University of Oulu

Ozaki, M., Yagitani, S., Shiokawa, K., Tanaka, Y., Ogawa, Y., Hosokawa, K., Kasahara, Y., Ebihara, Y., Miyoshi, Y., Imamura, K., Kataoka, R., Oyama, S., Chida, T., & Kadokura, A. (2022). Slow contraction of flash aurora induced by an isolated chorus element ranging from lower‐band to upper‐band frequencies in the source region. Geophysical Research Letters, 49(9).

Slow contraction of flash aurora induced by an isolated chorus element ranging from lower-band to upper-band frequencies in the source region

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Author: Ozaki, Mitsunori1; Yagitani, Satoshi1; Shiokawa, Kazuo2;
Organizations: 1Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Japan
2Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Japan
3National Institute of Polar Research, Tachikawa, Japan
4Department of Polar Science, The Graduate University for Advanced Studies, SOKENDAI, Tachikawa, Japan
5Polar Environment Data Science Center, Joint Support-Center for Data Science Research, Research Organization of Information and Systems, Tachikawa, Japan
6The University of Electro-Communications, Chofu, Japan
7Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Japan
8Space Physics and Astronomy Research Unit, University of Oulu, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.5 MB)
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Language: English
Published: American Geophysical Union, 2022
Publish Date: 2022-12-01


Flash aurora driven by an isolated chorus element can be a useful ionospheric indicator for identifying the source wave properties via wave-particle interactions. Using ground observation and modeling approaches, here we report the temporal characteristics of flash aurora that depend on the chorus frequency width and the sweep rate. We found that the contraction time increases more than the expansion time in patchy auroral variations, due to the difference in the minimum electron energies resonated with the chorus wave packet away from the equatorial source to higher latitudes. Especially, the contraction time strongly depends on the higher-frequency chorus waves due to cyclotron resonance with lower-energy electrons. The model calculations support that the chorus element ranges from lower-band to upper-band frequencies with respect to half the gyrofrequency at the exact generation region. Our study provides the prompt (milliseconds) chorus-driven electron dynamics through the spatiotemporal characteristics of flash aurora in the ionosphere.

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Series: Geophysical research letters
ISSN: 0094-8276
ISSN-E: 1944-8007
ISSN-L: 0094-8276
Volume: 49
Issue: 9
Article number: e2021GL097597
DOI: 10.1029/2021gl097597
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This study was supported by JSPS KAKENHI grants JP15H05747, JP16H06286, and JP20H02162.
Dataset Reference: The EMCCD data ( we used to support the findings of this study were obtained from a link “100 Hz All-Sky imager data” in the ERG Science Center operated by ISAS/JAXA and ISEE/Nagoya University ( The EMCCD data release is partly supported by the IUGONET (Inter-university Upper atmosphere Global Observation NETwork) project ( The ray tracing model and the CER calculation are presented by Ozaki et al. (2021).
Copyright information: © 2022 The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.