B − ω diagram of the LoS velocity (left) and the CP (centre). The vertical dashed blue line represents the approximate position of the boundary of the umbra as inferred from intensity images. Each column represents the average power spectrum across bins equal to 80 G. The global spectra for LoS velocities and CP fluctuations, both outside and inside the magnetic structure, are shown in the right panel. These are obtained by integrating the B − ω diagram along the horizontal axis.