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

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

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    14 Citaten (Scopus)

    Samenvatting

    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
    Volume16
    Nummer van het tijdschrift1
    DOI's
    StatusPublished - jul.-2011

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