Critical Transitions and Perturbation Growth Directions

TL;DR

This paper investigates how changes in covariant Lyapunov vectors can serve as early warning indicators for critical transitions in complex dynamical systems, demonstrating their effectiveness over traditional measures especially under noisy conditions.

Contribution

It introduces a novel approach using covariant Lyapunov vectors to predict critical transitions and proposes a new method to estimate these vectors without future system knowledge.

Findings

Covariant Lyapunov vectors tend to become tangent during critical transitions.

Alignment of covariant Lyapunov vectors predicts transitions better than variance-based indicators.

New estimation method for covariant Lyapunov vectors enables transition prediction without future data.

Abstract

Critical transitions occur in a variety of dynamical systems. Here, we employ quantifiers of chaos to identify changes in the dynamical structure of complex systems preceding critical transitions. As suitable indicator variables for critical transitions, we consider changes in growth rates and directions of covariant Lyapunov vectors. Studying critical transitions in several models of fast-slow systems, i.e., a network of coupled FitzHugh-Nagumo oscillators, models for Josephson junctions and the Hindmarsh-Rose model, we find that tangencies between covariant Lyapunov vectors are a common and maybe generic feature during critical transitions. We further demonstrate that this deviation from hyperbolic dynamics is linked to the occurrence of critical transitions by using it as an indicator variable and evaluating the prediction success through receiver operating characteristic curves. In the presence of noise, we find the alignment of covariant Lyapunov vectors and changes in finite-time Lyapunov exponents to be more successful in announcing critical transitions than common indicator variables as, e.g., finite-time estimates of the variance. Additionally, we propose a new method for estimating approximations of covariant Lyapunov vectors without knowledge of the future trajectory of the system. We find that these approximated covariant Lyapunov vectors can also be applied to predict critical transitions.