Formation of a period-2 spiral wave and its subsequent transitions in a Belousov-Zhabotinsky system

Recent simulation studies on several different models for reaction-diffusion systems have suggested that complex spiral waves with line defects can arise in period-2 oscillatory media. Here, we report the observation of such wave structures in a laboratory experiment. As in the simulation studies, the underlying line-defects do play a significant role governing the morphology and the temporal dynamics of the observed period-2 spiral waves. Various transitions of the line defect are discussed, as well as the emergence of a line-defect at the onset of a period-1 (P-1) to period-2 (P-2) transition. At the onset, an intermittently breathing line defect with the shape of a P-1 spiral emerges. With a subsequent change in a control parameter, the line-defect first dilates and undergoes a meandering transition, producing a compound tip trajectory. Since line defects are a generic property of complex periodic media, the observed phenomena are expected to arise in a broad class of complex periodic systems.