The Gulf Stream Pathway and the Impacts of the Eddy-Driven Abyssal Circulation and the Deep Western Boundary Current
NAVAL RESEARCH LAB STENNIS SPACE CENTER MS OCEANOGRAPHY DIV
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A hydrodynamic model of the subtropical Atlantic basin and the Intra-Americas Sea 9-47 deg N is used to investigate the dynamics of Gulf Stream separation from the western boundary at Cape Hatteras and its mean pathway to the Grand Banks. The model has five isopycnal Lagrangian layers in the vertical and allows realistic boundary geometry, bathymetry, wind forcing, and a meridional overturning circulation MOC, the latter specified via ports in the northern and southern boundaries. The northward upper ocean branch of the MOC 14 Sv was always included but the southward Deep Western Boundary Current DWBC was excluded in some simulations, allowing investigation of the impacts of the DWBC and the eddy-driven mean abyssal circulation on Gulf Stream separation from the western boundary. The result is resolution dependent with the DWBC playing a crucial role in Gulf Stream separation at 116 deg resolution but with the eddy-driven abyssal circulation alone sufficient to obtain accurate separation at 132 deg resolution and a realistic pathway from Cape Hatteras to the Grand Banks with minimal DWBC impact except southeast of the Grand Banks. The separation from the western boundary is particularly sensitive to the strength of the eddy-driven abyssal circulation. Farther to the east, between 68 deg W and the Grand Banks, all of the 116 deg and 132 deg simulations with realistic topography with or without a DWBC gave similar generally realistic mean pathways with clear impacts of the topographically constrained eddy-driven abyssal circulation versus very unrealistic Gulf Stream pathways between Cape Hatteras and the Grand Banks from otherwise identical simulations run with a flat bottom, in reduced-gravity mode, or with 18 deg resolution and realistic topography.
- Physical and Dynamic Oceanography