Interaction of semidiurnal tide with a continental slope in a continuously stratified ocean

Data gathered during the Gastom 90 cruise in the Bay of Biscay are presented and show evidence of an internal tide of large amplitude (200 m from peak to trough) over the continental slope and the abyssal plain, between 500 and 1500 m in depth near the permanent pycnocline. An interpretation of these observations is investigated by, first, an analytical solution for the 2-D tidal circulation over the slope applied to “flat-bump” topographies (Deep Sea Res. 20 (1973) 197). In a second step, the solution is extended to any slope and stratification conditions with the classical characteristic method and sea-surface conditions. In the third part of the paper, the internal perturbations generated over the slope are propagated toward the plain by a simple matching of baroclinic modes at the shelf break. Data collected during the Gastom 90 cruise and model results are finally compared and show similar features in the localization of energy maxima over the slope and over the plain.