= Solution
For $\mathrm{Ri}>\mathrm{Ri}_c$, the <fixed-correlation equilibrium model for stratified turbulence> has $R_{\min}>1$. Thus <buoyancy> destruction plus dissipation exceeds shear production for every $q>0$, and the local kinetic-energy budget predicts decay rather than any positive statistically steady turbulent equilibrium. The stable and unstable turbulent branches have disappeared together at the critical point.
The implied outcome within this closure is suppression or decay of sustained <turbulence>. It is not a proof that every physical stratified shear flow above this value must be permanently laminar: energy transport, external forcing, intermittent mixing or variable correlations and length-scale ratios can violate the model assumptions. As <turbulence> decays, the original fully turbulent high-Reynolds-number approximation itself ceases to apply. The critical Richardson number is consequently a prediction of the stated local closure, not a universal nonlinear stability bound.
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