Double-zero internal-wave turning level
= Double-zero internal-wave turning level
{title2=$m^2\sim C(z-z_*)^2$}
A level where the squared vertical <wavenumber> of an <internal gravity wave> touches zero quadratically without changing sign. The ordinary <WKB approximation> fails there; unlike a simple sign-changing turning point, this does not itself provide an evanescent region on one side. Finite-wavelength analysis determines how solutions connect across or meet a boundary at the level.