arXiv2025
This paper investigates the stability and large-time behavior of solutions to the rotating Boussinesq system under the influence of a general gravitational potential $Ψ$, which is widely used to model the dynamics of stratified geophysical fluids on the $f-$plane. Our main results are threefold: First, by imposing physically realistic boundary conditions and viscosity constraints, we prove that the solutions of the system smust necessarily take the following steady-state form $(ρ,u,v,w,p)=(ρ_s,0,v_s,0, p_s)$. These solutions are characterized by both geostrophic balance, given by $fv_s-\frac{\partial p_s}{\partial x}=ρ_s\frac{\partial Ψ}{\partial x}$ and hydrostatic balance, expressed as $-\frac{\partial p_s}{\partial z}=ρ_s\frac{\partial Ψ}{\partial z}$. Second, we establish that any steady-state solution satisfying the conditions $\nabla ρ_s=δ(x,z)\nabla Ψ$ with $v_s(x,z)=a_0x+a_1$ is linearly unstable when the conditions $δ(x,z)|_{(x_0,z_0)}>0$ and $(f+α_0)\leq 0$ are simultaneously satisfied. This instability under the condition $δ(x,z)|_{(x_0,z_0)}>0$ corresponds to the well-known Rayleigh-Taylor instability. Third, although the inherent Rayleigh-Taylor instability could potentially amplify the velocity around unstable steady-state solutions (heavier density over lighter one), we rigorously demonstrate that for any sufficiently smooth initial data, the solutions of the system asymptotically converge to a neighborhood of a steady-state solution in which both the zonal and vertical velocity components vanish. Finally, under a moderate additional assumption, we demonstrate that the system converges to a specific steady-state solution. In this state, the density profile is given by $ρ=-γΨ+β$, where $γ$ and $β$ are positive constants, and the meridional velocity $v$ depends solely and linearly on $x$ variable.