Forbush Decrease Magnitude ≥4% and its Connection with Geomagnetic Storms During Solar Cycle 24

Abstract

Forbush decreases (FDs) of cosmic ray intensity, particularly those of ≥4%, are closely associated with geomagnetic disturbances triggered by solar events such as coronal mass ejections (CMEs) and solar flares. FDs magnitude ≥4% are observed and found 19 FD events during year 2008 to 2019.Solar Cycle 24, marked by relatively low solar activity compared to previous cycles, provides a unique opportunity to examine the impact of geomagnetic storms on cosmic ray modulation during a weaker solar cycle. This study explores the association between Forbush decreases of ≥4% and geomagnetic indices, specifically the Kp, Dst, and Ap indices, during Solar Cycle 24. Data from Solar Cycle 24 were studied to determine the temporal and statistical correlations between Forbush reductions and geomagnetic activity. The results show a substantial positive relationship between Forbush reductions and the Kp and Ap indices, with a weaker but still significant negative correlation with the Dst index. This study provides critical insights into the mechanisms behind cosmic ray modulation during geomagnetic storms, particularly in the context of a weaker solar cycle. The findings have implications for space weather forecasting, cosmic ray studies, and understanding the broader influence of solar activity on the Earth's magnetosphere during periods of reduced solar intensity.