Testing the impact of coronal mass ejections on cosmic-ray intensity modulation with algorithm selected Forbush decreases

Abstract

The relationship between coronal mass ejections (CMEs) and Forbush decreases (FDs) has been investigated in the past. But the selection of both solar events are difficult. Researchers have developed manual and automated methods in efforts to identify CMEs as well as FDs. While scientists investigating CMEs have made significant advancement, leading to several CME catalogues, including manual and automated events catalogues, those analyzing FDs have recorded relatively less progress. Till date, there are no comprehensive manual FD catalogues, for example. There are also paucity of automated FD lists. Many investigators, therefore, attempt to manually select FDs which are subsequently used in the analysis of the impact of CMEs on galactic cosmic-ray (GCR) flux depressions. However, some of the CME versus FD correlation results might be biased since manual event identification is usually subjective, unable to account for the presence of solar-diurnal anisotropy which characterizes GCR flux variations. The current paper investigates the relation between CMEs and FDs with emphasis on accurate and careful Forbush event selection.

Testing the effect of solar wind parameters and geomagnetic storm indices on Galactic cosmic ray flux variation with automatically-selected Forbush decreases

“…The FD-SWS correlation r=0.44 obtained in the present investigation is in agreement with their result. Our results for FD-SWS (r=0.44) and FD-IMF (r=0.44) do not reflect the submission of Okike et al (2021b) who obtained r=0.81 and ∼ 0.34 respectively. This could be a result of the data periods.…”

“…Investigations on the remaining FD data in Table 2 will be taken up in future work. FDs with (CR(%) ≤ −3) are often adopted as the common threshold to select large FDs (e.g., Kristjánsson et al 2008;Kane 2010;Okike et al 2021b). The matrix of correlation results for large FDs with corresponding solar wind and geomagnetic activity index data is given in Table 1.…”

The Frequency‐Domain Characterization of Cosmic Ray Intensity Variations Before Forbush Decreases Associated With Geomagnetic Storms

“…Kilpua et al (2017) investigated 300 ICMEs and found that 80% of them were associated with Forbush Decreases (FDs), and proposed that the acceleration effect by the ICMEs led to a 20%-25% decreases of CRI as observed by both ground-based neutron monitors and space instruments. Okike et al (2021) also found that the FDs of CRI were closely related to ICMEs.…”

Testing the Simultaneity of Forbush Decreases with Algorithm-Selected Forbush Event Catalogue

“…Harrison et al (2011) indicate the need to remove effect of solar cycle variations from CR data before FD event selection. Third, CR anisotropy, known to exert significant influence on the number, magnitude, and timing of Forbush events (Pomerantz & Duggal, 1971;Belov, 2008;Okike et al, 2021b) was not accounted for in the current work.…”

“…Besides the versions of our Fourier-R-based FD location algorithm which has be used in various applications such as Okike & Umahi (2019b), Okike (2019b), Okike & Umahi (2019a), Okike (2020) and Okike et al (2021b), we know of no other publications that have fully automated Forbush event identification.…”