Characteristics of Energetic Electrons Near Active Magnetotail Reconnection Sites

Abstract:

We present results from two studies focusing on the characteristics of energetic (>30 keV) electrons observed by Magnetospheric Multiscale (MMS) in the vicinity of candidate electron diffusion regions (EDRs) identified in the magnetotail. First, we compare the spectral indices of energetic (50-200 keV) electrons from all six of the magnetotail EDRs candidates identified by the MMS team to-date with those from “quiet-time” plasma sheet crossings occurring in the same region to test whether energetic electron enhancements result from direct energization or redirection of pre-existing populations. The study suggests that active reconnection can be a source of localized electron energization. However, the EDR spectra are not outside the range of those from the quiet-time plasma sheet, which often have very energetic electrons (>200 keV) present. Second, we present detailed observations and reconstructed magnetic field topologies from a singular magnetic reconnection event observed by MMS. Comparing and contrasting energy and angular distributions of >50 keV electrons observed by three MMS spacecraft separated by only ~18 km revealed a combination of chaotic motion and surprisingly coherent gyrophase bunching within a few thousand kilometers of the reconnection site. Results indicate that while the magnetic topology was relatively stable over several seconds (i.e., more than a thousand electron gyro-periods), the topology was also not uniform over spatial scales on the order of the electron gyroradius (~500 to ~1000 km). We hypothesize that the coherent gyrophase bunching was evidence of these energetic electrons being accelerated in the outflowing exhaust jets of the active reconnection.