Magnetic Coupling of the Solar Hemispheres During the Solar Cycle

Abstract

This work is devoted to the study of peculiarities in the magnetic coupling of the solar hemispheres over a solar activity cycle. Two approaches have been used. We have studied (i) the magnetic coupling of active regions (ARs) located in different hemispheres in the vicinity of the central meridian and, simultaneously, in the vicinity of the equator and (ii) the properties and time variation of the meridional component of the equatorial magnetic field derived from a potential-field source surface (PFSS) reconstruction at the heliocentric distance of 1.1 solar radii. In the first case, it was shown that most of the ARs in the selected pairs were magnetically connected by field lines in their leading parts. In the second case, the magnetic field monthly mean meridional component, $B_{\theta }$, in the equatorial plane, which magnetically connects the two hemispheres, displayed a cyclic time variation. In the process, the extreme values of $B_{\theta }$ (both positive and negative) coincided in time with the sunspot maxima, and the amplitude of the $B_{\theta }$ extreme values decreased with decreasing height of the sunspot activity cycle. The sign of the $B_{\theta }$ extreme value was opposite to the sign of the forthcoming extreme value of the polar field, while the sign of $B_{\theta }$ coincided with that of the field lines connecting the leading spots. This means that the polar field is indeed generated by the trailing spots of ARs, and the magnetic flux of the leading spots closes through the equator.