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Cosmic-ray short burst observed with the global muon detector network (GMDN) on 2015 June 22


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Munakata, K, Kozai, M, Evenson, P, Kuwabara, T, Kato, C, Tokumaru, M, Rockenbach, M, Dal Lago, A, de Mendonca, RRS, Braga, CR, Schuch, NJ, Al Jassar, HK, Sharma, MM, Duldig, ML ORCID: 0000-0001-7463-8267, Humble, JE ORCID: 0000-0002-4698-1671, Sabbah, I and Kota, J 2018 , 'Cosmic-ray short burst observed with the global muon detector network (GMDN) on 2015 June 22' , The Astrophysical Journal, vol. 862 , pp. 1-9 , doi: 10.3847/1538-4357/aacdfe.

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We analyze the short cosmic-ray intensity increase (“cosmic-ray burst”: CRB) on 2015 June 22 utilizing a global network of muon detectors and derive the global anisotropy of cosmic-ray intensity and the density (i.e., the omnidirectional intensity) with 10 minute time resolution. We find that the CRB was caused by a local density maximum and an enhanced anisotropy of cosmic rays, both of which appeared in association with Earth’s crossing of the heliospheric current sheet (HCS). This enhanced anisotropy was normal to the HCS and consistent with a diamagnetic drift arising from the spatial gradient of cosmic-ray density, which indicates that cosmic rays were drifting along the HCS from the north of Earth. We also find a significant anisotropy along the HCS, lasting a few hours after the HCS crossing, indicating that cosmic rays penetrated into the inner heliosphere along the HCS. Based on the latest geomagnetic field model, we quantitatively evaluate the reduction of the geomagnetic cutoff rigidity and the variation of the asymptotic viewing direction of cosmic rays due to a major geomagnetic storm that occurred during the CRB and conclude that the CRB is not caused by the geomagnetic storm, but by a rapid change in the cosmic-ray anisotropy and density outside the magnetosphere.

Item Type: Article
Authors/Creators:Munakata, K and Kozai, M and Evenson, P and Kuwabara, T and Kato, C and Tokumaru, M and Rockenbach, M and Dal Lago, A and de Mendonca, RRS and Braga, CR and Schuch, NJ and Al Jassar, HK and Sharma, MM and Duldig, ML and Humble, JE and Sabbah, I and Kota, J
Keywords: cosmic rays, interplanetary medium, coronal mass ejections (CMEs)
Journal or Publication Title: The Astrophysical Journal
Publisher: Univ Chicago Press
ISSN: 0004-637X
DOI / ID Number: 10.3847/1538-4357/aacdfe
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Copyright 2018 The American Astronomical Society

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