A new reconstruction of solar energetic particle fluence for GLE events

Sergey Koldobskiy (University of Oulu)
Osku Raukunen (University of Turku, Aboa Space Research Oy)
Rami Vainio (University of Turku)
Gennady Kovaltsov (University of Oulu)
Ilya Usoskin (University of Oulu)

A ground-level enhancement (GLE) is defined as a strong event with high-energy solar energetic particles (SEPs) detected by the network of ground-based neutron monitors. Until now, 73 GLEs have been registered. In this work, we report a new reconstruction of the event-integrated spectra (fluences) of SEPs during 59 moderate and strong GLE events detected by NM network and satellite experiments. The reconstructions of SEP fluences are based on the “bow-tie” method employing the latest advances in NM data analysis (time-dependent GCR background and the use of the altitude-dependent NM yield function directly verified with the AMS-02 experiment data) and a detailed study of different uncertainties. As a result of this work, we obtained fluences of SEPs in the energy range from 30 MeV to a few GeV for GLE events since 1956, which were fitted with the modified Band-function (a double power-law function with two exponential cutoffs). An easy-to-use presentation of SEP fluences in the form of an analytical expression makes a solid basis for new studies in various fields, such as the influence of SEPs on the atmosphere and a statistical study of extreme solar activity.