Eddies in the Bay of Biscay: A numerical approximation

The results of numerical modelling in the Bay of Biscay have been used to investigate eddy dynamics. The modelling has been carried out using mean climatological and atmospheric forcing as input for hydrodynamic simulations with the ROMS model (Regional Ocean Modeling System). The most significant regional circulation features have been simulated in a mesoscale model configuration, with 6.6 km horizontal resolution. Eddy characteristics (horizontal and vertical structure, origins and migration) have been analysed. During winter, jet-like extensions of the slope current off northern Spain (mainly in the vicinity of Cape Ortegal) and France (near Cap Breton, Cap Ferret and Audierne canyons) developed into anticyclonic and cyclonic eddies, with an upper core of slope water. Most of the eddies identified in the model area were anticyclonic, with diameters at sea surface of between 60 and 130 km and significant effects below 500 m in depth. After their generation, the eddies moved slowly westward, with a mean migration speed of less than 2 cm s−1; they dissipated later in the year in the deep basin of the Bay of Biscay. The mean annual surface kinetic energy, estimated with the model, was around 34 cm2 s−2. Both the kinetic energy and vorticity variability in the study area depend upon changes (magnitude and direction) in the wind stress, which have effects on the development of: the slope poleward current; the Galician upwelling; and the eddy generation and migration.

Research highlights
► ROMS model is used to investigate eddy dynamics in the Bay of Biscay.
► Jet-like extensions of the slope current off northern Spain develop into eddies.
► Most of the eddies identified in the model area are anticyclonic.
► Kinetic energy and vorticity depend upon changes in the wind stress.