Holmboe instability beyond the Boussinesq approximation revisited

Abstract

With no use of the Boussinesq approximation, the Holmboe instability is studied in sharply stratified shear flows with arbitrary monotonic and bounded velocity profiles without inflection points, including a piecewise-linear one. Particular attention is given to the separation and analysis of contributions to instability made by the wave–wave and wave–particle interactions which are the main physical mechanisms responsible for the loss of stability. It is shown that both mechanisms are equally important for understanding the instability properties and therefore should be taken into consideration simultaneously.