A bimodal distribution around the sunspot cycle maximum was suggested to exit for solar-terrestrial parameters (Storini et al., Adv. Space Res. 31, n° 4, 895- 900, 2003). The period between the two activity peaks was called the Gnevyshev Gap by the Rome Cosmic Ray Group (Storini and Pase, GBRSC News 5, Special Issue, 255-258, 1995) and it is world-wide accepted by the scientific community. Nevertheless, the concept was recently questioned by some investigators. In this paper we show the reliability of the Gap in sunspot areas, solar and galactic cosmic rays and in some geomagnetic parameters. A good knowledge of the Gnevyshev Gap phenomena is relevant for Space Mission planning during the 11-year solar activity cycle.

*: Work supported by the Italian Space Agency for BepiColombo Mission.

Proceedings of the 30th International Cosmic Ray Conference; Rogelio Caballero, Juan Carlos D'Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.); Universidad Nacional Autónoma de México, Mexico City, Mexico, 2008; Vol. 1 (SH), pages 533-536