Fig. 1: MMS2 observations of electron reconnection in Earth’s magnetotail.

The event was observed at [−19.4, −10.4, 5.5]R_E from 20:24:03 to 20:24:11 UT on 17 June 2017. a Magnetic field components; b ion bulk velocity; c electron bulk velocity; d current densities parallel and perpendicular to the magnetic field (here the current density is calculated using \({\bf{j}} = en_{\rm{e}}( {{\bf{V}}_{{i}} - {\bf{V}}_{{e}}} )\)); e electric field; f, g electron and ion differential energy flux (in unit of keV cm⁻² s⁻¹ sr⁻¹ keV⁻¹) as function of electron energy W_e and ion energy W_i, respectively; h–j electron bulk velocity V_e and the electric drift velocity E × B/B²; k electron velocity distribution in the plane perpendicular to the magneticfield (\({\bf{v}}_{{\rm{e}} \bot 1} = \left[ {\left( {{\bf{B}} \times {\bf{v}}_{\rm{e}}} \right) \times {\bf{B}}} \right]{\mathrm{/}}B^2\), \({\bf{v}}_{{\rm{e}} \bot 2} = \left( {{\bf{B}} \times {\bf{v}}_{\rm{e}}} \right){\mathrm{/}}B\)) at the electron reconnection site, from 20:24:06.913 to 20:24:06.920 UT. Photo electrons with energies <96 eV, as shown in f, are insignificant contaminants, so they are excluded in the calculation of electron bulk velocity.