Since the discovery of the Van Allen radiation belts over 50 years ago, an explanation for their complete dynamics has remained elusive. Especially challenging is understanding the recently discovered ultra-relativistic third electron radiation belt. Current theory asserts that loss in the heart of the outer belt, essential to the formation of the third belt, must be controlled by high-frequency plasma wave–particle scattering into the atmosphere, via whistler mode chorus, plasmaspheric hiss, or electromagnetic ion cyclotron waves. However, this has failed to accurately reproduce the third belt. Using a data-driven, time-dependent specification of ultra-low-frequency (ULF) waves we show for the first time how the third radiation belt is established as a simple, elegant consequence of storm-time extremely fast outward ULF wave transport. High-frequency wave–particle scattering loss into the atmosphere is not needed in this case. When rapid ULF wave transport coupled to a dynamic boundary is accurately specified, the sensitive dynamics controlling the enigmatic ultra-relativistic third radiation belt are naturally explained.

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I.R.M. is supported by a Discovery Grant from Canadian NSERC. I.J.R. is funded by STFC grant ST/L000563/1 and NERC grant NE/L007495/1. K.R.M. is supported by an NSERC Postdoctoral Fellowship. CARISMA is operated by the University of Alberta, funded by the Canadian Space Agency. We acknowledge the WDC for Geomagnetism, Kyoto University, Japan for the geomagnetic indices. We acknowledge NASA contract NAS5-02099 and V. Angelopoulos for use of data from the THEMIS Mission. Specifically D. Larson and R. P. Lin for use of SST data and C. W. Carlson and J. P. McFadden for use of ESA data. We thank A. Kellerman and T. Onsager for helpful discussions. This work was supported by RBSP-ECT funding provided by JHU/APL Contract No. 967399 under NASA’s Prime Contract No. NAS5-01072. The Sub-Auroral Magnetometer Network (SAMNET) is operated by the Space Plasma Environment and Radio Science (SPEARS) group, Department of Physics, Lancaster University. We thank the institutes who maintain the IMAGE Magnetometer Array. This work was supported in part by participation in the MAARBLE (Monitoring, Analyzing and Assessing Radiation Belt Loss and Energization) consortium. MAARBLE has received funding from the European Community’s Seventh Framework Programme (FP7-SPACE-2010-1, SP1 Cooperation, Collaborative project) under grant agreement no 284520. This paper reflects only the authors’ views and the European Union is not liable for any use that may be made of the information contained herein.

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  1. Department of Physics, University of Alberta, Edmonton, Alberta T6G 2G7, Canada

    • I. R. Mann
    • , L. G. Ozeke
    • , K. R. Murphy
    • , A. Kale
    •  & D. K. Milling
  2. NASA Goddard Spaceflight Center, Code 674 Greenbelt, Maryland 20771, USA

    • K. R. Murphy
  3. The Aerospace Corporation, Los Angeles, California 90009, USA

    • S. G. Claudepierre
    •  & D. L. Turner
  4. Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80309, USA

    • D. N. Baker
  5. Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK

    • I. J. Rae
  6. Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire 03824-3525, USA

    • A. J. Boyd
    •  & H. E. Spence
  7. Space and Atmospheric Sciences, NIS-1, Los Alamos National Laboratory, Los Alamos, New Mexico 87544, USA

    • G. D. Reeves
  8. Space Weather Prediction Center, NOAA, Boulder, Colorado 80305, USA

    • H. J. Singer
  9. National Observatory of Athens, Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, 15236 Penteli, Greece

    • S. Dimitrakoudis
    •  & I. A. Daglis
  10. Department of Physics, National and Kapodistrian University of Athens, 15784 Athens, Greece

    • I. A. Daglis
  11. Department of Physics, Lancaster University, Lancaster, LA1 4YB, UK

    • F. Honary


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I.R.M. wrote the manuscript and provided leadership for the project; L.G.O. completed all of the simulation work, including incorporation of observational data into the boundary conditions and incorporating the specifications of empirical loss; K.R.M. and I.J.R. analysed the CARISMA ULF wave data; D.L.T provided analysis support for the THEMIS data, H.J.S. for the GOES data, and S.G.C., D.N.B. and A.J.B. for the REPT data; D.K.M. supported interpretation of the CARISMA data; S.D. and I.A.D. analysed supporting storm-time ULF wave statistics; G.D.R. and H.E.S. provided ECT project leadership; F.H. provided SAMNET data; and A.K. developed Fig. 4. All authors contributed to editing the final manuscript.

Competing interests

The authors declare no competing financial interests.

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Correspondence to I. R. Mann.

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