= Axisymmetric geostrophic mode
{title2=$\omega=0,\quad u=0,\quad v=ik_x(\Phi_1+c_s^2\Sigma_1/\Sigma_0)/(2\Omega)$}
A stationary <mass density> disturbance can be balanced by a changed azimuthal <velocity> in a <shearing sheet>. The <continuity> and azimuthal equations give zero <radial velocity>, while the radial equation balances <Coriolis force> against <pressure> and gravity. This mode is separate from the density-wave pair in the <softened Toomre dispersion relation> and is lost if one divides every equation by frequency.
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