Properties of the neutral energetic atoms emitted from Earth’s ring current region

Abstract

Simulations of energetic neutral atoms (ENA) during the geomagnetic storm main phase have been carried out to provide reliable theoretical foundations for the development of an ENA detector on board the polar satellite of the Chinese Double Star Program (DSP), and to make preparation for the future ENA observational data analyses. In this research, an approximate analytical model for the ring current particle distributions, including the ion loss due to charge exchange processes, has been developed. The simulations have shown that there are two maximum ENA flux regions: The ring current inner boundary region, and the particle precipitation region at the northern and southern poles. The stronger the storms, the lower the particle injection, and the larger the flux of ENA emitted from the ring current region. The ENA detector at advantageous positions can measure the inner boundary of the injection region or the injection front. The ENA detector is able to measure the inhomogeneity of the ring current ions. The features of the energy fluxes of H, O, and He are different from each other due to the discrepancy of their charge exchange cross sections. The ENA at 10–80 keV are more easily observed owing to the large fluxes at this range of energy, and ENA H and O are easily measured because of their stronger fluxes. In contrast, ENA He is more difficult to detect due to its rather weak flux. These simulations have indicated that the polar satellite of DSP is capable of detecting the ring current ENA. The ENA detector at low latitudes, e.g., on board the equatorial satellite, is also useful for observing the ring current ENA. More importance should be placed on the detection for low- and mid-energy ENA during the development of the ENA instruments for the polar DSP satellite.