Letter | Published:

Pulsating aurora from electron scattering by chorus waves

Nature volume 554, pages 337340 (15 February 2018) | Download Citation


Auroral substorms, dynamic phenomena that occur in the upper atmosphere at night, are caused by global reconfiguration of the magnetosphere, which releases stored solar wind energy1,2. These storms are characterized by auroral brightening from dusk to midnight, followed by violent motions of distinct auroral arcs that suddenly break up, and the subsequent emergence of diffuse, pulsating auroral patches at dawn1,3. Pulsating aurorae, which are quasiperiodic, blinking patches of light tens to hundreds of kilometres across, appear at altitudes of about 100 kilometres in the high-latitude regions of both hemispheres, and multiple patches often cover the entire sky. This auroral pulsation, with periods of several to tens of seconds, is generated by the intermittent precipitation of energetic electrons (several to tens of kiloelectronvolts) arriving from the magnetosphere and colliding with the atoms and molecules of the upper atmosphere4,5,6,7. A possible cause of this precipitation is the interaction between magnetospheric electrons and electromagnetic waves called whistler-mode chorus waves8,9,10,11. However, no direct observational evidence of this interaction has been obtained so far12. Here we report that energetic electrons are scattered by chorus waves, resulting in their precipitation. Our observations were made in March 2017 with a magnetospheric spacecraft equipped with a high-angular-resolution electron sensor and electromagnetic field instruments. The measured13,14 quasiperiodic precipitating electron flux was sufficiently intense to generate a pulsating aurora, which was indeed simultaneously observed by a ground auroral imager.

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The observations presented here were obtained with the help of Mitsubishi Heavy Industries, Ltd, Meisei Electric Co., Ltd, Hamamatsu Photonics Co. Ltd, YS DESIGN Co., Ltd, NIPPI Co. Ltd, Sumitomo Heavy Industries, Ltd and TIERRA TECNICA Co. Ltd. We acknowledge the work of the members of the ERG project team over several years. Y.M. is supported by JSPS Kakenhi (15H05747, 15H05815 and 16H06286). Y. Kasahara is supported by JSPS Kakenhi (16H04056 and 16H01172). H.U.F. is supported by grant AGS-1004736 from the National Science Foundation (NSF) of the USA. I.S. is supported by JSPS Kakenhi (17H06140). We thank NASA for contract NAS5-02099, S. Mende and E. Donovan for use of the ASI data, the Canadian Space Agency for logistical support in fielding and data retrieval from the ground-based observatory stations, and the NSF for support of the Ground-based Imager and Magnetometer Network for Auroral Studies programme through grant AGS-1004736. The ERG (Arase) satellite science data is available from the ERG Science Centre operated by the Institute of Space and Astronautical Science of the Japan Aerospace eXploration Agency and the Institute for Space–Earth Environmental Research of Nagoya University (https://ergsc.isee.nagoya-u.ac.jp/index.shtml.en). We are grateful to J. Hohl for assistance in editing the manuscript. We also thank N. Umemura for assistance in source data archiving. S. Kasahara thanks T. Mukai and M. Fujimoto for discussions.

Author information


  1. Department of Earth and Planetary Science, School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan

    • S. Kasahara
    • , K. Keika
    •  & K. Seki
  2. Institute for Space-Earth Environmental Research, Nagoya University, Furo-cho, Chikusa-ku, 24105 Nagoya, Aichi, Japan

    • Y. Miyoshi
    • , S. Matsuda
    •  & S. Kurita
  3. Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka, Japan

    • S. Yokota
  4. Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa, Japan

    • T. Mitani
    • , A. Matsuoka
    •  & I. Shinohara
  5. Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa, Japan

    • Y. Kasahara
  6. Graduate School of Science, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai 980-8578 Japan

    • A. Kumamoto
  7. Academia Sinica Institute of Astronomy and Astrophysics, 11F Astronomy-Mathematics Building, AS/NTU, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan

    • Y. Kazama
  8. Space Sciences Laboratory, University of California, Berkeley, California 94720-7450, USA

    • H. U. Frey
  9. Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, California 90095-1567, USA

    • V. Angelopoulos


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S. Kasahara developed the MEP-e instrument used in this study with S.Y. and T.M., identified the event, analysed the combined dataset and wrote the paper. Y.M. oversaw the production of the combined dataset and discussed its interpretation. Y. Kasahara, S.M. and A.K. provided Plasma Wave Experiment data and discussed the interpretation. A.M. provided MaGnetic Field experiment data. Y. Kazama assisted in the evaluation of MEP-e data through comparison with the Low-Energy Particle experiments – electron analyser. H.U.F. and V.A. provided ASI/THEMIS data and discussed the event and presentation of the results. S. Kurita evaluated the spacecraft footprint with Y.M. and discussed the event. K.K. and K.S. discussed the event and presentation. I.S. oversaw the ERG project and discussed the interpretation of the event. All authors reviewed the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to S. Kasahara.

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Extended data

Supplementary information


  1. 1.

    Auroral motions obtained by all-sky imagers

    Successive clear sky images from two ground stations (Fort Simpson at the upper left, and The Pas at the lower right) are shown as a video. The red cross indicates the nominal spacecraft footprint. Dashed lines illustrate magnetic coordinates every 10o in latitude and 15o in longitude. The presented time period covers that of Fig. 3.

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