Biscale chaos in propagating fronts.

The propagating chemical fronts found in cubic autocatalytic reactiondiffusion processes are studied. Simulations of the reaction-diffusion equation near to and far from the onset of the front instability are performed and the structure and dynamics of chemical fronts are studied. Qualitatively different front dynamics are observed in these two regimes. Close to onset the front dynamics can be characterized by a single length scale and described by the Kuramoto-Sivashinsky equation. Far from onset the front dynamics exhibits two characteristic lengths and cannot be modeled by this amplitude equation. An amplitude equation is proposed for this biscale chaos. The reduction of the cubic autocatalysis reaction-diffusion equation to the KuramotoSivashinsky equation is explicitly carried out. The critical diffusion ratio δc, where the planar front loses its stability to transverse perturbations, is determined and found to be δc = 2.300. Typeset using REVTEX