Two-dimensional hydrodynamical alpha-disks, with viscosity transitions (upper panels) equivalent to the resistivity ones, and α_ν ≈ 0.02 in the “active” zone (the subscript ν underscores that this α corresponds to a Laplacian viscosity, not to turbulent stresses). The lower panels show the density, for snapshots at the same times as in Fig. 1. Only the first ones (h₁ = 0.1 and h₁ = 0.2) develop the RWI.