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Generalized Ohm’s Law Decomposition of the Electric Field in Magnetosheath Turbulence: Magnetospheric Multiscale Observations
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  • Julia E. Stawarz,
  • Lorenzo Matteini,
  • Tulasi N. Parashar,
  • Luca Franci,
  • Jonathan P. Eastwood,
  • Carlos A. Gonzalez,
  • Imogen Gingell,
  • James L Burch,
  • Robert E Ergun,
  • Narges Ahmadi,
  • Barbara L. Giles,
  • Daniel J Gershman,
  • Olivier Le Contel,
  • Per-Arne Lindqvist,
  • Christopher T. Russell,
  • Robert J. Strangeway,
  • Roy B. Torbert
Julia E. Stawarz
Imperial College London

Corresponding Author:[email protected]

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Lorenzo Matteini
Imperial College London
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Tulasi N. Parashar
Victoria University of Wellington
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Luca Franci
Queen Mary University of London
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Jonathan P. Eastwood
Imperial College London
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Carlos A. Gonzalez
University of Texas at Austin
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Imogen Gingell
University of Southampton
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James L Burch
Southwest Research Institute
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Robert E Ergun
Univeristy of Colorado
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Narges Ahmadi
Laboratory for Atmospheric and Space Physics, University of Colorado Boulder
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Barbara L. Giles
NASA Goddard Space Flight Center
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Daniel J Gershman
NASA Goddard Space Flight Center
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Olivier Le Contel
CNRS/Ecole Polytechnique/Sorbonne Université/Université Paris-Saclay/Obser. de Paris
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Per-Arne Lindqvist
KTH, Stockholm, Sweden
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Christopher T. Russell
University of California Los Angeles
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Robert J. Strangeway
University of California Los Angeles
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Roy B. Torbert
University of New Hampshire
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Abstract

Decomposing the electric field (E) into the contributions from generalized Ohm’s law provides key insight into both nonlinear and dissipative dynamics across the full range of scales within a plasma. Using high-resolution, multi-spacecraft measurements of three intervals in Earth’s magnetosheath from the Magnetospheric Multiscale mission, the influence of the magnetohydrodynamic, Hall, electron pressure, and electron inertia terms from Ohm’s law, as well as the impact of a finite electron mass, on the turbulent spectrum are examined observationally for the first time. The magnetohydrodynamic, Hall, and electron pressure terms are the dominant contributions to over the accessible length scales, which extend to scales smaller than the electron inertial length at the greatest extent, with the Hall and electron pressure terms dominating at sub-ion scales. The strength of the non-ideal electron pressure contribution is stronger than expected from linear kinetic Alfvén waves and a partial anti-alignment with the Hall electric field is present, linked to the relative importance of electron diamagnetic currents in the turbulence. The relative contribution of linear and nonlinear electric fields scale with the turbulent fluctuation amplitude, with nonlinear contributions playing the dominant role in shaping for the intervals examined in this study. Overall, the sum of the Ohm’s law terms and measured agree to within ~20% across the observable scales. These results both confirm general expectations about the behavior of in turbulent plasmas and highlight features that should be explored further theoretically.
Jan 2021Published in Journal of Geophysical Research: Space Physics volume 126 issue 1. 10.1029/2020JA028447