Amplitude spectra of the magnetospheric coefficient |$q_{10}^\mathrm{mag}$| (upper panel), the ionospheric coefficient |$q_{10}^\mathrm{ion}$| coefficient (middle panel) and the internally induced coefficient |$g_{10}^\mathrm{int}$| (lower panel). Spectral peaks observed in the spectra are marked with triangles, with their peak periods annotated. Selected theoretical periods of the system are plotted as solid vertical lines for reference.