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Unusual stable trapping of the ultrarelativistic electrons in the Van Allen radiation belts

Nature Physics volume 9, pages 699–703 (2013)Cite this article

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Abstract

Radiation in space was the first discovery of the space age. Earth’s radiation belts consist of energetic particles that are trapped by the geomagnetic field and encircle the planet1. The electron radiation belts usually form a two-zone structure with a stable inner zone and a highly variable outer zone, which forms and disappears owing to wave–particle interactions on the timescale of a day, and is strongly influenced by the very-low-frequency plasma waves. Recent observations revealed a third radiation zone at ultrarelativistic energies2, with the additional medium narrow belt (long-lived ring) persisting for approximately 4 weeks. This new ring resulted from a combination of electron losses to the interplanetary medium and scattering by electromagnetic ion cyclotron waves to the Earth’s atmosphere. Here we show that ultrarelativistic electrons can stay trapped in the outer zone and remain unaffected by the very-low-frequency plasma waves for a very long time owing to a lack of scattering into the atmosphere. The absence of scattering is explained as a result of ultrarelativistic particles being too energetic to resonantly interact with waves at low latitudes. This study shows that a different set of physical processes determines the evolution of ultrarelativistic electrons.

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Figure 1: Comparison of diffusive transport simulations with observations.
Figure 2: Wave observations and estimated timescales.
Figure 3: First-order resonance condition.

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Acknowledgements

This research was supported by a Presidential Early Career Award for Scientists and Engineers (PECASE) award grant to Y.Y.S. This research was also supported by the UC-Lab Fee programme, NASA grants NNX10AK99G, NNX09AF51G and NNX13AE34G and NSF AGS-1203747. We thank the Van Allen Probes team. ECT funding was provided by the Johns Hopkins University Applied Physics Laboratory (JHU/APL) contract no. 976399. We thank I. R. Mann, D. K. Milling and the rest of the CARISMA team. CARISMA is operated by the University of Alberta, funded by the Canadian Space Agency(CSA). K.O. was supported by the NASA LWS Jack Eddy Postdoctoral Fellowship Program, administrated by UCAR. D.L.T. is grateful for support from NASA THEMIS contract NAS5-02099 and grant NNX12AJ55G and the MAARBLE project. M.E.U. was supported by the Canadian Space Agency and the MAARBLE FP7 project.

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Authors and Affiliations

  1. Skolkovo Institute of Science and Technology, Skolkovo 143025, Russia

    Yuri Y. Shprits

  2. Department of Earth and Space Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    Yuri Y. Shprits

  3. University of California Los Angeles, Los Angeles, California 90095, USA

    Yuri Y. Shprits, Dmitriy Subbotin, Alexander Drozdov, Adam Kellerman, Ksenia Orlova & Drew L. Turner

  4. Lomonosov Moscow State University Skobeltsyn Institute of Nuclear Physics, Moscow 119991, Russia

    Alexander Drozdov & Ksenia Orlova

  5. Department of Physics, University of Alberta, Edmonton, Alberta P6G 2M7, Canada

    Maria E. Usanova

  6. University Corporation for Atmospheric Research, Boulder, Colorado 80301, USA

    Ksenia Orlova

  7. LASP, University of Colorado, Boulder, Colorado 80303-7814, USA

    Daniel N. Baker

  8. Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea

    Kyung-Chan Kim

Authors
  1. Yuri Y. Shprits
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  2. Dmitriy Subbotin
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  4. Maria E. Usanova
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Contributions

Y.Y.S. initiated the study and led modelling, analysis of observations, and writing of the manuscript. D.S. modelling, A.D. analysis of observations, M.E.U. analysis of observations, A.K. modelling and analysis of observations, K.O. modelling, D.N.B. provided Van Allen Probes data, D.L.T. provided THEMIS data, K-C.K. modelling.

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Correspondence to Yuri Y. Shprits.

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Shprits, Y., Subbotin, D., Drozdov, A. et al. Unusual stable trapping of the ultrarelativistic electrons in the Van Allen radiation belts. Nature Phys 9, 699–703 (2013). https://doi.org/10.1038/nphys2760

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