Simultaneous Observation of Two Isolated Proton Auroras at Subauroral Latitudes by a Highly Sensitive All-Sky Camera and Van Allen Probes

Kohki Nakamura, Kazuo Shiokawa, Yuichi Otsuka, Atsuki Shinbori, Yoshizumi Miyoshi, Martin Connors, Harlan Spence, Geoff Reeves, Herbert O. Funsten, Robert MacDowall, Charles Smith, John Wygant, John Bonnell

Research output: Contribution to journalArticlepeer-review

Abstract

Isolated proton auroras (IPAs) appearing at subauroral latitudes are generated by energetic protons precipitating from the magnetosphere through interaction with electromagnetic ion cyclotron (EMIC) waves. An IPA thus indicates the spatial scale and temporal variation of wave-particle interactions in the magnetosphere. In this study, a unique event of simultaneous ground and magnetospheric satellite observations of two IPAs were conducted on March 16, 2015, using an all-sky imager at Athabasca, Canada and Van Allen Probes. The Van Allen Probes observed two isolated EMIC waves with frequencies of ∼1 and 0.4 Hz at L ≈ 5.0 when the satellite footprint crossed over the two IPAs. This suggests that the IPAs were caused by localized EMIC waves. Proton flux at 5–20 keV increased locally when the EMIC waves appeared. Electron flux at energies below ∼500 eV also increased. Temperature anisotropy of the energetic protons was estimated at 1.5–2.5 over a wide L-value range of 3.0–5.2. Electron density gradually decreased from L = 3.5 to 5.4, suggesting that the EMIC wave at L ≈ 5.0 was located in the gradual plasmapause. From these observations, we conclude that the localized IPAs and associated EMIC waves took place because of localized enhancement of energetic proton flux and plasma density structure near the plasmapause. The magnetic field observed by the satellite showed small variation during the wave observation, indicating that the IPAs were accompanied by the weak field-aligned current.

Original languageEnglish (US)
Article numbere2020JA029078
JournalJournal of Geophysical Research: Space Physics
Volume126
Issue number5
DOIs
StatePublished - May 2021

Bibliographical note

Funding Information:
We thank Yasuo Katoh, Yoshiyuki Hamaguchi, Yuka Yamamoto, and Takumi Adachi, technical staff of the ISEE at Nagoya University, and Ian Schofield of Athabasca University for their helpful support in operating the ground‐based instruments at Athabasca, Canada. Database construction for the ground‐based instruments used in the present study was supported by the ERG Science Center ( https://ergsc.isee.nagoya-u.ac.jp/ ) and the Inter‐university Upper atmosphere Global Observation Network project ( http://www.iugonet.org/ ). The observatory at Athabasca was constructed with, and is operated with the support of, the Canada Foundation for Innovation. This work is supported by JSPS KAKENHI (15H05815, 16H06286, 20H01959).

Funding Information:
We thank Yasuo Katoh, Yoshiyuki Hamaguchi, Yuka Yamamoto, and Takumi Adachi, technical staff of the ISEE at Nagoya University, and Ian Schofield of Athabasca University for their helpful support in operating the ground-based instruments at Athabasca, Canada. Database construction for the ground-based instruments used in the present study was supported by the ERG Science Center (https://ergsc.isee.nagoya-u.ac.jp/) and the Inter-university Upper atmosphere Global Observation Network project (http://www.iugonet.org/). The observatory at Athabasca was constructed with, and is operated with the support of, the Canada Foundation for Innovation. This work is supported by JSPS KAKENHI (15H05815, 16H06286, 20H01959).

Publisher Copyright:
© 2021. American Geophysical Union. All Rights Reserved.

Keywords

  • isolated proton aurora

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