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-EM15] Dynamics of Magnetosphere and Ionosphere

Thu. May 29, 2025 10:45 AM - 12:15 PM 302 (International Conference Hall, Makuhari Messe)

convener:Shun Imajo(Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto University), Yuka Sato(Nippon Institute of Technology), Akiko Fujimoto(Kyushu Institute of Technology), Kazuhiro Yamamoto(Institute for Space-Earth Environmental Research), Chairperson:Kiyoka Murase(National Institute of Polar Research), Akimasa Ieda(Institute for Space-Earth Environmental Research, Nagoya University)


10:45 AM - 11:00 AM

[PEM15-06] Geomagnetic activity dependence of the auroral electron precipitation spectrum derived from 22-year EISCAT dataset

*Shin-ichiro Oyama1,2, Ilkka I Virtanen3, Habtamu W Tesfaw3, Tero Raita4, Lauri Holappa3, Yoshizumi Miyoshi1, Lei Cai3, Heikki Vanhamaki3, Anita T Aikio3, Yasunobu Ogawa2, Keisuke Hosokawa5 (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.National Institute of Polar Research, 3.University of Oulu, 4.Sodankylä Geophysical Observatory, University of Oulu, 5.The University of Electro-Communications)

Keywords:aurora, electron precipitation, EISCAT, ELSPEC

Auroral electron forcing with energy greater than tens keVs impacts D-region ionization in high-latitude regions, exhibiting increased energy from midnight to dawn. This increase, known as spectrum hardening, is characterized by a higher energy at the electron-precipitation peak flux and/or a gradual power-law spectrum gradient. The former relates to the Maxwellian component of the spectrum, while the latter pertains to the Kappa distribution component. However, limited research has distinguished these two components. This study investigated the dependence of the D-region ionization on geomagnetic activity using electron density data from the European Incoherent Scatter (EISCAT) radar in Norway and cosmic noise absorption (CNA) in Finland, sorted by the SuperMAG index (SME). An inversion method derived differential energy spectra from the EISCAT-measured height-resolved electron density. Statistical spectrum analysis by fitting the Kappa distribution function revealed that spectrum hardening from midnight to dawn at auroral latitudes is mainly driven by the Kappa distribution component, characterized by a gradual power-law spectrum gradient for moderately high geomagnetic activities (SME > 300 nT). Conversely, for SME < 300 nT, the Maxwellian component primarily also contributes to spectrum hardening. This study is the first to specify the energy range contributing to spectrum hardening.