Detection of bidirectional streaming of galactic cosmic rays caused by coronal mass ejection


The research group led by Dr. Kazuoki Munakata (Designated professor of Shinshu University) has been conducting observations of cosmic ray muons by using global network of detectors at various observation sites (Global Muon Detector Network: GMDN) under collaboration with ISEE of Nagoya University. These observations enable the detailed analysis of galactic cosmic ray variations driven by solar activities, and determination of the large-scale magnetic field structure in the interplanetary space. Dr. Munakata’s group identified bidirectional streaming of galactic cosmic rays in November 2021 from the analysis of GMDN observations (see Figure 1). This bidirectional streaming is considered to be caused by galactic cosmic rays trapped inside the magnetic flux rope erupted from the corona (see Figure 2). As the magnetic flux rope is one of key factors to cause geomagnetic storms, improvement of space weather forecast is expected from further in-depth analysis of GMDN observations.

K. Munakata, M. Kozai, C. Kato, Y. Hayashi, R. Kataoka, A. Kadokura, M. Tokumaru, R. R. S. Mendonça, E. Echer, A. Dal Lago, M. Rockenbach, N. J. Schuch, J. V. Bageston, C. R. Braga, H. K. Al Jassar, M. M. Sharma, M. L. Duldig, J. E. Humble, I. Sabbah, P. Evenson, P.-S. Mangeard, T. Kuwabara, D. Ruffolo, A. Sáiz, W. Mitthumsiri, W. Nuntiyakul, and J. Kóta, “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 (11pp),

Figure 1
Intensity map of the cosmic ray anisotropy during November 4, 2021 18:30-21:30 UT. Left, middle and right panels show the first-order (n=1), second order (n=2), and total (n=1 and 2) anisotropies, respectively. Solid and open circles indicate the orientations parallel and anti-parallel to magnetic field, respectively, while crosses indicate the orientations of maximum cosmic ray intensity. Black curve displays the magnetic equator. (adopted from Munakata et al., 2022)
Figure 2
Schematic illustration of bidirectional streaming of galactic cosmic rays (adopted and modified from Figure 7 of K. Marubashi, 2002)