The instability of a round jet surrounded by an annular shear layer.
Uses a simple stability model to identify some of the global properties of large scale eddies, in particular the radial dependence of the amplitudes of growing disturbances in order to study the extent to which the disturbances penetrate the jet and its surroundings. Shows a pronounced change in scaling behaviour as t/a increases above 0.5. Puffs correspond to the response of a jet with a thick shear layer while ripples correspond to the response of a jet with a very thin shear layer. Examines wavelength dependence and shows that depth of disturbance penetration inside and outside the jet is directly proportional to the wavelength of the disturbance, and for certain waves, depth is directly proportional to local thickness of the shear layer. Spade like puffs are attributed to phase variations. (C.J.U.)