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Buoyancy-Driven Interannual Sea Level Changes in the Tropical South Atlantic

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  • 1 Atmospheric and Environmental Research, Inc., Lexington, Massachusetts
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Abstract

Linear models of dynamical ocean adjustment to wind field changes, local atmospheric driving, and eastern boundary forcing are often invoked to explain observed patterns of interannual regional sea level variability. While skillful in some regions, these processes alone cannot explain low levels of interannual sea level variability observed in the tropical Atlantic. In this study, through a set of modeling approaches, interannual sea level changes in the tropical South Atlantic are attributed and the dynamical influence of buoyancy forcing is elucidated. Similar to recent findings in the southeast tropical Pacific, sea level patterns in the tropical South Atlantic (as estimated from a data-constrained ocean general circulation model) are found to result from the action of both surface wind and buoyancy forcing; in addition to static local effects, the buoyancy-driven changes comprise important nonlocal ocean dynamical processes. It is shown that the buoyancy-driven sea level changes can be understood within the framework of a linear first baroclinic mode Rossby wave model forced by atmospheric fields and variability along the eastern boundary. To lowest order, the linear model framework also reproduces qualitative patterns of basinwide compensation between wind- and buoyancy-driven sea level changes, which are mostly tied to the anticorrelation of both surface and boundary forcing. Results suggest that the ocean’s dynamical adjustment to buoyancy forcing exerts an important influence on interannual sea level changes across all tropical oceans.

Corresponding author address: Christopher G. Piecuch, Atmospheric and Environmental Research, Inc., 131 Hartwell Avenue, Lexington, MA 02421. E-mail: cpiecuch@aer.com

Abstract

Linear models of dynamical ocean adjustment to wind field changes, local atmospheric driving, and eastern boundary forcing are often invoked to explain observed patterns of interannual regional sea level variability. While skillful in some regions, these processes alone cannot explain low levels of interannual sea level variability observed in the tropical Atlantic. In this study, through a set of modeling approaches, interannual sea level changes in the tropical South Atlantic are attributed and the dynamical influence of buoyancy forcing is elucidated. Similar to recent findings in the southeast tropical Pacific, sea level patterns in the tropical South Atlantic (as estimated from a data-constrained ocean general circulation model) are found to result from the action of both surface wind and buoyancy forcing; in addition to static local effects, the buoyancy-driven changes comprise important nonlocal ocean dynamical processes. It is shown that the buoyancy-driven sea level changes can be understood within the framework of a linear first baroclinic mode Rossby wave model forced by atmospheric fields and variability along the eastern boundary. To lowest order, the linear model framework also reproduces qualitative patterns of basinwide compensation between wind- and buoyancy-driven sea level changes, which are mostly tied to the anticorrelation of both surface and boundary forcing. Results suggest that the ocean’s dynamical adjustment to buoyancy forcing exerts an important influence on interannual sea level changes across all tropical oceans.

Corresponding author address: Christopher G. Piecuch, Atmospheric and Environmental Research, Inc., 131 Hartwell Avenue, Lexington, MA 02421. E-mail: cpiecuch@aer.com
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