Dynamic modeling of radiation belt electrons by radial diffusion simulation for a 2 month interval following the 24 March 1991 storm injection

Diffusive radial transport of radiation belt electrons with variable outer boundary is computed using Brautigam and Albert (2000) diffusion coefficients parameterized by Kp, modeling power level at ULF wave frequencies in the range of MeV electron drift periods.We analyzed radial diffusion during a relatively quiet 2 month interval following the 24 March 1991, prompt injection to form a new radiation belt at L* = 2.5.The radial diffusion calculation is initialized with a computed phase space density (PSD) profile using differential flux values from the CRRES HEEF instrument, covering 0.65-7.5 MeV.The outer boundary phase space density is updated using Los Alamos National Laboratory (LANL) GEO satellite fluxes, changing the ratio of PSD relative to a quiet day by assuming the outer boundary is changing proportional to the flux at a LANL GEO satellite.The location of the plasmapause L_p* is computed using a Kp-dependent formula separating different loss rates inside and outside the plasmapause.A series of simulations for different values of the first invariant is performed for this 2 month period.The flux is then interpolated to find electron flux at a fixed energy, 1 MeV, in order to compare with the CRRES satellite 1 MeV flux.Radial diffusion appears to be the dominant mechanism for this 2 month interval, which contains moderate storms (|Dst|≲ 100).Modulation of fluxes measured by CRRES compare well with simulations of the outer zone flux peak at L* = 3-4 for moderate high-speed strea--driven storms, along with persistence and slow decay of the new population of electrons injected on 24 March 1991, into L* = 2.5.The strongest storm of the 2 month interval (Dst = -105 nT) produced a flux dropout, which is not well-captured by the model, suggesting that improvements to the Kp-parameterized loss model are needed for larger storms.