Electrostatic Solitary Waves in Earth's Magnetosheath: Properties, Nature, and Origin

We present the analysis of 2,152 electrostatic solitary waves observed aboard the Magnetospheric Multiscale in the Earth's magnetosheath. The electric field of the solitary waves is predominantly bipolar and parallel to the local magnetic field. In contrast to previous reports, we reveal similar occurrence rates of solitary waves of positive and negative polarity of the electrostatic potential. Both types of solitary waves have spatial half-widths of 10–150 m or 1–15 Debye lengths, amplitudes of the electrostatic potential of 0.01–1.5 V or 0.01%–1% of local electron temperature, and plasma frame speeds within ion thermal speed. We argue that the solitary waves are electron and ion holes produced separately in space or time by local processes, whose nature is, however, still elusive. We speculate that the solitary waves can mediate the energy between thermal electrons and ions in the Earth's magnetosheath and discuss other applications of the presented results.