AN INTERPRETATION OF THE POSSIBLE MECHANISMS OF TWO GROUND-LEVEL ENHANCEMENT EVENTS

Abstract

We have carried out this work to clarify the possible mechanisms of two important high-energy particle events (GLE69 2005 January 20, 06: 46 UT and GLE70 2006 December 13, 02: 45 UT). For this purpose, the cosmic-ray intensities registered by neutron monitors at several sites have been analyzed and studied with concurrent solar flares of different energy bands. To determine whether the ground-level enhancement (GLE) might be caused by the energy released from a solar flare or a CME-driven shock, we identify the particle injection time in terms of the lowest value of the spectral indices deduced from proton fluxes. If the GLE is caused by the energy released from particle acceleration in a solar flare, the intensive phase of the flare representing extreme emission should lie within the injection time. While fulfilling this criterion, it is further necessary to understand the possible relativistic energy computed in terms of the possible travel time deduced by employing the observational time lag between the GLE and the concurrent solar flare. Accordingly, we have found that GLE69 is procured with sufficient possible relativistic energy (similar to 1.619 GeV) by the energy released from particle accelerations in the intensive phases of a solar flare components that have been corroborated by the injection time. The intensive phases of the flare components have also been justified with the prominent phases of a solar radio type III burst. For event GLE70, the particle injection time lies within the CME-driven shock justified by a solar radio type II burst which seems to be capable of procuring sufficient possible relativistic energies (similar to 1.231 to similar to 2.017 GeV). It is also noted that any fractional amount of energy (similar to 0.226 to similar to 0.694 GeV) from preceding flare components might be considered as a contribution to the shock acceleration process. Thus, GLE70 is presumably caused by the sum of the energy released mostly from a CME-driven shock and partially from preceding flare components.