Magnetospheric Multiscale Dayside Reconnection Electron Diffusion Region Events

TL;DR

This paper reports the discovery of 21 new electron diffusion region events by MMS, with detailed analysis of three events showing complex plasma behaviors and the first evidence of field line reconnection during slow magnetopause motion.

Contribution

It introduces new EDR encounters identified by MMS, including the first observations of simultaneous perpendicular and parallel crescents during slow magnetopause motion.

Findings

21 new EDR events identified by MMS data

Detailed analysis of 3 events showing large electric fields and crescent-shaped electron distributions

First evidence of solar wind and magnetospheric field line reconnection during slow magnetopause motion

Abstract

We have used the high-resolution data of the Magnetospheric Multiscale (MMS) mission dayside phase to identify twenty-one previously unreported encounters with the electron diffusion region (EDR), as evidenced by electron agyrotropy, ion jet reversals, and j dot E greater than 0. Three of the new EDR encounters, which occurred within a one-minute-long interval on November 23rd, 2016, are analyzed in detail. These events, which resulted from a relatively low and oscillating magnetopause velocity, contained large electric fields (several tens to hundreds of milliVolts per meter), crescent-shaped electron velocity phase space densities, large currents (greater than 2 microAmperes per square meter), and Ohmic heating of the plasma (near or exceeding 10 nanoWatts per cubic meter). Because of the slow in-and-out motion of the magnetopause, two of these events show the unprecedented mixture of perpendicular and parallel crescents, indicating the first breaking and reconnecting of solar wind and magnetospheric field lines. An extended list of thirty-two EDR or near-EDR events is also included, and demonstrates a wide variety of observed plasma behavior inside and surrounding the reconnection site.