Surface currents in the Bay of Biscay as observed with drifters between 1995 and 1999

From 1995 to 1998 25 shallow drogued WOCE/TOGA surface drifters were deployed in the Bay of Biscay. The current velocity in the Bay of Biscay, derived from these drifters, has been analyzed for its long-term seasonal mean, meso-scale and high-frequency characteristics. Over the abyssal plain the kinetic energy of the high-frequency surface velocity (∼150 cm2/s2) is about 3.5 time the kinetic energy contributed by meso-scale eddies (∼42 cm2/s2). The eddies are mainly anti-cyclonic, with a typical diameter of about 45 km. In the centre of the eddies the magnitude of the relative vorticity amounts to several tenths of the planetary vorticity. The seasonal mean flow over the abyssal plain shows a magnitude (1.5–2 cm/s) and a direction in agreement with the seasonal mean wind-driven Ekman drift. Over the continental slope a stronger, poleward slope current is observed in winter (∼5 cm/s). This slope current is apparently divergent, in agreement with feeding of the slope current from the interior of the ocean. In summer the slope current appears to be absent or equatorward.