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Astron. Astrophys. 330, 764-772 (1998)

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Simulated effects at neutron monitor energies:
evidence for a 22-year cosmic-ray variation

H. Mavromichalaki 1, A. Belehaki 2 and X. Rafios 1

1 Nuclear and Particle Physics Section, University of Athens, Solonos Str. 104, GR-106 80 Athens, Greece
2 National Observatory of Athens, Institute of Space Research, Metaxa & Vas. Pavlou Str., GR-152 36 Palaia Penteli, Greece

Received 31 July 1996 / Accepted 24 June 1997


Determined systematic differences in the overall shapes of successive 11-year modulation cycles (1946-1995) and similarities in the shapes of alternate 11-year cycles seem to be related to the 22-year magnetic cycle and to the polarity reversals of the polar magnetic field of the Sun. This different behaviour of the odd and even solar cycles that are the two parts of the 22-year periodicity is discussed in terms of different processes influencing the transport of cosmic rays from the edges of the heliosphere to the near-Earth region. Taking into account these characteristic features, monthly cosmic-ray data from Inuvik and Climax Neutron Monitor Stations have been used to describe on a general basis the long-term modulation of galactic cosmic-rays during the last three solar cycles (1965-1994) where data are available. With the aid of appropriate selected source functions and calculating the time lag of cosmic-ray intensity against these indices, the modulated cosmic-ray intensity has been simulated with an approximation of 10% during this period. The hysteresis curves applied to the observed modulated as well as to the calculated cosmic-ray intensities with the expected differences between even and odd solar cycles confirm the good approximation of our generalised model. This is derived by the generalisation of Simpson's solar wind model using the diffusion-convection theory.

Key words: inteplanetary medium – Sun: activity – cosmic rays

Send offprint requests to: H. Mavromichalaki

© European Southern Observatory (ESO) 1998

Online publication: January 16, 1998