On instability of large amplitude long interfacial waves

The evolution of large amplitude interfacial waves in a system of two layers of different densities is investigated using a strongly nonlinear long wave model. A local stability analysis is presented to show that the solitary wave solution of this ‘inviscid’ model suffers from a Kelvin- Helmholtz type instability due to a velocity discontinuity across the interface between two layers. A numerical filter is used to eliminate the short-wave instability (that is absent in real observations) and its effects on long-term numerical simulations are discussed.