Angular distributions of albedo protons at the near earth orbit

Abstract

[1] A new insight into angular distributions of albedo proton fluxes is assessed by modeling the size of loss cone at 380-km altitude. The percentage occupied by particle populations of each categorized flight time at a spatial point can then be related to the local angular distribution of their fluxes; accordingly, the global percentage of each population thus can be obtained. The global percentages of the albedo protons that were derived from the Alpha Magnetic Spectrometer (AMS) data are chosen as the benchmarks. Angular distributions of particle fluxes were found to conform these benchmarks under the following three cases: (1) a very anisotropic pitch angle distribution when both the bounce-loss and drift-loss populations are assumed to be generated at the local atmosphere; (2) a zenith-angle distribution with an isotropic component exceeding the anisotropic component and include the drift-loss population originated from other locations; (3) a pure isotropic distribution with a drift-loss population originated from other locations included to account for the detected fluxes. Case 3 is most likely to represent what have really occurred since it could reproduce the observed results of AMS well. Our study has focused on the theoretical relation between angular distributions and percentages of various flight time populations. The consistency with observations suggests that it is worthwhile to feature future new instruments to measure the angular distributions of the albedo proton and to carry out further theoretical calculations to explore the energy input to the environment by the albedo particles.