Discovery of proton hill in the phase space during interactions between ions and electromagnetic ion cyclotron waves

Masafumi Shoji; Yoshizumi Miyoshi; Lynn M Kistler; Kazushi Asamura; Ayako Matsuoka; Yasumasa Kasaba; Shoya Matsuda; Yoshiya Kasahara; Iku Shinohara

doi:10.1038/s41598-021-92541-0

Discovery of proton hill in the phase space during interactions between ions and electromagnetic ion cyclotron waves

Sci Rep. 2021 Jun 29;11(1):13480. doi: 10.1038/s41598-021-92541-0.

Authors

Masafumi Shoji¹, Yoshizumi Miyoshi², Lynn M Kistler^{2

3}, Kazushi Asamura⁴, Ayako Matsuoka⁵, Yasumasa Kasaba⁶, Shoya Matsuda⁴, Yoshiya Kasahara⁷, Iku Shinohara⁴

Affiliations

¹ Institute for Space Earth Environmental Research, Nagoya University, Nagoya, Aichi, Japan. masafumi.shoji@nagoya-u.jp.
² Institute for Space Earth Environmental Research, Nagoya University, Nagoya, Aichi, Japan.
³ Space Science Center, University of New Hampshire, Durham, NH, USA.
⁴ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa, Japan.
⁵ Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto University, Kyoto, Kyoto, Japan.
⁶ Planetary Plasma and Atmospheric Research Center, Tohoku University, Sendai, Miyagi, Japan.
⁷ Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Ishikawa, Japan.

Abstract

A study using Arase data gives the first observational evidence that the frequency drift of electromagnetic ion cyclotron (EMIC) waves is caused by cyclotron trapping. EMIC emissions play an important role in planetary magnetospheres, causing scattering loss of radiation belt relativistic electrons and energetic protons. EMIC waves frequently show nonlinear signatures that include frequency drift and amplitude enhancements. While nonlinear growth theory has suggested that the frequency change is caused by nonlinear resonant currents owing to cyclotron trapping of the particles, observational evidence for this has been elusive. We survey the wave data observed by Arase from March, 2017 to September 2019, and find the best falling tone emission event, one detected on 11th November, 2017, for the wave particle interaction analysis. Here, we show for the first time direct evidence of the formation of a proton hill in phase space indicating cyclotron trapping. The associated resonance currents and the wave growth of a falling tone EMIC wave are observed coincident with the hill, as theoretically predicted.