Cyclic variations in the main components of the solar large-scale magnetic field

Abstract

We considered variations the dipole and the quadrupole components of the solar large-scale magnetic field. Both the axial and the equatorial dipoles exhibit a systematic decrease in the past four cycles in accordance with the general decrease of solar activity. The transition of the pole of a dipole from the polar region to mid latitudes occurs rather quickly, so that the longitude of the pole changes little. With time, however, this inclined dipole region shifts to larger longitudes, which suggests an acceleration of the dipole rotation. The mean rotation rate exceeds the Carrington velocity by 0.6%. The behavior of the quadrupole differs dramatically. Its decrease over last four cycles was much smaller than that of the dipole moment. The ratio of the quadrupole and dipole moments has increased for four cycles more than twice in contrast to the sunspot numbers, which displayed a twofold decrease for the same time interval. What about quadrupole rotation, the mean longitude of the poles of one sign decreased by 600 degrees over four cycles, which suggests that the mean rotation rate was lower than the Carrington velocity by 0.28%. We do not see however any conclusive evidence that, in the period under discussion, a mode of quadrupole symmetry was excited on the Sun along with the dipole mode.

arXiv comment10 pages, 14 figures. Accepted to Monthly Notices of the Royal Astronomical Society

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