Author(s)

G. E. Swaters

Abstract

Deep western boundary currents are an important component of the thermohaline circulation in the ocean, which plays a dominant role in Earth’s evolving climate. By exploiting the underlying Hamiltonian structure, sufficient stability (and hence necessary instability) conditions are derived for meridionally-flowing grounded abyssal currents, based on a baroclinic model corresponding to a low frequency limit of the three-layer shallow water equations on a β-plane with variable topography. Keywords: abyssal overflows, deep western boundary currents, meridional overturning circulation, baroclinic instability, climate dynamics. 1 Introduction In a source region of deep water formation, the Sverdrup vorticity balance predicts equatorward abyssal flow (Stommel and Arons [1]). Away from the source region, Stommel-Arons theory cannot infer the flow direction of abyssal currents. However, many abyssal currents are characterized by the isopycnal field being grounded against sloping topography and the flow being in geostrophic balance. As shown by Nof [2], a fully grounded abyssal water mass lying over sloping topography flows, in the fully nonlinear but reduced gravity dynamical limit, nondispersively and steadily in the along slope direction, irrespective of the specific height or vorticity field within the abyssal water mass. These two results provide a dynamical scenario for the initiation and maintenance of source-driven grounded abyssal flow. That is, in high latitude regions

Keywords

abyssal overflows, deep western boundary currents, meridional overturning circulation, baroclinic instability, climate dynamics.