Atmospheric density experienced by radiation belt protons

Abstract

The mean atmospheric density encountered by trapped particles in the earth's radiation belt is calculated. The Harris-Preister model of the atmosphere below 1000 km, smoothed into the Johnson model above 1000 km, is used to compute the density for two different times in the solar cycle. The density averaged over the solar cycle is also computed. Two different fits to the magnetic field, the Jensen and Cain 48- and the Jensen and Whitaker 512-coefficient fields, are used. These mean atmospheric densities are combined with the proton injection coefficients for cosmic ray albedo neutron decay of White, Austin, and Dragt and with the data of Freden and Paulikas and of Brown et al. to find the region of B-L space where cosmic ray albedo neutron decay and atmospheric ionization losses occur. For L < 1.9 the experimental data and the theory are in agreement within the uncertainties introduced by the model atmospheres and the trajectories in the model magnetic field. At higher L values an additional large loss mechanism is needed. The density calculated from the 512-coefficient magnetic field gives better agreement with the theory and data than the 48-coefficient magnetic field. The Johnson increase in the atmospheric hydrogen density during solar minimum gives better agreement than the corresponding Harris-Preister decrease.