWF (European Centre for Medium Range Weather Forecast). This background information will be useful for future design of operational monitoring networks in the region.