27-day variations of the galactic cosmic ray intensity and anisotropy

Abstract

We study the 27-day variations of the galactic cosmic ray (GCR) intensity and three dimensional (3-D) anisotropy in different polarity periods of the solar magnetic cycle. We found that the larger amplitudes of the 27-day variations of the galactic cosmic ray anisotropy and intensity in the minimum epochs of solar activity for the A > 0 polarity period than for the A < 0 period are related with the heliolongitudinal asymmetry of the solar wind velocity. We reveal the long -lived ( 22 years) active region of the heliolongitudes being the sources of the long-lived 27-day variation of the solar wind velocity during the A > 0 polarity period. The 27-day variation of the GCR 3-D anisotropy has a sporadic character; it appears and disappears as wave packages (wave oscillations) with an average duration of 4-6 solar rotations. We found that the rigidity R power law spectrum of the amplitudes (A27) of the 27-day variation of the GCR intensity (A27 R - ) is hard ( = 0.54 0.11) in the A > 0 polarity period (1996)(1997) and is soft ( = 0.95 0.12) in the A < 0 period (1986)(1987).