Bifurcations and strange attractors in the Lorenz-84 climate model with seasonal forcing

A low-dimensional model of general circulation of the atmosphere is investigated. The differential equations are subject to periodic forcing, where the period is one year. A three-dimensional Poincaré mapping P depends on three control parameters F, G, and ε, the latter being the relative amplitude of the oscillating part of the forcing. This paper provides a coherent inventory of the phenomenology of PF,G,ε. For ε small, a Hopf-saddle-node bifurcation HSN of fixed points and quasi-periodic Hopf bifurcations of invariant circles occur, persisting from the autonomous case ε = 0. For ε = 0.5, the above bifurcations have disappeared. Different types of strange attractors are found in four regions (chaotic ranges) in {F,G} and the related routes to chaos are discussed.