The large-scale magnetic field and sunspot cycles

Abstract

H magnetic synoptic charts of the Sun are processed for 1915 - 1999 and the spherical harmonics are calculated. It is shown that the polarity distribution of the magnetic field on H charts is similar to the polarity distribution of the Stanford magnetic field observations during 1975 - 1999. The index of activity of the large-scale magnetic field A.t/, representing the sum of the intensities of dipole and octupole components, is introduced. It is shown that the cycle of the large-scale magnetic field of the Sun precedes on the average by 5.5 years the sunspot activity cycle, W.t/. This means that the weak large-scale magnetic fields of the Sun do not result from decay and diffusion of strong fields from active regions as it is supposed in all modern theories of the solar cycle. On the basis of the new data the intensity of the current solar cycle 23 is predicted and some aspects of the theory of the solar cycle are discussed. The origin and role of the large-scale magnetic field in the organization of the general solar magnetism and its connection with sunspot activity is a key question for understanding the 22-yr cycle of magnetic activity. Conspicuous features of solar activity are the cyclic occurrences in the solar atmosphere of pairs (or groups) of sunspots with different polarity and with strong fields up to 5 kG. The polarity of these pairs has different orientation in both hemispheres and after a minimum of activity they reverse polarity. The large-scale magnetic field regions of the Sun are another remarkable magnetic manifestation. It changes polarity too, but at a maximumof sunspot activity. Many modern theories of a solar cycle consider the weak large-scale magnetic field as the result of breakup of strong fields of active regions and their drift to poles, i.e., as a secondary product of the activity of strong magnetic fields. The underlying idea is that the supergranular motions, differential rotation, and merid- ional flow transform the magnetic fields of active regions to form the large-scale field patterns (Babcock, 1961; Leighton, 1964; DeVore, Sheeley, and Boris, 1984; Wang, Nash, and Sheeley, 1989). However, many questions, e.g., concerning the duration of the solar cycle and magnetic field reversals of the Sun, remain open.