ABSTRACT
A liquid layer heated from below is stratified: it may not be stable, and above a certain instability threshold, rolls and stationary hexagonal cells are produced. This is the well-known Bénard convection. Now, when the liquid layer is heated from above, it is stratified and stable, but the variation of surface tension can lead to oscillatory surface convection, to stationary or traveling surface waves. Mass transfer through the interface between two stratified liquid layers can also produce similar surface waves when the latter results in a lowering of the interfacial tension. Namely, in the 1960s Linde and Schwarz
observed patterns at the surface of a shallow octane layer heated from above. Similarly, Orell and Westwater
observed stationary and propagating patterns, stripes, and ripples produced at an ethylene glycol-ethyl acetate interface by the interfacial transfer of acetic acid from the glycol phase. In both cases, the authors measured the wavelength and wave velocities, and from a simplified linear stability theory, the oscillation frequencies of the convective cells and the instability threshold could be fairly predicted.
