Dissipation spectra with periodic boundary conditions for a single interface with three different diffusivities (Ekman numbers), E = K = 10⁻³ (top), 10⁻⁴ (middle), and 10⁻⁵ (bottom), and an aspect ratio ε = 0.2. The total dissipation is represented by the solid orange line, and its viscous and thermal contributions are represented by the dotted blue and red lines, respectively. The dashed light blue line represents the spatially averaged dissipation for a fully convective medium, . For each panel, the quantity represented is , where as a functionof the normalised frequency ω∕2Ω. In the bottom panel the vertical dash-dotted lines indicate the position of characteristic frequencies discussed in Sect. 3.2 (from left to right): resonance with short-wavelength inertial modes (in grey), resonances with short-wavelength super-inertial gravito-inertial modes (in green), and resonance with a free gravity mode of the staircase (in light red).