The finite-wavelength instability gives rise to a new type of wave in reaction-diffusion systems: packet waves, which propagate only within a wave packet, are found in experiments on the Belousov-Zhabotinsky reaction dispersed in water-in-oil AOT microemulsion (BZ-AOT) as well as in model simulations. Inwardly moving packet waves with negative curvature occur in experiments and in a model of the BZ-AOT system when the dispersion $d{\omega }_k/dk$ is negative at the characteristic wave number $k_0$. This result sheds light on the origin of antispirals.

• Received 30 October 2001

DOI:https://doi.org/10.1103/PhysRevLett.88.088303