Published online by Cambridge University Press: 29 March 2006
We discuss non-axisymmetric instability of a thin cylindrical sheet of a gas which rotates concentrically with a rigidly rotating environment. For the sake of simplicity, we restrict ourselves to a linear single-mode analysis of a two-dimensional disturbance for which the axial component of the wavenumber vector vanishes. We further restrict ourselves to two limiting cases. In case 1 the gas can be treated as incompressible, while in case 2 the effect of radial stratification caused by the centrifugal force is extremely strong. In case 1 there are two unstable modes: a travelling and a stationary disturbance with respect to a system of co-ordinates which rotates with the environment. For each disturbance, we show the domains of instability on ρ vs. ω diagrams, where ρ is the density and ω is the angular velocity of the sheet non-dimensionalized with respect to those of the environment. A negative-viscosity phenomenon is also described. In case 2 both the travelling and the stationary disturbances are stabilized by the strong radial stratification. An outline of a WKB method of approximation is given.