Electron Mirror-mode Structure: Magnetospheric Multiscale Observations

Abstract

The small-scale mirror mode excited by electron dynamics is a fundamental physical process, attracting research interest in space, laboratory, and astrophysical plasma physics over the past half century. However, the investigations of this process were mostly limited to theories and numerical simulations, with no direct observational evidence for their existence. In this study we present clear observations of electron mirror-mode using Magnetospheric Multiscale data at unprecedented high temporal cadence. These structures are train-like, compressible, nonpropagating, and satisfy the theoretical excitation and electron trapping conditions. They were observed near the Earth's foreshock and its downstream turbulence during the corotating interaction region events, which could be involved with the interaction between solar wind and Earth.