27-day variations of the galactic cosmic ray intensity and anisotropy
08 Jul 2008
1Institute of Math. And Physics of University of Podlasie, 3 Maja 54, 08-110 Siedlce, Poland
2Institute of Geophysics, Georgian Academy of Sciences, Tbilisi, Georgia
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−γ) is hard (γ=0.54±0.11) in the A>0 polarity period (1996–1997) and is soft (γ=0.95±0.12) in the A<0 period (1986–1987).