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

Abstract

Abstract A new look at the inner-shelf circulation in the northern Gulf of Cadiz (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 Cadiz 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 ( ∼ 5 cm 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.