Synchronized chaos in extended systems and meteorological teleconnections

Abstract

While synchronized chaos is familiar in low-order systems, the relevance of this paradigm to natural phenomena and spatially extended systems is questionable because of the time lags introduced by finite signal propagation speeds. A form of partially synchronized chaos is here demonstrated in a low-order numerical model of the coupled large-scale atmospheric circulation patterns in the northern and southern hemispheres. The model is constructed using a Green's function method to represent the time-lagged boundary forcing of the flow in each hemisphere by Rossby waves emanating from the opposite hemisphere. The two hemispheric subsystems are semiautonomous because Rossby waves cannot penetrate the tropics except in narrow longitudinal bands where the background winds are westerly. Each hemisphere has previously been described by a 10-variable model, derived from a spectral truncation of the barotropic vorticity equation. The model exhibits dynamical regimes corresponding to ``blocked'' and ``zonal'' atmospheric flow patterns in the hemisphere. Applying the same spectral truncation to the Green's functions that define the coupling, we construct a 28-variable model of the coupled flow on a planet with simplified geometry and background wind field. Partial synchronization is manifest in a significant tendency for the two hemispheric subsystems to occupy the same regime simultaneously. This tendency is observed in actual meteorological data. Partial synchronization of this form can be viewed as an extension of on-off intermittency in a system with a synchronization manifold, to a region of parameter space that is far from the bifurcation point at which this manifold loses stability.