Low‐altitude energetic neutral atoms imaging of the inner magnetosphere: A geometrical method to identify the energetic neutral atoms contributions from different magnetospheric regions

Abstract

Energetic neutral atoms (ENA) imaging is an innovative technique of global magnetospheric observations, useful for studying geomagnetic storm and substorm processes. An intrinsic limitation of this technique is the difficulty of spatial distinction of the various magnetospheric regions contributing to the generation of the detected ENA fluxes. Here we apply a geometrical method able to distinguish the contribution to the ENA fluxes given by the inner radiation belt ions and by the ring current ion distributions. The ENA energy spectra are simulated by using the Active Magnetospheric Particle Tracer Explorers CCE charge‐energy‐mass energetic ion distributions, averaged over 2 years. The calculations are made for a specific vantage point (altitude is 550 km, MLT is 1930 and magnetic latitude is 0°); however, the technique can be easily extended to all locations on the equatorial plane, at similar altitudes. The simulated ENA spectra, taken at +30° and at −30° with respect to the midnight direction are used to reconstruct the inner radiation belt/ring current ENA spectra integrated along a general radial direction within the considered angular interval. For estimating the two contributions, we assume that the ion distributions are isotropic (within 17%) over the 4‐hour LT interval considered and that the functional form of the inner radiation belt ion distributions versus distance is not dependent on energy nor geomagnetic activity. The results show that there is a good agreement (within ∼5%) between the simulated ENA spectra along the radial direction (separately generated in the inner radiation belt and in the ring current) and those reconstructed through the proposed method. This technique can be applied to the real data for a zero‐order analysis.