Intense Ground-Level Enhancements of Solar Cosmic Rays During the Last Solar Cycles

Ground-level enhancements of solar cosmic rays are sharp increases of short duration in the counting rates of ground-based neutron monitors. Their study is of particular importance, mainly due to their involvement in a vast range of applications such as the prediction of particle fluxes that may be harmful for satellite systems and telecommunication, the analysis of the interplanetary conditions, and the prediction of strong geomagnetic storms. In this work, we make a statistical analysis of the ground-level enhancements events occurring during solar Cycles 22 and 23, in an effort to reveal their common properties and possible physical mechanisms. Data of one- and five-minute resolutions are used, obtained from the worldwide network of neutron monitors and from the high-resolution NMDB database. The analysis includes onset-time calculations, determination of the maximum cosmic ray intensity, and determination of the longitudinal and latitudinal distribution. Moreover, a brief description of the most intense events is given. Finally, the importance of such a statistical analysis in space weather studies is discussed.