Revised GLE database: Fluences of solar energetic particles as measured by the neutron-monitor network since 1956^⋆

¹ Space Physics and Astronomy Research Unit, University of Oulu, Oulu, Finland
e-mail: Ilya.Usoskin@oulu.fi
² Sodankylä Geophysical Observatory, University of Oulu, Oulu, Finland
³ National Research Nuclear University MEPhI, Moscow, Russia
⁴ A.F. Ioffe Physical-Technical Institute of Russian Academy of Sciences, St. Petersburg, Russia
⁵ Siedlce University, Faculty of Exact and Natural Sciences, Institute of Mathematics, Siedlce, Poland
⁶ Space Research Centre of Polish Academy of Sciences, Warsaw, Poland
⁷ Department of Physics, University of Helsinki, Helsinki, Finland
⁸ Independent Researcher, Helsinki, Finland

Received: 27 April 2020
Accepted: 1 June 2020

Abstract

Aims. Continuous measurements of ground-based neutron monitors (NMs) form the main data source for studying high-energy high-intensity solar energetic particle (SEP) events that are called ground-level enhancements (GLEs). All available data are collected in the International GLE Database (IGLED), which provides formal NM count-rate increases above the constant pre-increase level which is due to galactic cosmic rays (GCR). This data set is used to reconstruct the energy spectra of GLE events. However, the assumption of a constant GCR background level throughout GLE events is often invalid. Here we thoroughly revise the IGLED and provide a data set of detrended NM count-rate increases that accounts for the variable GCR background.

Methods. The formal GLE count-rate increases were corrected for the variable GCR background, which may vary significantly during GLE events. The corresponding integral omnidirectional fluences of SEPs were reconstructed for all GLEs with sufficient strength from the detrended data using the effective rigidity method.

Results. The database of the detrended NM count rate is revised for GLE events since 1956. Integral omnidirectional fluences were estimated for 58 GLE events and parametrised for 52 sufficiently strong events using the modified Ellison-Ramaty spectral shape.

Conclusions. The IGLED was revised to account for the variable GCR background. Integral omnidirectional fluences reconstructed for most of GLE events were added to IGLED. This forms the basis for more precise studies of parameters of SEP events and thus for solar and space physics.