Interaction of Internal Waves with a Topographic Sill in a Two-Layered Fluid

Abstract

Sills and seamounts may alter or even disrupt internal waves that approach them. The authors study by one-dimensional laboratory experiment: (i) the fission of an internal solitary wave of a two-layered fluid by a triangular obstruction, (ii) the form preservation of the transmitted wave, and (iii) the energy dissipated by the vortex induced by the obstruction. The potential energy stored in the wave signal is taken as a measure to quantify the above notions. Results are presented for upper to lower depth ratio rH = 3 and rH = ?. The results show in general a pronounced dependence on the degree of blocking (B ≡ depth of obstruction/lower layer depth), but experiments are less conclusive for dependence on particle speeds and slope angles of the triangle. The authors determine for a given degree of blocking how much energy of an approaching wave is fed into the reflected and transmitted wave. For B ≤ 0.6 the obstruction is virtually ineffective; for B ≥ 0.8 a compact solitary wave hump transforms into a dispersed wave train; and for B ≥ 1.2 wave transmission is practically blocked.