Physics
Scientific paper
Aug 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001icrc....9.3489d&link_type=abstract
Proceedings of the 27th International Cosmic Ray Conference. 07-15 August, 2001. Hamburg, Germany. Under the auspices of the Int
Physics
Scientific paper
Although 27-day recurrent variations have been studied for about 60 years, their importance for understanding the global modulation of galactic cosmic rays (CR) is still not fully realised. The recent Ulysses observations in the polar regions of the heliosphere generated new ideas about the importance of 27-day recurrent variations in global processes which lead to galactic CR modulation effects. To investigate the fine structure of CR variations it is important to exclude the influence of Forbush decreases (Fds) on the different types of CR variations, especially when one investigates 27-day variations and recurrent Fds. We investigate 27-day variations and Fds during 1986-1996 based on the data of neutron monitors and Nagoya meson telescopes. To exclude the influence of Fds we used data corrected for Fds. We found that the amplitude of pure 27-day variations (i.e. free from influence of Fds and other non-stationary changes) depends only on the global magnetic field polarity reversal. Because the differences between amplitude corrected and uncorrected for Fds 27-day variations are significant during 1989 and 1991, we investigated these periods in detail. Our data provide clear evidence that the differences in the upper rigidity limit of modulation of 27-day variation and Fds lead to a decay of the Fd contribution in formation of 27day variation with increasing rigidity of particles. Corrected for Fds data shows the existence of the 27-day CR variation caused by the long-lived magnetic irregularities travelling beyond 1 AU.
Despotashvili M. A.
Fluckiger Erwin O.
Nachkebia N. A.
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