Magnetic pore investigated in the study. Top left: instantaneous Fe I 617.3 nm line core intensity. The dotted red line represents the B = 800 G contour used as a reference in Fig. 2. Top right: magnitude of CP. Bottom left: instantaneous Doppler velocity map obtained in the Fe I 617.3 nm spectral line. Bottom right: average magnetic field strength obtained with the centre-of-gravity (COG) method. The white dashed box outlines the region considered when filtering in k − ω space (see text and Fig. 3).