Gulf Stream Dynamics: Part I: Mean Flow Dynamics at 73°W

Abstract

During 1984, five current meter moorings measured velocity and temperature in the Gulf Stream anticyclonic flank at a location approximately 250 km downstream of Cape Hatteras. Here, these data are used to analyze the energy budgets of the Gulf Stream mean flow with a view towards examining gulf stream vertical structure and inertial character. We find that Gulf Stream dynamics exhibits considerable vertical structure at our experiment site. At 380 m, the kinetic energy flux appears to be convergent, but the eddies augment mean kinetic energy. Order of magnitude estimates of processes involving vertical velocity appear to be too small to account for this mismatch; hence, we conclude that a conversion of mean kinetic to mean potential energy, via flow up a mean pressure gradient, must be occurring, Opposite tendencies are found at 880 m, leading to conclusion that the Gulf Stream is flowing down a mean pressure gradient at this depth. Evidence supporting a situation similar to the observations in terms of northward shifts of the gyre structure with depth. Of course, our observations are undoubtedly influenced by lateral topography, bottom topography and eddies and the effects of these are poorly understood from a theoretical point of view. We also present evidence that the Deep Western Boundary Current is restoring energy to the deep potential energy field by flow up a mean pressure gradient. The rates are considerably smaller than those in the Gulf Stream but structurally resemble our results at 380 m.