Analysis of the Forbush Decreases and Ground‐Level Enhancement on September 2017 Using Neutron Spectrometers Operated in Antarctic and Midlatitude Stations

Abstract

This work investigates solar events occurred in September 2017 characterized by a series of Forbush decreases and a ground level enhancement (GLE). Forbush decreases is a rapid decrease in the observed https://en.wikipedia.org/wiki/Galactic_cosmic_ray intensity following a coronal mass ejection while GLE is induced by a strong solar event for which the flux of high‐energy solar particles is sufficient to enhance the radiation level on the ground. These investigations were performed using data recorded by a neutron spectrometer network composed of a Bonner sphere system. Two instruments located at Pic‐du‐Midi Observatory (+2,885 m above sea level) and at Concordia station (Antarctica, +3,233 m) record simultaneously and continuously the neutron spectra, allowing to consider short‐term variations during solar events. The main objective is to analyze neutron spectral properties including their energy distributions and dynamics. This paper presents cosmic ray‐induced neutron spectra during active solar event leading to changes in the local cosmic ray spectrum (Forbush decreases and a GLE). Concerning the GLE, analyses show that neutrons in the evaporation domain are particularly amplified during the GLE, while other energetic domains increase uniformly.

High Energy Solar Particle Events and Their Relationship to Associated Flare, CME and GLE Parameters

“…Smaller increases are more common at stations closer to sea‐level at non‐polar latitudes that have to compete with geomagnetic shielding as well as atmospheric shielding. Varying cut‐off rigidities can influence the detection and intensity of GLEs together with other factors such as Forbush decreases (e.g., GLE 72 occurred toward the end of a Forbush decrease where count rates were still suppressed (Hubert et al., 2019), and GLE 67 occurred during a Forbush decrease following GLE 66 (Mishev et al., 2021).…”

Buoy‐Based Detection of Low‐Energy Cosmic‐Ray Neutrons to Monitor the Influence of Atmospheric, Geomagnetic, and Heliospheric Effects

“…Furthermore, Hubert et al. (2019) and Hubert (2024) found a different response to solar events for neutrons of different energies. Hence, for the correction of neutron intensities for incoming radiation in the scope of CRNS, it may not be sufficient to scale the neutron monitor response to different cutoff rigidities and atmospheric shielding depths only (Hawdon et al., 2014; McJannet & Desilets, 2023), but also to account for the different response of low‐energy neutron detectors and neutron monitors.…”

Potential benefit of retrospective use of neutron monitors in improving ionising radiation exposure assessment on international flights: issues raised by neutron passive dosimeter measurements and EPCARD simulations during sudden changes in solar activity

“…However, sometimes solar flares with increased flux of charged particles flowing towards the Earth deflect protons of the galactic component of the primary cosmic radiation and therefore decrease neutron flux of the secondary cosmic radiation in the atmosphere. Such events are called Forbush decreases and may lower neutron flux by more than 20 % ( 20 , 21 ). A case in point are our M1, M2, M4, and M6 measurements taken on the Belgrade–Dortmund flights at different times and therefore solar activities.…”