Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Pulsating aurora from electron scattering by chorus waves


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.

Your institute does not have access to this article

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Schematic of electron scattering by chorus waves, resulting in a pulsating aurora.
Figure 2: Auroral snapshots around the footprint of ERG.
Figure 3: In situ observations by ERG.
Figure 4: Correlations between electron flux and wave power spectral density.


  1. Akasofu, S. I. Polar and Magnetospheric Substorms 22–31, 222–224 (Springer, 1968)

  2. Angelopoulos, V. et al. Tail reconnection triggering substorm onset. Science 321, 931–935 (2008)

    CAS  ADS  Article  Google Scholar 

  3. Duthie, D. D. & Scourfield, M. W. J. Aurorae and closed magnetic field lines. J. Atmos. Terr. Phys. 39, 1429–1434 (1977)

    ADS  Article  Google Scholar 

  4. Johnstone, A. D. Pulsating aurora. Nature 274, 119–126 (1978)

    CAS  ADS  Article  Google Scholar 

  5. McEwen, D. J. & Duncan, C. N. A campaign to study pulsating auroras. Can. J. Phys. 59, 1029–1033 (1981)

    ADS  Article  Google Scholar 

  6. Lessard, M. R. in Auroral Phenomenology and Magnetospheric Processes: Earth And Other Planets (eds Keiling, A. et al.) 55–68 (American Geophysical Union, 2012)

  7. Ni, B. et al. Origins of the Earth’s diffuse auroral precipitation. Space Sci. Rev. 200, 205–259 (2016)

    ADS  Article  Google Scholar 

  8. Thorne, R. M., Ni, B., Tao, X., Horne, R. B. & Meredith, N. P. Scattering by chorus waves as the dominant cause of diffuse auroral precipitation. Nature 467, 943–946 (2010)

    CAS  ADS  Article  Google Scholar 

  9. Nishimura, Y. et al. Identifying the driver of pulsating aurora. Science 330, 81–84 (2010)

    CAS  ADS  Article  Google Scholar 

  10. Nishimura, Y. et al. Multievent study of the correlation between pulsating aurora and whistler mode chorus emissions. J. Geophys. Res. 116, A11221 (2011)

    ADS  Google Scholar 

  11. Miyoshi, Y. et al. Relation between fine structure of energy spectra for pulsating aurora electrons and frequency spectra of whistler mode chorus waves. J. Geophys. Res. Space Phys. 120, 7728–7736 (2015)

    ADS  Article  Google Scholar 

  12. Mozer, F. S., Agapitov, O. V., Hull, A., Lejosne, S. & Vasko, I. Y. Pulsating auroras produced by interactions of electrons and time domain structures. J. Geophys. Res. Space Phys. 122, 8604–8616 (2017)

    ADS  Article  Google Scholar 

  13. Miyoshi, Y. et al. in Dynamics of the Earth's Radiation Belts and Inner Magnetosphere (eds Summers, D. et al.) 103–116 (American Geophysical Union, 2012)

  14. Miyoshi, Y. et al. Geospace exploration project: Arase (ERG). J. Phys. Conf. Ser. 869, 012095 (2017)

    Article  Google Scholar 

  15. Kennel, C. F. & Petschek, H. E. Limit on stably trapped particle fluxes. J. Geophys. Res. 71, 1–28 (1966)

    ADS  Article  Google Scholar 

  16. Trakhtengerts, V. Yu., Tagirov, V. R. & Chernous, S. A. A circulating cyclotron maser and pulsed VLF emissions. Geomagn. Aeron. 26, 77–82 (1986)

    Google Scholar 

  17. Jaynes, A. N. et al. Pulsating auroral electron flux modulations in the equatorial magnetosphere. J. Geophys. Res. Space Phys. 118, 4884–4894 (2013)

    ADS  Article  Google Scholar 

  18. Mende, S. et al. The THEMIS array of ground-based observatories for the study of auroral substorms. Space Sci. Rev. 141, 357–387 (2008)

    ADS  Article  Google Scholar 

  19. Tsyganenko, N. A. & Sitnov, M. I. Modeling the dynamics of the inner magnetosphere during strong geomagnetic storms. J. Geophys. Res. 110, A03208 (2005)

    ADS  Article  Google Scholar 

  20. Nishimura, Y. et al. Estimation of magnetic field mapping accuracy using the pulsating aurora-chorus connection. Geophys. Res. Lett. 38, L14110 (2011)

    ADS  Article  Google Scholar 

  21. Horne, R. B. & Thorne, R. M. Potential waves for relativistic electron scattering and stochastic acceleration during magnetic storms. Geophys. Res. Lett. 25, 3011–3014 (1998)

    ADS  Article  Google Scholar 

  22. Sheeley, B. W., Moldwin, M. B., Rassoul, H. K. & Anderson, R. R. An empirical plasmasphere and trough density model: CRRES observations. J. Geophys. Res. 106, 25631–25641 (2001)

    ADS  Article  Google Scholar 

  23. Yahnin, A. G., Sergeev, V. A., Gvozdevsky, B. B. & Vennerstrom, S. Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles. Ann. Geophys. 15, 943–958 (1997)

    CAS  ADS  Article  Google Scholar 

  24. Katoh, Y. et al. Whistler mode chorus enhancements in association with energetic electron signatures in the Jovian magnetosphere. J. Geophys. Res. 116, A02215 (2011)

    ADS  Google Scholar 

  25. Menietti, J. D. et al. Saturn chorus intensity variations. J. Geophys. Res. Space Phys. 118, 5592–5602 (2013)

    ADS  Article  Google Scholar 

  26. Kasahara, S. et al. Cusp type electrostatic analyzer for measurements of medium energy charged particles. Rev. Sci. Instrum. 77, 123303 (2006)

    ADS  Article  Google Scholar 

  27. Kasahara, S., Takashima, T. & Hirahara, M. Variability of the minimum detectable energy of an APD as an electron detector. Nucl. Instr. Meth. A 664, 282–288 (2012)

    CAS  ADS  Article  Google Scholar 

Download references


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 ( 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

Authors and Affiliations



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.

