Modeling Abrupt Climate Change as the Interaction Between Sea Ice Extent and Mean Ocean Temperature Under Orbital Insolation Forcing - Abrupt Climate Change: Mechanisms, Patterns, and Impacts - page 61

Appendix A). Comparison with the NGRIP time series ex-
emplifies the organizing role of the insolation, as it forces
bistable random

some similarity with NGRIP, which then loses its apparent
random look. Besides frequency modulation, one other im-
portant fact this experiment reveals is a form of fluctuations into a time series that bears “ aperiodic ”

Figure 4. (a) Using Taken ' s delay method [Williams, 1997], the phase-space trajectory of the NGRIP record (band-pass-

filtered corner frequencies between 16 and 1 kyr 1 ) is reconstructed. The resulting embedding dimension is 3 (estimated
by the method of near false neighbors), and the delay u is 10 sample units or 500 years, determined by mutual information
autocorrelation [Sprott, 2003]. (b) Synthetic phase-space trajectory computed with a generic, weakly nonlinear van der Pol
oscillator. The two-dimensional (2-D) phase-space trajectory of the van der Pol oscillator is very similar to a 2-D projection
of Figure 4a. The van der Pol trajectory is a limit cycle that maintains its shape under perturbation. It will, however, be
changed from a single loop to multiple loops as a consequence of external forcing (e.g., frequency modulation).