General Magnetic Field of the Sun as a star (GMF): Variability of the frequency spectrum from cycle to cycle

Abstract

AbstractDuring 42 years of observations the General Magnetic Field of the Sun as a star demonstrates a stable picture of variability with the activity cycle: during maximum activity GMF reaches ∼2 G, and during minimum it reaches ∼0.2 G. The frequencies of prominent peaks in the power spectrum of GMF significantly vary from one cycle of activity to another one. All data folded in phase with the equatorial synodic period ∼26.d9 shows a specific phase curve similar to a dipole with amplitude ∼0.2 G and the absolute ratio of positive to negative magnetic flux ∼0.9. That is, during four decades of observations the excess of the positive magnetic flux is concentrated on the one side of the Sun, the excess of the negative flux is concentrated on the opposite side, and this magnetic field does not reverse its polarity with the 22‐year Hale solar cycle. In the case, when poloidal dipole axis coincides with rotation axis one can see a more complex picture of variability: the power spectrum for GMF values obtained at four minima of activity between 20 and 24 sunspot cycles demonstrates a large difference in relative amplitude of frequencies from the power spectrum for total GMF array and indicates the presence of the quadrupole component. Rough empirical estimation of the upper limit of the mean velocity of the poloidal dipole sign reverse for the Hale cycles from 1749 to 1997 gives 〈V 〉 ≈ 6.85 ± 0.05 m s–1. We suppose the presence of additional weak large‐scale magnetic field on the Sun. The axis of the field lies near the equatorial plane. This weak large‐scale magnetic field reflects properties of the stationary global magnetic field of the solar radiative interior on the surface of the Sun, which appears to be a third large‐scale component of the magnetic field along with known toroidal and poloidal fields (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)