Modelling the Low-Altitude Trapped Radiation Environment

Abstract

Knowledge of the trapped energetic particle radiation at low altitudes (<1000 km), particularly in the vicinity of the South Atlantic Magnetic Anomaly region, is important for studying the space environmental effects on space systems in this region. Standard empirical models, such as the NASA AP-8 model for protons and the AE-8 model for electrons constructed more than two decades ago, are dated and are deficient in this region because of the lack of long-term data coverage and the presence of steep atmospheric and magnetic cutoffs at low altitudes. Recent analyses of the trapped particle data at energies up to a few MeV taken from the Japanese OZHORA (1984-87) and NOAA-10 (1986-91) satellites (both at altitudes up to 850 km) have revealed that the long-term trends in the observations are generally consistent with the NASA trapped radiation models, though individual measurements may differ significantly from the models. The discrepancies between the observations and the standard trapped radiation models are being investigated by using a three-dimensional diffusive model and realistic atmospheric and magnetic field models. In this paper, we will show the results of inter-comparisons among the observations, diffusive model calculations and the NASA models. We will also outline the requirements for future efforts in modeling the low-altitude trapped radiation environment.