The Warm Plasma Composition in the Inner Magnetosphere During 2012–2015

Abstract Ionospheric heavy ions play an important role in the dynamics of Earth's magnetosphere. The greater mass and gyroradius of ionospheric oxygen differentiates its behavior from protons at the same energies. Oxygen may have an impact on tail reconnection processes, and it can at least temporarily dominate the energy content of the ring current during geomagnetic storms. At sub‐keV energies, multispecies ion populations in the inner magnetosphere form the warm plasma cloak, occupying the energy range between the plasmasphere and the ring current. Lastly, cold lighter ions from the midlatitude ionosphere create the corotating plasmasphere whose outer regions can interact with the plasma cloak, plasma sheet, ring current, and outer electron belt. In this paper we present a statistical view of warm, cloak‐like ion populations in the inner magnetosphere, contrasting, in particular, the warm plasma composition during quiet and active times. We study the relative abundances and absolute densities of warm plasma measured by the Van Allen Probes, whose two spacecraft cover the inner magnetosphere from plasmaspheric altitudes close to Earth to just inside geostationary orbit. We observe that warm (>30 eV) oxygen is most abundant closer to the plasmasphere boundary, whereas warm hydrogen dominates closer to geostationary orbit. Warm helium is usually a minor constituent but shows a noticeable enhancement in the near‐Earth dusk sector.