Proton ring current pitch angle distributions - Comparison of simulations with CRRES observations

• Published in: Journal of Geophysical Research 1999-08, Vol.104 (A8), p.17
• Main Authors: Chen, Margaret W, Roeder, James L, Fennell, Joseph F, Lyons, Larry R, Lambour, Richard L, Schulz, Michael
• Format: Article
• Language: English
• ISSN: 0148-0227

We compare the proton pitch angle distributions (PADs) in the ring current region (L of about 3-4) obtained from Combined Release and Radiation Effects Satellite (CRRES) observations during the large magnetic storm on August 19, 1991, with results of phase-space mapping simulations in which we trace the bounce-averaged drift of protons during storm-associated enhancements in a model of the convection electric field. We map the phase-space density f according to Liouville's theorem except for attenuation by charge exchange, which we compute for both an empirical model and a theory-based model of the neutral H density distribution. We compare simulated pitch angle distributions at 48, 81, and 140 keV at L = 3 and 4 directly with the CRRES distributions at the same energies and L values before and during the storm. A steady-state application of our transport model, using the empirical neutral H density model of Rairden et al. (1986), reproduces the absolute intensities well except for E = 140 keV at L = 3 (M = 10 MeV/G) and E = 48 keV at L = 4 (M = 13 MeV/G). The anisotropies of the CRRES and modeled pre-storm pitch angle distributions agree within factors less than about 2. It appears that charge exchange alone is not enough to explain the observed rapid decay of the ring current proton intensities during the recovery phase of this storm. (Author)