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Statistical Study of EMIC Waves and Related Proton Distributions Observed by the Arase Satellite
  • +17
  • Chae-Woo Jun,
  • Yoshizumi Miyoshi,
  • Satoko Nakamura,
  • Masafumi Shoji,
  • Masahiro Kitahara,
  • Tomoaki Hori,
  • Chao Yue,
  • Jacob Bortnik,
  • Larry R. Lyons,
  • Kyungguk Min,
  • Yoshiya Kasahara,
  • Fuminori Tsuchiya,
  • Atsushi Kumamoto,
  • Kazushi Asamura,
  • Iku Shinohara,
  • Ayako Matsuoka,
  • Shun Imajo,
  • Shoichiro Yokota,
  • Satoshi Kasahara,
  • Kunihiro Keika
Chae-Woo Jun
Institute for Space-Earth Environmental Research, Nagoya University

Corresponding Author:[email protected]

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Yoshizumi Miyoshi
Institute for Space-Earth Environmental Research, Nagoya University
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Satoko Nakamura
Institute for Space-Earth Environmental Research, Nagoya University
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Masafumi Shoji
Nagoya University
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Masahiro Kitahara
Tohoku University
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Tomoaki Hori
Institute for Space-Earth Environmental Research, Nagoya University
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Chao Yue
Peking Univeristy
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Jacob Bortnik
University of California Los Angeles
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Larry R. Lyons
University of California Los Angeles
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Kyungguk Min
Chungnam National University
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Yoshiya Kasahara
Kanazawa University
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Fuminori Tsuchiya
Tohoku University
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Atsushi Kumamoto
Tohoku University
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Kazushi Asamura
The Institute of Space and Astronautical Science
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Iku Shinohara
Japan Aerospace Exploration Agency
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Ayako Matsuoka
Kyoto University
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Shun Imajo
Kyoto University
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Shoichiro Yokota
Osaka University
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Satoshi Kasahara
The University of Tokyo
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Kunihiro Keika
The University of Tokyo
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Abstract

We performed a statistical study of electromagnetic ion cyclotron (EMIC) wave distributions and their coupling with energetic protons in the inner magnetosphere using the Arase satellite data from May 2017 to December 2020. We investigated the energetic proton pitch-angle distributions and partial thermal pressures associated with EMIC waves using inter-calibrated proton data in the energy range of 30 eV/q-187 keV/q. With a cold plasma approximation, we computed the proton minimum resonance energies using the observed EMIC wave frequency and plasma density values. We found that the EMIC waves had left-handed polarization near the magnetic equator close to the threshold of proton cyclotron instability, and propagated to higher latitudes along the field line with polarization reversal. H-EMIC waves showed two peak occurrence regions in the morning and noon sectors at L=7.5-9 outside the plasmasphere. The flux enhancements associated with morning side H-EMIC waves appeared at E<1 keV/q among all pitch angles, while H-EMIC waves in the noon sector exhibited flux enhancement in field-aligned directions at E=1-100 keV/q. He-EMIC waves showed a broad occurrence region from 12 to 20 magnetic local time at L=5.5-8.5 inside the plasmasphere with strong flux enhancements at all pitch-angle ranges at E=1-100 keV/q. The proton minimum resonance energy using the obtained central frequency was consistent with the observed flux enhancements at different peak occurrence regions. We conclude that the free energy sources of EMIC waves in different geomagnetic environments drive the two different types of EMIC waves, and they interact with energetic protons at different energy ranges.