An extreme distortion of the Van Allen belt arising from the "Hallowe'en"
solar storm in 2003

D. N. Baker, S. G. Kanekal, X. Li, S. P. Monk, J. Goldstein and J. L. Burch


The EarthÕs radiation belts - also known as the Van Allen belts - contain
high-energy electrons trapped on magnetic field lines. The centre of the outer
belt is usually 20,000Š25,000 km from Earth. The region between the belts is
normally devoid of particles, and is accordingly favoured as a location for
spacecraft operation because of the benign environment. Here we report that the
outer Van Allen belt was compressed dramatically by a solar storm known as the
"Hallowe'en storm" of 2003. From 1 to 10 November, the outer belt had its centre
only ~10,000 km from EarthÕs equatorial surface, and the plasmasphere was
similarly displaced inwards. The region between the belts became the location of
high particle radiation intensity. This remarkable deformation of the entire
magnetosphere implies surprisingly powerful acceleration and loss processes deep
within the magnetosphere.

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Nature, 432, 878, 16 December 2004.