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Abstract Observations of temporary Forbush decreases (FDs) in the Galactic cosmic-ray (GCR) flux due to the 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 (1) fitting count rate decreases for power-law rigidity spectra in space with anisotropy up to second order and (2) 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 the Alpha Magnetic Spectrometer. 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 postanalysis. 

Abstract The coupling response between solar wind structures and the magnetosphere is highly complex, leading to different effects in the outer radiation belt electron fluxes. Most Coronal Mass Ejections cause strong geomagnetic storms with short recovery phases, often 1–2 days. By contrast, High‐Speed Solar Wind Streams lead to moderate and weak storms often with much longer recovery phases, from several to ∼10 days. The magnetosphere receives energy for a long time under the influence of the HSSs, considerably changing its dynamics. This in turn has an effect on the charged particles trapped in the outer radiation belt. Although the high‐energy electron flux enhancements have received considerable attention, the high‐energy electron flux enhancement pattern (L > 4) has not. This paper identifies 37 events with this enhancement pattern in the high‐energy electron flux during the Van Allen Probes era. We find the enhancements coincident with HSS occurrence. The interplanetary magnetic field (IMF) exhibits north/south Bz fluctuations of Alfvénic nature with moderate amplitudes. The high‐energy electron flux enhancements also correspond to long periods of auroral activity indicating a relationship to magnetotail dynamics. However, the AE index only reaches moderate values. Ultra‐Low Frequency waves were present in all of the events and whistler‐mode chorus waves were present in 89.1% of the events, providing a convenient scenario for wave‐particle interactions. The radial gradient of the ULF wave power related to theL, under the influence of the HSSs, is necessary to trigger the physical processes responsible for this type of high‐energy electron flux enhancement pattern.