@article{oai:nipr.repo.nii.ac.jp:00016074,
 author = {Kataoka, Ryuho},
 issue = {124},
 journal = {Earth, Planets and Space, Earth, Planets and Space},
 month = {Sep},
 pages = {1--10},
 title = {Extreme geomagnetic activities: a statistical study},
 volume = {72},
 year = {2020}
}