The region where the Deep Western Boundary Current (DWBC) crosses underneath the Gulf Stream, near its separation point at Cape Hatteras, is a source for natural variability for the North Atlantic Ocean. Both observations and modelling studies have shown that the flow in this region is complicated, due to the strong interactions between the surface currents and the deeper undercurrent.
The question arises whether the observed variability can be explained by internal ocean dynamics related to the presence of the Deep Western Boundary Current. In particular, one can ask whether the flow becomes unstable due to growing perturbations which are linked directly to the presence of the DWBC, or if the variability arises due to instabilities of the surface flow which exist without the DWBC and are only modified by its presence.
This question is addressed by studying the internal variability of a wind-driven flow, for varying amplitudes of both the surface wind forcing which drives the model equivalent of the Gulf Stream, as well as for varying strength of the DWBC. The stationary solutions for the flow as well as the fastest growing perturbations for these solutions can be monitored continuously, while the strength of the DWBC is increased from zero towards realistic values. Focus will be on the growth rates, spatial patterns and other characteristics of these specific perturbations that can grow on the stationary state.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics