Electron-scale Magnetic Peaks Upstream of the Terrestrial Bow Shock Observed by the Magnetospheric Multiscale Mission

Abstract

Abstract The solar wind has rich wave activity and various magnetic structures. Here we report on a new type of magnetic structure in the solar wind using the unprecedented high temporal resolution data from the Magnetospheric Multiscale Mission. We find that a train of magnetic peaks with a size less than 1 ion inertial length exists upstream of the terrestrial bow shock. The electron number density and the perpendicular electron temperature have a slight decrease inside the magnetic peaks, leading to a decrease of the electron thermal pressure in the structure. These structures are pressure-balanced, and they are approximately stationary in the ambient electron flow. These electron-scale magnetic peaks are identified as magnetic bottle–like, and their cross sections are roughly circular. The electron velocity has a bipolar feature relative to the ambient flow in the cross section, indicating the existence of an electron vortex. The current density is mainly contributed by electrons. The peaks occur in a marginally mirror-stable environment; thus they are not locally generated by mirror instabilities. We suggest that the origin of the electron vortex might help to shed light on the formation of electron-scale magnetic peaks in the solar wind.