Azimuthally averaged power spectra of the Ca II line-centre intensity as a function of the normalised radial distance from the pore’s centre and frequency (left) and a sketch of geometry used (right). The solid line encircles the safe boundary of the pore (see text). The radial distance is normalised with respect to this boundary (here R ≡ 1 for all angles). Two white dashed lines limit the angles used in the azimuthal average of the power spectra. The black dashed lines mark the cuts in x and y used to construct time-slice diagrams in Fig. 9.