Continued activity of the 25th cycle: largest in 20 years. Ground-level enhancement and Forbush decrease

TL;DR

This paper analyzes recent solar activity events, including a Ground Level Enhancement and Forbush decrease, using global neutron monitor and SEVAN detector data to understand cosmic ray modulation during extreme solar events.

Contribution

It provides a detailed spectral analysis of GLE and FD events, demonstrating their intrinsic asymmetry and the complementary nature of neutron and muon observations in cosmic ray studies.

Findings

FD suppresses galactic cosmic rays, GLE introduces harder particles

Neutron and muon spectra differ at high energies

Combined observations improve understanding of cosmic ray modulation

Abstract

After a very calm 24th solar activity cycle, the 25th cycle has already seen several interesting events. A Ground Level Enhancement GLE77 was observed on 11 November 2025 following an X5.1 class solar flare. A strong Forbush decrease occurred on 19 and 20 January 2026 during one of the most intense geomagnetic storms of Solar Cycle 25. Events were recorded coherently by the global neutron monitor network and by SEVAN detectors at multiple altitudes. Using spectrometric capabilities, we reconstruct energy spectra of missing neutrons and muons during the FD and compare them with corresponding spectra measured during GLE77. The analysis demonstrates that FD and GLE signatures are intrinsically asymmetric. FDs selectively suppress the preexisting galactic cosmic ray population, whereas GLEs introduce an additional, harder particle component. Neutron and muon channels exhibit markedly different spectral behavior, particularly at higher deposited energies, reflecting their sensitivity to different primary energy ranges. These results show that combined NM and SEVAN observations provide robust, complementary diagnostics of rigidity dependent cosmic ray modulation during extreme heliospheric disturbances.