ION RADIAL DIFFUSION IN AN ELECTROSTATIC IMPULSE MODEL FOR STORMTIME RING CURRENT FORMATION

Guiding-center simulations of stormtime transport of ring-current and radiation-belt ions having first adiabatic invariants mu greater-than- or-similar-to 15 MeV/G (E greater-than-or-similar-to 165 keV at L appr oximately 3) are surprisingly well described (typically within a facto r of less-than-or-similar-to 4) by the quasilinear theory of radial di ffusion. This holds even for the case of an individual model storm cha racterized by substorm-associated impulses in the convection electric field, provided that the actual spectrum of the electric field is inco rporated in the quasilinear theory. Correction of the quasilinear diff usion coefficient D(LL)ql for drift-resonance broadening (so as to def ine D(LL)rb) reduced the typical discrepancy with the diffusion coeffi cients D(LL)sim deduced from guiding-center simulations of representat ive-particle trajectories to a factor approximately 3. The typical dis crepancy was reduced to a factor approximately 1.4 by averaging D(LL)s im, D(LL)ql, and D(LL)rb over an ensemble of model storms characterize d by different (but statistically equivalent) sets of substorm-onset t imes.