Mechanism of finite-amplitude double-component convection due to different boundary conditions

Abstract

A new mechanism of double-component convection is discovered. It emerges in a horizontal layer of Boussinesq fluid as a stable stratification due to flux boundary conditions is added to an unstable gradient specified by fixed boundary values. A large enough perturbation substantially decreases the stable flux gradient but fails to mix the unstable fixed-value gradient. Steady finite-amplitude flows reminiscent of Rayleigh--Benard convection then arise even as the net background stratification is stable, emphasizing the importance of the identified mechanism for double-component fluid systems. V2 Abstract: A new mechanism of double-component convection is discovered. It emerges in a horizontal layer of Boussinesq fluid as a stable stratification due to flux boundary conditions is added to an unstable gradient specified by fixed boundary values. Driven by this mechanism, steady finite-amplitude flows reminiscent of Rayleigh--Benard convection arise even when the background density stratification is stable.