  This study is devoted to the experimental analysis of the Strato-rotational
Instability (SRI). This instability affects the classical cylindrical Couette
flow when the fluid is stably stratified in the axial direction. In agreement
with recent theoretical and numerical analyses, we describe for the first time
in detail the destabilization of the stratified flow below the Rayleigh line
(i.e. the stability threshold without stratification). We confirm that the
unstable modes of the SRI are non axisymmetric, oscillatory, and take place as
soon as the azimuthal linear velocity decreases along the radial direction.
This new instability is relevant for accretion disks.
