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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, C03038, doi:10.1029/2003JC002048, 2004

Shallow water modeling of Antarctic Bottom Water crossing the equator

Paul F. Choboter

College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon, USA


Gordon E. Swaters

Department of Mathematical and Statistical Sciences, University of Alberta, Edmonton, Alberta, Canada


Abstract

The dynamics of abyssal equator-crossing flows are examined by studying simplified models of the flow in the equatorial region in the context of reduced-gravity shallow water theory. A simple “frictional geostrophic” model for one-layer cross-equatorial flow is described, in which geostrophy is replaced at the equator by frictional flow down the pressure gradient. This model is compared via numerical simulations to the one-layer reduced-gravity shallow water model for flow over realistic equatorial Atlantic Ocean bottom topography. It is argued that nonlinear advection is important at key locations where it permits the current to flow against a pressure gradient, a mechanism absent in the frictional geostrophic model and one of the reasons this model predicts less cross-equatorial flow than the shallow water model under similar conditions. Simulations of the shallow water model with an annually varying mass source reproduce the correct amplitude of observed time variability of cross-equatorial flow. The time evolution of volume transport across specific locations suggests that mass is stored in an equatorial basin, which can reduce the amplitude of time dependence of fluid actually proceeding into the Northern Hemisphere as compared to the amount entering the equatorial basin. Observed time series of temperature data at the equator are shown to be consistent with this hypothesis.

Received 15 July 2003; accepted 21 January 2004; published 24 March 2004.

Index Terms: 4512 Oceanography: Physical: Currents; 4532 Oceanography: Physical: General circulation; 4231 Oceanography: General: Equatorial oceanography.

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Citation: Choboter, P. F., and G. E. Swaters (2004), Shallow water modeling of Antarctic Bottom Water crossing the equator, J. Geophys. Res., 109, C03038, doi:10.1029/2003JC002048.