Our laboratory experiments and numerical simulations of stratified tidal flow past model topography

a half sphere on a horizontal plane reveal several three-dimensional flow features, including an
unexpected flow perpendicular to the forcing plane
the vertical plane through the center of the
sphere, in the direction of the oscillating tide. This perpendicular flow has a time-independent
component and a component oscillating at twice the tidal frequency. Our results show that the
time-independent part of the perpendicular flow forms a large-scale horizontal circulation, which
could enhance material transport and mixing near bottom topography in the oceans. In addition, for
small forcing amplitude we find that the azimuthal dependence of the internal wave field is
described by the functional form cos
, as predicted by linear inviscid theory. At higher forcing
amplitude, the internal wave energy is more concentrated in the forcing direction. Finally, we
observe a wave intensity asymmetry in the polar direction and explain the asymmetry using a
geometrical argument.© 2009 American Institute of Physics. doi:10.1063/1.3253692