Two periods of fast (covering one or two solar rotations) global variations of solar magnetic fields have been found to exist in each 11-year cycle of solar activity. Solar activity that is determined from commonly employed indices (Wolf numbers, radio flux, etc.) changes little during these periods. These periods are characterized by both an enhancement of flaring activity, which accounts for the fast changes in current, and, accordingly, magnetic structures. One occurs during the rising phase of solar activity and is accompanied by an enhancement of large-scale magnetic fields and fast changes in global magnetic structure of the corona. In this case, favorable conditions are created for an effective acceleration of high-energy solar cosmic rays. The other occurs during the declining phase of solar activity and is characterized by a structural simplification of large-scale magnetic fields and largely by the attenuation of magnetic fields in the corona. The observed significant increase in solar wind mass flux, an enhancement of the interplanetary magnetic field, and anomalously strong geomagnetic disturbances are heliospheric manifestations of transient phenomena and processes in the solar corona associated with the dynamics of large-scale magnetic fields. This period is most conspicuous in long-term cosmic ray intensity variations, which are analogous to a Forbush decrease. These findings are explained by the commencement and cessation of an active interaction between magnetic fields of the old cycle and emerging fields of the new cycle, which trigger transient, flare-related, coronal processes.¿ 1997 American Geophysical Union