THE SURFACE-TEMPERATURE FIELD AND DYNAMICAL STRUCTURE OF THE ALMERIA-ORAN FRONT FROM SIMULTANEOUS SHIPBOARD AND SATELLITE DATA

A comparative analysis is presented of data sets gathered simultaneous ly from satellite and field measurements during the ''Almofront-1'' cr uise of April-June 1991 in the Almeria-Oran front region of the Wester n Mediterranean. The synoptic fields of temperature, salinity, density and dynamic height are found to be well correlated at depths greater than 50-75 m. All are dominated by strong meridional gradients associa ted with a zonal jet at approximately 35-degrees-45'N flowing eastward from Cape Tres Forcas to Oran. Two regions of anticyclonic vorticity are also observed at these depths, one between the jet and the African coast, and the other to the north, lying off the Spanish coast. The s ynoptic surface parameter fields show strong coupling between the geos trophic velocity fields at the surface and at depth, relatively homoge neous salinity and density fields and a surface temperature field that appears to be unrelated to the other fields. At the position of the z onal jet, the remotely-sensed thermal data show regions of anticycloni c vorticity associated with Cape Tres Forcas, which are anomalously co ol and show evidence of entrainment of warm coastal water in their str ucture. They are also observed to propagate along the African coast du ring the time of the survey. The in situ derived surface temperature f ield, however, is characterized by small scale patchiness. This is con sidered to be due to the time scale over which the data used to compil e this map were gathered. The surface velocity field measured in situ is found to be more closely correlated with the surface temperature fi eld than the dynamic height field. Fine scale comparisons of the in si tu and remotely-sensed temperature fields show them to correlate well, although significant discrepancies were found when the temperature va riations were of small amplitudes and length scales. The theory put fo rward to explain the vertical variations observed is that the weakenin g of the density gradients in the mixed layer leads to the increased d ominance of the boundary layer separation process at Cape Tres Forcas, which leads, in turn, to a lack of coupling between the surface tempe rature and velocity fields and the surface dynamic height field.