The dynamics of a low-order model for the Atlantic multidecadal oscillation

H. Broer, H. Dijkstra, C. Simó, A. Sterk, R. Vitolo

    OnderzoeksoutputAcademicpeer review

    14 Citaten (Scopus)


    Observational and model based studies provide ample evidence for the presence of multidecadal variability in the North Atlantic sea-surface temperature known as the Atlantic Multidecadal Oscillation (AMO). This variability is characterised by a multidecadal time scale, a westward propagation of temperature anomalies, and a phase difference between the anomalous meridional and zonal overturning circulations.

    We study the AMO in a low-order model obtained by projecting a model for thermally driven ocean flows onto a 27-dimensional function space. We study bifurcations of attractors by varying the equator-to-pole temperature gradient (Delta T) and a damping parameter (gamma).

    For Delta T = 20 degrees C and gamma = 0 the low-order model has a stable equilibrium corresponding to a steady ocean flow. By increasing gamma to 1 a supercritical Hopf bifurcation gives birth to a periodic attractor with the spatio-temporal signature of the AMO. Through a period doubling cascade this periodic orbit gives birth to Henon-like strange attractors. Finally, we study the effects of annual modulation by introducing a time-periodic forcing. Then the AMO appears through a Hopf-Neimark-Sacker bifurcation. For Delta T = 24 degrees C we detected at least 11 quasi-periodic doublings of the invariant torus. After these doublings we find quasi-periodic Henon-like strange attractors.

    Originele taal-2English
    Pagina's (van-tot)73-107
    Aantal pagina's35
    TijdschriftDiscrete and Continuous Dynamical Aystems. Series B
    Nummer van het tijdschrift1
    StatusPublished - jul.-2011

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