MMS/FEEPS Observations of Electron Microinjections Due to Kelvin‐Helmholtz Waves and Flux Transfer Events: A Case Study

Abstract

AbstractThe Energetic Particle Detector (EPD) suite onboard the Magnetospheric Multiscale (MMS) spacecraft observes dispersive and repetitive fluxes of high‐energy (50–400 keV) electrons within the Pc5 frequency band (2–8 MHz) in the dusk to midnight region of Earth's magnetotail. These microinjections are a new phenomenon in this region of the magnetosphere, presently poorly understood, but clearly a new signature that remotely senses large‐scale magnetospheric boundary dynamics. It is therefore important to understand their properties and driver mechanisms. Here we have combined global magnetohydrodynamic simulations and particle tracing results with the MMS EPD Fly's Eye Energetic Particle Spectrometer (FEEPS) observations to investigate possible origins and source regions of the electron microinjections. Our simulation results suggest that the electron microinjections, observed in the dusk to premidnight sector, are associated with Kelvin‐Helmholtz waves (KHWs) and flux transfer events (FTEs). Energetic electrons launched from a limited range of locations near the postnoon dusk magnetopause and at times when KHWs and FTEs pass by that region have drift paths that connect with MMS and thus create time‐dependent microinjection electron signatures. Test‐particle tracing results in the magnetohydrodynamic fields also support the field‐aligned nature of electron microinjections observed by MMS. Though identifying the mechanism by which KHWs and FTEs might periodically inject electrons is beyond the scope of this work, our study does identify these duskside magnetopause boundary phenomena as likely agents of microinjection origins.