On the inner-shelf circulation in the northern Gulf of Cádiz, southern Portuguese shelf

A new look at the inner-shelf circulation in the northern Gulf of Cádiz (SW Iberian Peninsula) is taken. Results reveal the introduction of a sharp spatial heterogeneity in the wind field by the coastal geometry around Cape St. Vincent and nearby mountain chains. Direct observations taken in November-December 2001 reveal the alternating nature of the coastal flow along the SW Iberian Peninsula, featuring a sharp current inversion on time scales of less than 2 days. Along-shore gradients of the oceanic wind stress were detected, which may contribute to the coastal circulation patterns in the region. Over the observational period, the sea-level variability in the Gulf of Cádiz is better explained by the action of along-shore winds outside the Gulf, than by local winds. This is confirmed by a scale analysis done on the vertically integrated momentum equation. It is shown that, to a first approximation, the expected behaviour of the inner-shelf flow responds to linear dynamics. In this approximation, the along-shore sea-level slope (∼5cm over 100 km) is the dominant term, overriding the linear (bottom and surface) stress terms. This suggests control by large-scale atmospheric pressure systems, and negligible dynamical influence from local wind stress.