Journal of The Korean Astronomical Society (천문학회지)

The Korean Astronomical Society (한국천문학회)
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Asymmetric Cosmic Ray Modulation of Forbush Decreases Associated with the Propagation Direction of Interplanetary Coronal Mass Ejection

  • Jongil Jung (Astronomy, Space Science and Geology, Chungnam National University) ;
  • Suyeon Oh (Department of Earth Science Education, Chonnam National University) ;
  • Yu Yi (Astronomy, Space Science and Geology, Chungnam National University) ;
  • Jongdae Sohn (Korean Astronomy and Space Science Institute)
  • Received : 2023.01.10
  • Accepted : 2023.05.13
  • Published : 2023.12.30
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Abstract

A Forbush decrease (FD) is a depression of cosmic ray (CR) intensity observed by ground-based neutron monitors (NMs). The CR intensity is thought to be modulated by the heliospheric magnetic structures including the interplanetary coronal mass ejection (ICME) surrounding the Earth. The different magnitude of the decreasing in intensity at each NM was explained only by the geomagnetic cutoff rigidity of the NM station. However, sometimes NMs of almost the same cutoff rigidity in northern and southern hemispheres observe the asymmetric intensity depression magnitudes of FD events. Thus, in this study we intend to see the effects on CR intensity modulation of FD event recorded at different NMs due to different ICME propagation directions as an additional parameter in the model explaining the CR modulation. Fortunately, since 2006 the coronagraphs of twin spacecraft of the STEREO mission allow us to infer the propagation direction of ICME associated with the FD event in 3-dimension with respect to the Earth. We suggest the hypothesis that the asymmetric CR modulations of FD events are determined by the propagation directions of the associated ICMEs.

Keywords

Acknowledgement

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2018R1D1A1B07046522). This work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (2023R1A2C1004304). The authors are grateful to the STEREO/SECCHI team (Goddard Space Flight Center, Naval Research Laboratory). The authors also thank the directors of the Thule, Forth Smith, Peawanuck, Nain, Inuvik, McMurdo (Bartol Research Institute; http://www.bartol.udel.edu/gp/neutronm/), Mawson (University of Tasmania and the Australian Antarctic Division), Kerguelen and Terre Adelie (Observatoire de Paris and the French polar institute (IPEV)), and Sanae (Centre for Space Science, North-West University of South Africa) neutron monitors.

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