Letter | Published:

An impenetrable barrier to ultrarelativistic electrons in the Van Allen radiation belts

Nature volume 515, pages 531534 (27 November 2014) | Download Citation

Abstract

Early observations1,2 indicated that the Earth’s Van Allen radiation belts could be separated into an inner zone dominated by high-energy protons and an outer zone dominated by high-energy electrons. Subsequent studies3,4 showed that electrons of moderate energy (less than about one megaelectronvolt) often populate both zones, with a deep ‘slot’ region largely devoid of particles between them. There is a region of dense cold plasma around the Earth known as the plasmasphere, the outer boundary of which is called the plasmapause. The two-belt radiation structure was explained as arising from strong electron interactions with plasmaspheric hiss just inside the plasmapause boundary5, with the inner edge of the outer radiation zone corresponding to the minimum plasmapause location6. Recent observations have revealed unexpected radiation belt morphology7,8, especially at ultrarelativistic kinetic energies9,10 (more than five megaelectronvolts). Here we analyse an extended data set that reveals an exceedingly sharp inner boundary for the ultrarelativistic electrons. Additional, concurrently measured data11 reveal that this barrier to inward electron radial transport does not arise because of a physical boundary within the Earth’s intrinsic magnetic field, and that inward radial diffusion is unlikely to be inhibited by scattering by electromagnetic transmitter wave fields. Rather, we suggest that exceptionally slow natural inward radial diffusion combined with weak, but persistent, wave–particle pitch angle scattering deep inside the Earth’s plasmasphere can combine to create an almost impenetrable barrier through which the most energetic Van Allen belt electrons cannot migrate.

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References

  1. 1.

    , , & Observation of high intensity radiation by satellites 1958 alpha and gamma. Jet Propuls. 28, 588–592 (1958)

  2. 2.

    & Radiation around the Earth to a radial distance of 107,400 km. Nature 183, 430–434 (1959)

  3. 3.

    & Combined Release and Radiation Effects Satellite (CRRES): spacecraft and mission. J. Spacecr. Rockets 29, 556–563 (1992)

  4. 4.

    , , , & Correlation of changes in the outer-zone relativistic electron population with upstream solar wind and magnetic field measurements. Geophys. Res. Lett. 24, 927–929 (1997)

  5. 5.

    & Equilibrium structure of radiation belt electrons. J. Geophys. Res. 78, 2142–2149 (1973)

  6. 6.

    , , , & Correlation between the inner edge of outer radiation belt electrons and the innermost plasmapause location. Geophys. Res. Lett. 33, L14107 (2006)

  7. 7.

    et al. A long-lived relativistic electron storage ring embedded in Earth’s outer Van Allen belt. Science 340, 186–190 (2013)

  8. 8.

    et al. Rapid local acceleration of relativistic radiation belt electrons by magnetospheric chorus. Nature 504, 411–414 (2013)

  9. 9.

    et al. The Relativistic Electron-Proton Telescope (REPT) instrument on board the Radiation Belt Storm Probes (RBSP) spacecraft: characterization of Earth’s radiation belt high-energy particle populations. Space Sci. Rev. 179, 337–381 (2013)

  10. 10.

    et al. Science goals and overview of the Radiation Belt Storm Probes (RBSP) Energetic Particle, Composition, and Thermal Plasma (ECT) suite on NASA’s Van Allen Probes mission. Space Sci. Rev. 179, 311–336 (2013)

  11. 11.

    et al. Science objective and rationale for the Radiation Belt Storm Probes mission. Space Sci. Rev. 179, 3–27 (2013)

  12. 12.

    , , & Injection of electrons and protons with energies of tens of MeV into L < 3 on March 24, 1991. Geophys. Res. Lett. 19, 821–824 (1992)

  13. 13.

    et al. An extreme distortion of the Van Allen belt arising from the ‘Hallowe’en’ solar storm in 2003. Nature 432, 878–881 (2004)

  14. 14.

    , , , & Low-altitude measurements of 2–6 MeV electron trapping lifetimes at 1.5 ≤ L ≤ 2.5. Geophys. Res. Lett. 34, L20110 (2007)

  15. 15.

    & Inward shift of outer radiation belt electrons as a function of Dst index and the influence of the solar wind on electron injections into the slot region. J. Geophys. Res. Space Phys. 118, 756–764 (2013)

  16. 16.

    et al. The Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on RBSP. Space Sci. Rev. 179, 127–181 (2013)

  17. 17.

