Lifetimes and rotation within the solar mean magnetic field

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We have used very high-cadence (sub-minute) observations of the solar mean magnetic field (SMMF) from the Birmingham Solar Oscillations Network (BiSON) to investigate the morphology of the SMMF. The observations span a period from 1992 to 2012, and the high-cadence observations allowed the exploration of the power spectrum up to frequencies in the mHz range. The power spectrum contains several broad peaks from a rotationally modulated (RM) component, whose linewidths allowed us to measure, for the first time, the lifetime of the RM source. There is an additional broadband, background component in the power spectrum which we have shown is an artefact of power aliasing due to the low fill of the data. The sidereal rotation period of the RM component was measured as 25.23 ± 0.11 d and suggests that the signal is sensitive to a time-averaged latitude of ∼12°. We have also shown the RM lifetime to be 139.6 ± 18.5 d. This provides evidence to suggest that the RM component of the SMMF is connected to magnetic flux concentrations (MFCs) and active regions (ARs) of magnetic flux, based both on its lifetime and location on the solar disc.

Bibliographic note

Acknowledgements: We would like to thank all those who are, or have been, associated with BiSON. The authors would like to acknowledge the support of the UK Science and Technology Facilities Council (STFC). Funding for the Stellar Astrophysics Centre (SAC) is provided by The Danish National Research Foundation (Grant DNRF106). This research also made use of the open-source PYTHON packages: ASTROPY,2a community-developed core PYTHON package for Astronomy (Robitaille et al. 2013; The Astropy Collaboration et al. 2018), CORNER (Foreman-Mackey 2016), EMCEE (Foreman-Mackey et al. 2013), MATPLOTLIB (Hunter 2007), NUMPY (Harris et al. 2020), PANDAS (McKinney 2010), and SCIPY (Virtanen et al. 2020).


Original languageEnglish
Pages (from-to)5603-5611
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date11 Feb 2021
Publication statusPublished - Apr 2021


  • astro-ph.SR, Sun: activity, Sun: rotation