High latitude observation of the Forbush decrease during the May 2024 solar storms with muon and neutron detectors on Svalbard

During the series of intense solar flares and coronal mass ejections, that occurred in May 2024, a remarkable Forbush decrease in the cosmic ray flux was observed on the Earth. While this event was observed by particle detectors around the world, the archipelago of Svalbard was heavily exposed to it due to the weak geomagnetic shielding in the polar region. In this study, an analysis of the Forbush decrease event was carried out with a unique combination of muon and neutron detectors on Svalbard: at Ny-Ålesund three scintillator-based muon telescopes of the Extreme Energy Events (EEE) project, 14 channels of a Bonner Sphere neutron Spectrometer (BSS), and thermal and epithermal neutron sensors used for hydrological monitoring; and, at Barentsburg, a high-energy neutron monitor operated by the Polar Geophysical Institute. Most sensors showed significant responses and correlation during the event. The observed relative magnitude of the Forbush decrease was found to depend on the detector’s energy sensitivity and was $\approx 9\%$ for thermal neutrons, $\approx 8\%$ for high-energy neutrons, and $\approx 3\%$ for muons. The uncertainty of these results strongly depends on factors like the count rate, which ranged from ${10}^1$ to ${10}^5$ cph and resulted in a low signal-to-noise ratio particularly for the BSS. These multi-particle and multi-energy observations provide an unprecendented view on the Earth’s exposure to cosmic rays during solar events.