Vendredi 11 septembre à 11h00, salle des séminaires IRPHE
Abstract: Thermal gradients in the oceans, atmosphere and stellar interiors can produce either unstable density gradients, which drive thermal convection, or stable density stratification which enables the propagation of internal gravity waves. Environments supporting both internal waves and thermal flows are of significant interest. Indeed, internal waves are a source of mixing, and allows the transport of energy on large scales. They are known to exist alongside the convection flow in the case of side-heated convection, they can be triggered by thermal plumes shot into a stratified layer, or impinging upon the interface between a convective layer and a stratified layer.
In this talk, I will present two experimental model systems where thermal flow and internal waves can also co-exist: the first is a model of subglacial lakes which exhibits hysteretic transitions between Rayleigh-Bénard and Horizontal Convection; the second is a cryogenic apparatus which allows to produce a turbulent thermal plume in a stratified bath a liquid helium. Because the Prandtl number of cryogenic liquid helium is of order 0.6 (gas-like), this is an experimental model system for atmospheric plumes.
In both cases, there is a range of parameters where the thermal flow can impinge in a stably stratified layer, and produce internal gravity waves.