    Dynamics of Geomagnetically Trapped Radiation (Springer, 1970)

  18. 18.

    & Induced precipitation of inner zone electrons, 1. Observations. J. Geophys. Res. 83, 2543–2551 (1978)

  19. 19.

    , & Precipitation of inner zone electrons by Whistler mode waves from the VLF transmitters UMS and NWC. J. Geophys. Res. 86, 640–648 (1981)

  20. 20.

    & Electron scattering loss in Earth’s inner magnetosphere: 1. Dominant physical processes. J. Geophys. Res. 103, 2385–2396 (1998)

  21. 21.

    et al. Simulation of the prompt energization and transport of radiation particles during the March 23, 1991 SSC. Geophys. Res. Lett. 20, 2423–2426 (1993)

  22. 22.

    et al. Gradual diffusion and punctuated phase space density enhancements of highly relativistic electrons: Van Allen Probes observations. Geophys. Res. Lett. 41, 1351–1358 (2014)

  23. 23.

    , , , & Resonant scattering and resultant pitch angle evolution of relativistic electrons by plasmaspheric hiss. J. Geophys. Res. 118, 7740–7751 (2013)

  24. 24.

    et al. Evolution and slow decay of an unusual narrow ring of relativistic electrons near L  3.2 following the September 2012 magnetic storm. Geophys. Res. Lett. 40, 3507 (2013)

  25. 25.

    , & Emission from closed and filled magnetospheric shells and its application to the Crab pulsar. Astrophys. J. 483, 857–867 (1997)

  26. 26.

    NASA Goddard Space Flight Center. Coordinated Data Analysis Web, (11 September 2014)

  27. 27.

    & Radial diffusion analysis of outer radiation belt electrons during the October 9, 1990 magnetic storm. J. Geophys. Res. 105, 291–309 (2000)

  28. 28.

    et al. The Engineering Radiation Monitor for the Radiation Belt Storm Probes Mission. Space Sci. Rev. 179, 485–502 (2013)

  29. 29.

    et al. First results from CSSWE CubeSat: characteristics of relativistic electrons in the near-Earth environment during the October 2012 magnetic storms. J. Geophys. Res. Space Phys. 118, 6489–6499 (2013)

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Acknowledgements

We thank the entire Van Allen Probes mission team for suggestions about this work. Data access was provided through the Johns Hopkins University/Applied Physics Lab Mission Operations Center and the Los Alamos National Laboratory Science Operations Center. This work was supported by JHU/APL contract 967399 under NASA’s prime contract NAS5-01072. All Van Allen Probes data used are publicly available at http://www.rbsp-ect.lanl.gov.

Author information

Affiliations

  1. Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80303, USA

    • D. N. Baker
    • , A. N. Jaynes
    • , V. C. Hoxie
    • , X. Li
    • , Q. Schiller
    • , L. Blum
    •  & D. M. Malaspina
  2. Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California 90095, USA

    • R. M. Thorne
    • , W. Li
    •  & Q. Ma
  3. Massachusetts Institute of Technology, Haystack Observatory, Westford, Massachusetts 01886, USA

    • J. C. Foster
    •  & P. J. Erickson
  4. Aerospace Corporation Space Sciences Lab, Los Angeles, California 90009, USA

    • J. F. Fennell
  5. School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA

    • J. R. Wygant
  6. NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA

    • S. G. Kanekal
  7. Department of Physics, University of Iowa, Iowa City, Iowa 52242, USA

    • W. Kurth
  8. Center for Solar-Terrestrial Research, New Jersey Institute of Technology, Newark, New Jersey 07102, USA

    • A. Gerrard
    •  & L. J. Lanzerotti

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Contributions

D.N.B. developed the project, directed the data analysis and was primarily responsible for writing the paper. A.N.J., V.C.H. and S.G.K. analysed REPT data and produced related figures. R.M.T. provided theoretical guidance. J.C.F. and P.J.E. provided ground-based data for context. J.F.F. provided access to supplementary Van Allen Probes particle data. X.L., L.B. and Q.S. provided REPTile data. D.M.M. provided plasmapause location from EFW data. J.R.W. provided electric field data and W.K. provided EMFISIS data access. W.L. performed hiss data statistical analysis. Q.M. performed particle scattering and diffusion lifetime calculations. A.G. and L.J.L. provided ERM data from the Van Allen Probes mission.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to D. N. Baker.

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DOI

https://doi.org/10.1038/nature13956

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