Three-dimensional stratified flow over Alarcon Seamount, Gulf of California entrance

In situ hydrographic measurements at the entrance to the Gulf of California (GC) over the Alarcon Seamount (ASM) show that isopycnals and isotherms undulate, being displaced in an upward direction and generating a dome-like structure in the density, temperature and salinity fields, while only small perturbations in both fields are observed longitudinally. On the other hand, some along-gulf observations show an 80-m amplitude internal lee wave. We hypothesize that these perturbations result from the interaction of the mean flow with local topography, which generates internal lee waves as the flow passes over the ASM. Geostrophic velocities over the ASM (at 750 db level) show a meandering jet flow and two associated eddies. A fully three-dimensional boundary-fitted curvilinear ocean model in primitive variables is used to simulate and accurately represent the 3D circulation with high resolution in the neighborhood of the ASM. The simulated flow pattern shows a meandering jet over the topography with increased velocities on the flanks of the ASM. Interaction of current and topography generates a pair of baroclinic eddies similar to those observed during winter over the ASM. The associated density field consists of an upwelling on the upstream side of the seamount, leading to a patch of relatively dense water over the seamount and a downwelling on the lee side leading to a patch of relatively less dense water downstream. (C) 2004 Elsevier Ltd. All rights reserved.