Energetic Electron Precipitation Observed by FIREBIRD‐II Potentially Driven by EMIC Waves: Location, Extent, and Energy Range From a Multievent Analysis. Issue 5 (4th March 2021) - Capannolo, L.
Abstract: We evaluate the location, extent, and energy range of electron precipitation driven by ElectroMagnetic Ion Cyclotron (EMIC) waves using coordinated multisatellite observations from near‐equatorial and Low‐Earth‐Orbit (LEO) missions. Electron precipitation was analyzed using the Focused Investigations of Relativistic Electron Burst Intensity, Range and Dynamics (FIREBIRD‐II) CubeSats, in conjunction either with typical EMIC‐driven precipitation signatures observed by Polar Orbiting Environmental Satellites (POES) or with in situ EMIC wave observations from Van Allen Probes. The multievent analysis shows that electron precipitation occurred in a broad region near dusk (16–23 MLT), mostly confined to 3.5–7.5 L‐shells. Each precipitation event occurred on localized radial scales, on average ∼0.3 L. Most importantly, FIREBIRD‐II recorded electron precipitation from ∼200 to 300 keV to the expected ∼MeV energies for most cases, suggesting that EMIC waves can efficiently scatter a wide energy range of electrons. Plain Language Summary: ElectroMagnetic Ion Cyclotron (EMIC) waves occur in the Earth's magnetosphere and are excited during injections of hot ions from the magnetotail toward Earth. EMIC waves are known to cause precipitation of ∼MeV electrons into the upper atmosphere, which can lead to enhancements of ionization and chemical reactions, but some studies suggest that this energy can extend down to a few hundred keV as well. In this study, we focus on identifying the location, extent and energy range of electron precipitation driven by EMIC waves by analyzing multiple events using coordinated multisatellite observations. We found that energetic electron precipitation primarily occurred on the duskside and within ∼7.5 Earth Radii ( R E ). The precipitation was localized radially (on average ∼0.3 R E ), and the energy range of precipitation extended from at least ∼200–300 keV up to ∼MeV. Our findings are important to understand the effects of EMIC waves on energetic electron precipitation, including their dependence on location, extent, and energy. Key Points: Conjunctions between FIREBIRD‐II and RBSP or POES with clear EMIC‐driven precipitation signatures are analyzed FIREBIRD‐II systematically observed EMIC‐driven electron precipitation with an energy range extending from ∼200 to 300 keV up to ∼1 MeV Electron precipitation occurred in a broad region (16–23 MLT, L < 7.5), but the extent per event was highly localized (on average ∼0.3 L)