tokens: magnetic fields across the solar surface (Mackay Yeates 2012 ). Although synoptic maps of the stellar vector field exist for a couple of decades and have been derived for hundreds of systems (e.g. Donati Collier Cameron 1997 ; Donati et al. 1999 , 2006b ; Donati Landstreet 2009 ), there are significantly fewer synoptic maps of the vector field of the Sun. Earlier synoptic maps of the vector solar field were created on the basis of the rotational modulation of LOS magnetograms (Pevtsov Latushko 2000 ; Wang Zhang 2010 , also called ‘pseudo-vector reconstruction method’). With this method, these authors assumed that the field on large spatial scales does not change over several days. Because of this assumption, these early synoptic maps reconstructed only large-scale magnetic fields of the Sun. More recently, Gosain et al. ( 2013 ) used daily full-disc vector magnetograms from the SOLIS/Vector Spectromagnetograph (VSM) spectrograph to reconstruct the vector solar field of a series of 23 Carrington Rotations. This is a significant advance compared to the large majority of synoptic charts of the solar magnetic field, which are restricted to the LOS component of the solar magnetic field, used to derive B r . An important conclusion reached by Gosain et al. ( 2013 ) is that the solar magnetic field is not normal (i.e. purely radial) to the surface at the photospheric level. This is somewhat disturbing, as the assumption that the solar magnetic fields are purely radial are used in several studies. With the new existing capabilities in producing vector synoptic fields, we can now start to investigate the behaviour of the meridional B θ and azimuthal B φ components of the solar magnetic field and investigate how the three magnetic field components in the Sun compare to the ones derived in stellar observations (e.g. Fig. 1 ). However, direct comparison between stellar and solar magnetic field topologies are hampered by their dramatic differences in resolutions. To provide a direct comparison between solar and stellar magnetic field synoptic maps, it is first required to ‘filter out’ the small-scale field (i.e. the finely resolved magnetic features) of the solar observations, since this component is currently not accessible to ZDI studies. After this, we are left with only the solar large-scale field, whose spatial scale is comparable to those achieved by stellar observations. One way to filter out the small-scale structure of the solar field is to express the solar magnetic field as spherical harmonics of different l degrees, up to a maximum degree l max . The smallest l degrees represent the largest-scale components, e.g. l = 1 for the dipole, l = 2 for the quadrupole, l = 3 for the octupole and so on. By retaining only the components of low l degrees in the spherical harmonics decomposition, we are then able to calculate the large-scale component of the magnetic map. This approach has been extensively applied to the LOS and radial components of the
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