Application of the verified neutron monitor yield function for GLE analysis

Abstract

Systematic study of solar energetic particles provides an important basis to understand their acceleration and propagation in the interplanetary space. After solar eruptive processes, such as solar flares and/or coronal mass ejections, solar ions are accelerated to high energy. In the majority of cases, the maximum energy of the accelerated solar ions is several tens of MeV/nucleon, but in some cases, it exceeds 100 MeV/nucleon or even reaches the GeV/nucleon range. In this case, the energy is high enough, so that solar ions generate an atmospheric cascade in the Earth’s atmosphere, whose secondary particles reach the ground, being eventually registered by ground-based detectors, specifically neutron monitors. This particular class of events is known as ground-level enhancements (GLEs). Several methods for analysis of GLEs, using neutron monitor data were developed over the years. Here, we present a method for assessment of the spectral and angular characteristics of the GLEs using data from the world-wide NM network, namely by modeling the global neutron monitor network response with a new verified yield function. The method is based on consecutive steps, specifically detailed computation of asymptotic cones and rigidity cut-off of each station used in the analysis and optimization of the global neutron monitor response over experimental and modeled count rate increases. The method is compared with other methods, including in-situ measurements. A very good agreement between our method and space-borne measurements with PAMELA space probe, specifically the derived fluence of solar protons during GLE 71 was achieved, therefore verification of the method is performed.