First joint in situ and global observations of the medium‐energy oxygen and hydrogen in the inner magnetosphere

Abstract

AbstractWe present the first simultaneous observations of the in situ ions and global Energetic Neutral Atom (ENA) images of the composition‐separated, medium‐energy (~1–50 keV) particle populations of the inner magnetosphere. The ENA emissions are mapped into L shell/magnetic local time space based on the exospheric density along the line of sight (LOS). The ENA measurement can then be scaled to determine an average ion flux along a given LOS. The in situ ion flux tends to be larger than the scaled ENAs at the same local time. This indicates that the ion population is more concentrated in the Van Allen Probes orbital plane than distributed along the Two Wide‐angle Imaging Neutral‐atom Spectrometers LOS. For the large storm of 14 November 2012, we observe that the concentration of O (in situ ions and ENAs) increases during the storm's main phase with a relatively larger increase than H. The ratio of the O+/H+ can be measured both from the in situ observations and from the ENA images. During the main phase, this O+/H+ increase is initially seen near midnight, but when the storm reaches its peak value the O+/H+ ratio increases across all local times, with the largest at dusk and dawn.