The magnetic field vector of the Sun-as-a-star – II. Evolution of the large-scale vector field through activity cycle 24
MetadataShow full item record
Altmetrics Handle Statistics
Altmetrics DOI Statistics
In this work, we investigate how the large-scale magnetic field of the Sun, in its three vector components, has evolved during most of cycle 24, from 2010 January to 2018 April. To filter out the small-scale field of the Sun, present in high-resolution synoptic maps, we use a spherical harmonic decomposition method, which decomposes the solar field in multipoles with different ℓ degrees. By summing together the low-ℓ multipoles, we reconstruct the large-scale field at a resolution similar to observed stellar magnetic fields, which allows the direct comparison between solar and stellar magnetic maps. During cycle 24, the ‘Sun-as-a-star’ magnetic field shows a polarity reversal in the radial and meridional components, but not in the azimuthal component. The large-scale solar field remains mainly poloidal with ≥70 per cent of its energy contained in the poloidal component. During its evolution, the large-scale field is more axisymmetric and more poloidal when near minima in sunspot numbers, and with a larger intensity near maximum. There is a correlation between toroidal energy and sunspot number, which indicates that spot fields are major contributors to the toroidal large-scale energy of the Sun. The solar large-scale magnetic properties fit smoothly with observational trends of stellar magnetism reported in See et al. The toroidal (⟨B2tor⟩) and poloidal (⟨B2pol⟩) energies are related as ⟨B2tor⟩ α ⟨B2pol⟩1.38±0.04. Similar to the stellar sample, the large-scale field of the Sun shows a lack of toroidal non-axisymmetric field.
Vidotto , A A , Lehmann , L T , Jardine , M & Pevtsov , A A 2018 , ' The magnetic field vector of the Sun-as-a-star – II. Evolution of the large-scale vector field through activity cycle 24 ' , Monthly Notices of the Royal Astronomical Society , vol. 480 , no. 1 , pp. 477-487 . https://doi.org/10.1093/mnras/sty1926
Monthly Notices of the Royal Astronomical Society
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://doi.org/10.1093/mnras/sty1926
DescriptionLTL acknowledges support from the Scottish Universities Physics Alliance (SUPA) prize studentship and the University of St Andrews Higgs studentship. AAP acknowledges partial support by NASA grant NNX15AN43G. National Solar Observatory is operated by the Association of Universities for Research in Astronomy (AURA) Inc., under a Cooperative agreement with the National Science Foundation.
Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.