Mechanisms of extensive spatiotemporal chaos in Rayleigh-Bernard convection

Spatially extended dynamical systems exhibit complex behaviour in both spac e and time-spatiotemporal chaos(1,2). Analysis of dynamical quantities (suc h as fractal dimensions and Lyapunov exponents(3)) has provided insights in to low-dimensional systems; but it has proven more difficult to understand spatiotemporal chaos in high-dimensional systems, despite abundant data des cribing its statistical properties(1,4,5). Initial attempts have been made to extend the dynamical approach to higher-dimensional systems, demonstrati ng numerically that the spatiotemporal chaos in several simple models is ex tensive(6-8) (the number of dynamical degrees of freedom scales with the sy stem volume). Here we report a computational investigation of a phenomenon found in nature, 'spiral defect' chaos(5,9) in Rayleigh-Benard convection, in which we rnd that the spatiotemporal chaos in this state is extensive an d characterized by about a hundred dynamical degrees of freedom. By studyin g the detailed space-time evolution of the dynamical degrees of freedom, we rnd that the mechanism for the generation of chaotic disorder is spatially and temporally localized to events associated with the creation and annihi lation of defects.