Energetic neutral atom imaging of the earth's ring current region

A simulation investigation has been carried out on the observed properties of energetic neutral atoms (ENA) during geomagnetic storm main phase in order to provide reliable theoretical foundations for the development of ENA detector on board the polar satellite of Double Star Program (DSP) of China and also make preparation for the future ENA observation data analyses. In this research, an approximate analytical model for the ring current particle distribution including the ion loss due to charge exchange has been developed. The simulation shows that there are two maximum ENA flux regions, i. e., the ring current inner boundary region and particle precipitation region at the northern and southern poles. The stronger the storm is the lower the particle injection is and the larger flux of ENA is 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 with each other due to the discrepancy of their charge exchange cross sections. The ENA at 10 ∼ 80keV are easier to be observed owe to the large fluxes. ENA H and O are easier to be measured because of their stronger fluxes. On the contrast, ENA He is more difficult to be detected due to its rather weak flux. This simulation research has 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 stressed on the detectability for low- and midenergy ENA during the development of the ENA detection on board the polar satellite of DSP.