Ground-level enhancements during solar cycle 23: results from SVIRCO, LOMNICKY STIT and LARC neutron monitors

The list of Ground-Level Enhancements (GLEs) occurring during the on-going solar cycle (no. 23) is used to show that they are absent during a time interval of the maximum phase in which a relative reduction in the sunspot area extent occurs. This period refers to October 2000 to March 2001 and it is associated with the concept of the Gnevyshev Gap, introduced 10 years ago by the Rome cosmic ray group. Also, effects of the Gnevyshev Gap in the solar cycle modulation of the atmospheric attenuation coefficient for Rome neutron monitor during the past solar cycle (no. 22) are illustrated. Moreover, it is suggested that GLE data files should be prepared by using the appropriate attenuation coefficient for each level of solar activity.