Magnetospheric Multiscale Observations of the Source Region of Energetic
Electron Microinjections along the Dusk-side, High-latitude Magnetopause
Boundary Layer
Abstract
The present paper demonstrates the first observations by the
Magnetospheric Multiscale (MMS) mission of the counter-streaming
energetic electrons and trapped energetic protons, localized in the
magnetic field depressions between the mirror mode peaks, in the Earth’s
dusk sector high-latitude magnetosphere. This region is characterized by
high plasma beta, strong ion temperature anisotropy and intermediate
plasma density between magnetospheric and magnetosheath plasma. We show
that these plasma conditions are unstable for the drift mirror
instability. The counter-streaming electron feature resembles those of
the previously reported energetic electron microinjections, but without
the energy-time dispersion signature. This suggests that MMS is passing
through one of the potential microinjection source regions. The
energetic ion data in the present study is mainly used to estimate the
scale size of the mirror mode structures.