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Explaining sudden losses of outer radiation belt electrons during geomagnetic storms

Nature Physics volume 8, pages 208212 (2012) | Download Citation


The Van Allen radiation belts were first discovered in 1958 by the Explorer series of spacecraft1. The dynamic outer belt consists primarily of relativistic electrons trapped by the Earth’s magnetic field. Magnetospheric processes driven by the solar wind2 cause the electron flux in this belt to fluctuate substantially over timescales ranging from minutes to years3. The most dramatic of these events are known as flux ’dropouts’ and often occur during geomagnetic storms. During such an event the electron flux can drop by several orders of magnitude in just a few hours4,5 and remain low even after a storm has abated. Various solar wind phenomena, including coronal mass ejections and co-rotating interaction regions6, can drive storm activity, but several outstanding questions remain concerning dropouts and the precise channels to which outer belt electrons are lost during these events. By analysing data collected at multiple altitudes by the THEMIS, GOES, and NOAA–POES spacecraft, we show that the sudden electron depletion observed during a recent storm’s main phase is primarily a result of outward transport rather than loss to the atmosphere.

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We thank J. Green and J. Rodriguez for providing details concerning the NOAA–POES and GOES-Magnetospheric Electron Detector (MAGED) data, respectively, and for useful comments. Thanks to the NOAA, THEMIS (D. Larson and R. P. Lin for the SST data, K. H. Glassmeier, U. Auster, and W. Baumjohann for the flux gate magnetometer data, and the University of Alaska for the ground-based magnetometer data), OMNI, and Kyoto World Data Center for Geomagnetism (Kyoto-WDC) teams for their online data access. This work was supported by NASA contract NAS5-02099.

Author information


  1. Department of Earth and Space Sciences, University of California, Los Angeles, California 90095-1567, USA

    • Drew L. Turner
    • , Yuri Shprits
    • , Michael Hartinger
    •  & Vassilis Angelopoulos
  2. Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095-1567, USA

    • Drew L. Turner
    • , Yuri Shprits
    •  & Vassilis Angelopoulos
  3. Department of Atmospheric Sciences, University of California, Los Angeles, California 90095-1567, USA

    • Yuri Shprits


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D.L.T. conducted the majority of the data processing and analysis and writing for this study. Y.S. suggested to simultaneously study precipitating and trapped data and assisted with data interpretation and the diffusion simulations. M.H. analysed the THEMIS ULF wave data and provided input on ULF waves and activity. V.A. assisted with data interpretation and provided the THEMIS-SST data.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Drew L. Turner.

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