The large-scale solar magnetic field and 11-year activity cycles

Magnetic Ha synoptic maps of the Sun for 1915-1999 are analyzed and the int ensities of spherical harmonics of the large-scale solar magnetic field com puted. The possibility of using these Ha maps as a database for investigati ons of long-term variations of solar activity is demonstrated. As an exampl e, the magnetic-field polarity distribution for the Ha maps and the analogo us polarity distribution for the magnetographic maps of the Stanford observ atory for 1975-1999 are compared. An activity index A(t) is introduced for the large-scale magnetic field, which is the sum of the magnetic-moment int ensities for the dipole and octupole components. The 11-year cycle of the l arge-scale solar magnetic field leads the 11-year sunspot cycle by, on aver age, 5.5 years. It is concluded that the observed weak large-scale solar ma gnetic field is not the product of the decay of strong active-region fields . Based on the new data, the level of the current (23rd) solar-activity cyc le and some aspects of solar-cycle theory are discus sed. (C) 2000 MAIK "Na uka/Interperiodica".