Using Unstable Periodic Orbits to Understand Blocking Behaviour in a Low Order Land-Atmosphere Model

Unstable Periodic Orbits (UPOs) are distributed densely in a chaotic attractor, meaning that any trajectory is finitely close to a UPO at any given time. They therefore provide a means of describing properties of the attractor. In this paper we use UPOs to classify the regimes of a simple climate model and to identify the transitions between regimes. The origin of the regimes is also investigated using continuation software to track key UPOs through parameter space. The regimes of this model correspond to atmospheric blocking behaviour, which is linked with heat waves and cold snaps in the real atmosphere. Currently the physical mechanisms of atmospheric blocking are still not fully understood and simple climate models can play a useful role in identifying key physical behaviour.

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