On Stability Estimates for the Inviscid Boussinesq Equations

We consider the (in)stability problem of the inviscid 2D Boussinesq equations near a combination of a shear flow $v=(y,0)$ and a stratified temperature $θ=αy$ with $α>\frac{1}{4}$. We show that for any $ϵ>0$ there exist non-trivial explicit solutions, which are initially perturbations of size $ϵ$, and grow to size 1 on a time scale $ϵ^{−2}$. Moreover, the (simplified) linearized problem around these non-trivial states exhibits improved upper bounds on the possible size of norm inflation for frequencies larger and smaller than $ϵ^{−4}$.