CHAOS AND QUASI-PERIODICITY IN DIFFEOMORPHISMS OF THE SOLID TORUS

This paper focuses on the parametric abundance and the 'Cantorial' persistence under perturbations of a recently discovered class of strange attractors for diffeomorphisms, the so-called quasi-periodic Henon-like. Such attractors were first detected in the Poincare map of a periodically driven model of the atmospheric flow: they were characterised by marked quasi-periodic intermittency and by Lambda(1) > 0, Lambda(2) approximate to 0, where Lambda(1) and Lambda(2) are the two largest Lyapunov exponents. It was also conjectured that these attractors coincide with the closure of the unstable manifold of a hyperbolic invariant circle of saddle-type. This type of attractor is here investigated in a model map of the solid torus, constructed by a skew coupling of the Henon family of planar maps with the Arnol'd family of circle maps. It is proved that Henon-like strange attractors occur in certain parameter domains. Numerical evidence is produced, suggesting that quasi-periodic circle attractors and quasi-periodic Henon-like attractors persist in relatively large subsets of the parameter space. We also discuss two problems in the numerical identification of so-called strange non-chaotic attractors and the persistence of all these classes of attractors under perturbation of the skew product structure.