Critical level of an internal gravity wave
= Critical level of an internal gravity wave
{title2=$\widehat\omega=\omega-kU=0$}
A critical level is a height at which the <intrinsic frequency> of an <internal gravity wave> vanishes. For finite positive <buoyancy frequency>, its local vertical <wavenumber> diverges as $\widehat\omega\to0$. The inviscid <Taylor–Goldstein equation> is singular there; viscosity, diffusion or nonlinear wave breaking can regularize the resulting small scales.