Magnetospheric MultiscaleMission Observations of Reconnecting Electric Fields in the Magnetotail on Kinetic Scales

Abstract

We examine the role of ions and electrons in reconnection using the highest resolution observations from the Magnetospheric Multiscale mission on kinetic ion and electron scales. We report magnetic field and plasma observations from several approaches to the electron diffusion region in the current sheet in 2018. Besides magnetic field reversals, changes in the direction of flow velocity, ion and electron heating, Magnetospheric Multiscale observed large fluctuations in the electron flow speeds in the magnetotail. We have verified that when the field lines and plasma become decoupled, a large reconnecting electric field related to the Hall current (1–10 mV/m) is responsible for fast reconnection in the ion diffusion region. Although inertial acceleration forces remain moderate (1–2 mV/m), the electric fields resulting from the electron pressure tensor provide the main contribution to the generalized Ohm's law at the neutral sheet (as large as 200 mV/m). This illustrates that when ions decouple electron physics dominates.

Self-consistent kinetic model of nested electron- and ion-scale magnetic cavities in space plasmas

“…At the electron scale, the convection term becomes negligible, whereas the radially inward Hall term (resulting from the decoupled proton and electron fluid motion, or equivalently, the nonzero electric current) and the radially outward electron pressure divergence term both contribute to the electric field (the former being stronger to result in an inward net electric field). Similar observations have been also made in other small-scale structures, most noteworthy the electron diffusion region of magnetic reconnection, in which the electron pressure divergence term becomes very important only next to the Hall term 54 or even dominant 55 , 56 in the generalized Ohm’s law.…”

Magnetospheric Multiscale Observations of Markov Turbulence on Kinetic Scales

“…Papini et al (2021) have recently argued that the turbulence energy at kinetic scales could not be related to KAW activity but is mainly driven by localized nonlinear structures. Certainly, it is possible that the observed stochastic nature of fluctuations in the sub-ion scale could be due to the interaction between coherent structures (e.g., Chang 2015;Echim et al 2021), including local reconnection processes at kinetic scales (Macek et al 2019a(Macek et al , 2019b. Admittedly, the nature of wave modes in operation cannot be determined by statistical analysis, but we hope that the Markov approach will provide a contact point with a dynamical system approach to turbulence and hence that the results of this study will be useful in future investigations.…”