Hydrodynamical integrations using the Pr76-parameters (Table 1) with increasing value of the viscosity parameter β = 0.85–1.35 (see Fig. 6) from top to bottom. The surface density profiles (left panels) as well as their wavelet-powers (right panels) reveal the co-existence of a resonantly forced density wave and short-scale viscous overstability for the cases β = 1.10–1.35. All integrations use a scaled torque , a grid of size L_r = 450 km and resolution h = 25 m. The plots correspond to times t ≳ 20 000 ORB.