Abstract
Abstract The data of mean magnetic field (MMF) of the Sun obtained at the Wilcox Solar Observatory (Stanford, USA) in 1975–2020 are analysed. It was concluded that the MMF maximum occurs, on average, 1.5–2 years later relative to the maximum of Wolf numbers. To analyze the changes in the MMF, a new method for searching for periodicities has been developed, which takes into account the change in the sign of the magnetic field from cycle to cycle. This method made it possible to find the main synodic periods of rotation of the magnetic field with values of 27d.021 ± 0d.008, 26d.796 ± 0d.008 and 27d.260 ± 0d.008, each of which has two splitting components associated with a change in the polarity of the magnetic field during the transition from one cycle of solar activity to another. The stability of these periodicities for more than 45 years indicates that the Sun as a star looks like a horizontal magnetic dipole (in addition to the observed vertical one), which changes its sign every 11 years and rotates with different periods.
Highlights
The mean magnetic field (MMF) of the Sun is the average value of the magnetic flux from the entire visible solar hemisphere
To analyze the changes in the MMF, a new method for searching for periodicities has been developed, which takes into account the change in the sign of the magnetic field from cycle to cycle
A new method of analysis was applied, which takes into account the change in the sign of the magnetic field in each cycle of solar activity
Summary
The mean magnetic field (MMF) of the Sun is the average value of the magnetic flux from the entire visible solar hemisphere. Its measurements were started in 1968 by Severny (1969) at the Crimean Astrophysical Observatory, and were continued by a few observatories. The MMF measurements were carried out by various groundbased instruments. There are data from seven observatories, as well as measurements from the SOHO and SDO satellites, where the MMF signal can be extracted. Of all the available observational series, the Wilcox Solar Observatory (Stanford, USA) data set is the longest, most numerous and homogeneous (Scherrer et al 1977). The observations have been started here in 1975 and are continued to the present by the same instrument. This series was chosen to study the variability of the MMF.
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