Ca. Katsman et al., The interaction of a deep western boundary current and the wind-driven gyres as a cause for low-frequency variability, J PHYS OCEA, 31(8), 2001, pp. 2321-2339
Recent modeling and observational studies have indicated that the interacti
on of the Gulf Stream and the deep western boundary current (DWBC) in the N
orth 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-driv
en circulation using techniques of dynamical systems theory. In an idealize
d 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 timesc
ale.