Instabilities of a columnar vortex in a stratified fluid

In this paper, we show that the presence of a vertical density gradient candestabilise a Gaussian vortex in two different ways. First, when the vortex axis isslightly tilted with respect to the vertical and if its Froude number is larger than one,the vortex exhibits strong axial flows inside a critical layer, which lead to a violentthree-dimensional instability. Second, when the vortex axis is vertical, the vortex isweakly unstable by emission of internal gravity waves. Theoretical predictions forboth instabilities are compared with experimental evidences