Interfacial gravity wave
= Interfacial gravity wave
An interfacial gravity wave is a displacement of an interface between two fluids of different <mass density>, restored by <buoyancy> when the denser fluid is below. For two deep layers in the <Boussinesq approximation>, density difference $\delta\rho$ and horizontal <wavenumber> $k$ give intrinsic squared <phase velocity> $g\delta\rho/(2\rho_0k)$. Background flow shifts the laboratory <phase velocity> by its local speed.