Shear layer instability in a highly diffusive stably stratified atmosphere

The linear stability of a shear layer in a highly diffusive stably stratifi ed atmosphere has been investigated. This study completes and extends previ ous works by Dudis (1974) and Jones (1977). We show that (i) an asymptotic regime is reached in the limit of large thermal diffusivity, (ii) there exi sts two different types of unstable modes. The slowest growing modes corres pond to predominantly horizontal motions and the fast growing ones to isotr opic motions, (iii) the physical interpretation of the stability properties in this asymptotic regime is simple. Applications to the dynamics of stell ar radiative zone are discussed.