Hydrodynamical integrations using the Pr76-parameters (Table 1) with increasing forcing strength from top to bottom panels (). 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. All integrations use β = 1.25, a grid of size L_r = 450 km, and resolution h = 25 m. As in Fig. 7, the blue dashed lines indicate the wavelength of vanishing nonlinear group velocity of overstable waves (by margins ± 20 m). The plots correspond to times t ≳ 20 000 ORB.