Corresponding author

Correspondence to S. Kasahara.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Additional information

Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Figure 1 In situ observations by ERG with an additional dataset.

a, b, Frequency–time spectrograms of the power spectral densities of the electric (a) and magnetic field (b), showing chorus waves. The magenta and white lines indicate 0.5fce and 1.0fce, respectively, based on local magnetic field observations. c–e, Energy–time spectrograms for differential fluxes of loss-cone electrons parallel (pitch angles PA < 2°) (c) and anti-parallel (PA > 178°) (d) to the magnetic field and electrons perpendicular to the magnetic field (PA = 80°–100°) (e). Quasiparallel (PA = 20°–40°) and quasiantiparallel (PA = 140°–160°) electrons show essentially the same trend as that of the perpendicular flux. f, Flux(PA < 2°)/flux(PA = 20°–40°); g, flux(PA > 178°)/flux(PA = 140°–160°). The graphs in b and c are the same as those in Fig. 3a and b, respectively (but replotted here for comparison with a and d). The faint signature of an upper hybrid resonance wave at 12–16 kHz in a at about 11:10 ut is consistent with the assumed density of approximately 3 cm−3.

Extended Data Figure 2 Correlation coefficients for auroral intensity.

a, The colours (red, yellow, cyan and magenta) show the correlation coefficients between the auroral intensity and the loss-cone electron flux. b, Time series data of the loss-cone electron flux and the auroral intensity at a pixel at which electrons and chorus waves have nearly the highest correlation. The auroral intensity is plotted at the same time resolution as the electrons (about 8 s). c, d, The same as a and b, but for the chorus wave intensity. The wave intensity in d is plotted at the same time resolution as the auroral intensity (3 s). In a and c, the background auroral images are magnified around the centre of the field of view of the Pas station. Highest-correlation pixels are consistently located near the centre of both panels, suggesting the spacecraft footprint. The dashed lines in a and c illustrate magnetic coordinates every 2° in latitude and 5° in longitude. The displacement of the model footprint from the high-correlation pixels is approximately −0.5° and −5° in latitude and longitude, respectively, consistent with typical modelling errors20. Cross-correlations were calculated for the period 10:54:00–10:58:00 ut. In other time periods, high-correlation pixels were not commonly obtained, perhaps because of the fine structures of pulsating patches and the equatorial modulation regions near the spacecraft. For example, if the spacecraft leaves the localized modulation region as a result of magnetospheric configuration change, chorus waves and associated electron precipitation disappear at its location, but pulsating patches can continue to be ‘on’ if the equatorial modulation region still exists. In other words, although the spacecraft’s footprint in the ionosphere can leave an illuminated patch owing to spatial reconfiguration of magnetic field line structures or plasma phenomena, the auroral intensity remains high at some pixels. Other reasons that make the above correlations difficult to identify, such as the contribution of soft electron (<10 keV) precipitation to higher-altitude (>100 km) illumination, may be studied in future work.

Extended Data Figure 3 The angular response of MEP-e in two orthogonal directions.

a, Sensor response as a function of elevation angle with respect to the sensor’s mounting plane. b, Response in the sensor’s azimuthal direction, which is orthogonal to the elevation angle. Blue circles, laboratory data; black line, Gaussian model. The model curves were used to obtain the analysis results shown in Extended Data Fig. 4. Profiles for one detector are shown here; similar profiles were obtained for the other 15 detectors.

Extended Data Figure 4 Results of PAD model taking the sensor’s angular resolution into account.

Because of the finite angular resolution, contamination from outside the loss cone cannot be completely negligible. The blue line indicates the model input PAD, which is isotropic except for the step-function drop at the loss-cone angle of 2.5° (the nominal loss-cone angle in the event presented in this paper, based on a local magnetic field of about 100 nT). The red curve shows how the electron PAD is modulated by the effect of the sensor’s finite angular resolution. The grey dashed line indicates the threshold, 2°, for loss-cone selection (that is, if the angle between the centre of the field of view and the magnetic field is smaller than the threshold, the measured flux is considered to be the flux inside the loss cone). For this calculation, the sensor’s field of view is modelled by a Gaussian cone (full-width at half-maximum, 3.5°), based on the ground calibration. For example, even when the middle of the sensor’s field-of-view is centred along the magnetic field line and the actual electron PAD has an ideally empty loss cone, the instrument can inadvertently record about a few tens per cent of the flux from outside the loss cone. In our observations, however, the electron flux in the loss cone most often exhibits a filling ratio larger than 0.5, sometimes about 1, when the precipitation is ‘on’ (Fig. 4 and Extended Data Fig. 1f and g), too large to be explained by contamination alone. Also, synchronization with chorus waves cannot be produced by this instrumental effect.

Supplementary information

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. (MPG 27428 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Kasahara, S., Miyoshi, Y., Yokota, S. et al. Pulsating aurora from electron scattering by chorus waves. Nature 554, 337–340 (2018).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing