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Low-Latitude Circulation and Mass Transport Pathways in a Model of the Tropical Atlantic Ocean

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  • 1 Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts
  • | 2 Division of Meteorology and Physical Oceanography, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida
  • | 3 Ocean Dynamics and Prediction Branch, Naval Research Laboratory, Stennis Space Center, Mississippi
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Abstract

An eddy-resolving numerical ocean circulation model is used to investigate the pathways of low-latitude intergyre mass transport associated with the upper limb of the Atlantic meridional overturning cell (MOC). Numerical experiments with and without applied wind stress and an imposed MOC exhibit significant differences in intergyre transport, western boundary current intensity, and mesoscale ring production. The character of interaction between low-latitude wind- and overturning-driven circulation systems is found to be predominantly a linear superposition in the annual mean, even though nonlinearity in the form of diapycnal transport is essential to some segments of the mean pathway. Within a mesoscale band of 10–100 day period, significant nonlinear enhancement of near-surface variability is observed. In a realistically forced model experiment, a 14 Sv upper-ocean MOC return flow is partitioned among three pathways connecting the equatorial and tropical wind-driven gyres. A frictional western boundary current with both surface and intermediate depth components is the dominant pathway and accounts for 6.8 Sv of intergyre transport. A diapycnal pathway involving wind-forced equatorial upwelling and interior Ekman transport is responsible for 4.2 Sv. Translating North Brazil Current rings contribute approximately 3.0 Sv of intergyre transport.

Corresponding author address: Dr. David M. Fratantoni, Woods Hole Oceanographic Institution, Woods Hole, MA 02543.

Email: dfratantoni@whoi.edu

Abstract

An eddy-resolving numerical ocean circulation model is used to investigate the pathways of low-latitude intergyre mass transport associated with the upper limb of the Atlantic meridional overturning cell (MOC). Numerical experiments with and without applied wind stress and an imposed MOC exhibit significant differences in intergyre transport, western boundary current intensity, and mesoscale ring production. The character of interaction between low-latitude wind- and overturning-driven circulation systems is found to be predominantly a linear superposition in the annual mean, even though nonlinearity in the form of diapycnal transport is essential to some segments of the mean pathway. Within a mesoscale band of 10–100 day period, significant nonlinear enhancement of near-surface variability is observed. In a realistically forced model experiment, a 14 Sv upper-ocean MOC return flow is partitioned among three pathways connecting the equatorial and tropical wind-driven gyres. A frictional western boundary current with both surface and intermediate depth components is the dominant pathway and accounts for 6.8 Sv of intergyre transport. A diapycnal pathway involving wind-forced equatorial upwelling and interior Ekman transport is responsible for 4.2 Sv. Translating North Brazil Current rings contribute approximately 3.0 Sv of intergyre transport.

Corresponding author address: Dr. David M. Fratantoni, Woods Hole Oceanographic Institution, Woods Hole, MA 02543.

Email: dfratantoni@whoi.edu

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