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The Electron Loss and Fields Investigation with a Spatio-Temporal Ambiguity-Resolving option (ELFIN-STAR, or simply: ELFIN) mission comprises two identical 3-Unit (3U) CubeSats on a polar (~93deg inclination), nearly circular, low-Earth (~450 km altitude) orbit. Launched on September 15, 2018, ELFIN is expected to have a >2.5 year lifetime. Its primary science objective is to resolve the mechanism of storm-time relativistic electron precipitation, for which electromagnetic ion cyclotron (EMIC) waves are a prime candidate. From its ionospheric vantage point, ELFIN uses its unique pitch-angle-resolving capability to determine whether measured relativistic electron pitch-angle and energy spectra within the loss cone bear the characteristic signatures of scattering by EMIC waves or whether such scattering may be due to other processes. Pairing identical ELFIN satellites with slowly-variable along-track separation allows disambiguation of spatial and temporal evolution of the precipitation over minutes-to-tens-of-minutes timescales, faster than the orbit period of a single low-altitude satellite (~90min). Each satellite carries an energetic particle detector for electrons (EPDE) that measures 50keV to 5MeV electrons with deltaE/E, Submitted to Space Science Reviews April 2020. 51 pages, 7 tables, 21 figures

©2015. American Geophysical Union. All Rights Reserved. A new 3-D diffusion code is used to investigate the inward intrusion and slow decay of energetic radiation belt electrons (>0.5MeV) observed by the Van Allen Probes during a 10day quiet period on March 2013. During the inward transport, the peak differential electron fluxes decreased by approximately an order of magnitude at various energies. Our 3-D radiation belt simulation including radial diffusion and pitch angle and energy diffusion by plasmaspheric hiss and electromagnetic ion cyclotron (EMIC) waves reproduces the essential features of the observed electron flux evolution. The decay time scales and the pitch angle distributions in our simulation are consistent with the Van Allen Probe observations over multiple energy channels. Our study suggests that the quiet time energetic electron dynamics are effectively controlled by inward radial diffusion and pitch angle scattering due to a combination of plasmaspheric hiss and EMIC waves in the Earth's radiation belts.

© 2014. American Geophysical Union. All Rights Reserved. Due to its importance for global energy dissipation in the ionosphere, the diffuse aurora has been intensively studied in the past 40years. Its origin (precipitation of 0.5-10keV electrons from the plasma sheet without potential acceleration) has been generally attributed to whistler-mode chorus wave scattering in the inner magnetosphere (R < ~8 R E ), while the scattering mechanism beyond that distance remains unresolved. By modeling the quasi-linear diffusion of electrons with realistic parameters for the magnetic field, loss cone size, and wave intensity (obtained from Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations as a function of magnetospheric location), we estimate the loss cone filling ratio and electron cyclotron harmonic (ECH) wave-induced electron precipitation systematically throughout the entire data set, from 6 R E out to 31 R E (the THEMIS apogee). By comparing the wave-induced precipitation directly with the equatorially mapped energy flux distribution of the diffuse aurora from ionospheric observations (OVATION Prime model) at low altitudes, we quantify the contribution of auroral energy flux precipitated due to ECH wave scattering. Although the wave amplitudes decrease, as expected, with distance from the Earth, due to the smaller loss cone size and stretched magnetic field topology, ECH waves are still capable of causing sufficient scattering of plasma sheet electrons to account for the observed diffuse auroral dissipation. Our results demonstrate that ECH waves are the dominant driver of the diffuse aurora in the outer magnetosphere, beyond ~8 R E .