Thermosolutal convection in a rotating couple-stress fluid

In this paper we study the nonlinear Lyapunov stability of the conduction-diffusion solution of a rotating couple-stress fluid, in a layer heated and salted from below. After reformulating the perturbation evolution equations in a suitable equivalent form, we derive the appropriate Lyapunov function and we prove that, if the principle of exchange of stabilities holds, the linear and nonlinear stability bounds are equal. The nonlinear stability bound is exactly the critical Rayleigh number obtained solving the linear instability of the conduction-diffusion solution