Features of 27-day variations of galactic cosmic rays and of solar activity

Neutron monitor and solar activity data have been used to investigate the features of the 27-day variation of galactic cosmic rays (GCR) for the last maximum epoch of solar activity (1988-1992). The amplitude of the 27-day variation of GCR significantly diminishes in 1990 coinciding with the sun's polar magnetic field reversal period. The existence of the longitudinal asymmetry of the sunspot areas for the 30-40(0) heliolatitudinal interval in 1989 coinciding with the first maximum of the 27-day variation of GCR and the asymmetry for the 0-10(0) heliolatitudinal interval in 1991-1992 corresponding to the second maximum of the 27-day variation of GCR has been revealed. It is assumed that the destruction of the heliolongitudinal asymmetries of the solar wind velocity and of the interplanetary magnetic field strength by merged interaction regions and global merged interaction regions in the. heliosphere is the partial cause for the dip in the amplitude of the 27-day variation of GCR during maxima epochs of solar activity. (C) 1999 COSPAR. Published by Elsevier Science Ltd.