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

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 temp...

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Bibliographic Details
Published in:Discrete & Continuous Dynamical Systems - B
Main Authors: Broer, H., Dijkstra, H., Simó, C., Sterk, A., Vitolo, R.
Format: Article in Journal/Newspaper
Language:English
Published: 2011
Subjects:
Atlantic Multidecadal Oscillation
dynamical systems
periodic and quasi-periodic dynamics
bifurcations
SADDLE-NODE BIFURCATION
FIXED-POINTS
INTERDECADAL VARIABILITY
OCEAN CIRCULATION
HEAT-FLUX
3D-DIFFEOMORPHISMS
INSTABILITY
CHAOS
North Atlantic
Online Access:https://hdl.handle.net/11370/e9378c8a-21d5-4813-9b2e-b21b0828e66d
https://research.rug.nl/en/publications/e9378c8a-21d5-4813-9b2e-b21b0828e66d
https://doi.org/10.3934/dcdsb.2011.16.73
Description
Summary: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.

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