The Van Allen radiation belts1 are two regions encircling the Earth in which energetic charged particles are trapped inside the Earth's magnetic field. Their properties vary according to solar activity2,3 and they represent a hazard to satellites and humans in space4,5. An important challenge has been to explain how the charged particles within these belts are accelerated to very high energies of several million electron volts. Here we show, on the basis of the analysis of a rare event where the outer radiation belt was depleted and then re-formed closer to the Earth6, that the long established theory of acceleration by radial diffusion is inadequate; the electrons are accelerated more effectively by electromagnetic waves at frequencies of a few kilohertz. Wave acceleration can increase the electron flux by more than three orders of magnitude over the observed timescale of one to two days, more than sufficient to explain the new radiation belt. Wave acceleration could also be important for Jupiter, Saturn and other astrophysical objects with magnetic fields.
This is a preview of subscription content, access via your institution
Open Access articles citing this article.
Nature Communications Open Access 25 March 2022
Experimental Astronomy Open Access 30 October 2021
Nature Communications Open Access 10 September 2020
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Van Allen, J. A. in Discovery of the Magnetosphere (eds Gillmor, C. S. & Spreiter, J. R.) 235–251 (Vol. 7, History of Geophysics, American Geophysical Union, Washington DC, 1997)
Baker, D. N., Blake, J. B., Klebesadel, R. W. & Higbie, P. R. Highly relativistic electrons in the Earth's outer magnetosphere 1. Lifetimes and temporal history 1979–1984. J. Geophys. Res. 91, 4265–4276 (1986)
Li, X., Baker, D. N., Kanekal, S. G., Looper, M. & Temerin, M. Long term measurements of radiation belts by SAMPEX and their variations. Geophys. Res. Lett. 28, 3827–3830 (2001)
Baker, D. N., Allen, J. H., Kanekal, S. G. & Reeves, G. D. Disturbed space environment may have been related to pager satellite failure. Eos 79, 477 (1998)
Webb, D. F. & Allen, J. H. Spacecraft and ground anomalies related to the October-November 2003 solar activity. Space Weath. 2, doi:10.1029/2004SW000075 (2004)
Baker, D. N. et al. An extreme distortion of the Van Allen belt arising from the Hallowe'en solar storm in 2003. Nature 432, 878–881 (2004)
Falthammar, C.-G. Effects of time dependent electric fields on geomagnetically trapped radiation. J. Geophys. Res. 70, 2503–2516 (1965)
Schulz, M. & Lanzerotti, L. J. Particle Diffusion in the Radiation Belts (Springer, New York, 1974)
Elkington, S. R., Hudson, M. K. & Chan, A. A. Acceleration of relativistic electrons via drift resonant interactions with toroidal-mode Pc-5 ULF oscillations. Geophys. Res. Lett. 26, 3273–3276 (1999)
Summers, D., Thorne, R. M. & Xiao, F. Relativistic theory of wave-particle resonant diffusion with application to electron acceleration in the magnetosphere. J. Geophys. Res. 103, 20487–20500 (1998)
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)
Tsurutani, B. T. & Smith, E. J. Postmidnight chorus: A substorm phenomenon. J. Geophys. Res. 79, 118–127 (1974)
Brautigam, D. H. & Albert, J. M. Radial diffusion analysis of outer radiation belt electrons during the October 9, 1990, magnetic storm. J. Geophys. Res. 105, 291–309 (2000)
Shprits, Y. Y. & Thorne, R. M. Time dependent radial diffusion modeling of relativistic electrons with realistic loss rates. Geophys. Res. Lett. 31, doi:10.1029/2004GL019591 (2004)
Kennel, C. F. & Petschek, H. E. Limit on stably trapped particle fluxes. J. Geophys. Res. 71, 1–28 (1966)
Helliwell, R. A. A theory of discreet emissions from the magnetosphere. J. Geophys. Res. 72, 4773–4790 (1967)
Horne, R. B., Glauert, S. A. & Thorne, R. M. Resonant diffusion of radiation belt electrons by whistler-mode chorus. Geophys. Res. Lett. 30, doi:10.1029/2003GL016963 (2003)
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)
Meredith, N. P., Horne, R. B., Thorne, R. M. & Anderson, R. R. Favoured regions for chorus-driven electron acceleration to relativistic energies in the Earth's outer radiation belt. Geophys. Res. Lett. 30, 1871, doi:10.1029/2003GL017698 (2003)
Horne, R. B. et al. Timescale for radiation belt electron acceleration by whistler mode chorus waves. J. Geophys. Res. 110, A03225, doi:10.1029/2004JA010811 (2005)
Glauert, S. A. & Horne, R. B. Calculation of pitch angle and energy diffusion coefficients with the PADIE code. J. Geophys. Res. 110, A04206, doi:10.1029/2004JA010851 (2005)
Lyons, L. R. & Thorne, R. M. Equilibrium structure of radiation belt electrons. J. Geophys. Res. 78, 2142–2149 (1973)
We thank E. Lucek for providing fluxgate magnetometer data from the Cluster spacecraft, and N. Cornilleau-Wehrlin for an independent assessment of the wave magnetic power spectral density. This work was supported in part by the UK Natural Environment Research Council (NERC), the NSF and NASA.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
About this article
Cite this article
Horne, R., Thorne, R., Shprits, Y. et al. Wave acceleration of electrons in the Van Allen radiation belts. Nature 437, 227–230 (2005). https://doi.org/10.1038/nature03939
Nature Communications (2022)
Physics of plasmas confined by a dipole magnet: insights from compact experiments driven at steady state
Reviews of Modern Plasma Physics (2022)
Reviews of Modern Plasma Physics (2021)
Experimental Astronomy (2021)
Nature Communications (2020)