Inertial waves near corotation in three-dimensional hydrodynamical discs

Abstract

This paper concerns the interaction between non-axisymmetric inertial waves and their corotation resonances in a hydrodynamical disk. Inertial waves are of interest because they can localise in resonant cavities circumscribed by Lindblad radii, and as a consequence exhibit discrete oscillation frequencies that may be observed. It is often hypothesised that these trapped eigenmodes are affiliated with the poorly understood QPO phenomenon. We demonstrate that a large class of non-axisymmetric 3D inertial waves cannot manifest as trapped normal modes. This class includes any inertial wave whose resonant cavity contains a corotation singularity. Instead, these `singular' modes constitute a continuous spectrum and, as an ensemble, are convected with the flow, giving rise to shearing waves. Lastly, we present a simple demonstration of how the corotation singularity stabilizes three-dimensional perturbations in a slender torus.