Japan Geoscience Union Meeting 2025

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[E] Oral

P (Space and Planetary Sciences ) » P-EM Solar-Terrestrial Sciences, Space Electromagnetism & Space Environment

[P-EM13] Dynamics of the Inner Magnetospheric System

Wed. May 28, 2025 9:00 AM - 10:30 AM 302 (International Conference Hall, Makuhari Messe)

convener:Kunihiro Keika(Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo ), Yoshizumi Miyoshi(Institute for Space-Earth Environmental Research, Nagoya University), Jerry Goldstein(Southwest Research Institute), YIXIN Sun(Peking University), Chairperson:Chae-Woo Jun(Institute for Space-Earth Environmental Research, Nagoya University), Yoshizumi Miyoshi(Institute for Space-Earth Environmental Research, Nagoya University), Kazuhiro Yamamoto(Institute for Space-Earth Environmental Research)


9:00 AM - 9:15 AM

[PEM13-01] Temporal and spatial evolution of cold ions in the inner magnetosphere during large geomagnetic storms

*Khan-Hyuk Kim1, Junhyun Lee2, Lynn M Kistler3 (1.School of Space Research, Kyung Hee University, Yongin, Gyeonggi, Republic of Korea, 2.Korea Astronomy and Space Science Institute, Daejeon, Republic of Korea, 3.Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH, USA)

Keywords:Cold ions, Inner magnetosphere, Large magnetic storm, Plasmapause

In order to understand how cold ions (< 10 eV) evolve temporally and spatially within the inner magnetosphere (L < 6.5) during geomagnetic storms, we performed superposed epoch analyses on the partial ion densities of H+ (NH+), He+ (NHe+), and O+ (NO+) using flux data from the Van Allen Probes in the 1-10 eV energy range. The analyses were conducted on a set of 14 large storms (Dst < -100 nT) over a five-year period from September 2013 to September 2017. We examined the ion density ratios (NH+/Ne, NHe+/Ne, and NO+/Ne) normalized to the electron number density (Ne) and found that the NO+/Ne ratio dramatically increases during the early recovery phase outside the model plasmapause. The enhanced NO+/Ne ratio persisted for a period exceeding three days subsequent to the Dst minimum. The variation of the NHe+/Ne ratio observed outside the plasmapause exhibited a trend similar to that of the NO+/Ne ratio during the recovery phase. However, the NHe+/Ne ratio is more than an order of magnitude smaller than the NO+/Ne ratio. In contrast to the NHe+/Ne and NO+/Ne ratios, the NH+/Ne ratio does not exhibit a significant increase during the recovery phase. The enhanced cold O+ ions outside the plasmapause exhibit a bi-directional, predominantly field-aligned population, and the NO+/NH+ ratio decreases in the afternoon sector (MLT = 12-18 hr). Based on these observations, we suggest that the enhanced cold O+ ions outside the plasmapause drift into the inner magnetosphere from the tail during large storms.