Suprathermal electrons in Earth's Magnetotail: a statistical picture

Based on measurements from NASA's Magnetospheric Multiscale mission, statistical analyses of suprathermal electrons in Earth's magnetotail reveal two main categories of magnetic configurations where suprathermal electrons are observed. The first one is created by the earthward flow of the reconnected magnetic flux. Occurrence of suprathermal electron flux enhancements peaks statistically at regions with elevated magnetic flux and weak plasma flows behind the reconnection front. The earthward transport of reconnected fluxes gives rise to an electric field in the same direction as the reconnection electric field. This electric field occurs in the region extending from the X line to the reconneciton front, much larger

than that containing the reconnection electric field. Electrons bounce along the closed field lines earthward of the X line continue to be accelerated by this electric field at every return to the region. The second configuration is represented by high magnetic field fluctuations surrounding a main reconnection X line. The thermal component in the second configuration tends to be much hotter than that in the first configuration. The statistical results also indicate that coherent magnetic islands, although effective in accelerating electrons, are not the dominant process for energizing electrons to suprathermal energies in the magnetotail. We discuss the potential analogy of these observations to solar flare electron energization.