Abstract
The stability of a rotating doubly diffusive fluid is considered. It is shown that (1) a non-rotating layer can be destabilized by rotation, (2) a rotating layer can be destabilized by the addition of a bottom-heavy solute gradient, and (3) under some conditions, three thermal Rayleigh numbers are required to specify linear stability criteria. Numerical results are presented on the basis of which the explanation by Acheson (1979) of the second of these three anomalies can be assessed, and Acheson's explanation is adapted to the two other anomalies.