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High frequency (HF) radar stations have been working operationally in the southeastern part of the Bay of Biscay since 2009. The (2) systems provide hourly surface currents, with 5 km spatial resolution and a radial coverage lying close to 180 km. The detailed and quantitative description of the spatial patterns observed by the HF radar offers new evidence on the main ocean processes, at different time scales, affecting a study area where surface currents show marked temporal and spatial variability. A clear seasonality in terms of sea surface currents and along-slope circulation is observed, with cyclonic and anticyclonic patterns during the winter and summer months, respectively. From the analysis of low-pass filtered currents, a key component of this seasonal variability is associated with the surface signature of the slope current (Iberian Poleward Current (IPC)). Clearly intensified over the upper part of the slope, this current circulates eastward off the Spanish coast and northward over the French shelves in winter. Highlights A seasonality in terms of sea surface current and along slope circulation is observed. ► Cyclonic and anticyclonic patterns are observed during winter and summer months. ► Surface signature of the slope current contributes to the seasonal variability. ► The presence of mesoscale structures in the area is reported. ► Globally, inertial currents represent 10 to 40% of the total variability.

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