Electron Acceleration and loss in the Van Allen Radiation Belts during 
the 2003 Halloween storm

R.B. Horne, R.M. Thorne, Y.Y. Shprits, N.P. Meredith, S.A. Glauert, 
A.J. Smith, S.G. Kanekal, D.N. Baker, M.J. Engebretson, J.L. Posch, 
M. Spasojevic, U.S. Inan, J.S. Pickett, D.A. Gurnett, and P.M.E. Decreau


During the 2003 ÒHalloween stormÓ, the outer radiation belt was depleted
and then reformed inside the slot region near L ~ 2.5. This rare event
provided a unique set of conditions to test the leading theories of
electron acceleration. We show that the depletion of the outer belt,
and the initial injection to L = 2.5, occurred during an increase in
ULF wave power, consistent with inward radial diffusion and
acceleration. However, the major increase in the radiation belt flux
occurred over a period of 2-3 days, during which ULF wave power
decreased rapidly. Estimates of the timescale for inward radial
diffusion show that to inject MeV electrons inside L ~ 4 would take
more than 1 day, and to L ~ 2.5 would take substantially longer than
observations show. During the flux increase, IMAGE data shows that the
plasmapause was compressed to L as low as L = 2.5 and intense whistler
mode chorus waves were observed by CLUSTER at L ~ 4, and on the ground
at Halley (L = 4.3) and Palmer (L = 2.6). The ground data suggest that
strong whistler mode waves were present outside the plasmapause to
unusually low L shells, and that these waves could be responsible for
electron acceleration and MeV flux increase in the slot region. To
test this idea we construct a model of the chorus wave amplitudes based
on satellite data, and use pitch angle and energy diffusion
coefficients from the PADIE code. We solve the Fokker-Planck equation
to find the timescale for electron acceleration by whistler mode chorus
waves. We find the timescale for electron acceleration by the whistler
mode chorus waves in the slot region is about 1-2 days. The results
suggest that wave acceleration was primarily responsible for the MeV
electrons observed in the slot region. The results suggest that wave
acceleration may be an important process in accelerating electrons in
the radiation belts of other magnetised planets, such as Jupiter,
Saturn, Uranus, and Neptune. 

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Presented at the 28th URSI General Assembly, New Delhi, India, 
23 - 29 October, 2005