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Ann. Geophys., 24, 2583-2598, 2006
www.ann-geophys.net/24/2583/2006/
© European Geosciences Union 2006
Simulating radial diffusion of energetic (MeV) electrons through a model of fluctuating electric and magnetic fields
T. Sarris1,2, X. Li1, and M. Temerin3
1Lab. for Atmospheric and Space Physics, Univ. of Colorado, Boulder, CO, USA
2Demokritus University of Thrace, Xanthi, Greece
3Space Sciences Lab, University of California, Berkeley, CA, USA
Abstract. In the present work, a test particle simulation is performed in a model of
analytic Ultra Low Frequency, ULF, perturbations in the electric and
magnetic fields of the Earth's magnetosphere. The goal of this work is to
examine if the radial transport of energetic particles in quiet-time ULF
magnetospheric perturbations of various azimuthal mode numbers can be
described as a diffusive process and be approximated by theoretically
derived radial diffusion coefficients. In the model realistic compressional
electromagnetic field perturbations are constructed by a superposition of a
large number of propagating electric and consistent magnetic pulses. The
diffusion rates of the electrons under the effect of the fluctuating fields
are calculated numerically through the test-particle simulation as a
function of the radial coordinate L in a dipolar magnetosphere; these
calculations are then compared to the symmetric, electromagnetic radial
diffusion coefficients for compressional, poloidal perturbations in the
Earth's magnetosphere. In the model the amplitude of the perturbation fields
can be adjusted to represent realistic states of magnetospheric activity.
Similarly, the azimuthal modulation of the fields can be adjusted to
represent different azimuthal modes of fluctuations and the contribution to
radial diffusion from each mode can be quantified. Two simulations of
quiet-time magnetospheric variability are performed: in the first
simulation, diffusion due to poloidal perturbations of mode number m=1 is
calculated; in the second, the diffusion rates from multiple-mode (m=0 to
m=8) perturbations are calculated. The numerical calculations of the
diffusion coefficients derived from the particle orbits are found to agree
with the corresponding theoretical estimates of the diffusion coefficient
within a factor of two.
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