a1 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
a2 Department of Mathematics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
a3 Scripps Institution of Oceanography and Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093, USA
a4 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
We analyse the low-mode structure of internal tides generated in laboratory experiments and numerical simulations by a two-dimensional ridge in a channel of finite depth. The height of the ridge is approximately half of the channel depth and the regimes considered span sub- to supercritical topography. For small tidal excursions, of the order of 1% of the topographic width, our results agree well with linear theory. For larger tidal excursions, up to 15% of the topographic width, we find that the scaled mode 1 conversion rate decreases by less than 15%, in spite of nonlinear phenomena that break down the familiar wave-beam structure and generate harmonics and inter-harmonics. Modes two and three, however, are more strongly affected. For this topographic configuration, most of the linear baroclinic energy flux is associated with the mode 1 tide, so our experiments reveal that nonlinear behaviour does not significantly affect the barotropic to baroclinic energy conversion in this regime, which is relevant to large-scale ocean ridges. This may not be the case, however, for smaller scale ridges that generate a response dominated by higher modes.
(Received December 15 2008)
(Revised April 11 2009)
(Accepted April 13 2009)