panel shows a comparison with the ISN. The different activity cycles are indicated by different colours (see legend).[]{data-label="figure[proxy vs shift]"}](freq_shifts_vs_flux_2500_3500_365d.jpg "fig:"){width="45.00000%"}![Comparison of frequency shifts with surface proxies of the Sun’s magnetic field. The left-hand panel shows a comparison with the 10.7cm flux, while the right-hand panel shows a comparison with the ISN. The different activity cycles are indicated by different colours (see legend).[]{data-label="figure[proxy vs shift]"}](freq_shifts_vs_ISN_2500_3500_365d.jpg "fig:"){width="45.00000%"}\

Fig. \[figure\[proxy vs shift\]\] shows a comparison between two proxies of the Sun’s magnetic field and low-$l$ frequency shifts. Although the agreement is approximately linear the well-known hysteresis is clearly visible, particularly in the case of the sunspot number. This can be explained in terms of the variation in the latitudinal distribution of the surface magnetic field throughout the solar cycle [@2000MNRAS.313..411M]: The different modes have different latitudinal dependencies, as described by the appropriate spherical harmonics (see Section \[section\[intro\]\]), and so the relative influence of the surface magnetic flux on the modes changes throughout the solar cycle as the strong surface magnetic field migrates towards the equator.

As mentioned in Section \[section\[intro\]\] the even splitting coefficients can provide information about departures from spherical symmetry, such as those produced by the presence of a magnetic 