Ground-based Observations of Temporal Variation of Cosmic Ray Spectrum during Forbush Decreases

TL;DR

This paper presents ground-based methods using neutron monitors and muon detectors to accurately track cosmic ray spectral changes during solar-induced Forbush decreases, aligning well with space-based data.

Contribution

It introduces new techniques for measuring GCR spectral variations during FDs using ground-based networks, validated against space-based observations.

Findings

Ground-based methods reliably track GCR spectral changes during FDs.

Results are consistent with space-based measurements like AMS-02.

Real-time neutron monitor leader fraction data is now publicly available.

Abstract

Observations of temporary Forbush decreases (FDs) in the Galactic cosmic ray (GCR) flux due to passage of solar storms are useful for space weather studies and alerts. Here we introduce techniques that use global networks of ground-based neutron monitors and muon detectors to measure variations of GCR rigidity spectra in space during FDs by: A) fitting count rate decreases for power-law rigidity spectra in space with anisotropy up to second order, and B) using the "leader fraction" derived from a single neutron monitor. We demonstrate that both provide consistent results for hourly spectral index variations for five major FDs and they agree with daily space-based data when available from AMS-02. We have also made the neutron monitor leader fraction publicly available in real time. This work verifies that ground-based observations can be used to precisely monitor GCR spectral variation over a wide range of rigidities during space weather events, with results in real time or from short-term post-analysis.