Nonpropagating oscillatory modes in Couette-Taylor flow

We have made power-spectral measurements in both laboratory and rotating reference frames on fluid flow between rotating concentric cylinders. The oscillating modes identified in previous experiments were traveling azimuthal waves; in contrast, three of the oscillatory modes observed in the present experiment were found to be nonpropagating. One of the modes gives an instrumentally sharp component in the spectra, while the other two produce broad spectral components; hence the latter two flows are nonperiodic.