A comprehensive study of solar energetic particle propagation during the first ground-level enhancement of the solar cycle 24

Abstract

The first ground-level enhancement (GLE) of the 24 th solar cycle was observed on 2012 May 17 by the ground-based neutron monitor network. Correspondingly, space-based high-energy particle detectors at the Earth orbit observed the typical signatures of a solar energetic particle (SEP) event. The SEP/GLE event occurred during the transit of a large-scale magnetic cloud. A comprehensive study of the event is presented here by analyzing both space-and ground-based high-energy particle measurements as well as by estimating the magnetic cloud configuration through the Grad-Shafranov reconstruction. In order to give an estimate of the GLE primary energy spectrum we use the neutron monitor based anisotropic GLE pure power law (NMBANGLE PPOLA) model and we compare results with spacecraft observations by using data gathered by the PAMELA experiment, which was in a favorable position with respect to the arrival directions of primary protons during the event main phase. The anisotropy of the particle flux during the SEP/GLE event is also investigated through the NMBANGLE PPOLA. Our results suggest that the large-scale magnetic cloud configuration played an important role in leading the high-energy particle propagation.