The Interaction of a Deep Western Boundary Current and the Wind-Driven Gyres as a Cause for Low-Frequency Variability

Katsman, Caroline A., Drijfhout, Sybren S. and Dijkstra, Henk A. (2001) The Interaction of a Deep Western Boundary Current and the Wind-Driven Gyres as a Cause for Low-Frequency Variability. Journal of Physical Oceanography, 31 (8), 2321-2339. (doi:10.1175/1520-0485(2001)031<2321:TIOADW>2.0.CO;2).

Abstract

Recent modeling and observational studies have indicated that the interaction of the Gulf Stream and the deep western boundary current (DWBC) in the North Atlantic may induce low-frequency (decadal timescale) variability. To understand the origin of this low-frequency variability, a line of studies is continued here addressing the stability and variability of the wind-driven circulation using techniques of dynamical systems theory. In an idealized quasigeostrophic 2-layer model setup, stationary solutions of the coupled wind-driven gyres/DWBC system are computed, using the lateral friction as control parameter. Simultaneously, their stability is assessed. When a DWBC is absent, only oscillatory instabilities with intermonthly timescales are found. However, when the strength of the DWBC is increased, the coupled 2-layer flow becomes susceptible to instabilities with interannual timescales. By computing transient flows at relatively low friction, it is found that the existence of these interannual modes induces low-frequency variability in the coupled Gulf Stream/DWBC system with a preferred interannual timescale.

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Contributors

Author: Sybren S. Drijfhout

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