Relative amplitudes of the components of a fundamental p-mode with large k_z, of topological origin, induced by a pressure bump located close to r_max. The amplitudes are displayed as functions of the distance to the central object in the mid-plane (top right panel) and for a (r,z) slice of the disc (bottom panel). The selected mode is marked with a cross in the top left panel (same as Fig. 3). This mode has an amplitude in u_z and h and, as such, is of acoustic nature. Interestingly, it mixes with both the fundamental r-mode of the gap and an inertial mode of the inner disc, which both have amplitudes in u_r and u_θ. It is more spatially extended around r_max than the fundamental r-mode is around r_min (see below).