Structures of Various Types of Symmetry in the Solar Activity Cycle

Abstract

The solar cycle is a complex phenomenon. To comprehensively understand it, we have to study various tracers. The most important component of this complex is the solar dynamo, which is understood as self-excitation of the solar magnetic field in the form of traveling waves somewhere in the convection zone. Along with the solar dynamo, the formation of the solar cycle involves other processes associated with the dynamo but not its necessary part. We review such phenomena that have not yet been explained in terms of dynamo theory. We consider the manifestations of the solar cycle in harmonics of the solar large-scale surface magnetic field, including zonal, sectorial, and tesseral harmonics; analyze their contribution to magnetic energy; and identify phases of the activity cycle using harmonics of different types of symmetry. The universal magnetic scenario of a solar activity cycle does not depend on its number and amplitude. At the beginning of the cycle in the photosphere, the zonal harmonics account for 37 – 42% of the total energy (not 100%, as assumed in simplified descriptions). Sectorial harmonics do not disappear but account for 5 – 10% of the total energy. At this stage, the greatest energy (about 40%) is contained in the tesseral harmonics. As the cycle develops, the relative energy of zonal harmonics gradually decreases, reaching a minimum of 15 – 18% immediately before the onset of the sunspot maximum. The relative energy of sectorial harmonics increases and reaches a maximum (60 – 65%) somewhat later than the calendar date of the sunspot maximum. A particular feature of the tesseral harmonics is that their relative energy index changes in a much narrower range and never falls below 40%, even at the cycle minimum. This is due to active regions and nonglobal magnetic fields. Tesseral harmonics may be formed in shallow subphotospheric layers.