= Displacement pseudomomentum of an internal gravity wave
{title2=$P=\overline{\xi_xu+\zeta_xw}=-\omega K^2|\widehat\sigma|^2/(2kN^4)$}
The displayed displacement convention is the negative of the usual positive-frequency <wave pseudomomentum> $k\overline E/\omega$ for a rightgoing <internal gravity wave>. Here <energy> per unit reference <mass density> is $\overline E=|\widehat\sigma|^2/(2N^2)$. From the <buoyancy polarization of a plane internal gravity wave>, horizontal averaging gives $\overline{\zeta_xp}=km|\widehat\sigma|^2/(2N^2K^2)=c_{gz}P$, where $p$ is <kinematic pressure>. The sign convention changes both density and flux and leaves their propagation at the <group velocity> unchanged.
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