Meridional cuts of (from top to bottom) the dust-to-gas ratio at 450 orbits, the averaged Solberg–Høiland expressions (39), (40) (the left hand side terms) and root mean squared vertical Reynolds stress. Averages are taken over the time 350–450 orbits. In the panels ⟨SH₁ ⟩ and ⟨SH₂⟩, negative values are indicated by a black color. These plots compare the same simulations as in Fig. 4 and illustrate the emergence of a dusty gas instability through a violation of the Solberg–Høiland criteria.