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Advances in Astronomy
Volume 2012, Article ID 607172, 8 pages
Research Article

Long-Term Cosmic Ray Variability and the CME-Index

Faculty of Physics, National and Kapodistrian University of Athens, Zografos, 15784 Athens, Greece

Received 25 September 2012; Accepted 28 November 2012

Academic Editor: Karel Kudela

Copyright © 2012 Helen Mavromichalaki and Evangelos Paouris. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The cosmic ray modulation in relation to solar activity indices and heliospheric parameters during the period January 1996–October 2011, covering the solar cycle 23 and the ascending phase of solar cycle 24, is studied. The new perspective of this contribution is that the CME-index, obtained from only the CMEs with angular width greater than 30 degrees, gives much better results than in previous works. The proposed model for the calculation of the modulated cosmic ray intensity obtained from the combination of solar indices and heliospheric parameters gives a very satisfactory value of the standard deviation. The best reproduction of the cosmic ray intensity is obtained by taking into account solar and interplanetary indices such as sunspot number, interplanetary magnetic field, CME-index, and heliospheric current sheet tilt. The standard deviation between the observed and calculated values is about 6.63% for the solar cycle 23 and 4.13% for the ascending part of solar cycle 24.