Waves on a columnar vortex in a strongly stratified fluid

This paper investigates the discrete bounded waves sustained by a vertical columnar Rankine vortex in a strongly stratified fluid. We show that these waves are very different from their well-known counterpart in homogeneous fluid (Kelvin vortex waves); they exist only for nonzero azimuthal wavenumber m, their frequency lies in the interval [0, m Omega] (Omega is the angular velocity in the vortex core) and they are unstable because of an outward radiation from the vortex. The instability mechanism is explained in terms of an over-reflection phenomenon by means of a Wentzel Kramers-Brillouin-Jeffreys analysis for large axial wavenumber. (C) 2009 American Institute of Physics. [doi:10.1063/1.3248366]