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Electron currents supporting the near‐Earth magnetotail during current sheet thinning
Author(s) -
Artemyev A. V.,
Angelopoulos V.,
Liu J.,
Runov A.
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2016gl072011
Subject(s) - current sheet , substorm , physics , electron , plasma sheet , geophysics , magnetic reconnection , current (fluid) , heliospheric current sheet , curvature , transverse plane , current density , magnetic field , magnetosphere , magnetohydrodynamics , solar wind , interplanetary magnetic field , geometry , nuclear physics , thermodynamics , structural engineering , engineering , mathematics , quantum mechanics
Formation of intense, thin current sheets (i.e., current sheet thinning) is a critical process for magnetospheric substorms, but the kinetic physics of this process remains poorly understood. Using a triangular configuration of the three Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft at the end of 2015 we investigate field‐aligned and transverse currents in the magnetotail current sheet around 12 Earth radii downtail. Combining the curlometer technique with direct measurements of ion and electron velocities, we demonstrate that intense, thin current sheets supported by strong electron currents form in this region. Electron field‐aligned currents maximize near the neutral plane B x ∼0, attaining magnitudes of ∼20 nA/m 2 . Carried by hot (>1 keV) electrons, they generate strong magnetic shear, which contributes up to 20% of the vertical (along the normal direction to the equatorial plane) pressure balance. Electron transverse currents, on the other hand, are carried by the curvature drift of anisotropic, colder (<1 keV) electrons and gradually increase during the current sheet thinning. In the events under consideration the thinning process was abruptly terminated by earthward reconnection fronts which have been previously associated with tail reconnection further downtail. It is likely that the thin current sheet properties described herein are similar to conditions further downtail and are linked to the loss of stability and onset of reconnection there. Our findings are likely applicable to thin current sheets in other geophysical and astrophysical settings.