A preliminary statistical analysis of the GLEs in solar cycles 22 and 23

Registration of ground level enhancement events (GLEs) at ground based neutron monitors has started in the 1940's. Analytical studies of various GLEs have shown that each one of them constitutes a unique case, characterized by the specific solar and interplanetary conditions during the time period that it took place. However, possible similarities of the GLE characteristics between different event cases may be evidence for the existence of common physical mechanisms. Therefore realizing a statistical analysis of ground level enhancements is of great importance in order to reveal the inner relationship among these events. In this study the results of a preliminary statistical analysis of the ground level enhancements occurring during the solar cycles 22 and 23 (1986-2007) are presented, using data from both polar and middle latitude neutron monitors. A detailed comparison of the characteristics of these events is being held out in order to reveal possible similarities and differences among them. Special emphasis also discusgiven to the event recorded on April 15th, 2001 (GLE 60) as well as to the event of April 18th (GLE 61). The analysis of the various characteristics of these two events and their relation with the solar parameters reveals important information for the solar cosmic rays reaching the ground level. This statistical output can be also useful for GLE-modelling and other space weather applications. (authors)