THE COUPLING OF WAVES AND CONVECTION

Experiments with layers of salt and sugar solution separated by a diff usive interface are described. Interfacial waves were spontaneously ge nerated by the convection once the system evolved to a critical value of the density-anomaly ratio R-rho = beta Delta S/alpha Delta T. The w aves locally modulated the interfacial fluxes by modifying the interfa ce thickness and thereby organized otherwise random convective motions into large-scale circulations. In turn, the waves themselves persiste d for unusually long times owing to energy input from the organized co nvection. The dependence of the wave speed on the layer properties and channel dimensions was successfully predicted by assuming that coupli ng requires a matching of the wave and convection speeds, and that the system selects waves of an amplitude for which this resonance can occ ur. This 'wave-convection coupling' also appeared to increase the inte rfacial fluxes at low R-rho. The interaction of waves and convection m ay be important for oceanic thermohaline staircases and other systems where convection is driven by interfacial fluxes.