Sources of the global magnetic field of the Sun

Abstract

Data on the global magnetic field (GMF) of the Sun as a star for 1968–1999 are used to determine the correlation of the GMF with the radial component of the interplanetary magnetic field (IMF) |Br|; all data were averaged over a half year. The time variations in the GMF |H| are better correlated with variations in |Br|; than the results of extrapolating the field from the “source surface” to the Earth’s orbit in a potential model based on magnetic synoptic maps of the photosphere. Possible origins for the higher correlation between the GMF and IMF are discussed. For both the GMF and IMF, the source surface actually corresponds to the quiet photosphere—i.e., background fields and coronal holes—rather than to a spherical surface artificially placed ≈2.5 R⊙ from the center of the Sun, as assumed in potential models (R⊙ is the solar radius). The mean effective strength of the photospheric field is about 1.9 G. There is a nearly linear dependence between |H| and |Br|. The strong correlation between variations in |H| and |Br| casts doubt on the validity of correcting solar magnetic fields using the so-called “saturation” factor δ−1 (for magnetograph measurements in the λ 525.0 nm FeI line).