Mean absolute strength of the solar magnetic field in 1968–2006

Measurements of the mean magnetic field of the Sun as a star (the line-of-sight component of the magnetic field of the visible hemisphere for a given day) carried out at six observatories are used to compile a catalog of the mean magnetic field for 1968–2006 (containing about 18 000 daily values). The cataloged data are compared with direct daily measurements of the absolute line-of-sight field made at the Kitt Peak Observatory in 2003–2006 (original data with a resolution of 1″ averaged over the solar disk). The true absolute mean field strength averaged over the visible solar hemisphere is determined for 1968–2006 to be B 0 = 7.7 ± 0.2 G. This figure exceeds previous estimates by almost a factor of four. B 0 exhibits no appreciable slow trend over the entire 39-year interval, but varies substantially with the cycle. The period of this variation is 10.5 ± 0.7 yr, and its harmonic amplitude is 1.7 G. The magnetic flux of spots and active regions makes B 0 almost twice the field strength in the “normal” photosphere at the solar minimum, i.e., for the “quiet” Sun.