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High energy resolution DEMETER satellite observations from the Instrument for the Detection of Particle (IDP) are analyzed during an electromagnetic ion cyclotron (EMIC)‐induced electron precipitation event. Analysis of an Interval Pulsation with Diminishing Periods (IPDP)‐type EMIC wave event, using combined satellite observations to correct for incident proton contamination, detected an energy precipitation spectrum ranging from ∼150 keV to ∼1.5 MeV. While inconsistent with many theoretical predictions of >1 MeV EMIC‐induced electron precipitation, the finding is consistent with an increasing number of experimentally observed events detected using lower resolution integral channel measurements on the POES, FIREBIRD, and ELFIN satellites. Revised and improved DEMETER differential energy fluxes, after correction for incident proton contamination shows that they agree to within 40% in peak flux magnitude, and 85 keV (within 40%) for the energy at which the peak occurred as calculated from POES integral channel electron precipitation measurements. This work shows that a subset of EMIC waves found close to the plasmapause, that is, IPDP‐type rising tone events, can produce electron precipitation with peak energies substantially below 1 MeV. The rising tone features of IPDP EMIC waves, along with the association with the high cold plasma density regime, and the rapidly varying electron density gradients of the plasmapause may be an important factor in the generation of such low energy precipitation, co‐incident with a high energy tail. Our work highlights the importance of undertaking proton contamination correction when using the high‐resolution DEMETER particle measurements to investigate EMIC‐driven electron precipitation. 

Abstract A specialized ground‐based system has been developed for simultaneous observations of pulsating aurora (PsA) and related magnetospheric phenomena with the Arase satellite. The instrument suite is composed of (a) six 100 Hz sampling high‐speed all‐sky imagers (ASIs), (b) two 10 Hz sampling monochromatic ASIs observing 427.8 and 844.6 nm auroral emissions, (c) a 20 Hz sampling fluxgate magnetometer. The 100 Hz ASIs were deployed in four stations in Scandinavia and two stations in Alaska, which have been used for capturing the main pulsations and quasi 3 Hz internal modulations of PsA at the same time. The 10 Hz sampling monochromatic ASIs have been operative in Tromsø, Norway with the 20 Hz sampling magnetometer. Combination of these multiple instruments with the European Incoherent SCATter (EISCAT) radar enables us to detect the low‐altitude ionization due to energetic electron precipitation during PsA and further to reveal the ionospheric electrodynamics behind PsA. Since the launch of the Arase satellite, the data from these instruments have been examined in comparison with the wave and particle data from the satellite in the magnetosphere. In the future, the system can be utilized not only for studies of PsA but also for other classes of aurora in close collaboration with the planned EISCAT_3D project. 

Abstract We review comprehensive observations of electromagnetic ion cyclotron (EMIC) wave-driven energetic electron precipitation using data collected by the energetic electron detector on the Electron Losses and Fields InvestigatioN (ELFIN) mission, two polar-orbiting low-altitude spinning CubeSats, measuring 50-5000 keV electrons with good pitch-angle and energy resolution. EMIC wave-driven precipitation exhibits a distinct signature in energy-spectrograms of the precipitating-to-trapped flux ratio: peaks at >0.5 MeV which are abrupt (bursty) (lasting ∼17 s, or $$\Delta L\sim 0.56$$ Δ L ∼ 0.56 ) with significant substructure (occasionally down to sub-second timescale). We attribute the bursty nature of the precipitation to the spatial extent and structuredness of the wave field at the equator. Multiple ELFIN passes over the same MLT sector allow us to study the spatial and temporal evolution of the EMIC wave - electron interaction region. Case studies employing conjugate ground-based or equatorial observations of the EMIC waves reveal that the energy of moderate and strong precipitation at ELFIN approximately agrees with theoretical expectations for cyclotron resonant interactions in a cold plasma. Using multiple years of ELFIN data uniformly distributed in local time, we assemble a statistical database of ∼50 events of strong EMIC wave-driven precipitation. Most reside at $$L\sim 5-7$$ L ∼ 5 − 7 at dusk, while a smaller subset exists at $$L\sim 8-12$$ L ∼ 8 − 12 at post-midnight. The energies of the peak-precipitation ratio and of the half-peak precipitation ratio (our proxy for the minimum resonance energy) exhibit an $$L$$ L -shell dependence in good agreement with theoretical estimates based on prior statistical observations of EMIC wave power spectra. The precipitation ratio’s spectral shape for the most intense events has an exponential falloff away from the peak (i.e., on either side of $$\sim 1.45$$ ∼ 1.45 MeV). It too agrees well with quasi-linear diffusion theory based on prior statistics of wave spectra. It should be noted though that this diffusive treatment likely includes effects from nonlinear resonant interactions (especially at high energies) and nonresonant effects from sharp wave packet edges (at low energies). Sub-MeV electron precipitation observed concurrently with strong EMIC wave-driven >1 MeV precipitation has a spectral shape that is consistent with efficient pitch-angle scattering down to ∼ 200-300 keV by much less intense higher frequency EMIC waves at dusk (where such waves are most frequent). At ∼100 keV, whistler-mode chorus may be implicated in concurrent precipitation. These results confirm the critical role of EMIC waves in driving relativistic electron losses. Nonlinear effects may abound and require further investigation. 

This paper presents observations of electromagnetic ion cyclotron (EMIC) waves from multiple data sources during the four Geospace Environment Modeling challenge events in 2013 selected by the Geospace Environment Modeling Quantitative Assessment of Radiation Belt Modeling focus group: 17 and 18 March (stormtime enhancement), 31 May to 2 June (stormtime dropout), 19 and 20 September (nonstorm enhancement), and 23–25 September (nonstorm dropout). Observations include EMIC wave data from the Van Allen Probes, Geostationary Operational Environmental Satellite, and Time History of Events and Macroscale Interactions during Substorms spacecraft in the near-equatorial magnetosphere and from several arrays of ground-based search coil magnetometers worldwide, as well as localized ring current proton precipitation data from low-altitude Polar Operational Environmental Satellite spacecraft. Each of these data sets provides only limited spatial coverage, but their combination shows consistent occurrence patterns and reveals some events that would not be identified as significant using near-equatorial spacecraft alone. Relativistic and ultrarelativistic electron flux observations, phase space density data, and pitch angle distributions based on data from the Relativistic Electron-Proton Telescope and Magnetic Electron Ion Spectrometer instruments on the Van Allen Probes during these events show two cases during which EMIC waves are likely to have played an important role in causing major flux dropouts of ultrarelativistic electrons, particularly near L* ~4.0. In three other cases, identifiable smaller and more short-lived dropouts appeared, and in five other cases, these waves evidently had little or no effect.