Supplementary material from "Basin bifurcations, oscillatory instability and rate-induced thresholds for Atlantic meridional overturning circulation in a global oceanic box model. 29 January 2019 11 April 2019"

• Main Authors: Alkhayuon, Hassan, Ashwin, Peter, Jackson, Laura C, Quinn, Courtney, Wood, Richard A.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Figshare 2019
• Subjects: Oceanography; FOS Earth and related environmental sciences; 10109 Ordinary Differential Equations, Difference Equations and Dynamical Systems; FOS Mathematics; 10110 Partial Differential Equations; 10299 Applied Mathematics not elsewhere classified; 10302 Numerical Solution of Differential and Integral Equations; North Atlantic
• Online Access: https://dx.doi.org/10.6084/m9.figshare.c.4481501.v1; https://rs.figshare.com/collections/Supplementary_material_from_Basin_bifurcations_oscillatory_instability_and_rate-induced_thresholds_for_Atlantic_meridional_overturning_circulation_in_a_global_oceanic_box_model_29_January_2019_11_April_2019_/4481501/1

The Atlantic meridional overturning circulation (AMOC) transports substantial amounts of heat into the North Atlantic sector, and hence is of very high importance in regional climate projections. The AMOC has been observed to show multi-stability across a range of models of different complexity. The simplest models find a bifurcation associated with the AMOC ‘on’ state losing stability that is a saddle node. Here, we study a physically derived global oceanic model of Wood et al. with five boxes, that is calibrated to runs of the FAMOUS coupled atmosphere-ocean general circulation model. We find the loss of stability of the ‘on’ state is due to a subcritical Hopf for parameters from both pre-industrial and doubled CO 2 atmospheres. This loss of stability via subcritical Hopf bifurcation has important consequences for the behaviour of the basin of attraction close to bifurcation. We consider various time-dependent profiles of freshwater forcing to the system, and find that rate-induced thresholds for tipping can appear, even for perturbations that do not cross the bifurcation. Understanding how such state transitions occur is important in determining allowable safe climate change mitigation pathways to avoid collapse of the AMOC.