@inproceedings{Balmforth2001DisturbingV,
title={Disturbing Vortices},
author={Neil J. Balmforth and Stefan G. Llewellyn Smith and William R. Young},
year={2001}
}

Inviscid spatially compact vortices (such as the Rankine vortex) have discrete Kelvin modes. For these modes, the critical radius, at which the rotation frequency of the wave matches the angular velocity of the fluid, lies outside the vortex core. When such a vortex is not perfectly compact, but has a weak vorticity distribution beyond the core, these Kelvin disturbances are singular at the critical radius and become ‘quasi-modes’. These are not true eigenmodes but have streamfunction… CONTINUE READING