Observation of the Forbush decrease during the May 2024 solar storms with different muon and neutron detectors in the high-latitude site of the Svalbard archipelago

During the series of intense solar flares that occurred in May 2024, a remarkable Forbush decrease in the cosmic ray flux was observed on the Earth by particle detectors around the world. The Svalbard archipelago, which is located at polar latitudes, is particularly exposed to geomagnetic storms because the Earth's magnetic field provides a particularly weak shielding and is therefore a privileged observation point. In this contribution, we report an analysis of the Forbush decrease event using data from a unique combination of muon and neutron detectors installed in Ny-Ålesund, on Svalbard: three scintillator-based muon telescopes of the Extreme Energy Events (EEE) Project, 14 channels of a Bonner Sphere neutron Spectrometer (BSS), thermal and epithermal neutron sensors used for hydrological monitoring, and a high-energy neutron monitor located in Barentsburg and operated by the Polar Geophysical Institute. We found that most sensors showed significant responses and correlation during the event. The observed magnitude of the Forbush decrease depended on the detector’s energy sensitivity and was ≈ 10% for thermal neutrons, ≈ 8% for high-energy neutrons, and ≈ 3% for muons. The uncertainty of these results strongly depends on factors like the count rate, which ranged from 10 to 105 cph and resulted in low signal-to-noise ratio, particularly for the BSS. A detailed correlation analysis was carried out among the various time series originated from the different detectors in the “quiet” period (before the Forbush decrease) and during the Forbush event. Multi-particle and multi-energy observations provide an unprecedented view on the Earth’s exposure to cosmic rays during solar events.