A multifractal approach to understanding Forbush Decrease events: Correlations with geomagnetic storms and space weather phenomena

Abstract

The Forbush decrease phenomenon has significant impacts on several environmental conditions, including interference in radio communications, satellite navigation systems, and the health of astronauts in space, among others. It is characterized by a temporary and noticeable reduction in the observed flux of galactic cosmic rays recorded at the Earth’s surface. This decrease occurs due to the modulation of cosmic rays through their interaction with shock waves generated by coronal mass ejections. As these shock waves traverse the interplanetary medium, which includes the solar wind and galactic cosmic rays, they exert compression forces on the cosmic ray flux, leading to a reduction in observed flux levels at Earth. This study investigates Forbush Decrease events across different solar cycles and explores their correlation with geomagnetic storm conditions using multifractal detrended fluctuation analysis. The findings indicate variations in the multifractal spectra for series under different geomagnetic storm conditions compared to the full Forbush decrease series. Moreover, it is observed that the amplitude of the multifractal spectrum is greater in the series that include events with a maximum index exceeding 6, suggesting a significant influence of geomagnetic storm conditions on the fractality and variability of Forbush Decrease magnitudes.