New insights from cross-correlation studies between solar activity indices and cosmic-ray flux during Forbush decrease events

TL;DR

This study analyzes the relationship between solar activity, cosmic-ray flux, and Forbush decreases using cross-correlation of space and ground-based data, revealing new predictive parameters for cosmic-ray variations.

Contribution

It introduces the use of power exponents of fluence spectra as predictors for Forbush decrease magnitude, improving understanding of solar-terrestrial interactions.

Findings

Power exponents of fluence spectra correlate with Forbush decrease parameters.

These exponents are better predictors of Forbush decrease magnitude than CME velocities.

The study combines space-borne and ground-based observations over two solar cycles.

Abstract

Observed galactic cosmic ray intensity can be subjected to a transient decrease. These so-called Forbush decreases are driven by coronal mass ejection induced shockwaves in the heliosphere. By combining in situ measurements by space borne instruments with ground-based cosmic ray observations, we investigate the relationship between solar energetic particle flux, various solar activity indices, and intensity measurements of cosmic rays during such an event. We present cross-correlation study done using proton flux data from the SOHO/ERNE instrument, as well as data collected during some of the strongest Forbush decreases over the last two completed solar cycles by the network of neutron monitor detectors and different solar observatories. We have demonstrated connection between the shape of solar energetic particles fluence spectra and selected coronal mass ejection and Forbush decrease parameters, indicating that power exponents used to model these fluence spectra could be valuable new parameters in similar analysis of mentioned phenomena. They appear to be better predictor variables of Forbush decrease magnitude in interplanetary magnetic field than coronal mass ejection velocities.