This second paper of the series is devoted to Kelvin-Helmholtz instabilities in cylindrical boundary layer flows (jets). The vortex-sheet approximation is still used, and compressible flows are studied in subsonic, transonic, supersonic and relativistic regimes. Magnetic field effects are analysed, together with density contrast inside and outside the jet. The general result is that, due to the onset of a so-called reflection branch of resonant modes, jets are always unstable, both to pinching and helical perturbations with wavelengths of the order of the jet circumference. In particular the time-scales for instability are such that this certainly plays a significant part in the morphology and energetics of extended radio sources.
Ferrari, A;  Consiglio Nazionale delle Ricerche, Turin (Italy). Lab. di Cosmo-Geofisica); Trussoni, E; Zaninetti, L 
- Max-Planck-Institut fuer Extraterrestrische Physik, Garching b. Muenchen (Germany, F.R.)
- Consiglio Nazionale delle Ricerche, Turin (Italy). Lab. di Cosmo-Geofisica