MMS FEEPS Energetic Electron Microinjection Observations

The early MMS energetic electron data taken in the dusk to pre midnight regions above 9 RE showed many clusters of electron injections we call microinjections because of their short duration signatures. These microinjections of 50-400 keV electrons have energy dispersion signatures indicating that they gradient and curvature drifted from earlier local times. A particular cluster of about 40 electron microinjections occurred in a 4.5-hour interval starting at 21:15 UT on 6 August 2015. We show detailed results from microinjections taken with burst mode data starting near 21:16 UT. These high temporal resolution data showed that the electrons in the microinjections were trapped and had bidirectional field-aligned angular distributions. Drift calculations constrained by the observed electron dispersion times indicate the electrons had drifted from near the magnetopause approximately two hours earlier in local time. Many multiple clusters of microinjections were observed as MMS apogee traversed the premidnight to dusk region. They were not observed as the MMS apogee passed from dusk through the dayside regions. Later, as the MMS apogee once again moved through the midnight to pre midnight region, during mission phase 1X, injections were once again observed. We provide statistics on the occurrence of the injections and discuss possible implications. These injection clusters are a new phenomenon in this region of the magnetosphere.