Upwelling in the Gulf of Lions
Résumé
The hydrological and meteorological characteristics of the Gulf of Lions are such that upwelling occurs with no bias due to tides or strong longshore circulation. The sky is generally cloud-free, an uncommon feature in an upwelling area that allows extensive use of satellite infrared data. The observations are adequate to compute mean maps of the sea-surface temperature during upwelling events. Undoubtedly upwelling is much more intense along straitght coastal segments 10 to 20 km long that near capes and small bays; upwelling locations are mainly related to the coastline shape. The imagery also suggests that the surface circulation varies markedly in space and time; this has been verified by in situ measurements, as has the existence of wind-induced eddies in the surface layer. Satellite images from the largest upwelling regions (nothwest Africa, Oregon, Peru) show similar spatial variability of the sea-surface temperature, but because of the rectilinear coastline, and except for some specific areas characterized by highly variable wind stress or bottom topography, plumes and eddies move slightly alongshore and are not characteristic of a mooring point. The geomorphology of the Gulf of Lions is such that eddies have a fixed location and mean currents are significant. Upwelling studies in such areas might be simplified by the reduction of the perturbations associated with the general circulation and geostrophic trubulence.
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