Anelastic approximation for a rotating barotropic star
= Anelastic approximation for a rotating barotropic star
{title2=$\nabla\cdot(\rho\mathbf v)=0$}
For slow rotation and low-frequency inertial motion, neglect the time derivative of the Eulerian <mass density> perturbation relative to the mass-weighted <velocity> divergence. This filters acoustic compressibility while retaining background <mass density> variation. A spherical background <mass density> is often sufficient at leading order in rotation.