Simulating the Decay of Inner Radiation Belt Electrons

Thursday, 18 December 2014
Richard Selesnick1, Jay Albert1, William R Johnston1, James Parker McCollough II1, Xinlin Li2 and Weichao Tu3, (1)Air Force Research Laboratory, Kirtland AFB, NM, United States, (2)University of Colorado at Boulder, Boulder, CO, United States, (3)Los Alamos National Laboratory, Los Alamos, NM, United States
Inner radiation belt electron intensity, for kinetic energies ~100 to 800 keV,
is characterized by occasional rapid injections followed by extended intervals
of steady decay. Observed decay rates at low L are slower than expected on the
basis of scattering and energy loss from Coulomb collisions with atmospheric
neutral atoms and ambient plasma. This discrepancy has been attributed to
steady replenishment of the trapped electrons by inward radial diffusion,
despite the required diffusion coefficient being anomalously high. Theoretical
decay rate predictions have depended on a simplified diffusive formulation of
pitch angle scattering combined with a steady or fluctuating rate of energy
loss. In fact, these two processes occur in jumps, caused by collisions with
atomic nuclei and bound or free electrons respectively. Here we describe a
Monte Carlo simulation of inner belt electron decay including true
jump-process scattering and energy loss. Results are compared to those from
diffusive simulations with emphasis on the role of range straggling, which has
not been considered previously. The necessity for inward radial diffusion or
an alternative local electron source will be reassessed.