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Large-amplitude bidirectional anisotropy of Cosmic-Ray intensity observed with worldwide networks of ground-based neutron monitors and muon detectors in 2021 November

Citation

Munakata, K and Kozai, M and Kato, C and Hayashi, Y and Kataoka, R and Kadokura, A and Tokumaru, M and Mendonca, RRS and Echer, E and Dal Lago, A and Rockenbach, M and Schuch, NJ and Bageston, JV and Braga, CR and Al Jassar, HK and Sharma, MM and Duldig, ML and Humble, JE and Sabbah, I and Evenson, P and Mangeard, P-S and Kuwabara, T and Ruffolo, D and Saiz, A and Mitthumsiri, W and Nuntiyakul, W and Kota, J, Large-amplitude bidirectional anisotropy of Cosmic-Ray intensity observed with worldwide networks of ground-based neutron monitors and muon detectors in 2021 November, The Astrophysical Journal, 938, (30) pp. 1-11. ISSN 1538-4357 (2022) [Refereed Article]


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Copyright Statement

© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) License, (https://creativecommons.org/licenses/by/4.0/). Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

DOI: doi:10.3847/1538-4357/ac91c5

Abstract

We analyze the cosmic-ray variations during a significant Forbush decrease observed with worldwide networks of ground-based neutron monitors and muon detectors during 2021 November 3–5. Utilizing the difference between primary cosmic-ray rigidities monitored by neutron monitors and muon detectors, we deduce the rigidity spectra of the cosmic-ray density (or omnidirectional intensity) and the first- and second-order anisotropies separately for each hour of data. A clear two-step decrease is seen in the cosmic-ray density with the first ∼2% decrease after the interplanetary shock arrival followed by the second ∼5% decrease inside the magnetic flux rope (MFR) at 15 GV. Most strikingly, a large bidirectional streaming along the magnetic field is observed in the MFR with a peak amplitude of ∼5% at 15 GV, which is comparable to the total density decrease inside the MFR. The bidirectional streaming could be explained by adiabatic deceleration and/or focusing in the expanding MFR, which have stronger effects for pitch angles near 90°, or by selective entry of GCRs along a leg of the MFR. The peak anisotropy and density depression in the flux rope both decrease with increasing rigidity. The spectra vary dynamically, indicating that the temporal variations of density and anisotropy appear different in neutron monitor and muon detector data.

Item Details

Item Type:Refereed Article
Keywords:cosmic rays, space weather, ICME, muon telescope
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:High energy astrophysics and galactic cosmic rays
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Duldig, ML (Dr Marc Duldig)
UTAS Author:Humble, JE (Dr John Humble)
ID Code:153886
Year Published:2022
Deposited By:Physics
Deposited On:2022-10-13
Last Modified:2023-01-09
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