The Implication of Solar-Geophysical Parameters on High-Amplitude Forbush Decreases

Abstract

Space weather research is crucial to Earth’s civilization. Forbush decreases (FDs) short-term, rapid depressions in the time-intensity flux of cosmic rays (CRs) are key indicators of space weather conditions. However, the identification, selection, and calculation of FD magnitude and timing present significant challenges to their use as space weather probes. The manual methods that dominate the field are subjective, leading to inconsistent and controversial solar-terrestrial correlations. Recently, accurate Forbush decrease (FD) catalogs were developed for Moscow (MOSC) and Oulu (OULU) neutron monitor data. This study identifies high-amplitude FDs from these catalogs to test correlations with solar-geomagnetic variables, including solar ejections, interplanetary magnetic fields, geomagnetic activity, and cosmic ray anisotropies. The results suggest that the magnitude of FDs and their correlation with solar-geomagnetic variables are location-dependent. Due to differences in geomagnetic cutoff rigidity and the sensitivity of the MOSC and OULU stations, event magnitude varies appreciably between the two locations. We conclude that, rather than judging event strength by magnitude alone, the test of event simultaneity across both stations is a more reliable indicator of FD event size.