Publication: Galactic Cosmic-Ray Anistropy during the Forbush Decrease Starting 2013 April 13
Issued Date
2018-01-10
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ISSN
20418213
20418205
20418205
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2-s2.0-85040657024
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Mahidol University
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SCOPUS
Bibliographic Citation
Astrophysical Journal Letters. Vol.852, No.2 (2018)
Suggested Citation
U. Tortermpun, D. Ruffolo, J. W. Bieber Galactic Cosmic-Ray Anistropy during the Forbush Decrease Starting 2013 April 13. Astrophysical Journal Letters. Vol.852, No.2 (2018). doi:10.3847/2041-8213/aaa407 Retrieved from: https://repository.li.mahidol.ac.th/handle/20.500.14594/45747
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Title
Galactic Cosmic-Ray Anistropy during the Forbush Decrease Starting 2013 April 13
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Abstract
© 2018. The American Astronomical Society. All rights reserved. The flux of Galactic cosmic rays (GCRs) can undergo a Forbush decrease (FD) during the passage of a shock, sheath region, or magnetic flux rope associated with a coronal mass ejection (CME). Cosmic-ray observations during FDs can provide information complementary to in situ observations of the local plasma and magnetic field, because cosmic-ray distributions allow remote sensing of distant conditions. Here we develop techniques to determine the GCR anisotropy before and during an FD using data from the worldwide network of neutron monitors, for a case study of the FD starting on 2013 April 13. We find that at times with strong magnetic fluctuations and strong cosmic-ray scattering, there were spikes of high perpendicular anisotropy and weak parallel anisotropy. In contrast, within the CME flux rope there was a strong parallel anisotropy in the direction predicted from a theory of drift motions into one leg of the magnetic flux rope and out the other, confirming that the anisotropy can remotely sense a large-scale flow of GCRs through a magnetic flux structure.