On stability of rotation of the mean magnetic field of the Sun

Crimean Astrophysical Observatory, Nauchny, Crimea 98409, Ukraine Isaak Newton Institute of Chile, the Crimean Branch e-mail: han@crao.crimea.ua, vkotov@crao.crimea.ua

Corresponding author: V. I. Haneychuk, han@crao.crimea.ua

Received: 30 September 2002
Accepted: 14 February 2003

Abstract

New data on the mean magnetic field of the Sun (MMFS) as a star measured at the Crimean Astrophysical Observatory in 1998–2001 are presented. The 34-year time series of the MMFS using similar data from three other observatories (1968–2001, with the total number of daily MMFS values N = 12 428), is considered. It is found that (a) the primary synodic period of the equatorial rotation of solar magnetic field,  days, did not vary over the last 34 years, but (b) the average intensity H₀ of the photospheric large-scale fields, by modulus, decreased by about 4.5% (with a confidence level of about 80%). The conclusion is made that the longer, 90-year, cycle might be responsible for this potential gradual decrease of H₀. The average curve of MMFS variation as plotted with the primary rotational period demonstrates an obvious N-S asymmetry of polarities, perhaps associated with the quadrupole component and “magnetic disequilibrium” of the Sun as a whole.