On the interpretation of phase measurements of oscillatory thermocapillary convection in liquid bridges

In their study of time-dependent thermocapillary convection in cylindrical liquid bridges Velten et al. [Phys. Fluids A 3, 267 (1991)] determined the azimuthal flow structure by measuring the phase of the temperature oscillations at three different azimuthal angles. Their explanation of the data in terms of modes with wave number m=0 is not always compatible with the normal-mode decomposition of the disturbances at the threshold. A new interpretation is given that explains the peculiar phase measurements in terms of pairs of m≠0 counterpropagating waves.