HR: 1330h
AN: SM42C-0615    [PDF]
TI: Radial diffusion simulation of relativistic electron transport by ULF waves in the September 1998 storm
AU: * Fei, Y
EM: yfei@rice.edu
AF: Rice University, 6100 Main St, MS-108, Houston, TX 77005
AU: Chan, A A
EM: aac@rice.edu
AF: Rice University, 6100 Main St, MS-108, Houston, TX 77005
AU: Elkington, S R
EM: scot.elkington@lasp.colorado.edu
AF: LASP, University of Colorado, 1234 Innovation Drive, Boulder, CO 80303
AU: Wiltberger, M
EM: wiltbemj@ucar.edu
AF: UCAR/HAO, P.O. Box 3000, Boulder, CO 80307
AB: The MHD-particle simulation of radiation belt electron fluxes during the September 1998 storm gives results which are in reasonable agreement with major features of spacecraft flux measurements at synchronous orbit. The evolution of the MeV electron radial flux profile appears to be diffusive, and diffusion caused by ULF waves has been invoked as the probable mechanism. In this work we solve a diffusion equation with ULF-wave diffusion coefficients and a time-dependent outer-boundary condition to better quantify the radial diffusion coefficient. We use a radial diffusion coefficient DLL which includes contributions from symmetric resonances and asymmetric resonances. DLL depends on the ULF power spectrum which is obtained from Fourier analysis of the MHD fields. The radial diffusion calculation uses the Roederer L value calculated in MHD magnetic field as the radial coordinate. The location of the simulation outer-boundary is defined as the last closed drift shell. The fluxes from the MHD-test particle simulation are converted to phase space density for comparison with the radial diffusion calculations. The radial diffusion simulation can reproduce the main features of the MHD-particle results quite well. The analytic ULF-wave-driven radial diffusion coefficients must be increased by factors of 2 to 3 to give the best fit to the MHD-particle result, and the asymmetric resonances dominate in the outer region of the simulation, whereas the symmetric resonances dominate in the inner region. Using both symmetric and asymmetric terms gives a better result than using one or the other, and better than using a simple power law diffusion coefficient.
DE: 2788 Storms and substorms
DE: 7867 Wave/particle interactions
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting