May 5: "Laboratory experiments on internal wave beams: transport and attractors"



Stratified fluids support oblique internal wave beams. I will
consider the question if these beams transport tracers and enhance
mixing. I will present proof, from theory and laboratory experiments,
that internal wave beams indeed drive transport, both horizontally
and vertically, and consequently contribute to mixing. The transport
is caused by the localised shear motion in the beam and is in a
direction opposite to that of the energy propagation. The discovery
of this transport establishes that in stratified fluids enhanced
vertical mixing takes place near internal wave beams, even when their
amplitude is small. Internal waves provide a source of energy for
mixing in the deep sea. At locations with rough topography these
internal waves often take the shape of beams. The transport found
provides insight in the causes of spatial inhomogeneities in vertical
mixing in general and in the dynamics of sediments and nutrients near
rough topography in particular. We observe the transport of the
tracers on an internal wave attractor. These attractors are known to
play a role in the dynamics of rotating stars. This finding therefore
suggests that in rotating stars strong transport of chemicals might
take place along attractors.