Vertical structure of tidal currents over Espartel and Camarinal sills, Strait of Gibraltar

Abstract

ADCP velocity data collected in the two main sills of the Strait of Gibraltar (Camarinal and Espartel sills) have been used for analysing the vertical structure of main tidal constituents (M 2, S 2, O 1 and K 1) currents in this area. Two different periods (winter and summer) were considered in correspondence to seasonal variations in density profiles. Amplitudes and phases of the various tidal constituents have been compared for both periods and locations. Barotropic and baroclinic parts of the tidal currents have been extracted using the dynamical mode decomposition technique and the relative importance of each mode has been established in terms on the energy associated. In Espartel sill, the barotropic mode is more energetic in wintertime for all constituents except for K 1. Baroclinic modes have smaller contribution to total energy. Second and third baroclinic modes tend to be more energetic than the first one, especially during winter, this indicating a relatively complex vertical structure of the tidal currents. Over Camarinal sill, barotropic mode accounts for more than 90% of total energy in all the tidal constituents, the highest value (97%) observed for M 2.