On the origin of lowâ energy electrons in the inner magnetosphere: Fluxes and pitchâ angle distributions

Accurate knowledge of the plasma fluxes in the inner magnetosphere is essential for both scientific and programmatic applications. Knowledge of the lowâ energy electrons (approximately tens to hundreds of eV) in the inner magnetosphere is particularly important since these electrons are acted upon by various physical processes, accelerating the electrons to higher energies, and also causing their loss. However, measurements of lowâ energy electrons are challenging, and as a result, this population has been somewhat neglected previously. This study concerns observations of lowâ energy electrons made by the Helium Oxygen Proton Electron instrument on board the Van Allen Probes satellites and also observations from geosynchronous orbit made by the Magnetospheric Plasma Analyzer on board Los Alamos National Laboratory satellites. The fluxes of electrons from ~30â eV to 1â keV are quantified as a function of pitchâ angle, McIlwain L parameter, and local time for both quiet and active periods. Results indicate two sources for lowâ energy electrons in this energy range: the lowâ energy tail of the electron plasma sheet and the highâ energy tail of the dayside ionosphere. These populations are identified primarily as a result of their different pitchâ angle distributions. Fieldâ aligned outflows from the dayside ionosphere are observed at all L shells during quiet and active periods. Our results also demonstrate that the dayside electron fieldâ aligned fluxes at ~30â eV are particularly strong between L values of 6 and 7, indicating an enhanced source within the polar ionosphere.Key PointsLowâ energy electrons (tens to hundreds of eV) originate from two main sources: the ionosphere and the plasma sheetLowâ energy electrons pervade the inner magnetosphere where they can drive waveâ particle interactionsFluxes of electrons from ~30â eV to 1â keV are quantified by pitchâ angle, L value, and local time for both quiet and active periodsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136397/1/jgra53305_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136397/2/jgra53305.pd